Question

A rigid strip footing with a width of B is constructed above the ground on a clay deposit, overlying bedrock. The depth of clay layer is H and the water level is at the natural ground surface. Before construction of the footing, laboratory tests on a saturated clay sample, taken at a depth of H/2 below the ground surface, provided the following properties:

Compression Index = Cc , Recompression Index = Cr , Consolidation Coefficient = cv

Over Consolidation Ratio = OCR, Water Content = w% and Specific Gravity = Gs

Assume the vertical uniform surcharge stress on the footing including the weight of footing and column = q

(a) Calculate the initial saturated unit weight of clay deposit.

(b) Based on the elastic theory (Boussinesq’s equation), calculate the excess pore water pressures at the depth of H/2 immediately after applying the surcharge load. Assume the vertical stress (q) is applied instantaneously.

(c) Using theory of 1-D consolidation, calculate the total average settlement of this rigid footing due to consolidation of the clay layer, long time after applying the total load.

(d) Determine the average settlement of this rigid footing after n days of applying the total load due to consolidation of clay deposit. Assume the bedrock is permeable (i.e. Drainage path = H/2)

(e) Plot the graph of settlement versus time (in log scale) for this footing.

Answer 1