Characterization of groundwater dynamics in landslides in varved clays

摘要

Groundwater dynamics may play a significant role in landslides. A detailedmodel is developed of the groundwater dynamics in landslides in varved claysin the Trièves area in the French Alps. The varved clays consist of asequence of alternating silt and clay layers, covered by a colluvium layerand intersected by fissures. The hydraulic conductivity of the clay layersis negligible compared to the silt layers. It is conceptualized thatfissures form a hydraulic connection between the colluvium and the varvedclays. Groundwater recharge flows through the colluvium into the fissures,where water is exchanged horizontally between the fissure and the siltlayers of the varved clays. Groundwater flow in the colluvium is simulatedwith the Boussinesq equation, while flow in the silt layers of the varvedclays is simulated with the Richards equation. Longitudinal outflow fromthe fissure is simulated with a linear-reservoir model. Scattered data ofrelatively short monitoring periods is available for several landslides inthe region. A good similarity between observed and simulated heads isobtained, especially when considering the lack of important physicalparameters such as the fissure width and the distance between the monitoringpoint and the fissure. A simulation for the period 1959–2004 showed somecorrelation between peaks in the simulated heads and the recorded occurrenceof landslides, while the bottom of the varved clays remained saturated duringthe entire simulation period.