Influence of soil-rock composite stratum on mechanical response and failure modes of underground utility tunnel

This research combines scaled model experiments with theoretical analysis to investigate the impact of underground utility tunnels (UUTs) on foundation bearing capacity and to examine the interaction between soil-rock composite strata and the stress-strain responses of the tunnel. The findings indicate that UUTs alter the foundation mechanism by reducing soil depth, streamlining the load transfer path, and causing stress to converge at the tunnel's top. Additionally, the results reveal that the influence range of the tunnel on both sides is approximately 1.5 times its width and remains unaffected by the position of load application, the tunnel's burial depth, or the width of the composite stratum. Moreover, when the width of the soil-rock composite stratum equals the width of the tunnel, the tunnel experiences a laterally flexural stress state. Within this specific stratum context, the central axis area of the tunnel roof and the connection with the side panels represent the core sensitive areas for crack initiation and propagation. In the failure scenario, the tunnel roof displays typical characteristics of fracture and depression, with the damage degree decreasing from the load center towards both ends. Meanwhile, the side panels do not exhibit characteristics of plastic deformation. This research provides a theoretical framework for the design, construction, and maintenance of UUTs, emphasizing its practical significance in engineering.