Analysis and Design Method for Slope Stabilization Using a Row of Drilled Shafts

Drilled shafts have been widely used as an effective means for slope stabilization. In this paper, a design procedure for stabilizing an unstable slope with a row of equally spaced drilled shafts is presented. The limiting equilibrium-based slope-stability analysis method, modified to incorporate the drilled-shaft-induced arching effects through a semiempirical load-transfer factor, is formulated and coded into a general slope-stability computer program, UASLOPE, for complex slope geometry, soil profile, and groundwater table conditions. The UASLOPE program is validated with three-dimensional (3D) finite-element simulation results concerning factor of safety of the drilled-shaft/slope system and net force imparted on drilled shafts. Regression analysis performed on more than 40 cases of 3D finite-element simulation results has led to a semiempirical predictive equation for the drilled-shaft-induced load-transfer factor, from which the phenomenon of soil arching in a drilled-shaft/slope system is elucidated by identifying the influencing factors, such as soil-strength parameters, shaft dimension and spacing, slope geometry, and shaft location on slope. With an objective to achieve the required FS and minimized drilled-shaft quantity and construction cost, two design examples are given to illustrate an iterative process seeking optimization of design outcome in terms of drilled-shaft location on slope, dimension of drilled shafts (diameter and length), spacing between adjacent drilled shafts, and reinforcement requirements.