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1.0

Capacity of Stone column of 600 dia. 15m length & 1.5m traingular spacing

1.1

Column Dimensions : Diameter of Stone Columns Initial Spacing of Column Pattern of Grid

1.2

= = =

0.6 m 1.5 m c/c Triangular

Soil Details : Cohesion of Soil Bulk density of soil (above WT) Bulk density of soil (below WT) Deck level Design Water level Height of soil above water level Angle of internal friction of fill (Stone material)

= = = = = = =

35 16 6 0 -2 2 45

Loading intensity over the column

=

2.0

Calculation

2.1

Bearing Support Provided by Surrounding Soil Ultimate Bearing capacity qult

kN/m2 kN/m3 kN/m3 m above MSL m above MSL m deg.

140 kN/m2

Where, c = Cohesion of surrounding soil Nc = Bearing capacity factor

= = =

c * Nc 35 kN/m2 5.14

Hence, Ultimate Bearing capacity qult

=

179.9 kN/m2

Safe Bearing capacity, qsafe Where, FoS = Factor of Safety

= =

Hence, Safe Bearing capacity, qsafe

=

59.97 kN/m2

Area covered by each stone column Where, S = Spacing of Stone columns

= =

0.866 * S2 1.50 m c/c

Area covered by each stone column, As Area of each stone column , Ac

= =

1.95 m2 0.28 m2

Area of surrounding soil for each column A = As - Ac

= =

Safe load taken by surrounding soil

= =

As - Ac 1.67 m2 A * q safe

qult / FoS 3

99.90 kN ……(1 )

1

2.2

Yield load of Stone Column Yield stress on stone column = Where, N = tan2 (45 + /2) = ro = Effective radial stress = Ko x vo Ko = Coefficient of lateral earth pressure vo = Effective vertical stress (taken at a depth of 4 times dia.of column) c = Cohesion of surrounding soil Yield stress on stone column

2.3

5.809 0.6

=

34.4 kN/m2

=

35 kN/m2 Nx (ro + 4c)

= =

933.1225078 kN/m2

Yield load on stone column

= =

Yield Stress x Area of Column 263.7004207 kN

Safe load on stone column Where, FoS = Factor of Safety

= =

Yield Load / FoS 1.5

Hence, Safe load on stone column

=

175.8 kN ……(2)

Surcharge Effect Increase in radial Stress r qsafe

=

qsafe / 3 * (1 + 2 Ko)

= =

59.97 kN/m2 0.6

Hence, Increase in radial Stress r

=

43.98 kN/m2

Increase in yield Stress Fq' For  = 0,

=

Where,

ko

Hence, Increase in yield Stress Increase in yield load Safe Increase in yield Load Where, FoS = Factor of Safety Hence, Safe Increase in yield Load 2.4

=

Nx (ro + 4c)

= =

N* r * Fq' 1 255.44 kN/m2

= = = = =

Increase in Stress x Area of col. 72.19 kN Increase in Yield load / FoS 1.5 48.1 kN ……(3)

= =

Equations (1) + (2) + (3) 323.8 kN

Total Safe Load Total safe load of each column

2

2.5

Loading on Column Loading over the surface, q Area covered by each column, As Load on each column

3.0

= = = =