Laboratory study on mechanical behavior of hollow π-type steel–concrete composite support in loess tunnel

Abstract

Failure or over-deformation of tunnel supports is common when tunneling in loess areas. Steel-concrete composite support (SCCS) is an innovative new support system that could provide a viable solution to improve the support in loess tunnels. Due to a lack of research, there is only a preliminary understanding of the structural effects of employing π-type SCCS arch as the initial load-bearing element. Based on similarity theory, we perform a large-scale ring model test to investigate the mechanical behavior of the π-type SCCS arch without grouting under typical surrounding loess pressure, i.e., symmetric and asymmetric bias pressure distributions. The damage patterns, deformation evolution, and structural strain development are obtained via the experimental investigation and presented in detail. The progressive failure and ultimate bearing capacity of the hollow π-type SCCS arch are further compared under a designed loading situation. It is concluded that the failure of the π-type SCCS arch has three stages, including the coordinate deformation stage, the load-bearing stage, and the failure stage, respectively. However, the deformation and failure modes under different surrounding pressure behave differently. The stiffness and bearing capacity of the π-type SCCS arch under symmetrical pressure is 1.65 and 1.16 times greater than that under asymmetric pressure, respectively. This experimental study provides new insights into the mechanical behavior of new arch frames for loess tunnel construction, which can serve as a benchmark for further theoretical and numerical studies.