Question

The ground profile of a construction site consists of a 3 m thick layer of sand followed by a 2 m thick layer of clay lying on impervious bedrock. The watertable is at a depth of 2 m below the ground surface. The sand has a dry unit weight of 16 kN/m and a saturated unit weight of 18 kN/m3. The capillary rise in sand is 0.5 m. The clay has a bulk unit weight of 19 kN/m 1. One dimensional consolidation test carried out on an undisturbed sample taken from the middle of the clay layer gave the following results. Voids ratio (e) Pressure (p) kN/m 2550 100 200 400 800 Evaluate the maximum preconsolidation pressure of the sample and the overconsolidati 0.824 0.819 0.814 0.712 0.591 0.468 ratio of the clay layer, (40%) If the site is uniformly overloaded with a surcharge of 200 kN/m2 calculate the final settlement of the clay layer (30%) Calculate the ultimate settlement of the clay layer and time taken for 90% of the consolidation to take place. Use coefficient of consolidation calculated in Q2. (30%) What you understand by primary and secondary consolidation? One dimensional consolidation test described in Q1 gave the following readings when the pressure was increased 50 to 100 kN/m2. The thickness of the soil sample testing was 19 m and drainage was allowed from both ends of the sample Time (Mins.) Settlement (0.001 mm) 2. 16 36 64 100 144 196 117 239 360 476 594 690 765 256 324 400 24Hrs. 832 880 917 991 Determine the coefficient of consolidation of and the coefficient of compressibility of clay. Calculate the settlement of the clay layer in Q. 8 years after loadin

Answer 1

Draw the graph using an appropriate scale 2)determine the point of maximum curvature, 3) at, A draw a tangent to the curve 4) at, A draw a horizontal line Ac 5) draw the extension ED of the straight line portion of the curve 6) where line ED cuts the bisector AF of angle CAB, that point corresponding to the reconsolidation stress (sigma p_c^1) in our case using scale x-axis = 0.3 y-axis = 0.3 1 log p value we get sigma p_e^1 = 91.20 (cd intersection value was 1.56 so sigma p_c = 10^1.56 = 91.20 (10 base log)) note in order to get intersection point manuals value may slightly differ so to get exactly value use in software so, maximum pre consolidation pressure = 91.20KN/m^2 calculation of effective stress total stress diagram because (at mid od clay layer) perpendicular to pure water pressure diagram effective stress diagram