Chapter 11, Problem 11.9P

Refer to Figure 11.26b. For the drilled shaft with bell, given:Thickness of active zone, Z = 9 mDead load = 1500 kN Live load = 300 kNDiameter of the shaft, Ds = 1 mZero swell pressure for the clay in the active zone = 600 kN/m2Average angle of plinth-soil friction, Φ'ps = 20°Average undrained cohesion of the clay around the bell = 150 kN/m2. Determine the diameter of the bell, Db. A factor of safety of 3 against uplift is required with the assumption that dead load plus live load is equal to zero.

For the drilled shaft described in Problem 10.1, what skin resistance would develop in the top 6 m, which are in clay ?

A mine has a 6m diameter vertical ventilation shaft. Calculate the radial, circumferential and shear stresses 0.2m into the rock at the north point (A) for a depth of 2500m below surface. Draw a simple sketch of the shaft showing the stresses, directions, the point A with proper labels. The principal in situ horizontal stress in the north-south direction is equal to half the overburden stress, and the principal in situ horizontal stress in the east- west direction is twice the overburden stress. The unit weight of the rock y is 0,025 MN/mº. The modulus of elasticity of the rock E is 50 GPa, and Poisson's ratio for the rock v is 0,25. Assume that the rock behaves elastically.