Well Foundation 673z6b

Well Foundation: Well foundation is the most commonly adopted foundation for major bridges in India. Since then many major bridges across wide rivers have been founded on wells. Well foundation is preferable to pile foundation when foundation has to resist large lateral forces. The foundations may consist of a single large diameter well or of a group of smaller wells of circular or other shaped. The shape of wells may be circular, double D, Square, rectangular, Dum-bell shaped etc., The circular bell shapes are used when the bridges has multi lane carriage way. For the piers and abutments of very large size used in the cantilever, cable stayed or suspension bridges large rectangular wells with multi degree holes of square shape may be used. The size of the dredge holes is decided so as to facilitate ease of construction and inspection of the foundation. While deciding the bottom level of the foundation the following considerations may be kept in view. a. Normally, a sandy strata with adequate bearing capacity is preferred to a clayey strata. b. A thin stratum of clay occuring between two layers of sand is not relied upon but pierced through c. The foundation has to be laid on the clayey layer, a well is rested on stiff clay only.

The size of the well for a particular foundation would depend on a large number of factors. The minimum size of a dredge hole is 2.5m. The thickness of steining should be adequate to permit sinking of the well without excessive knowledge. From considerations of sinking effort and erection of shuttering , a large diameter well is nowadays preferred to a group of small sized wells. From practical considerations, the maximum size of a single circular well should be limited to about 12 m diameter for a concrete steining and 6m diameter for a brick masonry steining. If the wells are to rest on sloping rock, smaller wells may be advantageous for ensuring even seating of the wells on the rock. However, in the case of Twin circular wells or three wells with a common capping slab have been used in earlier constructions for wide piers and abutments. The wells in these cases had small diameter. Currently, this type is not so popular. Double D and dumbell shaped wells are suitable for deep foundations and double line railways. Multi cellular wells are adopted for deep foundations for long span bridges, as in the Howrah bridge and second Hoogly bridge.

Components:

A well foundation consists of the following components. a. Steining b. Well Curb c. Bottom Plug d. Sand filling e. Top Plug f. Well Cap g Cutting edge CREATE AN   

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Well Foundations for Bridges are Obsolete!!!

S.A.Reddi, Fellow Indian National Academy of Engineering

Introduction Bridge foundations are the most complicated and difficult to construct. Unexpected difficulties cause delays, extra costs and revision of designs due to altered situations. Loss of human lives was normal rather than exception. In the Sixties, more than 50 lives were lost due to the accident during pneumatic sinking operations for well foundations of Mahanadi bridge in Orissa. For Kali Bridge at Karwar in Karnataka, pneumatic sinking was required for inspection of the founding surface of the wells. Apart from delays and extra costs, large number of workers suffered caisson disease. Due to difficulties in well sinking, two contractors left the job and the third took more than 5 years to complete the well foundations. Alternative construction techniques and equipments have emerged. With the introduction of advanced piling equipment, large diameter piles up to 3.5 m dia are easily realized at a fast rate, with a significant reduction in cost and material quantities. Bridges elsewhere are now constructed with pile foundations.

Figure 1: Brahmaputra bridge foundations No. 17 & 18

Pre-cast RC bored piles of 2.5m diameter was first successfully realized in India for the old Thana Creek Bridge constructed in 1960s. For the 13 Km long Saudi–Baharain Causeway large diameter pre-cast prestressed bored piles were adopted. By 2005, piles of 2-3 m dia, upto 120m deep are extensively used in the rest of the world. These new techniques eliminate complicated weather-dependent and risky operations in water. They have reduced the delays considerably and minimized the technical and financial risks. The development of modern techniques has considerably reduced quantities of materials used for foundations as well as energy consumption and environmental impacts.

Well Foundation Problems at Brahmaputra Bridge at Tezpur The bridge was more than 3 km long with 26 spans of 120 m and 2 shore spans of 70 m each, founded on 12m dia Wells. Sinking well No.2 to full depth was not possible due to bouldery strata Despite best efforts, the well only went down by 35.25 m after three seasons and at extra cost! The well was plugged at RL 32.075 m and 5 nos 1.5 m dia RCC bored piles (25-35m) were provided to anchor the well, one in the middle through the dredge hole and 4 outside at the four corners. Further a launching apron of crated boulder 3 m thick was laid making a circle of 60 m dia around the well, at RL 61.00. These extra works caused further delay in the comp- letion of the substructure works.

Well foundations on sloping rock: Brahmaputra Bridge at Jogighopa (2.28 km)

Figure 2: Pile foundations for Jamuna bridge

The wells of main span were 11 m x 17 m double ‘D’ type. Foundations 17 & 18 were resting on hard rock at steep incline of almost 1:1 slope. It was not possible to rest the foundations partially on two types of strata. Hence to found these wells, 1500 mm dia anchor piles, 12 nos for each foundation were provided through the body of the steining, extending to about 10 m below the cutting edge. Due to the steep incline, part of the cutting edge was resting on the rock while the other parts were overhanging. In order to contain the bottom plug, two rows of jet grouted piles were introduced around the periphery of the well steining which acted as curtain wall (fig.1). 1500 dia piles also driven up to hard rock along the periphery through the steining. The completion of the project was extended by 3 years. Additional cost was several crores. Effective use of Pile Foundations - Jamuna River Bridge in Bangladesh (figs.2 &3).

Figure 3: Completed view of the Jamuna bridge

A 4.8 km long, four lane road bridge with 100 m spans was constructed in the 1990s on the Jamuna river (Brahmaputra in India). The foundation design was challenging. Very deep wells are extremely slow to construct, costly, increasing the total cost. Various alternatives were considered including caissons, driven precast piles and driven steel tubular piles. The only viable option was large diameter tubular steel piles driven at a rake (fig.2). The piles were fabricated in Korea, shipped to site and installed by hydraulic hammer. The diameter of the piles ranged between 2.5 and 3.15 m and the steel tubes were filled with concrete. Maximum pile length was 72 m below bed level. During one working season from October 1995 to June 1996 all the 121 main work piles plus two full scale trial piles were driven. This optimization resulted in overall reduction in the bridge costs by more than 50%. This solution also

reduced the use of resources (concrete and steel) considerably and was beneficial to environmental impact. The piles were installed in 8 months; the well foundations of three bridges across the same river constructed in India have taken 3-5 years each to complete.

Damages During Construction - Ganga Bridge at Bhagalpur (4.6 km) The well foundations consist of single circular wells 11.6 m dia. The calculated maximum scour depth was 36 m below water level. The soil strata were sandy up to about 30 m followed by hard stiff clay. During construction, the wells started tilting and the problems continued right through the sinking. Despite extensive chiseling, the rate of sinking was painfully slow.  

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Well 2 - The founding level was 64.7 m below the water level. The rate of sinking through clay was about 1.5 - 2 cm/hr. 3500 crane hours were used to sink the well. Well 17 - The well shifted by 1.86 m. The piers were to be retained at the original position; resulting in excessive moments in the well. To counter the moments counterweight was provided in the form of a dummy well sunk to a depth of 20 m in the adjacent area and connected to the main well through a common well cap. Well 32 - The well shifted by 1150 mm. A similar solution as in well 17 was adopted. Well 4 - During concreting of curb, sand leaked from the island and the entire curb tilted and sank by 4.5 m. A new sheet pile cofferdam had to be erected and a new well curb was cast. The total delay was one month. Well 9 - the total height of the steining except last 2 m was completed with 7.5 m balance sinking. Due to presence of stiff clay, 8 m sump was made to facilitate sinking. After several weeks, the well suddenly jumped by about 9 m with the top of steining below water level. Work resumed after monsoon. A temporary RC cofferdam was constructed and the sunk well dewatered to expose and build up further steining. Time loss: about 6 months. Wells 3 & 4 -Wells were sunk by about 44 and 37 m before the monsoon season in 1996. The wells were toppled due to scour and disappeared during the floods. Based on a number of trial bores well No.3 was found tilted along the bridge axis. Well No.4 was found on the upstream side along the direction of current. These wells weighing up to 9900 t could not be restored and were abandoned. New wells were cast and sunk by changing the span arrangement. Floating caissons were used. Extra cost and time - The cost on completion was Rs.106 cr against accepted tender cost of Rs.55 cr! The time overrun was 5 years!

Tilts and Shifts in Well Foundations - Vasai Creek Bridges Near Mumbai Bassein Creek road bridge near Mumbai (1970) faced problems of heavy tilting of the well foundations. Two of the foundations no.4 & 6 tilted very heavily and all attempt to correct the tile failed. The foundations were abandoned and the design of the bridge was changed to accommodate new foundations and longer spans. The project was delayed by six years with termination of the first contract, arbitration, litigation.

Despite previous histories of two bridges built across the same creek that faced problems with well foundations, the same were again adopted for another Vasai Creek Bridge. During construction, heavy tilting of wells was observed. The corrective measures for one well alone took almost two years delaying completion of the foundations; costing about Rs. 2 crores.

Sudden Jumping of Wells During Sinking Sometimes the well sinks suddenly due to excessive sump or weak soil layer and the steining disappears below water level, making it difficult to continue further work on the well steining. In one of the well foundations in a bridge across river Ganga, the total height of steining except last 2 m was concreted. The well was in the final stages of steining, with about 7.5 m to reach the founding level. As the well was stuck up in stiff clay, efforts were made to sink the well by creating a sump of about 8 m below the cutting edge. All of a sudden the well sank suddenly by about 9 m and the top of steining was below the water level by about 3.5 m. Rectification measures were very expensive and time consuming. Ganga bridge at Varanasi: Very stiff clay was encountered at 25 m below and sinking of well foundations No. 3 and 5 was very difficult, did not move for three months. Then well No.3 jumped by several meters without any warning when two workers and one supervisor were taking sump sounding. The tragic accident killed all the three people. The well No.5 also jumped by about 5 m and was submerged in the water by 1m.

Artesian Conditions During Construction of Well Foundations Nepal Bridge (Kohalpur / Mahakali Section ) Artesian conditions were encountered during soil investigations for the Shivganga bridge (8 spans of 32 m). At locations P-4 and P-5 artesian head of about 4.3 m was encountered at about 17 m below ground level. The well was redesigned with foundation terminating above the artesian layer, resulting in shallow foundations resting on clay. Due to founding the wells at shallow depth, it was necessary to provide adequate bed protection so as to prevent scour. The bed protection consisted of:   

Upstream and downstream aprons Cut-off walls, upstream & downstream Concrete floor

An Expensive Solution Indeed !! The completion was delayed by more than one season as the solution was based on an Expert Committee investigation and report. This led to delay in finalization of the designs and drawings for the foundation well and necessity of issuing variation orders to cover the items of cut-off walls and bed protection works which were not envisaged in the original contract.

Ganga Bridge, Patna

The 5.6 km long bridge comprises of 46 spans of 120 m each resting on 56 m deep well foundations (12m dia.). Two of the wells in the midstream (Nos. 41 and 45) encountered artesian conditions during the final stages of sinking There was continuous sand blowing filling the dredge hole to 5-6 m above the cutting edge. Months of efforts to sink the well proved futile. A technical advisory committee took about a year for arriving at a solution. Temporary steel cofferdam was built enveloping the well and an artificial head of about 6 m of water was created to counter act the sand bubbling. Delay: two years

Cracking of Well Steining During Construction Cracking of well steining is one of the serious problems faced many times in the construction of well foundations, resulting in time and cost overruns. The causes are usually: 1. 2. 3. 4. 5. 6.

Blasting, Dewatering Insufficient steining thickness Jumping due to excessive sump Sand blows Surcharge due to dumping dredge material close to well. Failure of cutting edges.

When such cracking occurs, at least one season is lost for the investigation, developing remedial measures, approvals of the same etc. In the last 45 years, the author is aware of more then 200 cases of bridges constructed by various construction agencies, where the dredge hole of well has to be filled with concrete due to cracks in steining.

Figure 4: Pasighat Bridge, AP Figure 5: Pasighat Bridge, Boulder dredged during well sinking

During well sinking of Tapi Bridge, Maharashtra, hard strata was met. Due to blasting, extensive cracks developed in steinings New steinings had to be constructed inside the wells. The original contract period was four years. Attempts were made for five years to sink the wells. Work was suspended for five years for want of decision to revise the founding level. An expert committee ultimately recommended raising the foundation level of wells by more than 20m The bridge was completed after fourteen years. The contractor suffered losses due to the delays. The owner suffered substantial losses due to time overrun. Delay: 10 years.

Extraordinary Delays in Construction of Well Foundations Pasighat Bidge, Arunachal Pradesh, 703 m long

The project started in 1987 and the construction of well foundations continued for the next 20 years! As per the design, based on misleading soil data, six wells were to be sunk to about 50 m below bed. The actual strata met with during sinking were hard conglomerate with densely compacted and very large boulders (fig.6) were found right from the beginning of sinking. After 15 years of struggle to pneumatically sink the wells to RL – 50 m, the designed founding level was drastically raised by 22m in 2002.

Major Bridges (Worldwide) on Pile Foundations Su Tong Bridge, China : The 6 km long Cable-stay bridge crosses Yangtze river near Shangai will carry a six lane highway with emergency lanes, with a record 1088 m main span and 300 m high concrete pylons. Each tower is ed on 131 cast-in-situ bored piles 120 m long and 2.7 m diameter. Due to strong currents, significant scour is expected around the foundations, and suitable scour protection is provided around the pylons. The central span has a clearance of 62 m for container ships to through. The bridge used 200,000 t of steel, 1 million cum of concrete. Stonecutters Bridge, Hong Kong: The 1600 m long Stonecutters Bridge Hong Kong with cable-stay span of 1018 m is one of the longest in the world. The bridge is founded on 3.0 m dia piles, up to 90 m deep, socketted into rock. Bandra Worli Sea Link Mumbai: The sea link consists of 5.6 km long, 8-laned bridge with cable stayed portion of 600 m. The bridge is founded on 1.5 m diameter bored piles. Concrete for the piles is M50 grade and for pile caps is M60. Silica fume and fly ash are used for concrete preparation.

Analysis by the Federal Highway istration (FHWA), USA More than 100,000 bridges would be constructed during the next two decades. Foundations represent about 30% or more of the cost of the highway bridges. The predominant type of foundation system used for the highway bridges in the US is pile. Many bridges can tolerate significant magnitudes of a total and differential vertical settlement without becoming seriously over-stressed

Appreciation The Indian Bridge Engineers are by and large mentally tuned to providing well foundations for bridges as a reflect action; whereas it is very necessary to analyze the comparative merits and demerits, construction time frame and cost of construction of bridges with well/pile foundations before finally choosing the type of foundation. An analysis of the history of well foundations during the last five decades indicates innumerable difficulties, delays and cost overruns in a majority of the cases. Realization of well foundations requires special skills and experience which are gradually dwindling. Developments have taken place in respect of large diameter pile foundations as well as equipment for the same. The time and cost advantages of opting for pile foundations have been amply demonstrated worldwide and to a limited extent in India. Piles up to a diameter of 3m and depth of up to 120m have been realized for a number of major bridges worldwide, with cost saving of up to 40% when compared to well foundations.

There is currently no restriction in the IRC Code regarding use of pile foundation. However, many Owners impose restrictions in the tender documents, without any justification. The example cited above concerning the problems of well foundations amply justifies a second look on the choice of foundations. In fact, the use of well foundations for bridges should be an exception rather than the rule.

Chenab River Bridge at Akhnoor Near Jammu The project was started in the early Seventies. A .scheme for a 231m long bridge with 5 spans (3x46+2x46.5) upstream of existing steel bridge was originally conceived. The scheme involved construction of five well foundations in the volatile Chenab River, to be sunk through difficult strata – hard conglomerate, in spite of insurmountable difficulties elsewhere under similar circumstances. Two successive contracts and 30 years later, the impossibility of sinking wells through such strata was realized.

Figure 6: Chenab Bridge at Akhnoor-Longest Span Cantilever PSC Bridge, eliminated wells

Based on lateral thinking, it was decided to abandon the partly sunk wells and go for a scheme with longer central span, eliminating the water foundations altogether. With a 160m central span, both the main pier foundations were located in the dry on the banks, resting on raft foundations. These foundations were completed in months instead of decades earlier in unsuccessful attempts to sink wells in water. The abutments consist of hollow box and piers consist of hollow rectangular section on raft foundations. The superstructure was designed and constructed as a continuous cantilever of 280m length, with a central span of 160m (longest in India at the time). Two pairs of cantilever gantries were deployed. The bridge with the new layout eliminating well foundations was completed in 20 months Other Records: The Chenab bridge deck was constructed with the shortest time cycle of 6 days consistently achieved for the construction of each pair of segments. This was made possible by an high early strength concrete which enabled pre-stressing at 60 hours after concreting. Fe500 steel reinforcement bars were used for the first time in India in a cantilever construction bridge. The huge Bearings with anchors were located among highly congested reinforcement; normal concrete placement, vibration was impossible. Special Conbextra Grout replaced normal High Strength Concrete below bearings. Self–compacting concrete (S.C.C) was used for the first time for concrete below the bearings. Segments on both sides of the Pier were concreted simultaneously balancing the weights. When the

22nd segments were facing each other and the shuttering of the 23rd segment i.e. the linking segment was to have been placed there was no level difference and the levels matched on both tips to the nearest millimeter both in plan (centre line) as well as in elevation. This was possible because every day the levels were maintained by a team of surveyors with the help of total station. These levels were sent to the Design consultant who monitored these personally. In fact, after the concreting of each pair of segments the levels as actually measured and as envisaged by the designer fitted almost like a ‘T’. This proves that the parameters fixed by the Design consultant and the parameters as actually achieved during execution were complimenting each other. The cables were so placed that almost all the cables were straight and without any curve. Thus prestressing results were exactly as shown in approved drawings both in of extension and gauge pressure.

Figure 7: Chenab Bridge, Giant Bearings Figure 8: Chenab Bridge Hydraulic Earthquake Dampers

The author was Value Engineering Consultant for the Fast Track Project. NBMCW September 2010 < Prev Search.....

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. 1. INTRODUCTION In the Indian subcontinent there are many rivers where the depth of alluvial deposits is very high and the scour around the pier foundations can be very deep if the piers are located within the active channel of river.

For such condition well foundation is a very appropriate type of foundation. To the author’s knowledge one 3 km long Railway bridge crossing a creek was ed on pile foundations. After some years, the sway of the pile foundations was so large when the mail trains crossed the creek; the Railways not only reduced the speed of the trains substantially but constructed another bridge adjacent to this bridge on well foundations. Thus under certain situation, well foundation is a highly desirable type of foundation. In India the technology for the design and construction of well foundation is quite advanced. In all rivers, including large rivers with torrential flow of water currents, well foundations were provided. In the foundations of Howrah Bridge in Kolkata giant monoliths were provided. In Second Hoogly Bridge also in Kolkata with one of the longest span cable stayed bridges in the world having the central span of 457 m being same as that of Howrah Bridge, an ingenius solution was adopted. Instead of a monolith for the foundation of each tower of the cable stay bridge, 2 well foundations up to 23 m dia were placed side by side at 30 m center and interconnected by a 14 m deep beam. This solution was construction-wise easier and more controllable and quantity of material used was much less. These wells were constructed purely by gravity sinking method. These well foundations under main towers were kept totally empty for the service condition. The entire well was designed as a water tight structure. At the junction of any two lifts of concreting of well steining, water stops were provided to prevent leakage of water through construction ts of well steining. The wells were constructed using gravity sinking method of construction. As stated earlier, the wells were kept totally empty and no water was inside the well during the service condition primarily to reduce the load of water on the foundations, since vertical loads were very large for the central spans of 457 m and side spans of 183 m. At the base of wells RCC slabs were constructed which were designed for the upward force from the base of the well. For of the slab and continuity of reinforcement, recesses were kept in the steining above the well curb where bond bar reinforcements were kept bent. A cover was provided with a steel plate which, were kept in position by bolts, to keep the bond reinforcement recesses free from blocking with mud’s. After the wells were sunk up to the designed level, the bottom plug was laid with colcrete. The wells were dewatered. It was noted that the colcrete bottom plug not only withstood the upward pressure but also was

reasonably leakproof. Thereafter, those steel plate covers were removed and reinforcements were bent back to the designed positions. Reinforcements were laid and concreting was done. In this way a fully water tight design was done for these wells. Deep well foundation up to 67 m deep across the river Ganga in Varanasi and upto 68 m deep across the river Brahmaputra at Jogighopa were used. In Varanasi Paper No.533

THE SINKING OF WELL FOUNDATIONS IN DIFFICULT SITUATIONS† GOURANGA PRASAD SAHA*

ABSTRACT Well foundations are quite appropriate foundations for alluvial soils in rivers and creeks where maximum depth of scour can be quite large. In India technology of well foundation for design and construction is quite well developed. Still there are situations where serious problems are encountered at site during construction of well foundations. Some of the typical problems have been identified and solutions adopted by the author and also elsewhere in some earlier jobs have been presented in this Paper. * Executive Director, M/s Construma Consultancy Pvt. Ltd. Mumbai Email: [email protected] † Written comments on this Paper are invited and will be received upto 30th September, 2007.

124 SAHA ON Bridge wells, no sand filling was done. These wells were filled with water only to reduce the weight at the founding level. In long span bridges or in bridges where the horizontal force is large, heavy foundation mass is desirable for stability and serviceability requirements point of view and hence well foundation is a highly appropriate solution. In spite of the excellent development of technology on well foundations there are still some areas where engineers face difficulty while sinking of wells, some of which are stated in this paper from the direct experience of the author. The author had the opportunity of having associated with construction of well foundations of many large and outstanding bridges including Second Hoogly Bridge, Varanasi Bridge, etc., while working with Gammon India Ltd., and Hindustan Construction Co. Ltd. 2. SINKING WELL THROUGH STIFF CLAY STRATA

If a very stiff clay layer is encountered during the sinking of a well, the engineer has to face a very tough and challenging situation if the well becomes stationery and does not move at all. At that time due to the action of horizontal water current force, the well may start tilting. The well becomes more vulnerable due to tilt if a step is provided on the outside face of the well steining to reduce the thickness of the steining. At the initial stage if the tilt is not brought under control, the tilt goes on increasing making the situation very difficult to control. This leads to a very expensive and time-consuming affair for attempting to make the well straight and vertical within practical limits. This is a very serious situation and one should

examine how this resistance is developed. A solution should be devised on the basis of insight into the causes for the resistance to sink. Referring to Fig. 1 it may be seen that the primary resistance comes on the sides and also by bearing at the base over the area of the well steining. The projection on the outside surface over the height of the kerb by 50 mm to 75 mm as recommended in IRC 78-2000 is very helpful to reduce the resistance due to stiff clay on the outside surface of the well. (a) To overcome this resistance to the author’s knowledge, the following measures have been tried by various engineers. (i) Continue grabbing much below the cutting edge level of the well. (ii) Dewater well up to certain depth to reduce the buoyancy and thereby increase the weight of the well. (iii) Remove soil in with the outside surface of the well by grabbing to a certain depth. (iv) Flushing with a jet of water on the outside soil through holes, which are kept in the steining at certain intervals during the construction of the steining of the well. (v) By thumping on the water inside the dredge hole. (vi) By Kentledge loading on the well. The merits and demerits of each of the above measures are discussed below. (i) Some engineers continue grabbing much below the cutting edge level of the well Fig. 1. Showing location of pipes within well steining (a) PIPES PLACED PERPENDICULARLY (B) PIPES PLACED VERTICALLY UPWARDS

THE SINKHINIGGHOLFI GWHTESLLO FF OTUHNE D1A7T8IOTHNCSOIUNN DCIILFFMICEUELTTIN SGITUATIONS 125 One site engineer with vast experience in construction of well foundations and claimed in achieving success by adapting this method, continued grabbing to a depth of about 10 m below the cutting edge of the well situated in the river Ganga in a major project when the well became stationary in a very stiff clay layer. This particular well was partly in the water and partly in the bank. One day the well suddenly sank to a depth of nearly 10 m leading to a major catastrophe. This was a very unwise decision, which should never have been taken. IRC 78 : 2000 specifies that sumps made by dredging below cutting edge shall preferably not be more then half the internal diameter. (ii) Dewatering well as a device to sink a well

The purpose of dewatering is to reduce the buoyancy. Thus the buoyant weight of the well is increased which increases the sinking effort of the well. But the major problem is the chance of occurring sand blow. If the sand blow occurs and if the sand blow is eccentric and the lateral force exerted on the well is high, the well may break into 4 segments along its height, which was noticed in many projects in this country. The author has developed a method for the design of a well foundation for resisting excessive sand blow forces, which was published in IRC Journal¹ in 1993. This method was used in a major bridge across river Ganga where the well foundations of 13 m diameter up to 67 m depth, which was the deepest well for a road bridge in India at that time was used. There is no literature available which specifies the evaluation of horizontal force for the design of a well foundation for the condition during construction when the well is like a hollow pipe and is in a most vulnerable condition. For such a large and deep well, IRC method of design was not used. Instead a rational and conceptual method developed by the author was used. The quantities of the well were nearly half even for such a deep well. It may be noted that all the wells were sunk to the designed founding level without any appreciable difficulty. According to the author for a major bridge with large and deep well foundations, the wells must be designed three dimensionally with a realistic lateral load during construction condition to avoid disastrous situation due to which the well steining may crack transversely. The cost of such an analysis and design is negligible compared with the unpleasant situation, which may become very expensive and delay the project badly. (iii) Remove soil in with the outside surface of the well If the top soil layers are soft, this does not help much. If the stiff clay layer exists at a shallow depth then it may help to some extent. (iv) Flushing with jet of water on the outside face of well In this process holes are kept in the well steining with outlets on the outside surface of the well. Two types of orientation of the outlets are shown in Fig. 1 (a) & (b). In Fig. 1 (a) the outlets are perpendicular to the vertical whereas in Fig. 1

(b), the outlets are inclined with the tip upwards. Experience shows that the outlet hole of the pipe gets blocked with the entry of the clay more easily than the inclined one. A plug was provided to prevent entry of sand or other softer material. This plug moves out with the force of water jet. When the well gets stuck in a very stiff clay layer, water is pumped from the top of the steining. Water coming out on the outer surface of the well is supposed to lubricate the surface and reduce the adherence of the clay on the surface of the well which consequently reduces the upward resistance against sinking down of the well. (v) By thumping on the water inside the dredge hole by dropping grab This also has been tried to overcome the resistance. (vi) By Kentledge loading on the well : The Kentledge loading is placed on the top of well either by sand bags or by concrete blocks leaving adequate space in the central zone of the dredge hole for grabbing. This weight helps 126 SAHA ON increase the sinking effort of the well. In case of tilt of a well, eccentric Kentledge load is placed for the correction of tilt. (b) The method which is different from the methods listed above had been tried by the author and briefly described below :In one project when the well became stationary in a stiff clay layer, this method was used. In those wells the outside projection of the well kerb was 75 mm. In the upper region the strata was of softer variety. Pipes were not kept in the well steining to inject water on the outside surface of the well. It has been stated earlier that the resistance to sinking comes from the outside surface of the well and also from the bearing on the stiff clay below the well kerb. In a large diameter well, the thickness of the steining is large and hence the resistance due to bearing on the stiff clay layer is quite substantial. To overcome this resistance veteran well sinking engineers continued grabbing inside the dredge hole much below the cutting edge level so that the soil below the well kerb fell off and this resistance was eliminated. The well of course used to sink down suddenly. In the design, designers used to design the well considering half the permissible tensile stress as specified in the IRC-78 to meet these eventualities . As stated earlier the method specified by the author for the design of a well three dimensionally can meet such a

situation of sudden sinking down of a well. However, due to sudden sinking down of a well there may be catastrophic consequences, hence such method of continuous grabbing is not recommended. Instead the method which will directly break the clay layer and remove the bearing below the – kerb was adopted. This was done directly by cutting the stiff clay layer by a jet of water through a pipe using a high pressure pump. This pipe was ed on a circular frame. Actually 4 vertical pipes were fixed at 4 quadrants as shown in Fig. 2. The central area was kept free in order to facilitate grabbing. The water was pumped through pipes using one high pressure pump for one pipe. Two high pressure pumps were used at one time and water was injected at two diagonally opposite points at a time. After some time, the other two perpendicularly placed pipes were used for pumping water. After some time the frame was lowered and water was injected in order to cut the stiff clay over the entire inside area at the bottom of the well kerb. The well was observed to sink down when the inside clay soil was cut and removed. After the removal of the bearing still clay strata, the wells started moving down. Thus this method was found to be quite effective, safe and efficient method. 3. BOULDERY STRATA

The bouldery strata can be dealt with 3 ways. (i) When the boulders are lying loose, they will come Fig. 2. Showing clayey strata below well kerb and layout of pipe lines ELEVATION OF WELL AND PIPE LINES

THE SINKHINIGGHOLFI GWHTESLLO FF OTUHNE D1A7T8IOTHNCSOIUNN DCIILFFMICEUELTTIN SGITUATIONS 127 out with normal grabbing. (ii) When they are cemented but not very firmly then underwater blasting may be effective. (iii) When the boulders are very firmly cemented and the thickness of the steining of the well is quite large then pneumatic sinking may have to be resorted to. In case of bouldery strata, the proper soil investigation should be done and what method of sinking is to be adopted must be decided. The design of the well must be done for such a condition. At least provision for limited blasting must be made and a three dimensional finite element analysis should be done for eccentric blasting force. The steining of the well must be designed not only in the vertical direction but also in the transverse direction providing appropriate design reinforcement. Steel strakes must be provided in such condition. It should be noted that in the past many well steining cracked due to

blasting. The wells of Varanasi Bridge of 13 m dia, 2.5 m thick steining and up to 67 m deep were analysed for eccentric sand below condition by using 3-D Finite Element analysis by the author1. This became helpful to take care of adverse situation during sinking of wells. Formation of Heaves in the Dredge Hole even after the well reaches the Designed Founding Level. When a well es through soft strata over a considerable depth, the upward resistance acting on the outside surface of the well is less than the weight of the well. In that situation the well sinks down and quite often a heap is formed inside the dredge hole as shown in Fig 3. When the formation of heaves takes place after the well reaches the designed foundation level, then the engineers face the problem of laying the bottom plug. If the bottom plug is laid inside the dredge hole then the very purpose of laying the bottom plug is defeated, since the load from the well is transmitted to the foundation through the well steining and the bottom plug which lies just below the well steining. The author had developed a method² to overcome this problem. In a number of well foundations where large heaves were formed inside the well, the author used this method and the formation of heaves was stopped. Thereafter the bottom plug was laid within the well kerb region. For the benefit of readers this method is stated briefly here below :How to achieve the condition that the weight of the well will be resisted through outside frictional force only. Fig. 3. Showing the formation of heave

It is reckoned that no further concreting of the well steining should be done and sinking should be continued. In that case, the weight of the well will remain nearly same and the frictional force outside the well will increase very fast, the founding strata being in good soil. It is thought that the equilibrium of the well will reach with shorter depth of sinking below the designed founding level. The following method is used to evaluate the approximate depth of further sinking and also the height of water to be considered for the design of the cofferdam along the outer perimeter of the well at top. When the heave develops in the dredge hole, the equilibrium of the well takes place as per the following equation : W = F+qa Eqn. ... (1) F = frictional force in the vertical direction along the outside surface of the well.

128 SAHA ON q = bearing pressure of soil. a = area of the well ed over the heave i.e. over the distance X, Fig. 4. X = tan A. h = height of heave. A = angle at the tip of well curb. The component qa is required to be balanced by the additional frictional force over the outside surface of the well, which will develop by sinking the well deeper. Thus fl al = qa Eqn. … (2) Where fl = the frictional force acting on the outside surface of the well over depth of further sinking of the well per unit area which is evaluated below. al = area of the outside surface of the well over depth of further sinking. Referring to Fig. 4 fl = p x (coefficient of friction) p = (pl + p2)/2 pl = active earth pressure at a depth H below the existing water level or ground level whichever is higher. p2 = active earth pressure at a depth H + h1 h1 = depth of further sinking. Substituting p in fl and fl in Eqn. 2 as shown in Fig. 4, hl can be evaluated. 4. FEW OTHER MEASURES WHICH CAN HELP RELATIVELY TROUBLE FREE SINKING OF WELLS

(i) Appropriate choice of cutting edge and adoption of Fig. 4. Showing additional sinking without any further concreting of steining (a) POSITION OF WELL AT DESIGNED FOUNDING LEVEL WITH HEAVES IN DREDGE HOLE (b) POSITION OF WELL AFTEER ADDITIONAL FURTHER SINKING WITH NO HEAVE IN DREDGE HOLE

THE SINKHINIGGHOLFI GWHTESLLO FF OTUHNE D1A7T8IOTHNCSOIUNN DCIILFFMICEUELTTIN SGITUATIONS 129 proper detailing Two types of cutting edges are of use for well foundations as shown in Fig. 5 (a) & (b) of IRC – 78 : 2000. The angle iron cutting edge works well when the well es through alluvial soil strata without any hard obstruction. There are instances when the cutting edge met some hard obstruction, it became dislodged and caused obstruction to the well. Compared with the angle iron cutting edge a V type cutting edge is more appropriate in meeting various obstructive situation provided correct detailing is adopted. The inclined plate should be stopped about 25 mm above the bottom tip of vertical plate and the welding of the t between the vertical plate and the inclined plate must be done as shown in Fig. No.5(b). The vertical and the inclined plates must not meet at the bottom most point and consequently the welding must not be done at the bottom tip. The

author is aware that in many bridges in the Himalayan region where the strata are full of boulders the welding at tip came off and the plates were bent out and caused lots of obstruction to sinking leading to various problems including delay in progress of construction. Hence it is advised to adopt detailing as shown in Fig. 5(b). (ii) Adequate no. of Borelogs must be taken in the location of each well As per the present practice only one Borehole is taken at each foundation location. The soil properties of various strata are available along the depth. To obtain the complete information of the existence of type of soil/rock or large boulders if any covering a part of well foundation at least 3 boreholes should be taken. If the diameter of well is large, then at least 4 bore holes should be taken. With this knowledge the span arrangements be made so that wells can be sunk smoothly. Soil properties should be taken of one borehole for the design of foundations whereas the other boreholes will present information on the type of strata, locations and their depths. Presence of very large boulder covering a part of the well at some depth in the bridge over third Brahmaputra at Jogighopa and similar type of problems including sudden change of bed profile are encountered in various rivers in India for which a very expensive time consuming measures were adopted. This can be avoided if enough information of the soil strata is available at the time of design. (iii) Floating Caisson Sinking When the depth of water at the location of a well is more than about 5 m then construction of well on temporary sand island is not only difficult but also uneconomical. In this situation steel caisson is fabricated on the bank and floated in water either by tilting platform or by a gantry. If the caisson is very large and very heavy then tilting platform is more convenient. In other cases normally the caisson Fig. 5 (b) :Typical details of V-shaped cutting edge Fig. 5 (a) :Typical details of angle iron cutting edge

130 SAHA ON is brought to the water using a gantry. However, the choice of tilting platform or a gantry or by some other means should be made as per the locally available resources and convenience. After the floating caisson is brought to the designed location of the well, further building up of caisson is done. This work together with concreting inside the caisson to the designed depth is done till the cutting edge reaches the bed level of the river. This is a very

critical stage. There is every possibility of tilt and shift occurring, since the caisson is subjected to unidirectional flow of water. In several projects, large tilt and shift occurred which subsequently created a lot of problem with that project. The tilt and shift must be checked very thoroughly before grounding and suitable corrective measures must be taken if any tilt or shift occurred. Some measures are suggested here below which if adopted judiciously should minimize the tilt and shift of the caisson. (a) For large diameter caissons After taking the caisson to the designed location the caisson should be anchored to the already installed dead anchors at least at 6 locations as shown in Fig.6 with ropes with adjustable device. Each anchoring should also be done at 2 locations in elevation. By pulling or releasing the anchor rope the tilt and shift can be eliminated. Steel piles may be driven inside the dredge hole at 4 corners after ensuring the correct position of the well. (b) For caissons with sinking sets The barges should be located towards upstream and downstream of the river and anchored at least at the locations as shown in Fig.7 with the device for adjustment so that the well can be positioned at the designed locations. The caisson is placed between the barges with very small clearance between any two barges and the caisson so that with the water current force acting on the caisson below the barges, tilting of the caisson is restrained. However, in case of any tilt or shift occurring the same is controlled by pulling or releasing the anchor ropes appropriately. WATER LEVEL WATER LEVEL WINCH

ELEVATION RIVER BED LEVEL WINCH

PLAN

Fig. 6 DIRECTION OF RIVER FLOW

ELEVATION WATER LEVEL WINCH WATER LEVEL WINCH RIVER BED LEVEL

PLAN

Fig. 7

THE SINKHINIGGHOLFI GWHTESLLO FF OTUHNE D1A7T8IOTHNCSOIUNN DCIILFFMICEUELTTIN SGITUATIONS 131 5. CONCLUSION

On this paper a list of difficult situations, which bridge engineers normally encounter during sinking of well foundations, is presented. In some cases the author himself devised some solutions to some perennial problems, which have been described in this paper. The problems like the formation of hump inside the dredge hole of a well foundation or wells cracking due to sand blow, or in a stiff clay layer wells becoming stationary

and not sinking down are quite common situations. In several major projects where such situations developed the author as the Technical Head of that organization, developed methods and adopted them to overcome those problems and these methods are presented in this paper. ACKNOWLEDGEMENT

The author is indebted to Dr. T N Subba Rao for making many valuable suggestions by sparing his valuable time, to make this Paper more complete. REFERENCES

1. Saha G.P. “Analysis and Design of Varanasi Bridge Well Foundations – A Conceptual Approach” Journal of Indian Roads Congress Vol. 54-2. Paper presented in the Annual Session of IRC in November 1993. 2. Saha G.P. “Method of Stopping the Formation of Heaves Inside the Dredge Hole of a Well

CE 1203 CONSTRUCTION TECHNIQUES, EQUIPMENT AND PRACTICES Foundation” Indian Highways,

(Two Mark Question and Answers) NAME: K.J.JEGIDHA, M.E. Lecturer, Civil Department NICE. UNIT-I CONSTRUCTION PRACTICES 1. What are the general specifications for first class building? Foundation and plinth. superstructure. damp-proof course. lintels. roofing. plastering. doors and windows. distempering and colour wasting. painting. 2. What are monolithic wall? write its classifications? Monolithic walls:-Walls built of a material requiring some kind of shuttering in the initial stages. Masonry can be classified into the following types stone masonry. brick masonry. hollow block concrete masonry. reinforced masonry. composite masonry.

3. Define plinth. Plinth:- It is the horizontal course of stone or brick provided at the base of the wall above ground level. It indicates the height of the ground floor level above the natural ground level. It protects the building from dampness. 4. What are classifications of stone masonry There are two types ,they are rubber masonry. ashlar masonry. 5. What is rubber masonry and ashlar masonry? Rubber masonry:Stones of irregular sizes are used. stones may be undressed or roughly dressed. using hammer having wider ts. Ashlar masonry:This is a costlier, high grade and superior quality of masonry. The work built from accurately dressed stones with uniform and very fine ts of about 3mm. thickness is termed as ashlar masonry. 6. Compare English bond and Double Flemish bond. English bond double Flemish bond. More compact and stronger for walls having thickness more than 1(1/2) bricks. Not pleasing appearance of the facing. No strict supervision and skill required for its construction. More in cost than Double Flemish bond. Less compact and stronger. Better appearance in the facing. Good workmanship and careful supervision is required. Cheaper in cost-because number of bricks bats are used. 7. What are the defects in brick masonry. Defects in brick masonry:Sulphate attack. Crystallization of salts from bricks. Corrosion of embedded iron or steel. Shrinkage on drying. 8. Mention the common sizes of building blocks. The common sizes of building blocks are 390x190x300 mm- standard size hollow block. 390x190x200 mm- hollow building tiles. 390x190x100 mm- hollow concrete blocks for partition. 9. What the types of flooring commonly used. mud flooring muram flooring

cement concrete flooring mosaic flooring tiled flooring marble flooring 10. Define damp proof course., what are its causes of dampness. Definition :-The courses which are laid to check the entry of water or moisture into the building are called damp proof courses. Causes:faulty design of structure faulty construction or poor workmanship use of poor quality materials in construction. 11. Define roofs. Roof:-A roof is defined as the uppermost part of the building which is constructed in the form of a frame work to give protection to the building against rain , heat wind etc.. 12. What are the uses of water proofing compounds. Uses:- When water proofing compounds is added to cement during construction it prevents leakage. It is available in powder form. It is mixed with cement by hand before cement is mixed with aggregate. 13. what are the condition for filters. Condition for filter:It should remove harmful particles from air. It should be workable under different velocity. It should have very low frictional resistance. It should not cause contamination of incoming air. it should be easy to clean. 14. Define fire resistance Fire Resistance:- It is the time during which an element of structure fulfils its function in building safely in the event of fire of known intensity. Fire resistance is also defined as an index of fire safety of buildings. 15. Define acoustics Acoustics:-The term acoustics is defined as the science of sound, and it describes the origin ,propagation and sensation of sound. 16. What are the conditions for good acoustics of an auditorium:Conditions for good acoustics of an auditorium:The initial sound should be of adequate intensity or loudness. It is important for a speaker to be heard over a long distance. The sound produced should be evenly spread over the whole area covered by audience. If the sound is not evenly distributed echoes will be established. the initial sound should be clear and distinct. For music hall ,the initial sound should reach the audience with same frequency and intensity. All undesired sound should be reduced. 17. Define scaffolding:Scaffolding:-It is defined as the temporary structure employed in the building construction for ing workers, materials and tools etc., during its

construction alteration, demolition, painting and repair etc., 18. Write the types of scaffolding. Types of scaffolding:Single scaffolding or Brick layer scaffolding. Double scaffolding or Masons scaffolding. Ladder scaffolding. Cantilever or Needle scaffolding. 19. Write any some materials used for ts. bituminous felt Metal strips Fibre board these are some of the materials used for ts. 20. Define flooring Flooring:- The properly ed horizontal surfaces which divide the building into different levels for providing accommodation one above the other within space are called floors.

UNIT-II SUB STRUCTURE CONSTRUCTION 1) What is a cofferdam? When it used ? Cofferdam is a temporary structure constructed to exclude water from the site to construct a permanent sub-structure, without the interface of water. It is used when the well foundation is to be carried in running water. 2) What is a caisson? What are the types of caisson? It is a special type of foundation used for the construction of bridge piers in v prevent ery deep water, where it is either difficult to construct a cofferdam or to prevent its leakage. Types: a) Box caisson b) Open caisson c) Pneumatic caisson 3) What are the components of well foundation? The components of the well foundations are, a) Well curb b) Cutting edge d) Steining 4) What are the operations involved in open caisson method of foundation? The open caisson method of foundation consists of the following operations: a) constructing or fabricating the caisson and preparing site to receive it. b) placing the caisson over the site of the pier. c) excavating the soil from the interior of the caisson and advancing the d) caisson so that its cutting edge is at or below the bottom of the excavation and continuing this process until the foundation in the hard stratum is reached. d) sealing the bottom of the caisson to exclude water and soil. 5) What are the uses of sheet piles?

The uses of sheet piles are, a) For preventing leakage of pile material and water. b) For preventing the structure from shocks ,vibrations, etc,. c) For deep excavations to enclose soils to prevent lateral crust or pressure. 6) What is a shoring? Shoring is a temporary structure used to tilted or endangered walls .The walls might have been endangered due to unequal settlement of foundation, removal of ading structures or making large opening in the walls. 7) What is meant by pipe jacking? Pipe jacking is a method of installing a pipe under roadway , railway or highways without using an open cut trench .The pipe jacking procedure uses a casing pipe of sheet or reinforced concrete ie, jacked through the soil. 8) What is dewatering? Where it is used? Dewatering means removal of excess water from the saturated soil. It is used where the water table is very high or in the case of deep excavations the foundation trenches for buildings and other structures, are filled with seeped water. 9) What is a under-ream pile? It is a pile with one or more bulbs in its vertical shaft .These bulbs are known as under-reams and it increases the bearing capacity of the soil. 10) Write about spacing of piles? For piles to be driven on hard stratum the minimum center to center spacing is 2.5 times the pile diameter. In case of friction piles minimum spacing of 3 times the diameter of the pile shaft is provided. In case of loose soil filled up area or sand the minimum center to center spacing is twice the pile diameter. 11) Explain about suspended scaffolding. During repair cleaning and painting various types of working platforms are required at various levels which can be easily provided and removed. Such types of platforms can be suspended by ropes or chains from parapet wall of buildings or cantilever beams placed at the top of the structure. This types of working are called suspended scaffolding. 12) Write about centering and shuttering? Centering is a temporary structure used for the construction of arches , whereas shuttering is a temporary structure used for the construction of R.B. or R.C.C. structures such as beam ,slab ,balcony ,porch ,etc ,. Centering are wooden shaped frames and shuttering are known as mould. 13) What is a Kent ledge? In well sinking ,to overcome the increased skin friction and the in weight of the well due to buoyancy, additional loading is applied on the well . It is called Kent ledge. 14) What are the methods used for tunnel driving? Following are the methods generally used for driving a tunnel, a) Full face heading b) Heading and bench method c) Drifts method

d) Pilot tunneling 15) What is mucking? The operation of removal of excavated material in tunneling operation is called mucking. 16) hat are the advantages of drift method? Drift method of tunnel excavation has the following advantages: a) It helps to determine the region of bad rock or excessive ground water before actually taking up the full excavation, so as to enable to take up the corrective measures. b) The drift provides ventilation while driving the main tunnel. c) It reduces the consumption of explosives. 17) Explain about cement grouting .Uses . In this method, cement grout which is a mixture of cement , sand and water is used. The process consists of making a number of holes in ground and then filling these holes by cement grout under pressure. This process is continued till no grout is coming up through the hole. Uses: a) The grouting procedure can be used in stopping leakages from rock. b) It can also be used to fill the voids in soil so as to strengthen the soil and to make the rock or soil water tight. 18) Write the situations under which pile foundation is recommended. The pile foundation is recommended for the following situations: a) When spread footing ,raft and grillage foundations are uneconomical. b) When heavy concentrated loads are to be transmitted by the foundations. c) Where there is scouring in the soil near the foundations. c) Where the soil is made up and of a compressible nature. 19) Write the essential features of a pump to be used for dewatering. The pump to be used for dewatering process should have the following features: a)The pump should be portable so that it can be easily moved as and when required. b)The pump should be capable of handling water mixed with impurities such as sand, earth, etc,. c)The pump should be of strong make. d)The performance of pump should be reliable. 20) What is the equipment used for driving a pre-cast pile in a sandy soil? The equipment used for driving a pre-cast pile in a sandy soil is a hammer. Hence maximum stresses are developed at the top due to direct strokes and at the point in overcoming the resistance to penetration. Therefore additional reinforcement is provided.

UNIT-III SUPER STRUCTURE CONSTRUCTION 1. What are launching girders? For erection of large beams in buildings or bridges, temporary girders are

used. Such girders are called launching girders. Launching girders are usually of steel as it would be light compared to concrete girders. 2. What are bridge decks? In bridges, the structure ing the carriageway is called decks. The bride deck transfers the load to the piers or abutments. The bride decks can be classified as slabs, T-beam and slab, or composite decks. In composite decks, beams are pre-stressed or of steel and the slabs would be concrete cast in situ. 3. What are offshore platforms? Offshore platforms are structures constructed in the ocean to explore or to produce oil and gas from the sources found below the sea. Offshore platforms are in steel or in concrete. 4. What are Jacket platforms? The steel offshore platforms are called Jacket platforms. They are vertical towers constructed with steel tubular ing the deck, where the machinery for drilling or processing oil or gas is located. They are connected to the ocean floor by means of piles. 5. What are gravity towers? In concrete construction, the offshore platforms are called Gravity towers which consist of concrete circular shafts ing the processing platforms. The offshore platforms are subjected to loads from ocean waves. 6. What is a bow-string bridge? In this type of bridge, the horizontal thrust is resisted by the horizontal ties. The s take up only the vertical reaction. They, therefore require thinner sections. Bow-string girdes of R.C.C are commonly adopted for arch bridges having span of 30m to 45m. At various points along the length of a tie beam, vertical posts or suspenders connecting the tie beam to the arched rib are provided. The flooring is resting on the tie beam and transfers its load to the arch through the suspenders. Thwe flooring may be of simple slab or beam and slab construction. 7. What are cable-stayed bridges? These bridges provide a larger width for purposes of navigation by eliminating intermediate piers. They consist of cables provided above the deck and are connected to the towers. The deck in case of cable stayed bridges is either ed by a number of cables meeting in a bunch at the tower (fan form) or by ing at different levels on the tower (harp form). 8. What are chimneys? Chimneys are structures used to escape the gases to such a height that the gases donot contaminate the surrounding atmosphere. The cross sectional area of the chimneyis kept large enough to allow the age of burnt gases. 9. State the dimension of flue hole opening in chimney. 40 x 40 cm 10. What are the various loads acting on a chimney? 1. Self weight of masonry chimney 2. Weight of lining 3. Wind pressure 4. Seismic forces 11. How is lining made in chimney?

The mareial used for lining should be capable of withstanding high temperature upto 2000 F. The fire bicks are used for lining in brick masonry chimneys. The fire brick lining must be free to expand and contract independently of the main chimney. Yhe height of lining depends on the purpose of chimney. 12. What are the various types of chimneys? R.C.C chimney Brick chimney Self ing stacks Guyed steel stack 13. What are the forms used in the construction of chimney? Jump forms, Slip forms 14. What are cooling towers? Cooling Towers are used to cool the water that is used to recondense the steam that is used to generate electricity. 15. What are the methods of prestressing? 1. Pre tensioned Metod 2. Post tensioned Method 16. What are the systems of prestressing? 1. Freyssinet System 2. Magnel-blaton System 3. Lee-Mc. Call or stress steel system 17. What are the advantages of prestressed cement concrete? 1. It is possible to take the full advantage of compressive strength of concrete and high tensile strength of the steel used. 2. 15 to 30% of the concrete is saved. 3. 60 to 80% of the steel is saved. 4. Presressed concrete are thinner in section and hence there is greater reduction of the self weight of the member. 18. How are domes erected? Domes are usually erected with a central temporary on which the ing ring rests. If the span is greater than 40 – 50m, the tower of an erecting frame serves a sthe . 19. What are shells? Shalls are three dimensional structures constructed as storage tanks or roof for large column free areas, such as exhibition halls, sports complex or theatres. 20. How are shells classified ? 1. Singly curved shells like cylindrical shells 2. Doubly curved or spherical shells

UNIT-IV REPAIR AND REHABILITATION 1. What are the causes of stresses in a building component? Stress in a building component can be caused by external forces such as dead, live, wind or seismic loads or foundation settlement or can be induced internally due to thermal movement, moisture changes, chemical action etc. 2. What is an Active and Dormant crack? Active:

A crack is said to be active if it is still in progress, that is, the crack is still developing. This may be ascertained by filling the crack with mortar and observing. If the crack reappears, it is considered live, that is, it will further. Dormant: A dormant crack is the one which once formed remains static and doesn’t get altered due to age of time. 3. What are the classifications of crack based on width? Fine : Width less than 0.1 mm Thin : Width 0.1 to 0.3 mm Medium : Width 0.3 to 0.7 mm Wide : Width 0.7 to 2.0 mm Very Wide: Width greater than 2 mm 4. What are the basic symptoms of distress in concrete? The three basic symptoms of distress in concrete are: Cracking Spalling Disintegration 5. What are the Defects in Masonry Structures? The Defects in Masonry Structures are: i. Dampness ii. Condensation iii. Efflorescence iv. Structural and Surface cracks v. Stains 6. What are the Defects in Masonry Structures? i. Rusting ii.Excessive deflections iii. Buckling and bending iv. Twisting v. Lateral Bending vi . Pitting vii Defects in welds such as shearing, bearing failure and tearing failure. 7. What are the types of Distress in structures? The following are the types of Distress in Structures: i. Local settlement of sub-grade ii. Movement of form work iii. Vibrations iv. Internal settlement of concrete shrinkage v. Setting shrinkage 8. What are the causes of Dampness? Dampness are attributed to the following i. Leakage from defective roofing system ii. Porous bricks iii. Vegetation Growth iv. Earth backi9ng against masonry construction 9. What is Condensation? The saturated air enters the building and coming in with cooler surfaces of windows glass panes, iron works, painted or varnished surfaces, losses temperature and is deposited on the impervious surfaces. This phenomenon is termed as condensation. Condensation causes dampness and affects brick wall. 10. What is Efflorescence? Efflorescence is purely the result of natural laws and is the direct outcome

of the situation of the brick work which causes large irregular shaped patches of whitish mould formed on the surface of the and thus disfigure its appearance, which usually contains various soluble salts. 11. What is meant by maintenance of Structure? Maintenance is a continuous cycle which involves e3very element of building science, namely, i. Structural ii. Electrical wiring iii. Plumbing- Water supply –Sanitation iv. Finishing on floors and walls v. Roof terrace vi. Service perform/verandah vii. Lifts viii. Doors windows and other elements 12. What are the Corrosion Prevention methods for Reinforcing Bars? Corrosion Prevention methods for Reinforcing Bars are, a) Cathodic Protection b) Application of a carbonation resistant polymer film on the surface of the concrete c) Application of the galvanizing coat on steel d) Application of poly coating like epoxy, polyurethane fusion bonded epoxy etc. on steel e) Application of specially formulated alkaline polymer emulsion 13. What are the preventive measures to be taken in the construction of new water tank? i.The mix of concrete ii.Blended cement iii.Aggregates iv.Sand v.Water vi.Curing vii.Cover ixSurface coatings x.Coating on Reinforcement 14. List any four factors which influence corrosion in a structure/ i. pH value ii. Moisture iii. Oxygen iv.Carbonation of Concrete 15. List out the various Damages that occur due to Corrosion. 1.Formation of white patches 2.Brown patches along reinforcement 3.Occurrence of cracks 4.Formation of multiple cracks 5.Spalling of cover concrete 6.Snapping of bars 7.Buckling of bars and bulging of concrete 16. What are the various non- destructive tests on Concrete? 1)Rebound hammer test 2)Ultrasonic pulse- velocity test 3)Potential measurement 17. What is the purpose of conducting Rebound hammer test? Rebound hammer test is conducted to evaluate the compressive strength of the affected portion and the same could be correlated with the desired strength of the element of structure.

18. Name the three electrodes used for potential measurement. i.Saturated calomel electrode ii.Silver/Silver Chloride electrodes iii.Copper/Copper Sulphate electrodes. 19. What is meant by Epoxy Grouting? Epoxy grouting is a technique which has been used in recent past with a high degree of success especially in treating deep routed and subcutaneous cracks. 20. What is Polymer Concreting? Polymer Concreting is a method in which polymer such as modified latex, neoprene, polyvinyl acetate, styrenebutadience, and acrylic polymers are used as polymer additives in conjunction with cement concrete. This results in very high impermeability and high acid resistance thereby making polymer concrete as a very suitable material fore use as original concrete to counteract corrosive forces. This can also be used as a repair material to replace the affected concrete.

UNIT-V CONSTRUCTION EQUIPMENT 1. What are the advantages of using trenchers? The advantages of using trenchers are _ It is a faster and cheaper method of trenching _ It digs only as much as is necessary _ It is a continuous process and is not like that of back hoe excavator 2. Define dredging. Dredging is the process of excavating from river bed, lake or sea for the purpose of deepening them. It is an important operation in navigation canals, harbours, dams etc. Dredgers are of three types namely 3. Mention the various operations involved in grading? The various operations involved in grading are _ grading _ spreading _ finishing and leveling _ Ditch digging _ cutting _ bank cutting _ earthen road maintenance _ earthen road construction and _ repairing gravel road 4. What are the factors affecting the selection of drilling equipment? The factors affecting the selection of drilling equipment are _ the nature of terrain _ required depth of holes _ rock hardness _ the size of the project and _ the purpose for which holes are required. 5. Define hardness. Which is the hardest known substance?

Hardness is defined as the resistance of a smooth plane surface to abrasion. It is the hardest known substance with hardness 10. 6. Define texture. What are its classification. Texture is defined as the grain size of the rock. It is classified into 5 categories such as _ porous rock _ Loose grained rock _ Granitoid rock _ Fine grained rock and _ Dense rock 7. What are the types of drilling equipment? The types of drilling equipment are Percussion drills and Rotary drills Rotary drills are further classified as Pressure drilling and Abrasion drilling 8. Define blasting? Blasting is the process of discharging of an explosive to loosen the rock. 9. What are the parameters to be examined while blasting for quarrying? While blasting for quarrying or excavation, the following parameters are to be examined. _ Spacing of the drill holes _ Diameter of the drill holes _ Depth of the drill holes _ Burden of the rock at the toe _ Burden of the rock at the crest _ Degree of fragmentation desired and _ Strength of the explosives to be used 10. What are the types of dredgers? Dipper dredger, Ladder dredger and Suction dredger 11. Mention the sequence of operations involved in driving the tunnel through rock? The sequence of operations involved in driving the tunnel through rocks are _ Setting up and drilling _ Loading the holes with explosives and firing _ Ventilating and removing the dust resulted by explosion _ Loading and hauling the muck _ Removing ground water from the tunnel _ Erection of s for the roof and sides _ Placing reinforcement _ Placing the concrete lining _ Curing and shuttering removal 12. What are the objectives of ventilation system in a tunnel? The main objects of ventilation system in a tunnel are _ to provide fresh air for workers _ to remove poisonous gases and fumes produced by explosion

_ to remove the dust caused by drilling, blasting mucking and other operations performed in the tunnel. 13. Define mucking? Mucking is the operation of loading the broken rock or earth for removal from a tunnel. Mucking is done by hand in small tunnels, drifts and pilot tunnels. 14. What is a tractor? Mention its types? Tractor is an earthmoving equipment which converts engine energy into tractive energy. The two types of tractors are _ crawler or tract type and _ wheel or pneumatic type 15. Define compaction? Compaction is defined as the process of densifying or increasing the unit weight of a soil mass through the application of static or dynamic force, with the resulting expulsion of air. 16. Define surface load? Surface load is defined as the ration of total applied load and the total area of the minimum number of feet which come simultaneously in with even ground without penetration. axle load kg (ie) Surface load = area of feet cm2 17. What are the factors influencing compaction? The factors which influence compaction are _ static weight _ number of vibratory drums _ roller speed _ drum diameter _ frequency and amplitude _ relationship between frame and drum weight _ driven or non driven drum _ centrifugal force and _ total applied force 18. Name the equipments used for volume batching? The equipments used for volume batching are _ aggregate feeders _ cement silo _ water measuring device and _ mixing unit 19. What are the various types of conveyors? The various types of conveyors are _ belt conveyor _ roller conveyor _ chain or cable conveyor _ pipe line conveyor _ screw conveyor and _ elevating conveyor

20. What are the advantages of using belt conveyors? The advantages of using belt conveyors are _ It is capable of handling light or heavy, fine or coarse, wet or dry material. _ It can handle, thousands of tons of material per hour for several kilometers. _ It can handle not materials up to 1600c. _ It operates without noise. June 2002.

Well Foundations

1200 Well Foundations 2

Section 1200 Well Foundations 1201 DESCRIPTION This work shall consist of construction of well foundation, taking it down to the founding level through all kinds of sub-strata, plugging the bottom, filling the inside of the well, plugging the top and providing a well cap in accordance with the details shown on the drawings and as per these Specifications, or as directed by the Engineer. In case of well foundations of size larger than 12 m diameter, supplemental construction specifications will be necessary. 1202 GENERAL 1202.1 Wells may have a circular, rectangular or D-shape in plan and may consist of one, two or more compartments in plan. The outer wall of the well, known as well steining may be cellular. The process of taking down the well to the founding level is known as well sinking. After reaching the founding level, the hollow inside the well, (“dredge hole”) is plugged at the bottom by concrete (“bottom plug”). The dredge hole is then filled with approved filling upto the level indicated on the drawings and provided with a concrete plug (“top plug”). To facilitate sinking of well, steel cutting edge is fabricated and connected to a concrete well curb of required shape. On top of the well curb, adequate height of well steining is cast and the process of sinking is carried out. After a portion of the well has been sunk, another height of well steining is cast on top of the previous section and further sinking carried out. This process is continued till the bottom level of the well reaches the founding level. At the top of the well steining, well cap” is laid which transmits the loads and forces from the sub-structure (piers or abutments) to the foundations. 1202.2 At least one bore-hole must be available/carried out in accordance with these

specifications at each well foundation location, prior to commencement of work. The depth of bore-holes should extend upto a depth equal to one and a half times the outer diameter/ least dimension of the well below the anticipated founding level. The results of soil exploration should be presented in accordance with Clause 704.3 of IRC:78. In case the well foundation is to rest on a rocky strata, it may be necessary to undertake additional borings/probings prior to commencement of work to ascertain the actual profile and the quality of the rocky strata, at the level at which the well has to be seated, etc. 1202.3 Blasting may have to be resorted to in order to facilitate sinking through difficult strata, such as boulders and rocks etc. In case blasting is anticipated, protective/ strengthening measures specified in Sub-Clause 6 of Appendix 4 of IRC:78 shall be 3

Well Foundations Section 1200 taken. The grade of concrete in bottom 3 m of steining shall not be leaner than M 20 or as shown on the drawings. 1202.4 In case the bore hole data shows the presence of steeply dipping rock, chiseling may have to be resorted to so as to obtain proper seating of the foundation. For this purpose, the well may require to be dewatered completely under high air pressure inside the well. This process is known as pneumatic sinking. Pneumatic sinking may also have to be resorted to in cases where obstacles such as tree trunks, large sized boulders or hard strata etc. cannot be removed by open dredging. The necessity of adopting pneumatic sinking shall be decided by the Engineer. The curb and steining have to be specifically designed for special loadings when pneumatic sinking is adopted. 1203 SETTING OUT AND PREPARATIONS FOR SINKING 1203.1 Necessary reference points shall be fixed, away from the zone of blow-ups or possible settlements resulting from well sinking operations. Such reference points shall be connected to the permanent theodolite stations with the base line on the banks. The center of the individual wells shall be marked with reference to these stations. The distance, wherever practicable, shall be checked with the help of accurate tapes and precision distomat. Reference points shall also be fixed to mark X-X axis (usually traffic direction) and Y-Y axis (normal to X-X axis) accurately. A temporary bench mark shall also be established near the well foundation, away from the zones of blow-ups or possible settlement. The bench mark shall be checked regularly with

respect to the permanent bench mark established at the bridge site. 1203.2 For wells which are to be located in water, an earthen or sand island shall be constructed. Sand islands are practicable for water depths of about 5 m under stable bed soil conditions. For greater depths or in fast flowing rivers or for locations where soil is too weak to sustain sand island, floating caissons may have to be adopted. The plan dimensions of sand islands shall be such as to have a working space of at least 2 m all around the steining. The dimension of the sand islands shall however be not less than twice the dimension in plan of the well or caisson. Sand islands shall be maintained to perform their functions, until the well is sunk to a depth below the bed level at least equal to the depth of water. Sand island shall be protected against scour and the top level shall be sufficiently above the prevailing water level to be decided by the Engineer so that it is safe against wave action. 4

Section 1200 Well Foundations While sand islands are constructed at well location, floating caissons are generally fabricated at or near the banks on dry land or dry docks. Floating caissons are towed into position in floating condition. Floating caissons may be of steel, reinforced concrete or a combination of the two. They should have at least 1.5 m free board above water level and increased, if considered necessary, in case there is a possibility of caissons sinking suddenly due to reasons such as scour likely to result from the lowering of caissons, effect of waves, sinking in very soft strata etc. Stability of floating caissons shall be ensured against overturning and capsizing while being towed and during sinking for the action of water current, wave pressure, wind etc. For floating caissons, a detailed method statement for fabrication, floating and sinking of caissons shall be prepared and furnished to the Engineer. Such statement shall include the total tonnage of steel involved, fabrication and welding specifications, list of materials and plant and a description of operations and manpower required for the work. The caisson shall be tested for leakages before being towed to site. For well placed in the banks of the river or in the dry area, the bed may be prepared by excavating the soil up to 1.5 m followed by leveling and dressing before placing the cutting edge. 1203.3 Equipment Equipment shall be deployed for construction of well foundation as required and as directed by the Engineer. Generally, the following equipments may be required for the work:

a) Crane with grab buckets – capacity 0.5 to 2.0 cu.m b) Submersible pumps c) Air compressors, air locks and other accessories where pneumatic sinking of well is anticipated d) Chisels of appropriate sizes e) Aqua-header for cutting rocky strata f) Diving helmets and accessories g) Equipments for concrete production, transportation and compaction 5

Well Foundations Section 1200 1204 CUTTING EDGE 1204.1 The mild steel cutting edge shall be made from structural steel sections and shall be strong enough to facilitate sinking of the well through the type of strata expected to be encountered. The weight of the cutting edge shall not be less than 40 kg per metre length and be properly anchored into the well curb, as shown in the drawing. When there are two or more compartments in a well, the bottom end of the cutting edge of the inner walls of such wells shall be kept at about 300 mm above that of outer walls. In V shaped cutting edge, the inclined plate should meet the vertical plate in such a way that full strength connection by welding is feasible. 1204.2 The parts of cutting edge shall be erected on level firm ground. Temporary s shall be provided to facilitate erection and maintaining the assembly in true shape. The fabrication may be carried out in the shop or at site. Steel sections shall not be heated and forced into shape. However, “V” cuts may be made in the horizontal portion, uniformly throughout the length, to facilitate cold bending. After bending, such “V” cuts should be closed by welding. ts in the lengths of structural sections, unless otherwise specified shall be filler welded using single cover plate to ensure the requisite strength of the original section. 1204.3 The cutting edge shall be laid about 300 mm above prevalent water level. 1205 WELL CURB 1205.1 The well curb shall be such that it shall offer minimum resistance while sinking, but shall be strong enough to be able to transmit superimposed loads from the steining to the bottom plug. The shape and the outline dimension of the curb as given in Appendix -3 (Fig. 2) of IRC:78 may be referred for guidance. The internal angle of the curb as shown in Appendix 3 shall be about 30o to 37o. depending upon geotechnical data. The well curb may be pre-cast or cast-in-situ. The well curb shall be reinforced concrete of mix not leaner than M 25 with minimum reinforcement of 72 kg/cu.m excluding bond rod. The steel shall be suitably arranged to prevent spreading and splitting of curb during sinking.

Steel formwork for well curb shall be fabricated strictly in conformity with the drawing. The outer face of the curb shall be vertical. The bottom ends of vertical bond rods of steining shall be fixed securely to the cutting edge with check nuts or by welds. The formwork on outer face of curb may be removed within 24 hours after concreting. The formwork on inner face shall be removed after 72 hours. All concreting in the well curb shall be done in one continuous operation. 6

Section 1200 Well Foundations 1205.2 In case blasting is anticipated, the inner faces of the well curb shall be protected with the steel plates of thickness not less than 10 mm up to the top of the well curb. If it is desired to increase the steel lining above the well curb then the thickness in the extended portion can be reduced to 6 mm. This extra height of the steel shall not exceed 3 m, unless specific requirement exists, as decided by the Engineer. The curb in cases involving blasting, shall be provided with additional hoop reinforcement consisting of 10 mm dia mild steel or deformed bars at 150 mm spacing which shall also extend up to a height of liner. 1206 WELL STEINING 1206.1 The dimensions, shape, concrete strength and reinforcements of the well shall strictly conform to those shown on the drawings. The formwork shall preferably be of M.S. sheets shaped and stiffened suitably. In case timber forms are used, they shall be lined with plywood or M.S. sheets. 1206.2 Steining built in the first lift above the well curb shall not be more than 2 m and in subsequent lifts it shall not exceed the diameter of the well or the depth of well sunk below the ading bed level at any time. For stability, the first lift of steining shall be cast only after sinking the curb at least partially for stability. Concreting of steining may be carried out in subsequent lifts of about 2 to 2.5 m. Attempts should be made to minimize the number of construction ts. The concreting layers shall be limited to 450 mm restricting the free fall of concrete to not more than 1.5 m. Laitance formed at the top surface of a lift shall be removed to expose coarse aggregates before setting of concrete at the proposed construction t. As far as possible, construction ts shall not be kept at the location of laps in the vertical steining bars. 1206.3 The steining of the well shall be built in one straight line from bottom to top such that if the well is titled, the next lift of steining will be aligned in the direction of the tilt. The work will be checked carefully with the aid of straight edges of lengths approved by

the Engineer. Plumb bob or spirit level shall not be used for alignment. After sinking of a stage is complete, damaged portions if any, of steining at top of the previous stage shall be properly repaired before constructing the next stage. 1206.4 The height of steining shall be calibrated by making at least 4 gauges (preferably in traffic direction and in a direction normal to traffic direction) distributed equally on the outer periphery of the well each in the form of a 100 mm wide strip painted on the well, with every metre mark shown in black paint. The gauges shall start with zero at the bottom of the cutting edge. Marking of the gauges shall be done carefully with a steel tape. 1206.5 After reaching the founding level, the well steining shall be inspected to check for any damage or cracks. The Engineer will direct and the Contractor shall execute 7

Well Foundations Section 1200 the remedial measures before acceptance of the well steining. In case the well cannot be accepted even with any remedial measure, then the well shall stand rejected. 1207 WELL SINKING 1207.1 General The well shall as far as possible be sunk true and vertical through all types of strata. Sinking or loading of the well with kentledge shall be commenced only after the steining has been cured for at least 48 hours or as specified in the drawings. No well shall be permitted to be placed in a pre-dredged hole. The well shall be sunk by excavating material uniformly from inside the dredge hole. Use of water jetting, explosives and divers may be adopted for sinking of wells through difficult strata with prior approval of the Engineer. Normally dewatering of well should not be permitted as a means for sinking the well. It shall never be resorted to if there is any danger of sand blowing under the well. Dewatering shall however be done when well is to be founded into rock. Pneumatic sinking may have to be resorted to where obstacles such as tree trunks, large size boulders, etc. are met at the bottom or when there is hard strata which cannot be removed by open dredging. The necessity for pneumatic sinking shall be decided by the Engineer. Sinking history of well shall be maintained in the format given in Appendix 1200/I. 1207.1.1 Sand blows in wells Dewatering shall be avoided, if sand blows are expected. Any equipment or men working inside the well shall be brought outside the well as soon as there are any indications of sand blow. Sand blow often can be minimized by keeping the level of water inside the well higher than the water table and also by adding heavy kentledge.

1207.2 Use of Kentledge as Sinking Load Kentledge shall be placed in an orderly and safe manner on the loading platform and in such a way that it does not interfere with the excavation of the material from inside the dredge hole and also does not in any way damage the steining of the well. Where tilts are present or there is a danger of well developing a tilt, the position of the load shall be regulated in such a manner as to provide greater sinking effort on the higher side of the well. 8

Section 1200 Well Foundations 1207.3 Use of Water Jetting Water jetting and jack down method may be employed for well sinking as per requirement. 1207.4 Use of Explosives Mild explosive charges may be used as an aid for sinking of the well only with prior permission of the Engineer. Blasting of any sort shall only be done in the presence of the Engineer and not before the concrete in the steining has hardened sufficiently and is more than 7 days old. When likelihood of blasting is predicted in advance, protection of the bottom portion of the well shall be done as per these Specifications. After blasting operations are completed, the well curb and steining should be examined for any cracks and remedial measures taken. If blasting has been used after the well has reached the design foundation level, normally 24 hours shall be allowed to lapse before the bottom plug is laid. The charges shall be exploded well below the cutting edge by making a sump so as to avoid chances of any damage to the curb or to the steining of the well. A minimum sump of 1 m depth should be made before resorting to blasting. Use of large charges, 0.7 kg or above, may not be allowed except under expert direction and with the permissions from the Engineer. Suitable pattern of charges may be arranged with delay detonators to reduce the number of charges fired at a time. The burden of the charge may be limited to 1 m and the spacing of holes may normally be kept as 0.5 to 0.6 m. All prevalent laws concerning handling, storing and using of explosives shall be strictly followed. All safety precautions shall be taken as per IS:4081 “Safety Code for Blasting and related Drilling Operations”, to the extent applicable, whenever blasting is resorted to. There should be no equipment inside the well nor shall there be any worker in the closed vicinity of the well at the time of exploding the charges. If rock blasting is to be done for seating of the well, the damage caused by flying debris should be minimised by covering blasting holes by rubber mats before blasting.

1207.5 Use of Divers Use of divers may be made both for the sinking purpose like removal of obstructions, rock blasting and for inspection. All safety precautions shall be taken as per any acceptable safety code for sinking with divers or any statutory regulations in force. 9

Well Foundations Section 1200 Only persons trained in the diving operation shall be employed and shall be certified to be fit for diving by an approved doctor. They shall work under expert supervision. The diving and other equipments shall be of acceptable standard and certified to this effect by an approved independent agency. It shall be well maintained for safe use. Arrangement for ample supply of low pressure clean cool air shall be ensured through an armoured flexible hose pipe. Standby compressor plant shall be provided in case of breakdown. Separate high pressure connection for use of pneumatic tools shall be made. Electric lights where provided shall be at 50 volts (maximum). The raising of the diver from the bottom of wells shall be controlled so that decompression rate conforms to the rate as laid down in appropriate regulations. 1207.6 Use of Pneumatic Sinking 1207.6.1 General The Engineer shall familiarize himself with particular reference to caisson diseases and working of the medical air-lock. A doctor competent to deal with cases of “Caisson Diseases” or other complications arising as a result of working under high pressure, shall be stationed at the construction site when pneumatic sinking is under progress. The contractor shall provide complete facilities including the issuing of orders to ensure strict enforcement of the requirements outlined in these Specifications. Safely provisions as contained in IS:4138 and in these Specifications shall be strictly followed. Pneumatic sinking shall be restricted to a depth of 30.0 m. 1207.6.2 Man-Locks and Shafts Locks, reducers, and shaft used in connection with caissons shall be of riveted construction throughout. The material used in their manufacture shall be steel plate with thickness not less than 6 mm. Shafts shall be subjected to hydrostatic or air pressure test of at least 0.5 MPa, at which pressure they shall be tight. The pressure at which testing has been done shall be clearly and visibly displayed. 10

Section 1200 Well Foundations Shaft shall be provided, with a safe, proper and suitable staircase for its entire length

including landing platforms which are not more than 6 m apart. Where this is impracticable due to space constraint, suitable ladders along with landing platforms shall be installed. These shall be kept clear and in good condition at all times and shall be constructed, inspected and maintained to the entire satisfaction of the Engineer. A 1.0 m wide platform with 1.0 m high railing shall be provided all round the caisson air locks. Where 15 or more men are employed, caissons shall have two locks, one of which shall be used as a man lock. Locks shall be located so that the lowest part of the bottom door shall not be less than 1 m above high water level. The supply of fresh air to the working chamber shall at all times be sufficient to permit work to be done without any danger or excessive discomfort. All air supply lines shall be supplied with check valves and carried as near to the face as practicable. A man-lock shall be used solely for the compression or de-compression of persons, and not for the age of plant and material and shall be maintained in a reasonably clean and sufficiently warm state. However, any hand tool or hand instruments used for the purpose of the work may be carried into the man-lock. Where is it not reasonably practicable to provide a separate man-lock for use by persons only, the lock when it is in actual use for compression or decompression of a person or persons shall not be put, simultaneously, to any other use and shall be in a reasonably clean and sufficiently warm state. 1207.6.3 Valves Exhaust valves shall be provided, having risers extending to the upper part of the chamber. These shall be operated, whenever necessary specially after a blast. Precautions shall be taken that men are not allowed to resume work after a blast until the gas and smoke are cleared. 1207.6.4 Medical supervision and certification Every employee absent from work for 10 or more consecutive days due to illness or any other disability shall be required to the regular physical examination by the doctor before being permitted to return to work. After a person has been employed continuously in compressed air for a period of 2 months, 11

Well Foundations Section 1200 he shall be re-examined by the doctor and shall not be permitted to work until such reexamination has been made and the repot is satisfactory. No person known to be addicted to the excessive use of intoxicants shall be permitted to work in compressed air.

The doctor shall, at all times, keep a complete and full record of examination made by him, which shall contain dates of examinations, a clear and full description of the persons examined, his age and physical condition at the time of examination and a statement as to the period such a person has been engaged in such employment. Records shall be kept at the place where the work is in progress and shall be subject to inspection by authorized officers. Every man lock shall always have a doctor or a responsible person in attendance. In case the person in charge is not a doctor, he must have positive means of promptly communicating with and securing the services of a competent doctor in case of emergency. Such arrangements shall invariably be subject to the approval of the Engineer. If the air pressure exceeds 0.2 MPa gauge or if 50 or more men are employed, it is obligatory for the person in charge of medical lock to be a doctor experienced in this type of work. All cases of compressed-air illness shall be reported and copies of all such reports shall be kept in file at the place of work. 1207.6.5 Lighting All lighting in compressed air chambers shall be operated only by electricity. Two independent electric lighting systems with independent sources of supply shall be used. These shall be so arranged that the emergency source shall become automatically operative in case of failure of the regularly used source. The minimum intensity of light on any walkway ladder, stairway, or lower working level shall be one-quarter (1/4) candlepower. In all work places, the lighting shall always be such as to enable workmen to see their way about clearly. All external parts of lighting fixtures and electrical equipment lying with in 2.5 m above the floor shall be constructed of noncombustible, non-absorbing insulating materials. If metal is used it must be effectively earthed. Portable lamp shall have non-combustible, non-absorbing insulating sockets, approved handles, basket guards and approved cables. The use of worn out or defective portable and pendant conductors, shall be prohibited. 12

Section 1200 Well Foundations 1207.6.6 Safety against fire hazard No oil, gasoline, or other combustible material shall be stored within 30 m of any shaft, caisson, or tunnel opening. However, oil may be stored in suitable tanks in isolated fireproof

buildings, provided such buildings are not less than 15 m from any shaft, caisson, or tunnel opening or any building directly connected thereto. Positive means shall be taken to prevent leaking flammable liquids from flowing into areas specifically mentioned in the preceding paragraph. Where feasible, a fire hose connected to a suitable source of water shall be provided at the top of every caisson. Where fire mains are not accessible, water shall be stored in tanks near the top of every caisson, provided fire pails or suitable pumps are kept available. Approved fire extinguishers shall also be provided. 1207.6.7 Sanitation Properly heated, lighted and ventilated dressing rooms shall be provided for all employees engaged in compressed air work. Such rooms shall contain lockers and benches and be open and accessible to person during intermissions between shifts. Adequate toilet accommodation of one for every twenty five employees shall be provided. Care shall be taken to keep all parts of the caissons and other working compartments, including locker rooms, dry rooms, rest rooms, and other equipments in a good sanitary condition and free from refuse, decaying or other objectionable matter. No nuisance shall be tolerated in the air chamber. Smoking shall be strictly prohibited and all matches and smoking materials shall be left out of the locker rooms. A separate dry-room shall be provided where working clothes may be dried in a reasonable time. 1207.6.8 Protection against gases In all cases where gas is expected including alluvium impregnated with decayed vegetable matter, the use of Davy Safety Lamp shall be compulsory. 1207.6.9 Additional safety provisions a) The weight of the pneumatic platform and that of steining and kentlege, if any, shall be sufficient to resist the uplift from air inside, skin friction being neglected in this case, If, at any section the total weight acting downwards is less than the uplift pressure of air inside, additional kentledge shall be placed on the well. 13

Well Foundations Section 1200 If it is not possible to make the well heavy enough during excavation, “blowing down” may be used. The men should be withdrawn and air pressure reduced. The well should then begin to move with small reduction in air pressure. “Blowing down” should only be used when the ground is such that it will not heave up inside the chamber when the pressure is reduced. When the well does not move with the reduction in air pressure, kentledge should be added. “Blowing down” should be in short stages and the drop should not exceed, 0.5 m at any stage. To control sinking during blowing down use of packing

are recommended. b) The pneumatic sinking plant and other allied machinery shall not only be of proper design and make, but also shall be operated by competent and well trained personnel. Every part of the machinery and its fixtures shall be minutely examined before installation and use. Availability of appropriate spares, standbys, safety of personnel as recommended in IS:4138 for working in compressed air must be ensured at site. Codes for safety and for working in compressed air and other labour laws and practices prevalent in the country, as specified to provide safe, efficient and expeditious sinking shall be followed. c) Inflammable materials shall not be taken into air locks and smoking shall be prohibited. Wherever gases are suspected to be issuing out of dredge hole, the same shall be analysed by trained personnel and necessary precautions adopted to avoid hazard to life and equipment. d) Where blasting is resorted to, it shall be carefully controlled and all precautions regarding blasting shall be observed. Workers shall be allowed inside after blasting only when a competent and qualified person has examined the chamber and steining thoroughly, and found the same to be safe. 1207.7 Precautions during sinking a) When the wells have to be sunk close to each other and clear distance between them is not greater than the diameter of wells, sinking shall be taken up on all wells and they shall be sunk alternately so that sinking of wells proceeds uniformly. Simultaneous and even dredging shall be carried out in the wells in such a manner that the difference in the levels of the sump and cutting edge in the adjacent wells does not exceed half the clear gap between them. Plugging of all the wells shall be done together. 14

Section 1200 Well Foundations b) During sinking of dumb-bell or double D-shaped wells, the excavation in both the dredge holes should be carried out simultaneously and equally. c) Bore chart shall be referred to constantly during sinking for taking adequate care while piercing different types of strata. The type of soil as obtained during the well sinking should be compared with bore chart so as to take prompt decisions. d) Before seasonal floods, all wells on which sinking is in progress shall be sunk to sufficient depths below the designed scour level. Further, they shall be temporarily filled and plugged so that they do not suffer any tilt or shift during the floods. e) All necessary precautions shall be taken against any possible damage to the foundations of existing structures in the vicinity of the wells, prior to commencement of dredging from inside the well. f) The dredged material shall not be allowed to accumulate over the

well. It shall be dumped and spread, as far away as possible, and then continuously and simultaneously removed, as directed by the Engineer. In case the river stream flows along one edge of the well being sunk, the dredged material shall not be dumped on the dry side of the bank but on the side on which the river current flows. g) Very deep sump shall not be made below the well curb, as it entails risk of jumping (sudden sinking) of the well. The depth of sump shall be generally limited to one-sixth of the outer diameter/least lateral dimension of the well in plan. Normally the depth of sump shall not exceed 3.0 m below the level of the cutting edge unless otherwise specially permitted by the Engineer. h) In case a well sinks suddenly with a jerk, the steining of the well shall be examined to the satisfaction of the Engineer to see that no damage has occurred to it. i) In pneumatic sinking, the well shall not, at any time, be dropped to a depth greater than 500 mm by the method of “blowing down”. j) Dewatering shall be avoided if sand blows are expected. Any equipment and men working inside the well shall be brought out of the well as soon as there are any indications of a sand-blow. k) Sand blowing in wells can often be minimised by keeping the level of water inside the well higher than the water table and also by adding heavy kentledge. 15

Well Foundations Section 1200 l) In soft strata prone to settlement/creep, the construction of the abutment wells shall be taken up only after the approach embankment for a sufficient distance near the abutment has been completed. 1207.8 Tilts and Shifts The inclination of the well from the vertical is known as tilt and the horizontal displacement of the center of the well at the founding level from its theoretical position is known as shift. Unless otherwise specified, the tilt of any well shall not exceed 1 (horizontal) in 80 (vertical), and the shift at the well base shall not be more than 150 mm in any resultant direction. Tilts and shifts shall be carefully checked and recorded in the format vide Appendix 1200/II regularly during sinking operations. For the purpose of measuring the tilts along the two axes of the bridge, reduced level of the marks painted on the surface of the steining of the well shall be taken. For determination of shift, locations of the ends of the two diameters shall be precisely measured along the two axes, with reference to fixed reference points. Whenever any tilt is noticed, adequate preventive measures like placing eccentric kentledge, pulling, strutting, anchoring or dredging unevenly and depositing dredge material unequally,

putting obstacles below cutting edge. Water jetting etc., shall be adopted before any further sinking. After correction, the dredged material shall be spread out uniformly. A pair of wells close to each other have a tendency to come closer while sinking. Timber struts may be introduced in between the steining of these wells to prevent tilting. Tilts occurring in a well during sinking in dipping rocky strata can be safeguarded by suitably ing the curb. In the event of a well developing tilt or shift beyond the specified permissible values, the Contractor shall have to carry out, at his own cost, suitable remedial measures to the satisfaction of the Engineer, to bring the tilt and shift within permissible values. If the resultant tilt and / or shift of any well exceeds the specified permissible values, generally it should not exceed 1 in 50 and 300 mm respectively. The well so sunk shall be regarded as not conforming to specifications and a sub-standard work. The Engineer in his sole discretion, may consider accepting such a well, provided: i) Calculations for foundation pressures and steining stresses, ing for the actual tilt and shift furnished by the Contractor show that the well is safe. Remedial measures required to bring the stresses within permissible values (such as increase in the dimension of the 16

Section 1200 Well Foundations well cap, provision of dummy weights on the well cap etc.), shall be carried out by the Contractor at his own cost. ii) The Contractor shall be subjected to reduction in rates as a penalty in accordance with Clause 1215(g). In case the Engineer, in his discretion, rejects the well, the Contractor shall dismantle the rejected well to the extent directed by the Engineer and remove the debris. Further, the Contractor shall, at his own risk and cost complete the bridge with modified span arrangement acceptable to the Engineer. 1207.9 Floating caissons Floating caissons may be of steel, reinforced concrete or any suitable material. They shall have at least 1.5 m free board above the water level and increased, if considered necessary, in case there is a possibility of caissons sinking suddenly owing to reasons, such as scour likely to result from lowering of caissons, effect of waves, sinking in very soft strata, etc. Well caissons should be checked for stability against over-turning and capsizing while being towed and during sinking, due to the action of water current, wave pressure, wind etc. The floating caisson shall not be considered as part of foundation unless proper shear transfer at the interface is ensured. 1207.10 Seating of Wells

The well shall be uniformly seated at the founding strata. It shall be ensured by test borings that the properties of the soil encountered at the founding strata and upto a depth of one and a half times the well diameter is identical to that adopted in the design. The procedure for test borings shall satisfy the provisions of these specifications. In case the soil encountered is inferior to that adopted in design, the well shall be re-designed by the Engineer adopting the soil properties actually encountered and the founding level intimated to the Contractor, who shall carry out the work accordingly. In case of seating of wells in hard rocky strata, where the rock profile is steeply sloping, pneumatic methods of sinking may be adopted to seat the well evenly as directed by the Engineer. The decision of adopting pneumatic sinking shall be taken by the Engineer. The cutting edge may also be embedded for a suitable depth in the rocky strata, as decided by the Engineer keeping in view the quality of rock. As an additional measure of safety, the well shall be anchored to the rocky strata by anchor bars provided in the steining of the well, as shown on the drawing irrespective of the fact that tension develops or not at the base of the well under design loads. After the well has been evenly seated on good hard rock, arrangements shall be made to facilitate proper inspection in dry and visible conditions before the bottom plug is laid. 17

Well Foundations Section 1200 1208 BOTTOM PLUG The bottom plug shall be provided in all wells and the top shall be kept not lower than 300 mm in the centre above the top of the curb, as shown in Appendix-3 of IRC:78. A suitable sump shall be below the level of the cutting edge. Before concreting the bottom plug, it shall be ensured that its inside faces have been cleaned thoroughly. The concrete mix used in bottom plug shall have a minimum cement content of 330 kg per cu.m with a slump about 150 mm to permit easy flow of concrete through tremie to fillup all cavities. Concrete shall be laid in one continuous operation till the dredge hole is filled to the required height. For under water concrete, the concrete shall be placed by tremie under still water condition and the cement content of the mix be increased by 10 percent. ixtures, if required may be added to the concrete to achieve the required characteristics. In case of grouted concrete, the grout mix shall not be leaner than 1:2. It shall be ensured that the grout fills up all interstices upto the top of the bottom plug by suitable means such

as, controlling the rate of pumping etc. Any dewatering required, shall be done 14 days after concreting of bottom plug. The concrete production equipment and placement equipment should be sufficient to enable under water concreting within stipulated time. Necessary standby equipment should be available for emergency situation. Before commencing plugging, all loose material from the bottom of the well shall be removed. Concreting shall be done in one continuous operation till the dredge hole is filled upto the required height and thereafter sounding shall be taken up to ensure that the concrete has been laid to the required height. Least disturbance shall be caused to the water inside the well while laying concrete in the bottom plug. Concrete shall not be disturbed in any way for at least 14 days. In order to check any rise in the level of the bottom plug soundings should be taken at the close of concreting and once every day for the subsequent 3 days. The soundness of the bottom plug may be tested by dewatering the well by 5 m below the surrounding water level and checking the rise of water. The rate of rise shall preferably be less than 10 cm per hour. In case the rate is higher, suitable remedial measures as directed by the Engineer, shall be taken by the Contractor at his own cost. 18

Section 1200 Well Foundations 1209 SAND FILLING Sand filling shall commence after a period of 14 days of laying of bottom plug. Also, the height of the bottom plug shall be verified before starting sand filling. Sand shall be clean and free from earth, clay clods, roots, boulders, shingles, etc. and shall be compacted as directed. Sand filling shall be carried out upto the level shown on the drawing or as directed by the Engineer. 1210 TOP PLUG After filling sand upto the required level a plug of 300 mm thick concrete shall be provided over it as shown on the drawing or as directed by the Engineer. 1211 WELL CAP A reinforced cement concrete well cap will be provided over the top of the steining in accordance with the drawing. Formwork will be prepared conforming to the shape of well cap. Concreting shall be carried out in dry condition. A properly designed false steining may be provided where possible to ensure that the well cap is laid in dry condition. The bottom of the well cap shall be laid preferably as low as possible but not below the

LWL, taking in to for this purpose, the water level prevalent at the time of casting Where the bed level is higher than the LWL, the bottom of the well cap may be suitably raised. Bond rods of steining shall be anchored into the well cap. 1212 TOLERANCES The permissible tilt and shift shall not exceed 1 (horizontal) in 80 (vertical) and the shift at the well base shall not be more than 150 mm in any resultant direction. For the well steining and well cap, the permissible tolerances shall be as follows: a) Variation in dimension : +50 mm, –10 mm b) Misplacement from specified position in plan : 15 mm c) Surface irregularities measured with 3 m straight edge : 5 mm d) Variation of level at the top : + 25 mm 19

Well Foundations Section 1200 1213 TESTS AND STANDARDS OF ACCEPTANCE The materials shall be tested in accordance with these Specifications and shall meet the prescribed criteria. The work shall conform to these Specifications and shall meet the prescribed standards of acceptance. 1214 MEASUREMENTS FOR PAYMENT All quantities shall be measured from the drawing, or as ordered by the Engineer, excepting those required to be provided by the Contractor at his cost. a) The cutting edge shall be measured in tonnes based on the net weight of metal used in it, as per Section 1900. b) The concrete in curb, well steining and well cap shall be measured in cubic metres in each of the items as per Section 1700. The reinforcements shall be measured in tonnes separately in each of the items, as per Section 1600. c) The measurement for well sinking shall be made in running metres for different depths and in different types of strata (for example, predominantly sand/clay soil, soft rock, hard rock, etc.) as specified in the Contract. The depth of sinking shall be measured from the level specified in the Contract. If no level has been specified in the Contract, sinking shall be measured from the low water level or from the level at which the cutting edge was laid, whichever is higher. d) The quantity of concrete in bottom and top plug shall be measured in cubic metres as per Section 1700. e) The quantity of sand filling shall be measured in cubic metres. f) Pneumatic sinking, where required shall be paid as a separate item and shall be measured in cubic metres of material to be excavated. 20

Section 1200 Well Foundations

1215 RATE All quantities shall be measured from the drawing or as ordered by the Engineer, excepting those required to be provided by the Contractor at his cost. a) The Contract unit rates of cutting edge shall cover all costs of labour, material, tools, plant and equipment, including placing in position, sampling and testing, and, supervision, all as per respective Section of Structural Steel Work and as described in this section. b) The Contract unit rates for concrete in curb, steining, bottom plug, top plug and well cap, shall cover all costs of labour, material, tools, plant and equipment, formwork and staging including placing in position, sampling and testing, and, supervision, all as per respective Section of Structural Concrete and as described in this section. c) The Contract unit rates for reinforcement in curb, steining, and well cap, shall cover all costs of labour, material, tools, plant and equipment, including bending to shape, placing in position, sampling, testing and supervision, all as per respective Section of Steel Reinforcement and as described in this section. d) The Contract unit rates for sand filling shall cover all costs of labour, material, tools, plant and equipment, including placing in position, sampling testing and supervision, all as described in this section. e) The Concrete unit rates for sinking shall cover the costs of labour, tools, and equipment and plant and for all operations and other incidentals for sinking of well including seating excepting provisions of pneumatic sinking as described in this Section. The unit rates shall specify the strata such as types of soil, rock, etc. The rate shall cover all testing and supervision required for the work. f) The Contract unit rate of material to be excavated by pneumatic sinking shall cover all costs of labour, material, tools, plant and other equipment and other incidentals and safety provisions and supervision required for pneumatic sinking as per this Section. g) Reduction in contract unit rates for sinking as a penalty, in pursuance of Clause 1207.8 21

Well Foundations Section 1200 If any well with tilt and/or shift exceeding the permissible values is accepted by the Engineer, the Contractor shall be subjected to a reduction in the rates as follows: S.No. Amount of tilt and/or shift Per cent deduction on the rate (s) for sinking of whole well 1. Tilt exceeding the specified permissible value but 5 percent equal to or within 1 in 60 2. Tilt exceeding 1 in 60 10 percent but equal to or within 1 in 50

3. Tilt exceeding 1 in 50 20 percent 4. Shift exceeding the specified permissible 2 percent value but equal to or within 200 mm 5. Shift exceeding 200 mm but equal 5 percent to or within 300 mm 6. Shift exceeding 300 mm 10 percent Rates for excessive tilt and shift shall be reduced separately.