In: Civil Engineering
You are conducting a geotechnical analysis on a 3-layer soil system. Layer 1 is a 5-ft sand with dry unit weight of 100 pcf. Layer 2 is a 6-ft silty sand with a saturated unit weight of 115 pcf. Layer 3 is a 15-ft low plasticity clay with a saturated unit weight of 117 pcf. There is an unknown granular soil below the clay layer. The ground water table is at a depth of 5 ft. A structural footing with dimension 5ft x 5ft is placed on top of the top sand layer. The footing must carry a load of 50,000 lbs. i. Draw a schematic diagram of the layered soil system. Show all details (6) ii. Draw the distribution of effective stresses in the soil (15) iii. Determine the effective stress in the middle of the clay layer (5) iv. At time T ≈0 (i.e. immediately after the structural load is applied), what would be the changes in total stress, pore water pressure and effective stress in the middle of the clay? Assume entire stress due to the footing is transmitted to the clay. (12) v. At time T ≈α, (i.e. long time after construction), what would be the changes in total stress, pore water pressure and effective stress in the middle of the clay? (12) vi. Laboratory consolidation test on the clay soil produced the following graph for the soil. Calculate the consolidation settlement of the clay layer when a foundation is placed on top of layer 1. Make any other necessary assumption. (50) 0.1 1 10 100