Experimental study on mechanical behavior of lining structure in closely spaced tunnel-landslide orthogonal system

ObjectiveWith the rapid development of expressways and railways in China's western mountainous areas, the distress of operational mountain tunnels under landslide actions are becoming increasingly prominent. Current research mainly focuses on tunnel-landslide systems, while studies on closely spaced tunnel-landslide systems are relatively insufficient. This study takes closely spaced tunnel-landslide orthogonal system as the study object. The closely spaced tunnels pass through the landslide section. The deep-buried side tunnel undercuts the sliding zone. The shallow-buried side tunnel intersects orthogonally with the sliding zone. Model tests are conducted to investigate the mechanical behaviors of lining structures.MethodBased on a certain closely spaced tunnel prototype, the acceleration of landslide sliding velocity, caused by the construction of a new tunnel or other factors, was simulated by using rear loading method through laboratory physical model test.ResultThe lining structure of shallow-buried side tunnel inhibits early-stage landslide sliding to some extent, leading to hysteresis in slope movement within variable-gradient section. The earth pressure at inner arch foot of shallow-buried side tunnel decreases. Its lining structure tends towards overturning failure. Compression damage is particularly prone to occur at its inner arch shoulder and outer arch foot. The tunnels are in an obvious biased compression state. When the landslide sliding rate increases, the biased compression state of deep-buried side tunnel becomes more pronounced. As the trailing edge load increases, the bending moment of lining structure increases rapidly. The axial force of shallow-buried side tunnel is mainly compressive at inner arch bottom and arch foot. It is more susceptible to shear failure at intersection with sliding zone. Conversely, the inner side of deep-buried side tunnel lining tends towards tensile failure, while the outer side tends towards compressive failure.ConclusionWhen closely spaced tunnels traverse a variable-gradient landslide section, the sliding initially occurs around the sliding zone. As the landslide thrust increases, the interaction develops between lining structures on both tunnel sides. Consequently, the lining on shallow-buried side bears significant landslide thrust. Meanwhile, the lining axial force at deep-buried side undergoes a pronounced change.