Interpretative Reports 4g2o20

GUIDELINES FOR THE PREPARATION OF THE GROUND REPORT

© Association of Geotechnical & Geoenvironmental Specialists Although every effort has been made to check the accuracy of the information and validity of the guidance given in this publication, neither the of the Working Party nor the Association of Geotechnical & Geoenvironmental Specialists accept any responsibility for mis-statements contained herein or misunderstanding arising herefrom. All brand names, trademarks and ed trademarks are the property of their respective owners.

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FOREWORD The need for a guidance document on the preparation of geotechnical reports was first raised by the late Sir John Knill when he made a presentation to the AGS Committee in July 2000. For the previous few years much of John Knill’s work had involved the provision of expert witness services. Through this work he saw a significant number of interpretative reports and had become aware that no comprehensive guidance existed on the range of topics which such reports should cover. He therefore sought the Association’s help in producing and publicising guidance on the scope of issues which should be considered for inclusion in interpretative reports on ground investigations. The original of reference for this document were restricted to geotechnical interpretative reports. During the course of preparing these Guidelines it became evident that it would be inappropriate to treat interpretative reports in isolation from the other reports generated as part of the site investigation process. The concept of the Ground Report, as a ‘live’ document which develops as the project progresses was therefore adopted, as described in more detail in the Introduction. It also became apparent that many of the proposals were applicable equally to certain aspects of geoenvironmental projects as to geotechnical ones. The extent of this applicability is explained by notes in the text, as set out in the Introduction. In response to Sir John Knill’s representations a new Task Group was set up to prepare this document, under the Chairmanship of Roger Epps of Foundation & Exploration Services Ltd (FES). The other of the group comprised representatives from Bachy Soletanche, Bechtel, BRE Ltd, Geotechnics, Knight Piesold, LBH Wembley and Ove Arup. The Association is grateful to this Group for their hard work in compiling the Guidelines, and to Sir John Knill for providing comments on the penultimate draft. This document is being made available on the AGS website in order to maximise its availability to the industry, as desired by Sir John Knill. It is hoped that it will become the industry standard guide, and that it will be particularly beneficial to young geospecialists and to those who train them. Keith R Gabriel Chairman Association of Geotechnical and Geoenvironmental Specialists

First Published 2003 © Association of Geotechnical & Geoenvironmental Specialists. All rights reserved.

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1.

Introduction

The objective of this document is to summarise the steps and procedures that should be followed in the preparation of reports associated with ground investigations. It is intended that this should complement other guidance documents published by the AGS1 and existing good practice guidance within the industry. D.J. Palmer2 wrote in 1957 on the framework and content of a report: ‘The essentials to regarding content are that the report should be an of the whole job from start to finish and should contain all the technical facts, good or bad, without reference to any personal istrative difficulties. Attention should be given to detail, but in such a way as to avoid incomprehensible catalogues, e.g. of strata borehole by borehole already better depicted on the borehole logs. The best approach is to make generalisations about the problem and then work to the particular, illustrating exceptions to the generalizations. Facts should be given first, theories afterwards. Drawings and sketches often help where words fail.’ It is in the context of the report as ‘an of the whole job from start to finish’ that this document has been prepared, since interpretation of geotechnical data is not simply confined to the ‘interpretative report’, but a continuous process encoming investigation, design, monitoring and construction. Figure 1 represents a schematic description of the process of gathering, interpretation and application of data. On larger projects, the individual reports described in the illustration are often presented as individual volumes. For smaller projects, one or more of the reports described in the illustration may be amalgamated. Eurocode 73 identifies three project categories (their use is not mandatory) which reflect both geotechnical uncertainty and structural complexity, as follows: Geotechnical Category 1 includes single 1 and 2 storey houses and agricultural buildings using conventional types of spread and piled foundations, retaining walls and excavation s where the difference in ground levels does not exceed 2 m and small excavations for drainage works, pipe laying, etc. For this Category, geotechnical reports may be as simple as single pages. Geotechnical Category 2 includes conventional types of structures and foundations with no abnormal risks or unusual or exceptionally difficult ground or loading conditions. Structures in Category 2 require quantitative geotechnical data and analysis to ensure that the fundamental requirements will be satisfied; routine procedures for field and laboratory testing and for design and execution may be used. Geotechnical Category 3 includes very large or unusual structures, structures involving abnormal risks, or unusual or exceptionally difficult ground or loading conditions and 1

The Selection of Soil Laboratory Testing. Guidelines for Combined Geoenvironmental and Geotechnical Investigations.

2

Writing Reports, D.J. Palmer, published by Soil Mechanics Limited, 1957

3

Eurocode 7: Geotechnical Design Part 1. General Rules. DD ENV 1997-1 : 1995.

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structures in highly seismic areas. For these, a comprehensive, related set of reports will usually be required. Whilst this document at various stages may touch on the significance of risk assessment and risk management, it is considered to be a separate subject. Nevertheless the report structure should provide for appropriate consideration of ground risk, some guidance on which may be found in a separate AGS publication4, albeit in the context of management of the Consultant's, rather than the Client's risks. For more information on this subject, reference should be made to the t ICE/DETR publication 'Managing Geotechnical Risk'5 and to Volume 4 of the Design Manual for Roads and Bridges6. The management of geotechnical risk also forms the basis of similar guidance published in North America7, where geotechnical reports are sometimes used as a benchmark for establishing 'baseline' conditions for tendering and contractual purposes. The following sections of the document describe in outline the key requirements of each stage in the process of data collection, interpretation and application in design, with a simple checklist to be used as an aide memoire presented in Appendix A. The design process and data collection procedures outlined here are equally applicable to Geoenvironmental projects and a brief comment is given in each section on the application of this process to Geoenvironmental issues. It is beyond the scope of this document to give detailed guidance on reporting Geoenvironmental information as this is already covered in other good practice guidance documents. However, the term 'the Ground Report' has been adopted in the title of this document in recognition of the different disciplines now involved in the process of report preparation. The Ground Report may be considered as consisting of following 5 sequential parts which may be combined or extended to suit the project, which are listed below. • • • • •

Desk Study Factual Report Interpretative Report Design Report Validation Report

The Ground Report will be prepared before construction starts. Further ground – related reports will also be prepared during and after construction. 4

Contractual Risk Management for Ground Reports,

5

Managing Geotechnical Risk - Improving Productivity in UK Building and Construction. C.R.I. Clayton. The Institution of Civil Engineers and Department of Environment, Transport and The Regions. 2001.

6

Design Manual for Roads and Bridges. Volume 4 Geotechnics and Drainage. Section 1 Earthworks Part 2 HD22/02 Managing Geotechnical Risk (In Preparation).

7

Geotechnical Baseline Reports for Underground Construction – Guidelines and Practices, prepared by the Technical Committee of the Underground Technology Council (ASCE, 1997), edited by Randall J. Essex. Subsurface Investigations and Geotechnical Report Preparation. Gary S. Brierley. pp 49 – 128 in Subsurface Conditions – Risk management for Design and Construction Management Professionals. Edited by David J. Hatem, John Wiley, 1998.

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Guidance documents published in North America identify the Geotechnical Report as comprising four components: Geotechnical Data Report (GDR - Factual); Geotechnical Interpretative Report (GIR); Geotechnical Design Summary Report (GDSR); and Geotechnical Baseline Report (GBR). A brief description of these is presented in Appendix B, as these may be encountered in international usage. The definitions described in the SISG Publication 28 apply to the Geotechnical Specialist or Geotechnical Adviser where they are adopted in these guidelines, namely: Geotechnical Specialist – a Chartered Engineer or Chartered Geologist with a postgraduate qualification in geotechnical engineering or engineering geology , equivalent to at least an MSc and with three years of Chartered practice in Geotechnics. or a Chartered Engineer or Chartered Geologist with five years Chartered practice in Geotechnics. Geotechnical Adviser - a Chartered Engineer or a Chartered Geologist with five years practice as a Geotechnical Specialist.

2.

Desk Study

The first stage of a properly structured site investigation process is a desk study and site reconnaissance which is considered to be an essential requirement. The AGS Code of Conduct for Site Investigation requires all practitioners to promote to Clients the need for a proper desk study. The Desk Study is used as a basis for subsequent investigation design and planning. The basic requirements for a desk study are described in Clause 6.2 and Annex A of BS5930. The desk study report shall draw together all relevant, accessible information as detailed in Appendix A. At the time of the reconnaissance, visits to local archives should also be made. Where possible with the Local Authority and Environment Authority should also be established to obtain local, often unpublished, information concerning the ground and groundwater conditions in the area. The principal components of a Desk Study Report are described in Annex F to BS 59309, Section 6.2 of BS 1017510 and Chapter 3 of the AGS Guidelines for Combined Geoenvironmental and Geotechnical Investigations11. Geoenvironmental reports shall also 8

Site Investigation in Construction. Planning, procurement and quality management. Site Investigation Steering Group. Thomas Telford, London, 1993. 9 British Standards Institution. BS 5930 : 1999. Code of Practice for Site Investigations. 10

British Standards Institution. BS 10175 : 2001. Investigation of potentially contaminated sites.

11

Guidelines for Combined Geoenvironmental and Geotechnical Investigations, Association of Geotechnical and Geoenvironmental Specialists, 2000.

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include, as appropriate: an evaluation of the historical development of the site and surrounding area to identify potential on-site and off-site sources of contamination; information on groundwater vulnerability; proximity of any surface water bodies; and results of consultations with local authorities, the Environment Agency and any databases in the public domain. The results of the desk study are used to design the subsequent investigation, in such a way that costs can be estimated, the programme can be established and all parties involved understand their responsibilities and the activities that they are expected to undertake.

3.

Factual Report

The factual report, which is referred to as the 'descriptive report' in BS5930 : 1999 should contain the information identified in Appendix A in the sections outlined below: 3.1

Introduction

This should state briefly the nature of the project for which the investigation was undertaken, the company undertaking it, the name of the client for whom the work was done and the name of any consultant who commissioned or directed the work on the client’s behalf. 3.2

Object and Scope

The purpose of the investigation should be explained briefly and the brief for the work referred to, preferably including it as an appendix. The section should also make clear whether the report contains only the factual data or is combined (or should be read in conjunction) with the other geotechnical reports such as those dealing with specialist testing or geophysics. The arrangements for QA of data and auditing should be explained. The responsibility for the interpretative assignment of litho-stratigraphical names in borehole logs, etc. should be defined. 3.3

Presentation

This should explain the structure of the report, where the descriptive sections and factual data are to be found and should draw attention to any general notes which accompany the report. 3.4

Site Location

This should clearly describe the location of the site relative to larger features such as a town centre, a feature of note within a city or its proximity to centres of population. The Ordnance Survey National Grid reference at the centre or extremities of a site should be given to the nearest 100m and a Site Location Plan, typically to a scale of 1:50,000, included in an Appendix to the report. (This latter feature will require a proportionate fee payable to the Ordnance Survey).

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3.5

Site Description

This should describe the size and shape of a site and its location relative to any roads and access. It should go on to describe its topography and the form and locations of any buildings or other features (actual presence or any evidence of) on the site or adjacent ground, which may affect the subsequent development. 3.6

Fieldwork Procedure

This section should describe the procedures followed in undertaking the work including commissioning, and the Codes of Practice and any other procedural guidelines under which the work was undertaken. It should be followed by an identification of each of the techniques of fieldwork used, the locations (as grid reference) and elevations at which each was used, the range of depths to which each was taken and the dates over which this work was done. Any supplementary references which define procedures for each investigation technique and references appropriate to interpretation should be given. Notes on any constraints on access and the limitations which these may impose on the techniques used should be given together with any limitations on penetration which each technique may have experienced. The sampling strategy should be stated, the types of samples taken identified and their transport and storage described. A description of any instrumentation which may have been installed and its purpose should also be given in this section. Groundwater conditions encountered during the investigation should also be presented. Any monitoring records should be presented and their location in the report identified. Detailed records of the fieldwork should be presented in an appendix, together with a site plan showing the position of each investigation point. 3.7

In-Situ Testing

Where in-situ tests are undertaken an outline description of each test procedure should be given, with reference to relevant standards or published methods. Reference should be made to the relevant location in the report where the test results are listed, (eg on the borehole records where relevant and in summary tables). 3.8

Laboratory Testing

This section should explain who devised the schedule of laboratory tests on the samples taken and to what standard the testing was undertaken. Typically in the UK this would be BS 1377 : 1990 Methods of Test for Soils for Civil Engineering Purposes and the UKAS accreditation status of each test performed by the laboratory should be declared, where this is required. The type of test, the numbers undertaken and the relevant test reference number together with the location in the report in which the results can be found should be given. Test results should be presented, together with tabulations of the results of all tests of the same type and if appropriate the results of different test types on the same material.

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Where chemical or microbiological testing to determine the presence and scale of any contaminants has been undertaken this should be similarly reported. The test results should be reported in an appropriate tabular form, ed by a brief statement of the method detection limit, the accuracy of the test and an identification of the test procedure. 3.9

Electronic Format

The Association of Geotechnical and Geoenvironmental Specialists (AGS) has established a standard format for the exchange and storage of Geotechnical and Geoenvironmental data by electronic means. The protocol allows producers to continue to use their own proprietary software packages but facilitates transfer into a format which can be readily absorbed and analysed by other software used by the Client or his advisors, without the interface of the printed report. The printed report remains the definitive document however. It should be stated whether the data has been presented in this format and the data should be checked to ensure that it complies with the format.

4.

Interpretative Report

4.1

Structure

The interpretative report as defined in BS 5930 : 1999 comprises three parts: an interpretation of the detailed site geology; a summary of the geotechnical properties of the ground; and an engineering interpretation of the implications of the ground conditions on the development project. It is in the preparation of the interpretative report that any gaps or deficiencies in the investigation can be identified and their significance evaluated. It will normally be the case that the interpretative report will commence with a description of the proposed development and as much relevant information as is necessary for the subsequent recommendations to be presented in context. It is particularly important that the writer presents sufficient detail for the nature of the proposals at that time to be understood, which will enable the reader to identify situations where the proposals may have altered to the extent that a re-evaluation is required. Such details may, for example, include: • • • •

Nature of proposed development in broad eg office, residential etc Scale of proposed development, eg number of storeys, length of road, depth of cut, diameter of tunnel etc Any significant features, eg basements, surcharging, sensitivity of adjacent structures Details of loads, tolerances, column spacings etc.

The interpretative report should be sufficiently explicit to define the ground conditions for use by those requiring assistance in their design who may not be geotechnical specialists. 4.2

Geological Interpretation – The Detailed Ground Model

The factual information, together with the desk study, should, if the investigation is sufficient, be enough to develop a detailed ground model, based on an evaluation of the geological, hydrogeological and geotechnical data. The factual report, interpretative report and

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derivation of basic design decisions are frequently presented in one volume, but there can be additional, more focused derivative reports, as described below. The interpretative report should bring together the data from the desk study and the results of the site investigation to formulate or refine the ground model on which the subsequent geotechnical evaluation will be based. The type and details of the proposed development and the Employer's requirements will have significantly influenced the form and scale of the investigation and testing undertaken but the interpretation of ground conditions and properties should be an independent process. The ground model creates a three dimensional picture of the site and its components where structures will be built, of the relative location and thickness of the types of strata encountered, of their properties and of groundwater conditions encountered and maintained. The published geology and hydrogeology of the area will assist in the classification of the materials encountered and indicate their likely extent both over the site and at depth. This allows correlation with the strata encountered and hence an identification of their probable geological association. Since this work involves interpretation it is considered inappropriate to the Factual Report. However, during any audit of the draft borehole logs the stratigraphical position of specific layers should be agreed between the site investigation contractor and consultant and recorded on the accordance with BS BS 5930 : 1999 Since extensive description of the strata sequences can be both difficult to write and to understand and hence can obscure rather than assist interpretation, the use of cross sections to illustrate this model is often of value both in preparing the report and in clarifying the model to the reader. Contour plans of boundaries (e.g. bedrock) and strata thicknesses, cross sections and isometric views also serve to assist in the identification of features such as buried channels and any sharp changes in thickness or dip of strata. Such diagrams also highlight deficiencies in the spatial coverage of the investigation. In preparation of cross sections care should be taken to highlight the degree of uncertainty when interpolating between investigation positions. As stated in the introduction to this document, the best approach is to describe the general aspects of the ground model and then highlight exceptions, discontinuities and interpreted features. 4.3

Ground Parameters

On the basis of this ground model, characteristics derived from the in-situ and laboratory testing and groundwater monitoring can be assessed for each stratum. As an aid to this, plots of the results can be used so that for example, vertical and lateral trends in properties can be assessed and characteristic values applied for use subsequently in design. Tables can often be useful in this respect. This process of ordering of the data can also be seen as a means of reviewing the results of the investigation and of highlighting apparent anomalies. This may stimulate further checking or investigation or identify extreme characteristics which the design will have to accommodate. In deriving the characteristic values of strata depth and properties, as well as groundwater conditions, the various assumptions or simplifications should be explained. Such derivations may include consideration of published data which may be related to the test results.

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The key assumptions are: • • • •

Assumed continuity of strata between investigation points Lateral changes in strata characteristics Seasonal variation in groundwater conditions That the results obtained fully define the ground properties.

Judgement based on knowledge and experience is clearly important in this respect but may be difficult to quantify. When linked to the Design Report this reduces the risks of misinterpretation by others. The evaluation of the geotechnical data should include a review of the derived values of geotechnical parameters, giving the range of values, median values and mean values and where relevant: • • • • • • •

tabulation and graphical presentation of the results of the field and laboratory work in relation to the requirements of the project and, if deemed necessary, histograms illustrating the range of values of the most relevant data and their distribution; depth of the groundwater table and its seasonal fluctuations; subsurface profile(s) showing the differentiation of the various formations; detailed description of all formations including their physical properties and their deformation and strength characteristics; comments on irregularities such as depressions, boulders, pockets and cavities; the range and any grouping of derived values of the geotechnical data for each stratum.

In all instances the derivation of ground parameters for design must consider the range of actions that the ground may be subjected to. As such it is necessary to take into the likely stress range and direction of loading that have been assumed when deriving the design parameter. 4.4

Engineering Interpretation

The Interpretative Report should assess the significance of the interpreted ground conditions and any geological or other hazards identified by the investigation in relation to the proposed development. A brief review of the available options should be presented before any design parameters are recommended. This review should show a clear relationship between the ground model and the available options for the construction or of the structure. Thus, for example, the available foundation options will be presented, the need for earthworks or retaining structures may be discussed, particular difficulties such as compressible soils or a high groundwater table will be highlighted and so on. It is likely to include a discussion on the type of foundations, the need for ground treatment or piling, likely settlements, groundwater control and expedients necessary to deal with the site problems. Any change in proposals should stimulate re-evaluation but not re-interpretation of baseline ground and groundwater conditions. Significant changes in proposals such as relocation of a building or the introduction of a basement or retaining structures, however, may require further investigation to obtain appropriate data to supplement the original work

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and hence to add to the interpretation of the ground model and evaluation of its significance. The types of recommendation will depend on the nature of the development and the extent to which design proposals have been finalised. It is not possible to be exhaustive but, as an example, a section on spread foundations may include recommended bearing pressures for various depths and foundation sizes, the associated likely settlements, and any precautions that may be required with respect to tree roots, dissolution features, other buried features such as sewers and tunnels, the effects of loading on adjacent structures and the need for groundwater control. In relation to embankment design and construction the report should include an assessment of both short and long term stability, recommendations for side slopes, a review of staged construction and other measures such as vertical drainage and an estimate of likely settlements. A discussion of cutting slopes would include drainage measures, consideration of the effect of weathering and recommended stabilisation measures. Similarly, for tunnels and underground works, the report should describe the anticipated geology and give an evaluation of the ease of excavation and suitability of differing tunnelling methods, the need for face and methods of groundwater control, together with comments on anticipated ground movements in urban areas. Dependent on the type of project under consideration, other issues to be addressed could include pavement design, protection of buried concrete, retaining walls and ground improvement. This list is necessarily incomplete, as a comprehensive review of these matters falls outside the of a general guidance document. It is, however, intended to highlight the nature of the topics covered by the interpretative report. The interpretation should include a review of the field and laboratory work and of the completeness of the ground and groundwater model. Any limitations in the data (e.g. defective, irrelevant, insufficient or inaccurate data) should be pointed out and commented upon. Any particularly adverse test results, perhaps as a result of sample disturbance or sample handling techniques, should be considered carefully in order to determine if they are misleading or represent a real phenomenon that must be ed for in the design. The sufficiency of the results should be evaluated, particularly with reference to those hazards identified during the desk study and any new hazards identified by the investigation. The implications of any gaps in the available data or deficiencies in the investigation on any design solutions should be brought to the reader's attention at this point. Similarly, any specific features or hazards newly recognized by the investigation should be highlighted and the risk and consequences of their occurrence should be assessed. Remedial measures or additional investigation works necessary for a complete design solution should also be identified Any recommendations for additional field and laboratory work should include proposals, with comments justifying the need for the extra investigation. Such proposals should be accompanied by a detailed programme for the extra investigations to be carried out with specific reference to the questions that have to be answered. Any recommendations for additional investigation works should identify whether this must be carried out prior to the start of the main contract, or whether it can wait until the construction commences. It may also be necessary, dependent on the complexity of the project for additional, 'Derivative Reports' to be prepared. These may address such specialist subjects as seismicity, groundwater control (including pump test interpretation or contaminant transport modelling), or definition of ground reference conditions for tunnelling contracts. Reports in the latter

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category may be regarded as equivalent to the Geotechnical Baseline Reports described in Appendix B. 4.6

Geoenvironmental Aspects

The interpretative report should also include a review of the results of the chemical and microbiological tests, on soil samples, on leachates prepared from soil samples where appropriate, on water samples and on any gas samples recovered from site. The review should also include results of field measurements and should evaluate the ranges of concentrations measured and their spatial distribution, identifying any gaps in the data and setting out any proposals for additional investigation work. The appraisal of the contamination data should also identify any hazards arising from the investigation and evaluate the sufficiency of the data to address such hazards. The report will also assess the significance of the Geoenvironmental test data in the context of the proposed development and identify whether or not there is a risk posed to specified receptors arising from the chemical or microbiological contamination and the pathways between the source and the receptor. The report should then set out whether measures are necessary to mitigate such risks to an acceptable level. It should be borne in mind that certain foundation proposals and engineering works need consideration as part of such a risk assessment. An obvious example of this is construction of piles through contaminated ground into a Major Aquifer.

5.

Design Report

The processes of gathering geological, geomorphological and geotechnical information and interpreting it in the context of the project culminate in the compilation of the Design Report (DR). The level of detail of DR's will vary greatly depending on the type of project. For simple projects, a single sheet may be sufficient. The DR should normally include some or all of the following information, depending on the Geotechnical Category (nature, scale, usage and location) of the project: Assumptions

-

The assumptions, data and method of ing the safety and serviceability of the geotechnical construction (e.g. method of calculation).

Description

-

Making reference to the Desk Study, Factual and Interpretative Reports, any Derivative Reports and any other contractual documents relating to the projects: A description of the site and its surroundings. A description of the ground conditions. A description of the proposed construction, including anticipated loading and any imposed deformations.

Design Values

-

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Design values of soil and rock properties, including any necessary explanation for their selection. Statements on any codes, design guides and standards used. Statements on the suitability of the site for the proposed construction and the level of risk assumed in the assessment.

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Calculations

-

Geotechnical design calculations and drawing. Foundation design recommendations.

Monitoring

-

A note of any items to be checked during construction or required maintenance or monitoring during the life of the structure. The DR may include a plan of supervision and monitoring depending on the type of project. Wherever monitoring is required it is necessary to provide thresholds for the parameter that is being modelled together with proposed actions to be taken when the threshold is approached or exceeded.

The DR should include a plan of supervision and monitoring as appropriate for the type of project. Items which require checking during construction or which require maintenance after construction should be clearly identified. The DR should state: • The purpose of each set of observations or measurements. • The parts of the structure which are to be monitored and the locations at which observations are to be made. • The frequency with which readings are to be taken. • The ways in which the results are to be evaluated. • The range of values within which the results are to be considered. • The period of time for which monitoring is to continue after construction is complete. • The parties responsible for making measurements and observations, for interpreting the results obtained and for monitoring and maintaining the instruments. The DR may give the sequence of construction operations envisaged in the design. Alternatively, the DR may state that the sequence of construction is to be decided by the contractor subject to approval or comment by the designer. The supervision plan should state acceptable limits for the results to be obtained by the construction monitoring. The plan should also specify the type, quality and frequency of supervision, which should be commensurate with: • The degree of uncertainty in the design assumptions. • The complexity of the ground and loading conditions. • The potential risk of failure during construction. • The feasibility of implementing design modifications or corrective measures during construction. An extract of the DR containing the supervision, monitoring and maintenance requirements for the completed structure should be provided to the client. Geoenvironmental Considerations The DR report will include the results of formal assessments made of the risk to receptors of concern arising from the site contamination or as a result of the site development, as identified in the Interpretative Report. Where remedial measures are required to reduce such risks to an acceptable level, the DR will include a strategy detailing method statements of the

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works to be undertaken, the desired target concentrations for soils and where appropriate, receptors such as groundwater or surface water. The strategy must be agreed by relevant regulatory bodies prior to development work proceeding. Detailed method statements presenting the level of monitoring and supervision to be undertaken and including appropriate sampling and testing regimes are then prepared.

6.

Validation Report

EC7-1 Section 4 sets out the basic requirements for supervision of construction, monitoring and maintenance. This is a worthwhile starting place. It does not extend to advice for planning for the reuse of foundations or other element of an existing structure but otherwise provides a sound starting place for implementation of a validation report. The Validation Report can meet a number of objectives. Firstly, it is essential that the validation is undertaken in order to ensure that the original design criteria have been met and that no design changes are needed. Preparation of a Validation Report also provides a record of the works carried out and records any changes from the original assumed conditions. This may then provide the basis for the Main Contractor or his sub-contractors to submit a claim and the Engineer to evaluate such claims. Preparation of the geotechnical Validation Report should form an integral part of the construction, paid for by the client and the report can be used to demonstrate that money spent in this manner has real value for future development. The Validation Report describes the geotechnical construction works undertaken as part of the project. It is usually incorporated into the Operation and Maintenance (O&M) Manual which, under CDM regulations, forms an essential part of the project documentation (this is actually part of the Health & Safety File which is required for all projects). The information presented within the “Validation” Report can be considered under the following headings: Construction

As-built records of both permanent and temporary works left in place, including drawings, schedules and s. These should probably include only the geotechnical drawings with reference to the rest of the civil engineering drawings, otherwise there could be serious and confusing duplication. Information provided by the contractor, such as concrete mixes, reinforcement bar details should be included.

Changes to the design

Where appropriate records of preliminary prototype scale testing should also be included (anchors, piles etc.). This should also identify the design assumptions (these should be in the Geotechnical Design Report), particular specification and the construction records for the structure. This information can be used in any design which involves reuse of the structure or even an academic review of performance.

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Monitoring records • Records of ground conditions encountered with particular reference to changes from the conceptual ground model. Cross reference to a good methodology for geological mapping. • Test records relating to additional geotechnical testing, materials testing and proof load testing, in particular piles and anchors. • Any Non Compliance Reports or similar raised during the course of the project with details of any remedial actions • Monitoring records on the effect of the works on adjacent properties etc. Where monitoring data are to be presented these should be compared with original predictions. • Where the Observational Method was used for temporary or permanent works this should be fully recorded. • Records of temporary works, particularly where these are left in-situ or may affect future developments. Maintenance requirements • Details of inspection regime including scope and frequency. • Proposed measures to be taken during the lifetime of the facility for maintenance of drainage and corrosion protection. • Long term settlement records, water levels, piezometers, etc. • Scour protection for maritime structures. Decommissioning

Critical elements of the structural system which may affect the methods and sequencing of demolition works should be identified, e.g. ground water, tensioned anchors, propped walls etc.

Re-use

The information contained in the Validation Report should allow re-use of the foundations or construction materials if this is feasible. Structures should be placed in such a manner that they can either be re-used or can be sensibly removed to make way for the next phase of construction. For example, for under-ream piles good records of construction, material and design could prove invaluable to the next development as they can form a significant obstruction to redevelopment, or indeed an opportunity to take advantage of their presence.

Detail of records.

There may be locations where top quality records have real value. The example of under-ream piles is one, others could be in areas of archaeological interest where preservation in-situ is the objective of planning authorities (the records in this case add real value to the site and this should be a positive selling point)

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7.

Reporting Responsibilities

A common form of investigation contract is that where the consulting engineer with in-house geotechnical expertise commissions a site investigation contractor to carry out the ground investigation and prepare the factual report. Under this arrangement, the responsibility for the desk study and the design of the investigation rests with the consultant. A well written specification for the ground investigation contract will ensure that the consultant's requirements for the factual report are met by the investigation. The consulting engineer will then prepare the subsequent interpretative and design reports, although where the project is let on a design and build basis, the responsibility es to the successful contractor for the construction project, and where appropriate, his advisers. It is often the case, particularly for smaller scale development projects where site investigations are commissioned by a structural engineer who has no any in-house Geotechnical or Geoenvironmental expertise, that the desk study, factual report and interpretative reports are prepared by the specialist site investigation contractor. Such reports, particularly those dealing with foundations, are then provided with the tender documents for specialist piling or ground improvement contractors to tender on a design and build basis. The validation report will normally be prepared by the consulting engineer. Whatever approach is adopted, the responsibility for both design and report preparation should be clearly defined within each report. It is not the intention of this document to be prescriptive on these matters. However, the whole process should be subject to full quality assurance procedures, with each stage being subject to internal peer review by someone of suitable qualifications and experience.

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Factual Report

Inception/ Planning

Interpretation and review of data Desk study conceptual ground model

Interpretative report – detailed ground model , ground parameters and engineering implications

Design Recommendations

Ground Investigation, fieldwork and laboratory testing Design Report

References: BS5930:1999 Code of Practice for Site Investigations

Construction monitoring, maintenance and decommissioning

Guidelines for Combined Geoenvironmental and Geotechnical Investigations, AGS, 2000 Eurocode 7: Geotechnical Design Part 1. General Rules. DD ENV 1997-1 : 1995

Figure 1 The Ground Report

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Validation Report Geotechnical Structures Manual

March 03

APPENDIX A Check lists for:-

Desk Study Report Factual Report Interpretative Report Design Report Validation Report

Reporting Stage

Activity/Contents

Desk Study Report

Description of work undertaken and of reference. Sources of information. Description of the site and surrounding area based on an inspection and walkover survey of the site. Regional and site geology and any features of the geology and known material properties which will impact on the project. Groundwater conditions and hydrogeology. Records of previous investigations undertaken at or close to the site, if any. Site history and past uses of the site and adjacent sites (maps, photos, etc.). Site characteristics. Records of mining, quarrying, landfill, bomb impacts, etc. Records of services and underground structures. The occurrence or possibility of occurrence of radon. Field reconnaissance of the general area of the project noting particularly: − evidence of groundwater; − location of surface waters and evidence of flooding. − behaviour of of any existing structures on the site or of neighbouring structures; − exposures in quarries and borrow areas; − areas of instability; − history of the site; − geology of the site, including faulting; − information from available aerial photographs; − anecdotal evidence of historical activities/site use; − information about the seismicity of the area; − types of field equipment used; − description of frost susceptibility of soils. Clear conclusions regarding the conceptual ground model. Overall strategy and objectives for subsequent intrusive investigation Purpose and scope of the investigation. Names of all consultants and sub-contractors used. Dates between which field and laboratory work was performed. A factual of all field and laboratory work. Exploratory hole records (boreholes, trial pits, window sample holes), including grid co-ordinates and ground elevation. In-situ test results Laboratory test results including any contamination test results

Factual Report

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Completed ( / )

March 2003

APPENDIX A Reporting Stage Factual (Cont'd)

report

Interpretative Report

Design Report

Validation Report

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Activity/Contents

Completed ( / )

Results of groundwater level monitoring and any Geoenvironmental monitoring Specialist sub-contract test results, (static or dynamic cone penetration test, geophysics, etc.) Site plan showing locations of exploratory holes. The provision of data in electronic format A review of the field and laboratory work. Detailed description of all formations including their geological context, physical properties and their deformation and strength characteristics. Comments on irregularities such as pockets, depressions, cavities and boulders. Sub-surface profile(s) showing the differentiation of the various formations. Identification of geological, geotechnical or other hazards. Depth of the groundwater table and its seasonal fluctuations. The range and grouping of any derived values of the geotechnical data for each stratum. Summary tables for chemical contamination data with listings of selected assessment criteria. Tabulation and graphical presentation of the results of the field and laboratory work in relation to the requirements of the project and if deemed necessary histograms illustrating the range of values of the most relevant data and their distribution. A review and summary of the derived values of geotechnical parameters. Any proposals for further field and laboratory work, with comments justifying the need for this extra work and a detailed programme for the extra investigations to be carried out. The assumptions, data and method of ing the safety and serviceability of the geotechnical construction (e.g. method of calculation), including: A description of the site and its surroundings. A description of the ground conditions. A description of the proposed construction, including anticipated loading and any imposed deformations. Design values of soil and rock properties, including any necessary explanation for their selection. Statements on any codes and standards used Statements on the suitability of the site for the proposed construction and the level of risk assumed in the assessment. Geotechnical design calculations and drawings. Design recommendations. A note of any items to be checked during construction or required maintenance or monitoring. A statement of the sequence of construction operations envisaged in the design. Alternatively, the DR may state that the sequence of construction is to be decided by the contractor. A plan of supervision and monitoring as appropriate for the type of project., stating acceptable limits for the results to be obtained by the supervision and specifying the type, quality and frequency of supervision. As-built records of both permanent and temporary works left in place. Where appropriate records of preliminary prototype scale testing .

March 2003

APPENDIX A Reporting Stage

Activity/Contents

Validation Report (Cont'd)

Records of ground conditions encountered. Test records relating to additional geotechnical testing, materials testing and proof load testing, in particular piles and anchors. Any Non Compliance Records or similar raised during the course of the project. Monitoring records on the effect of the works on adjacent properties etc. Where the observational method was used this shall be fully recorded. Records of temporary works, particularly where these are left insitu or may affect future developments. Details of inspection regime including scope and frequency. Proposed measures to be taken during the lifetime of the facility for maintenance of drainage, corrosion protection. Long term settlement records, water levels, piezometers, etc. Scour protection for maritime structures. Identification of critical elements of the structural system which may affect the methods and sequencing of demolition works .

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Completed ( / )

March 2003

APPENDIX B

DESCRIPTION OF GEOTECHNICAL REPORTS AS USED IN NORTH AMERICA Geotechnical Data Report The Geotechnical Data Report corresponds to the Factual Report in U.K. usage. It is a collection of facts, about what work was undertaken, how it was done and the results of such activities. It is intended for use by all actual or possible participants in a project, including planners, designers and contractors, and, possibly, adjacent third parties or of the legal profession. The three most important guiding principles for Geotechnical Data Reports are that they are thorough, accurate, and free from interpretation. Geotechnical Interpretative Report The Geotechnical Interpretative Report is written by the geotechnical engineer for use primarily by the project designer and should fulfil three important objectives: • • •

the description of all relevant sub-surface soil, rock and groundwater conditions at the subject site; the recommendation of the best technically feasible and most cost effective design criteria for each subsurface project element; and the identification of and recommendations for dealing with and/or mitigating construction considerations and impacts on third parties.

Geotechnical Design Summary Report The Geotechnical Design Summary Report has been adopted by a number of clients in the United States where they have a need to assume greater control over the construction means and methods to be employed on a project. The underlying approach to a GDSR is to: • • •

•

openly share available information about the geology and about sub-surface conditions as derived from the sub-surface investigation; explain the geotechnical basis for the design and the underlying approach used for the contract specification and drawings; provide a 'level geotechnical playing field' for the preparation of bids by avoiding overly optimistic assumptions about ground conditions and by openly discussing the advantages and disadvantages of various methods of construction for evaluation by prospective contractors; and provide a package of both factual sub-surface information and the interpretations derived from that information that can be used to help evaluate the validity of claims of differing site conditions during construction.

The GDSR represents a collaborative writing effort by the geotechnical engineer, the project designer and representatives of the project owner, working together to produce a document that is intended for use by the project contractor. The GDSR is a contract document that is mandated for use by the contractor.

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March 2003

APPENDIX B

Geotechnical Baseline Report The intention of the Geotechnical Baseline Report is that it should have the status of a contract 'specification' and that it would be used to establish definitive 'baselines' of information about certain sub-surface conditions to be expected at a site. Using these baseline conditions, the contractor would then be able to bid the project without having to provide an independent interpretation of sub-surface information and with a higher degree of confidence that claims for differing site conditions would be more easily resolved by comparison between the encountered conditions and what was said in the baseline statement regarding these conditions.

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March 2003