Question 3 The figure below shows a proposed foundation site, with 10 ft of sand overlying 15 ft of clay with consolidation properties shown. The clay is normally consolidated. Assume 1-D conditions. Sand 10' Foundation stress Ya 110 pcf 15' Clay Y₁ = 120 pcf C₁ = C₂ = 0.033 Ca=0.165 (a) Compute the initial σ' at the middle of the clay layer prior to excavation and construction. (b) After excavation and during construction, the foundation area will be heavily loaded with the structure and equipment so that σ', at the middle of the clay layer will be increased to 3900 psf. Determine the settlement that will occur under these conditions. (c) After construction is completed, the equipment will be removed and the final o' at the middle of the clay layer will be 3200 psf. Determine the settlement that will occur under these final conditions. Time Rate of Consolidation Question 4 The settlement analysis for a proposed structure indicates that the underlying clay layer will settle 7.5 cm in 3 years, and that ultimately the total settlement will be about 32 cm. However, this analysis is based on the clay layer being doubly drained. It is suspected that there may be no drainage at the bottom of the layer (i.e., clay has single drainage condition). Answer the following questions based on single drainage only, assuming c₁ = 1.5 x 104 cm²/s for both single and double drainage. (a) How will the total settlement change from the double to the single drainage case? (b) How long will it take for 7.5 cm of settlement to occur if there is only single drainage? Question 5 A field preloading test was performed on a 5.5 m thick clay layer with top and bottom drainage condition. From the observed settlement curve, 20 % consolidation has been achieved in 2.5 month. A nearby site with the similar soil has 7.0 m thick clay layer. Estimate (a) Time for 50% consolidation of 7.0 m thick clay layer (b) Time for 90 % consolidation of 7.0 m thick clay layer