Forensic investigation and chemical remediation of a collapsed highway embankment slope in Houston, Texas

Abstract

Transportation infrastructure, such as highway embankment slopes and retaining walls, are often constructed using locally available fill materials. Slopes constructed with such fills can pose problems as those fills can be expansive and experience surficial failures due to significant strength reductions over the years from cyclic moisture ingress and egress. Repeated wetting and drying cycles often result in the formation of desiccation cracks, which, when compounded by rainfall events, lead to moisture infiltration in the cracks and cause surficial slope failures. This paper provides a forensic investigation conducted on one such collapsed highway embankment slope in Houston, Texas, employing exhaustive timeseries optical image analysis, site characterization, laboratory studies, and numerical modeling. In-situ investigations included determining the site properties using the Texas cone penetration test and retrieving augered soil specimens. Site characterization indicated that the embankment soil was expansive in nature and susceptible to moisture-induced distress. Subsequently, laboratory shear strength studies were performed, and it was determined that the loss in cohesion in the problematic clay during the fully softening stage was responsible for initiating slope failure. Shallow slope failure was often attributed to surficial cracking due to moisture migration and reduction in shear strength from peak to fully-softened, and further aggravated by insufficient drainage along the slope and vegetation removal. Surficial soil treatment with a calcium-based stabilizer was determined as a potential mitigation method. Engineering studies and numerical analyses showed that soil stabilization using calcium-based stabilizers notably enhanced the mechanical strength properties and overall stability of the slope under future extreme precipitation conditions. Overall, the study emphasized the importance of moisture regulation and the inclusion of anticipated rainfall projections within numerical models along with suitable chemical stabilizers to stabilize problematic embankment subgrade conditions in order to ensure an adequate performance of transportation infrastructure for long-term serviceability.