The impact dynamics of dilute debris flows (typically volumetric solid fractions<50%) have been extensively investigated within the framework of hydraulics. For dense debris flows, the impact mechanisms have been poorly studied. From a geotechnical viewpoint, the feedback between granular dilatancy and pore-pressure response may play an important role in the dense debris-flow regime. In this study, the impact behavior of dense and dilute debris flows in an instrumented flume is analyzed. The basal stresses (normal/shear stresses, pore-fluid pressure) and impact pressure on a rigid barrier are measured. A time-dependent creeping mode is observed for the impact process of slow-moving dense debris flows, which cannot be accurately estimated using current debris-flow load models. At the grain scale, this macroscopic creeping mode is a result of the feedback between granular dilatancy and pore-pressure response. This feedback can be further characterized by examining the timescales associated with pore-pressure generation and dissipation. The regulation of pore-pressure feedback on basal shear stress, impact load, and state of static deposit is revealed. Finally, a tentative phase diagram is proposed for dense and dilute debris-flow impact. The proposed framework complements the theory for debris-flow impact loads.

中文翻译：

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孔隙压力反馈调节的致密泥石流冲击行为

稀泥石流（通常体积固体分数<50%）的冲击动力学已在水力学框架内进行了广泛研究。对于密集泥石流，其影响机制研究甚少。从岩土工程的角度来看，颗粒剪胀性和孔隙压力响应之间的反馈可能在致密泥石流流态中发挥重要作用。在本研究中，分析了仪表水槽中稠密和稀泥石流的冲击行为。测量刚性屏障上的基础应力（法向/剪切应力、孔隙流体压力）和冲击压力。缓慢移动的密集泥石流的冲击过程观察到随时间变化的蠕变模式，而使用现有的泥石流荷载模型无法准确估计该蠕变模式。在颗粒尺度上，这种宏观蠕变模式是颗粒剪胀性和孔隙压力响应之间反馈的结果。这种反馈可以通过检查与孔隙压力产生和消散相关的时间尺度来进一步表征。揭示了孔隙压力反馈对基底剪应力、冲击载荷和静态沉积物状态的调节作用。最后，提出了浓泥石流冲击和稀泥石流冲击的暂定相图。所提出的框架补充了泥石流冲击载荷的理论。