(Solved): solve it A group of piles is required to support a structural load of 25000kN. Circular concre ...

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A group of piles is required to support a structural load of $25000\mathrm{kN}$. Circular concrete piles $0.4\mathrm{m}$ in diameter will be driven through $2.5\mathrm{m}$ of soft clay, 6.5 $\mathrm{m}$ of firm-to-stiff clay into a deposit of dense gravel as shown in the figure below. The water table exists at depth $1\mathrm{m}$ below ground level. Design the pile group assuming the following data. factor of safety $=2.5$ Assume the following design parameters $a=0.5,Nc=9,?=1$ and an efficiency $E=0.75$ Soil properties are as follows Clay fill and Soft clay have same properties $\begin{array}{l}\mathrm{y}=18\mathrm{kN}/{\mathrm{m}}^3\text{ (above W.T) }\\ \mathrm{ysat}=20\mathrm{kN}/{\mathrm{m}}^3\\ \mathrm{cu}=12\mathrm{kN}/{\mathrm{m}}^2,?\mathrm{u}=0^{?}\end{array}$ Firm-to-stiff clay: $\begin{array}{l}\text{ Ysat }=19\mathrm{kN}/{\mathrm{m}}^3\\ \text{ cu }=55\mathrm{kN}/{\mathrm{m}}^2\text{ at depth }2.\\ \text{ of }5\mathrm{kN}/{\mathrm{m}}^2\text{ per metre. }\\ ?\mathrm{u}=0^{?}\\ \text{. }\\ \text{ Ysat }=21\mathrm{kN}/{\mathrm{m}}^3\\ \mathrm{Ks}=2\\ {\mathrm{c}}^{?}=0,{?}^{?}=40^{?}(\mathrm{Nq}=150)\\ {?}^{?}=30^{?}\end{array}$ $\mathrm{cu}=55\mathrm{kN}/{\mathrm{m}}^2\text{ at depth }2.5\mathrm{m}\text{ then increases linearly with depth at a rate }$ Dense gravel: $\begin{array}{l}\text{ Ysat }=21\mathrm{kN}/{\mathrm{m}}^3\\ \mathrm{Ks}=2\\ {\mathrm{c}}^{?}=0,{?}^{?}=40^{?}(\mathrm{Nq}=150)\\ {?}^{?}=30^{?}\end{array}$ General recommendations - The number of piles is to be determined as part of the design procedure - Negative skin friction is expected to take place in the layer of soft clay. - The total depth of piles should not exceed 25 meters.