Design Method for Drilled Shaft Stabilization of Unstable Slopes

A design method for using a row of drilled shafts to stabilize an unstable slope is presented in this paper. The method is based on the concept that the presence of drilled shafts in a slope reduces the driving forces on the down-slope side of the drilled shafts due to the soil arching behavior, which results in an increase in the computed safety factor using the limiting equilibrium method of slices. 3-D finite element simulation results are used to generate semi-empirical equations for soil arching effects. Complex slope geometry, soil stratifications, and general shape of slip surfaces can be handled in the developed method. The design variables in the slope/drilled shafts system, such as drilled shafts size, drilled shaft location, shaft fixity (the necessary rock-socket length), and the spacing between the drilled shafts can be optimally determined from the design method to achieve the desired safety factor of the system. The design method also presents a practical method for estimating the forces imparted onto the drilled shaft to allow for detailed soil-structure interaction analysis via LPILE (or other similar) program to determine the design internal moments and shear as well as the working deflection of the drilled shaft. A step-by-step design procedure, together with an illustrative example is given.