Case Study of Assessment of Reoccurring Failures in a High Plasticity Soil Cut-Slope and the Importance of Timely Stabilization

The author performed a geotechnical engineering assessment of repeated failures of a 24-ft-tall cut earth slope along a main highway corridor. The slope was cut into high plasticity native clay soils during the original highway construction and located in the vicinity of stormwater drainage. The purpose of the assessment was to evaluate potential for additional slope failure, identify probable causes of failures, and provide engineering recommendations for stabilization of the slope. Findings of the assessment indicated that shallow groundwater was present in the slope, the native slope soils were significantly disturbed during construction of adjacent below-grade structures, and extension of the slope failure to the upper part of the slope was likely. The author recommended stabilizing the slope as soon as practical. However, while the decision on the stabilization was underway, a slope failure re-occurred approximately three months after the author’s assessment and substantially increased the scope of the stabilization. An emergency slope stabilization for the extended failure areas using soil nails and lateral drains to reinforce the slope and alleviate the shallow groundwater was completed.