Reference no: EM13984975

Exercise3

A soil profile consists of 5m of compacted sandy clay followed by 5m of medium dense sand.  Below the sand is a layer of compressible silty clay 20m thick.  The initial ground water table is located at the bottom of the first layer (at 5m below the ground surface).  The densities are 2.05 Mg/m³(??), 1.94 Mg/m³ (??_sat), and 1.22 Mg/m³ (??^') for the three layers, respectively.  Compute the effective stress at a point at middepth in the compressible clay layer.  Then, assuming that the medium dense sand remains saturated, compute the effective stress in the clay layer at midpoint again, when the ground water drops 5m to the top of the silty clay layer.  Comment on the difference in effective stress. 

Exercise8

A geotechnical engineer is evaluating the stability of the slope in Figure 13.4 below.  This evaluation is considering the potential for a shear failure along the shear surface shown.  The soil has drained friction angle of 30 degrees and no cohesion strength. 

(A) Compute the soil shear strength at Point A along this surface when the groundwater table is located at level B

(B) Compute the new shear strength if the groundwater table rose to level C.  The moist unit weight of the soil is 120 pcf.  The saturated unit weight is 123 pcf. 

(C)  If the acting shear stress at point A is found to be around 1000 psf, determine the Factor of Safety (FOS) against shear failure at point A for the latter case.