地震期间的下沉：控制排水土壤液化的临界加速度准则
Sinking during earthquakes: Critical acceleration criteria control drained soil liquefaction
摘要：
这篇文章的重点是饱和粒状土的液化，由地震触发。液化在这里被定义为从刚性状态到流体状状态的转变，在刚性状态下，粒状土层支撑着置于其表面的结构，本文提出了一个简单的土壤液化理论模型，并指出由于颗粒介质中水的存在而引起的浮力对颗粒介质的稳定性有显著的影响。我们通过与实验室实验和离散元数值模拟的比较证实了这一假设。通过控制频率和振幅的水平正弦振动来模拟地震期间代表地面运动的外部激励。在实验中，我们使用的颗粒密度仅略高于水，这在理论上可以增加液化的效果，并允许清晰的下沉深度测量。在模拟中，微观力学模型使用分子动力学模拟相邻颗粒之间的摩擦。流体的影响是通过考虑浮力效应的颗粒时，他们被浸泡捕获。我们证明了侵入体在颗粒介质中的运动主要取决于地面运动的峰值加速度，并建立了液化发生条件的相图，该相图取决于土壤的体积密度、摩擦特性、水的存在和施加的大尺度土壤振动的峰值加速度。大多数情况下松弛向一个平衡位置以下的时间指数。我们还表明，平衡位置本身，对于大多数液化制度，对应于均衡平衡的入侵者内的介质的有效密度。松弛的特征时间基本上是峰值地面速度的函数。
英文摘要：
This article focuses on liquefaction of saturated granular soils, triggered by earthquakes. Liquefaction is definedhere as the transition from a rigid state, in which the granular soil layer supports structures placed on its surface, toa fluidlike state, in which structures placed initially on the surface sink to their isostatic depth within the granularlayer.We suggest a simple theoretical model for soil liquefaction and show that buoyancy caused by the presence ofwater inside a granular medium has a dramatic influence on the stability of an intruder resting at the surface of themedium.We confirm this hypothesis by comparison with laboratory experiments and discrete-element numericalsimulations. The external excitation representing ground motion during earthquakes is simulated via horizontalsinusoidal oscillations of controlled frequency and amplitude. In the experiments, we use particles only slightlydenser than water, which as predicted theoretically increases the effect of liquefaction and allows clear depth-of-sinkingmeasurements. In the simulations, a micromechanical model simulates grains using molecular dynamicswith friction between neighbors. The effect of the fluid is captured by taking into account buoyancy effects onthe grains when they are immersed. We show that the motion of an intruder inside a granular medium is mainlydependent on the peak acceleration of the ground motion and establish a phase diagram for the conditions underwhich liquefaction happens, depending on the soil bulk density, friction properties, presence of water, and peak acceleration of the imposed large-scale soil vibrations.We establish that in liquefaction conditions, most cases relaxtoward an equilibrium position following an exponential in time.We also show that the equilibrium position itself,for most liquefaction regimes, corresponds to the isostatic equilibrium of the intruder inside a medium of effectivedensity. The characteristic time to relaxation is shown to be essentially a function of the peak ground velocity.
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