Design Of A Deep Tube Well 4e3kq

Design of a Deep Tube Well Design a deep tube well for 2200 gallon/hr. water requirement with the grain size analysis of the subsoil layer from (360 – 600) ft. Solution: Grain size analysis for subsoil layer: Sub-soil Laver (ft.)

D60 (mm)

D10 (mm)

Cu

Over View

360 - 380 380 - 400 400 - 420 420 - 440 440 - 460 460 - 480 480 - 500 500 - 520 520 - 540 540 - 560 560 - 580 580 - 600

0.28 0.32 0.26 0.28 0.24 0.22 0.26 0.25 0.19 0.23 0.42 0.34

0.14 0.22 0.14 0.17 0.13 0.08 0.09 0.10 0.16 0.15 0.19 0.17

2.00 1.45 1.86 1.65 1.85 2.99 3.02 2.58 1.19 1.53 2.21 2.00

For the selected aquifer layer (460 ft. - 480 ft.) D10 < 0.25 mm D60 < 0.42 mm Cu 3.00 Remarks: Artificial gravel packing is Required.

Grain size analysis for selected subsoil layer (460 – 480) ft.: Sieve No

Opening (mm)

Wt. Retained (gm)

% Wt. retained

Cumulative % retained

% Finer

F.M.

4 8 16 30 50 100 200

4.76 2.38 1.2 0.6 0.3 0.15 0.075

0 0 0 1 9 139 31

0 0 0 0.5 4.5 69.5 15.5

0 0 0 0.5 5.0 74.5 90.0

100 100 100 99.5 95.0 25.5 10.0

0.80

Gravel Pack Design: We know, Pack aquifer ratio,

𝐷30 𝑜𝑓 𝐺𝑟𝑎𝑣𝑒𝑙 𝑃𝑎𝑐𝑘 𝐷30 𝑜𝑓 𝑎𝑞𝑖𝑓𝑒𝑟 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙

=4

D30 of Gravel pack material = 4* D30 of Aquifer material = 4*0.17 = 0.68 mm

Gradation Curve Subsoil layer 460-480 ft D60= 0.22 mm ; D10= 0.08 mm; D30= 0.17 mm 100

90 80

% Finer

70 60 50 40 30 20 10 0 10

1

0.17 Sieve Opening (mm)

0.1

0.01

Derivation of grain size distribution curve for gravel pack material:

Gradation Curve Subsoil layer 460-480 ft 100 90 80

% Finer

70 Sieve Analysis

60

Gravel Pack 50 40 30 20 10 0 100

10

1.2 1

0.6

0.3

Sieve Opening (mm)

0.1

0.01

Grain size distribution from curve for gravel pack material: Sieve No

Opening (mm)

% Finer

4 8 16 30 50

4.76 2.38 1.2 0.6 0.3

100 100 95 26 10

Cumulative % retained 0 0 5 74 90

Cumulative % retained zone (Dev. +- 5) 0 0 2-7 72-76 88-92

Strainer Design: From grain size distribution curve of gravel pack material effective size of the gravel pack material, D10 = 0.3 mm Slot number =

0.30 25.4

∗ 1000 = 11.81 ≈ 10

Yield calculation: Using 3 in. diameter strainer, open area = 19 in2/ft. Permissible safe entrance velocity = 2 cm/sec = 0.31 gallon/min/ft. So, Yield = 0.31*19 = 5.89 gallon/min/ft. Required water, Q = 2200 gallon/hr. = 36.67 gallon/min. Using factor of safety of 2, Yield = 5.89/2 = 2.95 gallon/min/ft. Required strainer length = 36.67/2.95 = 12.43 ft. Let, strainer length=20ft. Now, for 20-ft. strainer at subsoil layer 560-580 ft. Total yield = 20*2.95 = 59.0 gallon/min > 36.67 gallon/min. (OK!) Overview of subsoil layer: Sub-soil Laver (ft.) 360 - 380 380 - 400 400 - 420 420 - 440 440 - 460 460 - 480 480 - 500 500 - 520 520 - 540 540 - 560 560 - 580 580 - 600

FM Value 1.24 1.41 1.12 1.31 1.01 0.80 1.12 0.91 1.14 0.93 1.78 1.50

Sand Type Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Fine Sand Medium Sand Medium Sand