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# (Solved): A site consisted of 10m thick homogeneous clay deposit overlying an impermeable rock. The water tabl ...

A site consisted of 10m thick homogeneous clay deposit overlying an impermeable rock. The water table at the site remained always at the same elevation as the original ground surface. The site investigation results indicated that the clay deposit had an average saturated density of 1.5Mg/m3 , an average recompression index of 0.03 and an average coefficient of consolidation of 5 x 10-8m2/s. During the site investigation a piezometer standpipe was installed at the mid depth of the clay deposit. The consolidation test results indicated that the clay deposit at depths of 1m, 3m, 5m, 7m and 9m from the original ground surface had a preconsolidation pressure of 45 kPa, 35 kPa, 25 kPa and 44.5 kPa, respectively.

(a)(i) Calculate the overconsolidation ratio of the clay deposit at depth of 1m, 3m, 5m, 7m and 9m from the original ground surface. Briefly explain the possible reasons for the variation of the overconsolidation ratio of the clay deposit with respect to depth.

(a)(ii) After the site investigation, a sand fill, which was large in lateral extent, was placed on the ground surface. The height of the sand fill was 2m and the total density of sand fill was 2.0Mg/m3 above and below the water table. Calculate the total settlement of the clay deposit by dividing the clay deposit into 5 layers of equal thickness of 2m.

(b) Calculate the time required for the clay deposit to achieve 50%, 90% and 100% of the consolidation settlement caused by the placement of the sand fill. In this calculation, treat the clay deposit as one layer; subdivision are not required.

(c) Calculate the height of the water level in the piezometer standpipe with respect to the water table, 12.5 years after the placement of the sand fill. Also, calculate the total pore-water pressures at the top and bottom of the clay deposit, 12.5 years after placement of the sand fill.

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