3:30 PM - 5:00 PM
[HDS05-P07] Effect of non-plastic fines on the rainfall-induced landslides behavior based on experimental flume and ring shear tests
Introduction
Rainfall-induced landslides in the premise of climate change pose significant natural hazards all over the world. Many of them could fluidize with features of rapid and long run-out, which has resulted in the destructive damage and great loss of lives and properties. Fines are frequently found in many fluidized landslide materials including natural slopes, rock avalanche deposits and earthquake-induced landslides deposits, where non-plastic fines are significantly involved.
Materials and Methods
Flume tests were conducted on mixtures consisting of silica sand and non-plastic fines, and the content of fines and initial density of the model were varied. We measured diverse quantities, including displacement, tilting angle, and pore-water pressure. Based on these results, we discussed the effect of non-plastic fines on the landslide movements and PWP generation. In addition, undrained ring shear tests with DPRI 5 were conducted to study the liquefaction behavior of the mixtures.
Results and conclusions
In general, Fines content (FC) and density index (Id) could exert fundamental coupled controls in the landslide behavior. Figs. 1a~1b show that at the density index of -0.54 ~ - 0.52 and -0.21 ~ -0.19, an optimal fines content of 30% was observed at which the Vp reached its maximum. At other density index, the Vp increased in general with the increase of fines content. When fines content is low at 0-10%, the Vp decreased with the increase of density index, but at higher fines content, the optimal density index was observed, at which the Vp reached its maximum. The optimal relative density shifted from -0.2 to -0.04 when the FC increased from 20% to 40%. The maximum value of pore-water pressure (up) becomes greater in general with the increase of FC. Figs. 1c~1d shows that an optimal density index around -0.04 could be identified, at which the build-up of PWP (Δu) reached its maximum.
Figs. 2a~2b shows the typical results of undrained ring shear test using the mixtures of silica sand no. 7 and 30% content of silica powder. The result showed a typical liquefaction behavior with pure contractive generating high pore water pressure. It would be noted that at the final stage of ring shear (Fig. 2b), the shear stress straightly dropped with the constant high pore water pressure, which may involve with the phase change from landslides to debris flow, could draw more attentions. Preliminarily, we inferred that this phenomenon would be related that the fines could act as an interstitial fluid in the movement of landslides, thus enhancing the mobility of geophysical flows (fluidizing the granular materials).
Rainfall-induced landslides in the premise of climate change pose significant natural hazards all over the world. Many of them could fluidize with features of rapid and long run-out, which has resulted in the destructive damage and great loss of lives and properties. Fines are frequently found in many fluidized landslide materials including natural slopes, rock avalanche deposits and earthquake-induced landslides deposits, where non-plastic fines are significantly involved.
Materials and Methods
Flume tests were conducted on mixtures consisting of silica sand and non-plastic fines, and the content of fines and initial density of the model were varied. We measured diverse quantities, including displacement, tilting angle, and pore-water pressure. Based on these results, we discussed the effect of non-plastic fines on the landslide movements and PWP generation. In addition, undrained ring shear tests with DPRI 5 were conducted to study the liquefaction behavior of the mixtures.
Results and conclusions
In general, Fines content (FC) and density index (Id) could exert fundamental coupled controls in the landslide behavior. Figs. 1a~1b show that at the density index of -0.54 ~ - 0.52 and -0.21 ~ -0.19, an optimal fines content of 30% was observed at which the Vp reached its maximum. At other density index, the Vp increased in general with the increase of fines content. When fines content is low at 0-10%, the Vp decreased with the increase of density index, but at higher fines content, the optimal density index was observed, at which the Vp reached its maximum. The optimal relative density shifted from -0.2 to -0.04 when the FC increased from 20% to 40%. The maximum value of pore-water pressure (up) becomes greater in general with the increase of FC. Figs. 1c~1d shows that an optimal density index around -0.04 could be identified, at which the build-up of PWP (Δu) reached its maximum.
Figs. 2a~2b shows the typical results of undrained ring shear test using the mixtures of silica sand no. 7 and 30% content of silica powder. The result showed a typical liquefaction behavior with pure contractive generating high pore water pressure. It would be noted that at the final stage of ring shear (Fig. 2b), the shear stress straightly dropped with the constant high pore water pressure, which may involve with the phase change from landslides to debris flow, could draw more attentions. Preliminarily, we inferred that this phenomenon would be related that the fines could act as an interstitial fluid in the movement of landslides, thus enhancing the mobility of geophysical flows (fluidizing the granular materials).