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Design of Stone Column Page 1 of 2

Name of work :

Data Considered : a) Depth of Stone Column

: 12m

b) Let Cu =

: 0.27 Kg/cm2

c) Density above water table

: 1630kg/m3

d) Density below water table

: 980 kg/m3

e) Tank Diameter

: 28 m

f) Load

: 2500 T

Let diameter of stone column = 0.6m

a) Yield stress Yield stress on stone column = Nφ(σro+4c) Nφ=(45 + φ/2) Let φ be 50 degree Nφ= 7.52 σro = effective radial stress = ko x σvo Let ko = 0.6 σvo = 1630 * 1.0 + 980 (4 * 0.6 – 1) Yield stress = 7.51 * (3002 + 4 * 2700)

= 3002 kg/m2

= 103785.7 kg/m2

Yield load = π/4 * (0.6)2 * 103785.7 = 29329.9 Kg

Let FOS = 2.0 Yield safe load = 29329 / 2.0 = 14665 kg

…………….(a)

b) Bearing support provided by surrounding soil Qult = cNc = 270 * 6

= 1620kg/m2

Qsafe=1620/4=405 kg/cm2 (considering Factor of safety = 4) Consider Spacing of stone columns = 2.3 m c/c triangular grid pattern Area covered by each stone column=0.868 * (2.3)2 = 4.59 m2 Area of each column = 0.785 * 0.62 = 0.283 m2 Area surrounded by soil for each column = 4.59 – 0.283

= 4.31 m2

Safe load taken by surrounding soil = 4.31 * 405

= 1745.2 kg

…………………..…(b)

Design of Stone Column Page 2 of 2

c) Surcharge effect Increase in radial stress ∆σr = qsafe / 3(1 + 2Ko) = 405/3 (1 + 2 * 0.6) = 297 kg/m2 Increase in ultimate cavity expansion stress = Nφ ∆σrFq But Fq=1 for φ=0 ∆σro = 297 * 1 = 297 kg/m2 Increase in yield stress = Nφ * ∆ * σro * Fs = 7.52 * 297 * 1 = 2233.3 Kg/m2 Increase in Yield load = π/4 * (0.6)2 * 2233.3 = 631.1 kg

Fos = 2.0 Permissible load = 631.1 /2.0 = 315.6 kg Hence safe load = 14665 + 1745.2 + 631.1 = 17041 kg ~ Say

17 Ton

Total tank load = 2500 T No of columns required = 2500/17 = 147 (say) Area of Tank = 0.785 * 28 * 28 = 615.4 Sqm Area per column = 615.4 /147 = 4.18 m2 If effective spacing in triangular spacing is s then 0.868 * s2 = 4.18 sqm so spacing s = √4.18/0.868 = 2.19 m ( Say 2.0 m)

Stone columns of 12 m depth and 600 mm diameter may be considered at an effective triangular spacing of 2.0 m. The load carrying capacity of the column should be verified by conducting load test on the stone column.

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