Landslides, Slope Failures & Erosion
Landslides are downslope movements of masses of soil and/or rock. They can cause some of the most spectacular damage attributable to earth movement or ground movement. Landslides include mudflows ("mudslides"), earth slumps, rockfalls, and other types of slope failures. Landslides can be fast or slow, wet or dry, small or large, shallow or deep, and reactivated or brand new. Triggering mechanisms can include rainstorms, landscape irrigation, broken pipelines, grading, inadequate surface drainage, erosion, earthquakes, and other natural phenomena and human activities. Fast-moving mudflows and debris flows are of particular concern in wildfire burn areas. Slope instability is a complex phenomenon that includes not only landslides but more subtle processes such as soil creep.
Buildings and infrastructure such as transportation facilities and pipelines located within the boundaries of a landslide or in the path of a landslide can be damaged or destroyed. 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 might be determined to 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 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 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 hidden threat is a particular concern in the siting, design, construction, and failure analysis of dams.
How We Can Help
Exponent geologists and engineers use many tools to investigate pertinent aspects of landslides, slope failures, and erosion. Key elements in an investigation depend on site characteristics and the needs of the client and may include:
- Emergency response and evaluation of imminent hazards to persons and structures
- Assessment of damage to structures and infrastructure
- Evaluation of the boundaries of an unstable area
- Assessment of landslide, slope failure, or erosion causation
- Establishment of a history of previous ground movement
- Modeling of movement initiation and travel paths
- Determination of the relative contributions of multiple factors, including but not limited to, leaking utility lines, past grading, nearby construction, and rainfall
- Installation and monitoring of instrumentation for measuring ground movement and groundwater conditions
- Geotechnical laboratory testing for measuring rock and soil engineering properties
- Analysis of the stability and safety of existing natural or artificial slopes
- Assessment of various slope stabilization options
- Development of conceptual repair recommendations
- Third-party review of geologic and geotechnical investigations (“soil investigations”) as well as repair recommendations prepared by others.
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