Centrifuge test of face stability in sand-clay layered strata with different interlayer angles

Based on centrifuge model tests, this study systematically investigated the stability of shield tunnel face in sand-clay composite strata under different interlayer inclination angles and interface positions. The experiments employed high-speed camera and analysis systems to quantitatively analyze soil movement characteristics around the tunnel face, utilized both rear-mounted stress sensors and front-mounted earth pressure cells to measure support pressures, and captured the dynamic evolution of earth pressure fields during instability processes through real-time earth pressure monitoring systems. Three-dimensional discrete element model was established to validate the experimental results. The research findings indicate that interlayer inclination angles significantly influence the instability and failure modes of tunnel face. Under positive inclination conditions, sand and clay exhibit relatively independent deformation characteristics. Under negative inclination conditions, the two soil layers deform cooperatively, with instability ranges significantly expanding and continuous shear zones penetrating through the stratum interface. When the interlayer interface is located at the crown, positive inclination conditions result in limited instability zones, while negative inclination conditions still produce significant instability. The critical support pressure is primarily influenced by the interlayer interface position, with the required critical support pressure being smaller when the interface is at the crown compared to when it is at the tunnel axis, while the interlayer inclination angle has relatively limited impact on critical support pressure. Earth pressure in the instability zone exhibits a two-stage evolution pattern characterized by rapid initial decline followed by stabilization. The vertical soil arching ratio distribution in the sand layer aligns with the instability zone contour, forming significant lateral soil arching effects with the arch crown and arch waist located near the ground surface and at the interlayer interface. These research findings can deepen understanding of tunnel face instability mechanisms in inclined composite strata and provide guidance for construction risk control in engineering practice.