Research and insights on time-dependent reinforcement and collaborative load-bearing control technology for roadways in extremely soft stratum

The pronounced rheological behavior of extremely soft surrounding rock is a primary cause of large deformation and instability in roadway structures. Establishing a high-strength, collaborative load-bearing framework combined with a durable, rigid, and stable support system during the initial construction phase is essential to ensure long-term stability under such geological conditions. Using the Chagannur Coal Mine in China as a case study, this work elucidated the failure characteristics of the surrounding rock and the evolution of crack propagation. The instability mechanisms of roadways in extremely soft strata were analyzed from both macro and micro perspectives, and the geological setting, rock properties, and support design were systematically investigated. A time-dependent reinforcement support system with collaborative load-bearing control was proposed, incorporating five key elements: high-stiffness and high-strength initial support, a stable high-pressure zone, precise timing of passive support, targeted floor control, and a rigid long-term bearing capacity. This configuration forms an “active bearing arch + collaborative load-bearing shell + rigid structural body” system, whose performance was validated through FLAC3D simulations. Field tests demonstrated significant effectiveness: roof subsidence and average side displacement were controlled at 52.3 mm and 90.9 mm, respectively, the maximum bed separation reached only 20.5 mm, and the bolts and cables responded sensitively to rock mass deformation. Borehole inspection revealed that the average crack evolution depth in the roof decreased from 10.5 m to 1.6 m, representing an 84.8% reduction. In addition, this paper discusses the application of a hybrid TBM tunneling method in roadways in extremely weak surrounding rock. The findings of this study provide theoretical reference for the stability control of roadway surrounding rock under similar conditions.