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Question

# An undisturbed soil sample was taken from the middle of a clay layer (i.e., 1.5 m below GL), as shown in figure. The water table was at the top of clay layer. Laboratory test result are as follows: Natural water content of clay : 25% Preconsolidation pressure of clay : 60 kPa Compression index of clay : 0.50 Recompression index of clay : 0.05 Specific gravity of clay : 2.70 Bulk unit weight of sand : 17kN/m3 A compacted fill of 2.5 m height with unit weight of 20kN/m3 is placed at the ground level. Assuming unit weight of water as 10kN/m3, the ultimate consolidation settlement (expressed in mm) of the clay layer is .37.04

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Solution

## The correct option is A 37.04¯¯¯σ=17×1+0.5×γsubclay For clay w = 0.25 S = 1 g = 2.7 ⇒Se=Gw ⇒e=2.7×0.251 e = 0.675 ⇒γsub=G−11+eγw=2.7−11+0.675×10 ⇒γsub=10.15kN/m3 ¯¯¯σ=17+0.5×10.15 =22.07kN/m2 Δ¯¯¯σ=2.5×20=50kN/m2 Alternate Method ΔH1=CrH1+e0log6022.07 =0.05×10001.675log6022.07 ΔH1=12.966mm ΔH2=CcH1+e′log(72.0760) Cr=Δelog(6022.07)=0.05 Δe=0.0217 ⇒e′=0.653 ΔH2=0.5×10001.653log(72.0760) ΔH2=24.075mm ⇒ΔH=ΔH1+ΔH2=37.04mm

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