Internal Erosion Controls Failure and Runout of Loose Granular Deposits: Evidence From Flume Tests and Implications for Postseismic Slope Healing

Abstract

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.

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

“…These coarser debris flows indicate either reworking or winnowing of fines from landslide debris or more storage of coarser material in channel beds. Progressive depletion of erodible debris, increasing soil hydraulic conductivity, increasing friction in sediment due to compaction, and increasing root reinforcement in regrowing vegetation cover might explain the decay of debris‐flow activity in the years after the earthquake (e.g., Domènech et al, ; Hu, Scaringi, et al, ; Z. Li, Jiao, et al, ; Saito et al, ; Shen et al, ; Yang et al, ). Exhaustion of the total volume of available sediment (Cruden & Hu, ) is unlikely because most of the EQTL sediment (as much as 80–90%) can remain on the hillslope for many years after the initial event.…”

Rapidly Evolving Controls of Landslides After a Strong Earthquake and Implications for Hazard Assessments

“…Fan et al., 2019a). These deposits are typically constituted by loose materials with significant amounts of fines, hence they are susceptible to sudden collapse and liquefaction upon loss of suction or pore water pressure increase (Hu et al., 2017, 2018). Debris remobilization events may occur in the earthquake‐affected areas for years or decades (Hovius et al., 2011; Keefer, 1994; Yunus et al., 2020), even multiple times in the same deposit, largely depending on the volumes of coseismic deposits and rainfall intensities (Dadson et al., 2004; Hovius et al., 1997; Marc et al., 2016).…”

Enhanced Rainfall‐Induced Shallow Landslide Activity Following Seismic Disturbance—From Triggering to Healing

“…While this may be due to a variety of factors, such as bedrock fracturing, increased weathering rates, and deposition of loose, colluvial materials, and more (X. Fan et al., 2018; Gallen et al., 2015; Hovius et al., 2011; Hu et al., 2018; Yang et al., 2018); we focus on climatic forcing as the primary driver of post‐seismic failures in soil hillslopes. Using the approach proposed herein, we consider a sinusoidal flux of water with amplitude i max that alternates between wetting and drying conditions over a hydrological cycle arbitrarily selected to be 100 days (Figure 7c).…”

“…A variety of mechanisms have been proposed to describe the timescales for the attenuation of elevated landslide activity following shaking. These include weathering and weakening of bedrock (Mohammadi & Asimaki, 2019; Parker et al., 2015), occurrence of ground fissures and hillslope deformation (Hovius et al., 2011), precipitation events after shaking (Chuang et al., 2009; Yang et al., 2017), changes in material strength or healing of vegetation (Hovius et al., 2011; Marc et al., 2015; Yang et al., 2018), changes in hydrological pathways and conditions (Hu et al., 2018), and depletion of weakened hillslope sediment following failure (X. Fan et al., 2018).…”