Landslides & Slope Failures

Comprehensive landslide investigations

Landslides and slope instability are complex phenomena that include the failure of natural ground and engineered slopes alike. Landslides can cause considerable destruction from earth movement, including earth flows, earth slumps, rockfalls, and other types of slope failures. They can be fast moving and catastrophic like mud and debris flows in wildfire burn areas or more subtle, yet equally disruptive, as slow-moving slope creep. They can also be wet or dry, small or large, and shallow or deep, as well as reactivated or brand new. In every case, they can be triggered by a variety of mechanisms — rainstorms, landscape irrigation, broken pipelines, grading, inadequate surface drainage, erosion, earthquakes, or other natural phenomena and human activities. Determining the causes of landslides and slope failures is paramount in preventing further damage, as well as assessing future risk.

Exponent's experienced geologists and engineers use many tools for the investigation of slope failures and landslide hazards. Key elements in an investigation depend on site characteristics and client priorities; they may include emergency response, assessment of damage to structures and infrastructure, installation of monitoring instrumentation, determining the slide's cause, remote sensing, geotechnical laboratory testing, and many more analyses.

Causes and symptoms of landslide and slope damage

Landslides and slope failures threaten buildings, roads, bridges, dams, pipelines, and human and environmental life. Slope movements do not need to be large to be destructive. Slope creep or small, early-stage landslide movements can cause substantial structural damage to critical facilities such as dams and pipelines, potentially resulting in major economic damage and loss of life. Conversely, earth movements initially suspected to be caused by landslides may be the result of other processes such as fill settlement, heave of expansive soil or bedrock, or hydrocompaction of collapsible soil upon wetting.

Erosion is one mechanism that can destabilize slopes and damage structures. Erosion is movement of individual grains, rather than masses, of soil by water or wind. Cumulatively, this persistent grain-by-grain movement can also cause significant damage. Rapid coastal erosion during a period of high surf or a hurricane storm surge can undermine buildings, roads, and other coastal facilities. River scour is riverbed erosion that typically occurs during periods of high-flow, deepening river channels. This process can uncover bridge pier foundations and buried pipelines, or undermine levee slopes, risking potential failure. Erosion can also occur underground, creating linear cavities by a process known as "piping" in which soil particles are carried away by seeping ground water. This threat is a concern in the siting, design, construction, and failure analysis of dams and levees.