Interfacial flow contact resistance in stratified terrains: A hidden trigger for multi-hazard geological disasters

Geohazards such as cascading landslides, rockfalls, and debris flows in stratified terrains are often triggered by localized hydraulic failure at geological interfaces. When pore water seeps slowly along irregular pore channels at the interfaces with significantly varying permeability, abrupt changes in pore water pressure can be induced by the interfacial flow contact resistance (IFCR) under laminar flow conditions-defined herein as the flow gradient. For the first time, this study reveals that IFCR between geological layers is a key inducing factor for multi-hazard susceptibility, fundamentally reshaping the theoretical framework of the traditional load-driven instability models. The flow contact resistance coefficient (FCRC) across layered geological interfaces was measured using a self-developed testing system. The corresponding abrupt variations in pore water pressure at these interfaces were thereby characterized, providing novel insights into the instability mechanisms of geological media under complex environmental conditions. Test results indicate that the FCRC increases significantly with the dry density (1.3–1.45 g/cm³) and sand content (0–15%) of the geomaterials, but is insensitive to water injection pressure (40–100 kPa). Furthermore, the study reveals that a certain degree of IFCR persists at the contact interface even when the physical properties of the upper and lower geological layers are essentially identical. These findings offer important theoretical foundations and technical support for the prediction and prevention of geohazards.