A foundation (a slab of concrete) resting on the surface of a saturated over consolidated clay is to be designed to support a column load including the weight of the foundation of 250 kN. Groundwater level is at the surface. A one-dimensional consolidation test on a sample of the clay at its natural water content of w = 40% and taken at a depth of 2 m gave the following results: Cc = 0.54, Cr = 0.108, and OCR = 12. Atterberg limit tests gave LL = 70% and PL = 30%. No other tests were conducted. For a preliminary design, assume a circular footing 2.5 m in diameter and v' = 0.35.
(a) Determine if the increase in stresses from the foundation will cause the clay at a depth of 1 m to yield.
(b) If the clay does not yield, calculate the factor of safety for undrained condition.
(c) Calculate the excess pore water pressure due to the foundation load.
(d) Assuming that the stress state at the depth of 1 m represents the average stress state over a thickness of 2 m of the clay, calculate the settlement of the foundation. Is this settlement elastic or elastoplastic?
(e) How much long-term settlement would occur from the dissipation of the excess pore water pressure?