Advanced Earth Sciences, Inc., performed a geotechnical investigation of the Southeastern Cut expansion area at the Calabasas Landfill that consisted of subsurface exploration and laboratory testing to characterize overburden and bedrock materials. The data obtained from the geotechnical assessment are being used by the Sanitation Districts to perform limit equilibrium slope stability analyses, finite element modeling of seepage and underdrain design, and load-deformation. Field investigations included drilling, sampling, logging and abandonment of 25 exploratory boreholes to depths ranging up to 540 feet deep; excavation, sampling and logging of 8 test pits and 5 trenches; installation and development of 2 piezometers up to 150 feet deep and abandonment of 6 existing piezometers. Several drilling methods were used to advance and sample the boreholes during the project including hollow-stem auger, bucket auger, rotary core and standard rotary drilling methods. Continuous HQ and NQ core was obtained from boreholes drilled into the Modelo and Topanga formations and both California-type drive and CME continuous samples were obtained from boreholes encountering overburden materials consisting of artificial fill and alluvium.

A total of 16 detailed geologic cross sections were prepared to illustrate the subsurface geologic and groundwater conditions beneath critical areas of the proposed expansion. The cross sections provided the basis for the Sanitation Districts’ slope stability analysis of planned subgrade slopes and existing natural slopes. Topographic and proposed subgrade profiles, geologic contacts and correlatable marker beds, bedrock weathering profile, apparent structural orientation, and groundwater occurrence were depicted on the cross sections. An extensive laboratory testing program was implemented to characterize material properties. The tests included unsaturated hydraulic characteristics, shear strengths by direct shear and triaxial test methods, compressibility characteristics and materials properties including moduli, Poisson’s ratio and pore pressure parameters. Based on the results, unsaturated hydraulic conductivity functions and soil water storage functions were developed for modeling unsaturated flow.