Failure mechanism and stability control of roadways in weakly cemented soft rock strata supported by a closed structure consisting of mesh-reinforced shotcrete and inverted arch

Weakly cemented soft rock (WCSR) in western China is characterized by strong water sensitivity and pronounced creep behavior, which can result in severe large deformation and floor heave in roadways. Conventional open bolt–mesh–shotcrete support is unable to provide coordinated load bearing around the entire roadway section. Therefore, a closed full section composite support system comprising mesh–reinforced shotcrete and inverted arch is proposed. Laboratory tests showed that the WCSR experienced nearly complete disintegration after 120 min of water immersion, and accelerated creep failure occurred when the applied stress reached 80 − 90 % of its peak strength. The Nishihara model was fitted to describe the creep behavior, while an exponential cohesion degradation damage model was established to characterize strength degradation associated with plastic strain. Non-uniform stress similarity model tests identified a critical stress threshold corresponding to 78 % of the rock uniaxial compressive strength. Beyond this threshold, the magnitude order of lining bearing pressure changes drastically, indicating a transition in the full-section load-transfer mechanism. The arch springings constituted the main stress-concentration zones. The inverted arch transformed part of the floor bending stress into axial compression and effectively suppressed floor heave; its peak bending moment was only 40.4 % of that at the arch springings. Numerical simulations based on the cohesion-degradation model reproduced the asymmetric cracking and failure characteristics observed in the model tests, supporting the feasibility of the model under the investigated conditions. Field monitoring indicated that roadway deformation stabilized after 56 days, and the monitored deformation was 73.8 % lower than that observed under the conventional support scheme. These results clarify the failure evolution and load-transfer transition of WCSR roadways and reveal the synergistic control mechanism of the closed inverted arch support system, providing a theoretical basis and practical guidance for supporting analogous soft rock roadways.