Effect of soil suction on slope stability at Notch Hill

Abstract

The side slopes of a railway embankment in central British Columbia, constructed with local lacustrine silt, on relatively flat ground, began to fail several years after construction. Shallow instability ultimately developed on both sides of the embankment over a distance of several kilometres. Initially, the soil had a significant apparent cohesive strength. With time, the strength appeared to diminish owing to the dissipation of negative pore-water pressures. The remaining frictional strength was not sufficient to maintain stability, since the slopes were constructed at angles close to the peak effective friction angle of the soil. This case history, together with the laboratory saturated and unsaturated strength test results and field suction measurements, demonstrates the dramatic effect of negative pore-water pressures on near-surface slope stability. Key words: soil suction, slope stability, nonsaturated soils, shear resistance, tensiometers.