119
1. Average N= 15
Average unconfined strength corresponding to N=15
Cu=10.19t/m2
Average = 10.19/2 =5.09t/m2
Say, 5t/m2
2. safe bearing capacity of soil = 5.14X5.0/2.5 = 10.28t/m2
Lets take the S.B.C as 10.5t/m2
3. Average unit weight = 1.83t/m2
Submerged unit weight = 0.83t/m2
4. Nominal diameter of stone column = 500mm
Increased size after installation = 600mm
5. Critical depth = 4D
= 4X0.6
= 2.40m
6. Initial radial stress in the soil
ros = k0H
K0 = 0.6
ros = 0.6 X 0.83 X 2.40
= 1.1952t/m2
7. Radial stress in the soil due to surcharge effect equivalent
10.5
rss = 0.6 X 10.5
= 6.3t/m2
8. Vertical stress in the stone column
rc = tan2{45+c /2}[fc+ros+rss]
c = 30
F=4
C=5
tan2 [45++c /2] = 3
rc= 3 X [4 X 5 +1.1952+6.3]
= 82.4856t/m2
9. Ultimate load carried by a stone column = 82.4856 X /4 X
0.62
= 23.322t say 23.0t
10. Load at ground level
Weight of water = /4 X 392 X 20.7 X 1
= 24728.025t
=24729t
Self weight of the tank = 508t
Total weight = 25237t
11. Thickness of sand pad = 1m
Offset = 1m
Distribution of load assumed as 1t
Pressure on soil at ground level = 25237t / /4 [39+2X1.0]2
= 19.124t/m2
120
12.0 Disposition of stone column:
Equi- spacing of column at 1.25m
Intervals on an equi-interval
Triangular grid pattern
12.1 Load at ground level = 19.124t/m2
Spacing of columns, S=1.25m
Tributary area of a column A = 0.866 (1.25)2
= 1.353m2
Area of stone column:
Ap = /4 X 0.62 = 0.283m2
a= Ap/A =0.283/1.353 = 0.209 ; say 0.21
12.2 Elastic modulus of soil:
ES = 300t/m2 (assumed)
Elastic modulus of stone column:
Ep = 3300 (assumed)
13. Equivalent modulus of soil stratum, reinforced with stone
column
Eeq = Ep+(1-) ES
= 0.210 X 3300 + (1-0.210) X 300
= 930t/m2
qp= 19.124 X 3300/ 930
= 67.85t/m2
Qp=67.85 X 0.283
= 19.20
F.S = 23.0/19.20
= 1.197 = 1.2
qs= 19.124 X 300/ 930
= 6.16t/m2
Stone column to be terminated in a cohesion less soil stratum,
vide recommendation in the
report.
Depth of stone column will range from 7.5 to 9.5m.
