# (Solved): The answer is 11.6m, please show all workings: A 600mm square concrete pile is to be built to sup ...

600mm

square concrete pile is to be built to support a working compression load of

300kN

or a working tension load of

200kN

at a site with two layers of soil. The top layer is

6.0m

thick and consists of sands and gravels with bulk unit weight of

22k(N)/(m^(3))

and angle of friction of

\phi _(crit )^(')=35\deg

. The bottom layer is composed of clay with bulk unit weight of

18k(N)/(m^(3))

and undrained shear strength of

60kPa

. Determine the necessary minimum pile length immediately following construction assuming that the water table is at the depth of

2.0m

from the ground surface involved. The average adhesion factor may be taken as 0.4 for the clay layer. Assume that the horizontal effective stress at any depth is equal to

(1-sin\phi _(crit)^('))

times the vertical effective stress at the same depth, and that the angle of friction between the concrete and the sand is equal to

0.6\phi _(crit )^(')

. It may be assumed that the end bearing capacity factor is equal to 9 for the present conditions. The shaft resistance safety factor may be taken as 2.0 , while the end bearing safety factor may be taken as 2.5 .

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