Internal Erosion Controls Failure and Runout of Loose Granular Deposits: Evidence From Flume Tests and Implications for Postseismic Slope Healing
Landslides in granular soils can be highly hazardous when exhibiting flow-like behavior. The extensive mass wasting associated with the 2008 Mw = 7.9 Wenchuan earthquake (China) left several cubic kilometers of loose granular material deposited along steep slopes and in low-order channels. Rainfall-triggered remobilization of these deposits evolved often into catastrophic flow-like landslides. Ten years after the earthquake, most of the deposits are still in place but landslide rates have decreased significantly. Internal erosion-induced grain coarsening is one possible process producing this decrease. Through experiments on loose artificial slopes we demonstrate the major role of the internally erodible small grains in triggering failure and fluidization and producing grain coarsening. Under the same hydraulic boundary, if the erodible fraction is removed or reduced, the loose deposits remain stable or fail without fluidizing. Our results provide an experimental evidence to the patterns of sediment export and debris flows observed in nature after a strong earthquake.