Precast concrete circular piles with 1 ft diameter will be driven through water into a lakebed to support a pier. The soils in the lakebed consist of 10 ft of very soft clay with the undrained shear strength of 300 psf overlying 50 ft of stiff clay with the undrained shear strength of 1800 psf. The foundations will be installed to a penetration depth of 40 ft from the lakebed surface. The average gravimetric water contents of the soft clay and stiff clay are 30% and 25%. a. Estimate the buoyant unit weight values for the clay layers. Explain any assumptions. (10)
b. Using Tomlinson's charts (1971), identify the value of a for the lower stiff clay layer. Note that the value of a for the very soft clay should be 1. (10)
c. Draw a plot of the effective stress and the side shear stress as a function of depth from the soil surface up to a depth of 40 ft. Please put scales/labels on the axes and show numerical values. Show all calculations to justify the shape of these curves. (10)
d. Calculate the end bearing resistance of the pile and use your answer from part b to calculate the total side shear resistance of the pile. Use these values to calculate the total axial resistance of the pile, neglecting the self-weight of the pile. (20)