Abstract
In order to investigate the initiation mechanism of landslide and debris flow occurring on a gentle slope. The formation and evolution of water film (or crack) in saturated sand is analyzed by numerical and theoretical simulations under given conditions. First a psudo-three-phase model is presented considering the movement of skeleton and water and the erosion. Secondly, difference method is used to analyze the formation conditions and the evolution of the velocity of water and pore pressure and porosity. Thirdly, a simplified theoretical method is presented based on the consolidation theory to analyze the initiation, expansion and close. It is shown that there are stable water films when some point is blocked and the state keeps unchangeable or there exists a thin layer with very low permeability. Once the blocked point is open, the water film will disappear gradually. The evolution of water film may be calculated by a simplified method. The analytical results are agreement well with that of Kokusho.
Highlights
It is often observed that sand deposit on slope spreads laterally or even turns into landslide or debris flow, especially after earthquakes
Based on the model presented above, we will analyze the occurrence of the crack in saturated sand, This case is about the cracks in a liquefied sand ( e 0, 0 ) where the grains sink while the water is pressed to move upward just like the consolidation
Numerical simulations under four conditions have shown that the stable water films occur only in the conditions that: (1) the porosity of the upper part of the sand column is smaller than that of the lower, and (2) the keeping of the jamming state or the effective stress to prevent the free dropping of the grain or the skin friction in Kokusho’s experiments is needed
Summary
It is often observed that sand deposit on slope spreads laterally or even turns into landslide or debris flow, especially after earthquakes. When the deposit is multilayered, a water film will form once it is liquefied [1], which may serve as a sliding surface for the postliquefaction failure. Landslide or debris flow may happen on very gentle slope. Seed [2] was the first to suggest that the existence of “water film” in sand bed is the reason of slope failures in earthquakes. A theoretical and numerical analysis is presented in this paper. We present a pseudo-three-phase model describing the moving of liquefied sand and give some theoretical analysis. We present a simplified method to analyze the evolution of the water film
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