Design of Drilled Shaft Cutoff Walls for Slope Stability in Marginal Soils

The use of vertical or near-vertical buried structural members to stabilize slope failures is an established and effective approach to landslide correction and can be economical in urban areas constrained by property limits, access restrictions, and high land costs. Traditional designs for such slope stabilization methods have relied on assumed active and passive pressures mobilized by the failing soil mass. Increasingly, sites are being developed in soils of marginal slope stability where some form of stability enhancement is required to achieve a minimum safety factor against deep-seated failure. In such pre-failure situations, a different set of design criteria is required because the ground movements necessary to mobilize active and passive pressures might exceed structural tolerances and even result in strains that might initiate soil failure. A practical method is presented for the design of drilled shaft cutoff walls used to enhance slope stability in marginally stable soils. The method specifically addresses the pre-failure condition and applies limiting deflection criteria to structural members to preclude soil failure. The use of commercially available slope stability and soil-structure interaction programs is adopted. Emphasis is placed on practical application by the experienced practitioner.