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Soil Mechanics and Foundation Engineering - Engineering

Q1:

A coarse-grained soil has a voids ratio 0.75, and specific gravity as 2.75. The critical gradient at which quick sand condition occurs, is

A 0.25

B 0.50

C 0.75

D 1.00

ANS:D - 1.00

Water is flowing in an upward direction through the structure of sand 5m thick under a total head difference of 3m. The sand has a specific gravity of 2.55 and voids ratio of 0.55. The factor of safety against quick condition would be? Ic = G-1/1+e=2.67-1/1+0.67 = 1.67/1.67.

Hydraulic gradient i = hydraulic length/head.

1= h/1.5m.
H=1.5m. Critical gradient (ID) = (G-1)/(1+e),
= (2.75-1)/(1+0.75),
= 1. or Icr(for flowing water) = 3/5 = . 6.

And;
Icr (for soil) = (G-1)/(1+e) = (2.55-1)/(1+.55) = 1.
F.o.s = 1/.6 = 1.66.