Project Scope

The project scope was to evaluate landslide mass stability and provide recommendations for its stabilization.

Geotechnical Laboratory Testing

Moisture contents, index testing, sieve analysis, soil classification tests, rock core compressive strength tests, direct shear on intact, remolded and residual conditions; direct shear test on rock joints

Drilling and In Situ and Field Testing

Field work included an extensive existing condition field topography survey and installation of field horizontal/vertical displacement monitoring stations, deep borings thru the landslide mass up to 420 ft with installation of borehole inclinometers and monitoring wells. Drilling methods included rock coring from PQ to NQ size, down the hole hammer drilling thru large boulders

Geotechnical Analysis and Design

Engineering analysis included modeling of pre-landslide and post landslide conditions, including slope stability model calibration. The slope stability models were developed by both limit equilibrium(Slope/W) and finite element methods (Plaxis 2D). geometry, toe buttress and internal subdrains.

Challenges

Based on the models, including hydrogeologic and seismic conditions, it was concluded that the landslide mass had a FS of near unity. Monitoring results confirmed this since creep displacements were continous and larger movements could be related prolonged rain events. MSHA required owner to provide a plan for mitigation, which we helped elaborate.

Solutions

The team’s recommendations included geo-hazard identification, safety scaling, runoff diversion, deep excavation of soil mass on the upper portions of the slope and placing the material within the toe of the slide which was shaped into benches and provided with subdrain systems. The entire slope was shaped with cut terraces having a pattern developed based on iterations with the slope stability models which to had be analyzed in local and global scale due to the size of the mass.