LAUSR

Three-dimensional finite element (FE) analysis was carried out to investigate the behavior of a single row of drilled shafts installed in an unstable slope and to determine the soil pressures acting on the shafts. ABAQUS program was used and the built-in Mohr–Coulomb constitutive model was employed to model the elastic–plastic behavior of the purely cohesive soil, while the drilled shaft was assumed to behave as linear elastic. The length of the drilled shaft is 10 m with a diameter of 1 m. The center-to-center spacing between drilled shafts was taken as 2 m. Slope movement was simulated by imposing a uniform horizontal movement of the soil adjacent to the shaft. Soil pressures along the shaft were recorded at several uniform lateral soil movements until the ultimate soil movement was reached. Cohesion of soil was varied in the FE simulations from 30 to 100 kPa to study its influence on the soil pressure profiles. The effect of shaft stiffness on soil pressures was also included in the study through the relative shaft/soil flexibility factor K R . Two cases of drilled shafts were considered: (1) stiff shaft with K R  = 2.9; and (2) flexible shaft with K R  = 0.00004. Soil pressures from FE analyses were idealized and simplistic equations were developed and presented which will allow prediction of soil pressures acting on flexible and stiff shafts. The computed ultimate soil pressures agreed well with those from the literature. The computed soil movement to fully mobilize the ultimate contact pressure was found to vary from 10 to 35% of drilled shaft diameter ( D ) for flexible shafts and from 7 to 15% of the drilled shaft diameter for stiff shafts depending on soil cohesion. The relative displacement between the moving soil and the moving drilled shaft for the contact pressure to be fully mobilized at the soil/shaft interface was found to range from 3 to 15% of the shaft diameter.