Experimental–numerical insights into large-diameter shield tunneling through sand–clay and sand–pebble composite strata

Abstract

Large-diameter shield tunneling in composite strata presents significant challenges due to the heterogeneous mechanical properties, posing substantial risks to excavation safety. Existing research, however, provides limited insights into how specific layer configurations influence soil strength, failure mechanisms, and the soil arching effect. This study aims to bridge these knowledge gaps by systematically investigating the mechanical behaviors of sand–clay and sand–pebble composites, as well as their excavation-induced responses. Methodologically, we integrate laboratory triaxial tests on reconstituted composite specimens with 3-dimensional (3D) finite element simulations of the tunneling process. Key contributions of this work include: 1) the identification of a critical clay layer thickness (20–40 mm) that governs the transition from interfacial slippage to bulging failure in sand–clay composites; 2) the quantification of a progressive strength reduction (up to 14.52%) in sand–pebble composites as the sand layer shifts downward; and 3) a novel comparative analysis using a soil stress coefficient method, which reveals a more extensive destruction zone and a more fragile soil arching effect in sand–pebble strata, thereby indicating an elevated risk of collapse. These findings provide crucial insights into the performance of large-diameter shield tunnels in complex geological conditions and offer guidance for safer design and operational control.

Graphical abstract

Keywords

large-diameter shield tunneling / composite strata / laboratory triaxial test / numerical simulation / mechanical property / excavation response

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