Find the maximum allowable load on the shaft.

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Chapter 13, Problem 13.6P

To determine

Find the maximum allowable load on the shaft.

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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.

[2] A 12 m long and 600 mm diameter drilled shaft installed in a sand soil. The nominal side friction capacity of the drilled shaft, Σfn As, is 800 kN and nominal toe-bearing capacity, qn'At, is 700 kN. The modulus of elasticity of the drilled shaft, E, is 30,000 MPa. Compute the settlement of the drilled shaft for a surface load of 600 kN.

A drilled shaft designed in accordance with the AASHTO code must support the following downward and uplift axial design loads: P = 850 k, Pup. = 270 k. The soil profile consists of: Undrained Shear Strength, s,, (lb/ft²) Depth (ft) Soil Description Unit Weight, y (lb/ft³) N60 0-15 Clayey silt 115 1200 15-35 Silty clay 112 1800 35-55 Sandy silt (nonplastic) 115 24 55-80 Silty sand 124 43 Practice Problems 597 The groundwater is at a depth of 50 ft. Using the AASHTO resistance factors, select a diameter and depth for a single drilled shaft to support these design loads. Use a load factor of 0.9 on the weight of the shaft. Note there are many different diameter-length combinations that would be satisfactory, but select one that you think would be most appropriate.