Abstract:
Major Landslide Remediation in an Urban Setting
In 2004, in the affluent suburbs of Los Angeles, an active landslide, fueled by a major water line break, caused extensive damage to one residence and threated several others. Extensive investigation of the site over the next several years revealed an active landslide superimposed on an ancient landslide and initiated a twelve yearlong major slope stabilization and land development project that would test the limits of temporary and permanent earth retention.
The landslide removal phase required almost one-hundred-foot-deep excavation involving ninety thousand square feet of temporary shoring much of it adjacent to elaborate existing homes owned by the rich and famous. Final grading plans, that created new buildable lots, required the design and construction of almost ninety thousand square feet for permanent retaining walls up to fifty feet high. Although spread over four separate city parcels with four separate addresses, the project was under one private ownership and managed by the owner of the home destroyed in the initial landslide.
Due to the limitations on hauling soils on sensitive city streets in a highly desirable neighborhood and also due to the unwillingness of neighbors to permit temporary tiebacks in their property, the excavation to remove the landslide and build a buttress fill utilized a unique excavation/shoring scheme where the landslide was excavated in two halves orientated along the axis of the slide such that excavation spoils could remain on site for backfill and the reduced width of the excavations made cross lot bracing an option.
The final permanent retaining walls utilized a variety of earth support methodologies including conventions footing/stem walls, cantilever soldier pile walls, cantilever caisson walls and a novel system of dead men supported caisson walls where retained heights precluded cantilever designs.