The role of soil piping in rainfall-induced landslides: A case study from western Alabama

Abstract:

Rainfall-induced landslides are a major source of damage and deaths worldwide. Soil pipes are found within the scarps of many landslides and have been hypothesized to be a significant factor in initiation of rainfall-induced landslides based on both experimental and numerical studies. Other researchers have argued that soil pipes can be beneficial to slope stability by serving as a drainage path for water within the slope. Within the geotechnical community, rainfall induced landslides are commonly evaluated by using continuum-based approaches to analyze the response of an unsaturated slope to infiltration with a focus on evaluating changes in matric suction that can reduce the strength of the soil. This approach neglects any effects (beneficial or otherwise) of preferential flow paths, such as soil pipes. This is in sharp contrast to the field of hydrology where preferential flow through pipes and macropores is commonly recognized as essential part of estimating the response of catchments to storms. This disagreement regarding the importance of soil piping and slope stability is partly born out of lack of understanding of the fundamental aspects that control soil piping in sloping ground and how soil pipes can affect stability of slopes.

This presentation will describe a series of landslides in west Alabama that contain prominent piping features, including both open and collapsed pipes. These landslides are occurring within the Gordo formation consists of massive beds of sands, gravelly sands, and carbonaceous clay. The morphology of the landslides and the locations of collapsed pipes were mapped using field surveys and bare earth LiDAR data. A combined geotechnical and geophysical investigation was performed at one of the landslides where it intersects a nearby highway. Electrical resistivity tomography and seismic full waveform inversion were used to imaging one of the areas with active piping in the subsurface. The effect of piping on the stability of this landslide is investigated using numerical analyses. Implications of this study for the analysis of other landslides will be discussed along with research needs.