In the simulations, a micromechanical model simulates grains using molecular dynamics with friction between neighbors. In the experiments, we use particles only slightly denser than water, which as predicted theoretically increases the effect of liquefaction and allows clear depth-of-sinking measurements. The external excitation representing ground motion during earthquakes is simulated via horizontal sinusoidal oscillations of controlled frequency and amplitude. We confirm this hypothesis by comparison with laboratory experiments and discrete-element numerical simulations. We suggest a simple theoretical model for soil liquefaction and show that buoyancy caused by the presence of water inside a granular medium has a dramatic influence on the stability of an intruder resting at the surface of the medium. Liquefaction is defined here as the transition from a rigid state, in which the granular soil layer supports structures placed on its surface, to a fluidlike state, in which structures placed initially on the surface sink to their isostatic depth within the granular layer. This article focuses on liquefaction of saturated granular soils, triggered by earthquakes. A sinking test demonstrates that, due to buoyancy, it impossible to drown in the quicksand. This results in a densely packed system that practically impossible to dilate: it is for this reason that once trapped it is difficult to get out of quicksand. The stress liquefies the clay matrix, and the granular assembly collapses, expulsing water. By constructing 'laboratory quicksand', we demonstrate that the liquefaction is due to the structure: quicksand is a loose granular packing of sand particles stabilized by a clay matrix that forms a particulate gel. We show that a spectacular liquefaction of the material occurs when a stress is applied to the material: the liquefaction is the reason why one sinks away, and it is more pronounced for larger stresses. We provide an explanation for these observations by studying the most commonly encountered form of natural quicksand. Popular wisdom has it that one should not move when trapped in quicksand, as motion makes one sink in even deeper and that once trapped, it is difficult to escape. Quicksand is the generic name for unstable soils reputed to trap anyone who treads on it.
0 kommentar(er)
