Characterization and Stabilization of Reactivated Ancient Landslide, Soledad Mountain Road, La Jolla, California

摘要

Soledad Mountain Road transects Mount Soledad and provides one of the major accesses to La Jolla, California serving over 10,000 vehicles per day. On October 3, 2007, a catastrophic slope failure occurred along Soledad Mountain Road, destroying four homes and 61 meters of roadway and isolating eight homes from roadway access. Ancient bedding plane landslides were largely unrecognized as potential hazards during design and construction of residential subdivisions in the 1950's and 1960's in many areas of southern California including Mount Soledad. Consequently, numerous hillside developments rest over these ancient landslides which may reactivate decades after construction. The Soledad Mountain Road failure was part of an ancient landslide unidentified during residential construction in the early 1960's. It is concluded that creep along the basal shear plane occurred as a consequence of the grading operation that removed much of the landslide's toe and eventually weakened the clay to the point of mobilization. Landslide characterization included downhole geologic logging of large diameter boreholes. Stability and deformation analyses were performed with Limit Equilibrium stability programs and Finite Element modeling. Landslide stabilization included 119 shear pins up to 1.8 meters in diameter and 24.4 meters in depth and geosynthetic reinforced soils.