Impact Behavior of Dense Debris Flows Regulated by Pore‐Pressure Feedback

Abstract

AbstractThe 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.