Among the geophysical surface processes, mud and debris flows show one of the most complex and challenging behaviour for scientists and modellers. These flows consist of highly-unsteady gravity-driven movements of water-sediment mixtures with non-Newtonian rheology where the solid concentration could be about 40%–80% of the flow volume and which occur along steep and irregular terrains. Furthermore, the appearance of dynamic pressures in the fluid filling the intergranular pores increases the complexity and dominates the behaviour of the fluidized water-sediment material, leading to the appearance of significant density gradients during the movement. The dynamic pressure in the pore-fluid changes the effective normal stress within the mobilized material, affecting the frictional shear stress between grains and leading to the solid phase dilation/contraction. This must be properly accounted for when developing realistic models for water-sediment surface flows. In this work, a novel physically-based approach for modelling multi-grain dense-packed water-sediment flows is presented. A novel closure formulation for the pressure distribution within the pore-fluid during the movement of dense-packed water-sediment materials has been derived. This closure allows to relate the appearance of shear-induced dynamic pore pressures to the contractive/dilative behaviour of the solid aggregate. The resultant system of depth-averaged conservation laws includes continuity of the density-variable water-sediment material and the different solid classes transported in the flow, as well as the linear momentum equation for the fluidized bulk material, and it is solved using a well-balanced fully-coupled Finite Volume (FV) method. The resultant simulation tool is faced to synthetic, laboratory and real-scale benchmark cases to test its robustness and accuracy. The presence of dynamic pore pressures within the pore-fluid leads to the appearance of a deviatoric contribution to the solid flux, which causes the shear-induced separation of the solid and liquid phases and sustains the flow mobility for long distances, as it has been observed in real mud and debris events.

中文翻译：

---

非定常水-泥沙混合物流中剪切引起的收缩/膨胀效应的混合相模型


在地球物理表面过程中，泥浆和泥石流对科学家和建模者来说是最复杂和最具挑战性的行为之一。这些流动由具有非牛顿流变学的水-沉积物混合物的高度不稳定的重力驱动运动组成，其中固体浓度可能约为流量的 40%–80%，并且沿着陡峭和不规则的地形发生。此外，填充粒间孔隙的流体中动态压力的出现增加了流化水沉积物材料的复杂性并主导其行为，导致在运动过程中出现显着的密度梯度。孔隙流体中的动压力改变了流动材料内的有效法向应力，影响颗粒之间的摩擦剪切应力并导致固相膨胀/收缩。在开发水-沉积物表面流的现实模型时必须适当考虑这一点。在这项工作中，提出了一种基于物理的新颖方法来模拟多颗粒致密水-沉积物流。推导了一种新颖的封闭公式，用于在致密水沉积物运动过程中孔隙流体内的压力分布。这种闭合允许将剪切引起的动态孔隙压力的出现与固体骨料的收缩/膨胀行为联系起来。由此产生的深度平均守恒定律系统包括密度变化的水沉积物材料和流中传输的不同固体类别的连续性，以及流化散装材料的线性动量方程，并使用井来求解-平衡全耦合有限体积（FV）方法。 由此产生的模拟工具面临合成、实验室和实际规模的基准案例，以测试其稳健性和准确性。孔隙流体内动态孔隙压力的存在导致出现对固体通量的偏贡献，这导致剪切引起的固相和液相分离并维持长距离的流动流动性，正如它所描述的那样。在真实的泥浆和碎片事件中观察到。