Stress rotation of weakly-cemented soft rock during roadway excavation and its support strategies

To address the engineering challenges posed by poor self-stabilization, significant deformation, and support prone to failure of the weakly-cemented soft rock during roadway excavation, the laboratory test, numerical simulations, field monitoring and theoretical analysis were performed to investigate the principal stress rotation of the surrounding rock during roadway excavation and then asymmetrical coupling support strategies were explored. The results show that the principal stress of surrounding rock during tunnel excavation rotates by three stages: steady growth, severe disturbance, and restoration of stability. The adjustment of the principal stress is most pronounced when approaching the monitoring section at the working face. The major principal stress in the roof and floor increases to 1.62 times the initial value and that of the side walls to 1.35 times the initial value. At the rock wall, the dip angles/azimuths of the major principal stresses on the top and bottom plates are 30°/41° and 23°/151°, respectively. With the increase of the distance from the rock wall, the dip angles/azimuths exhibit a trend of first increase and then decrease, achieving the peak at 11°/5° and 14°/176° at a distance of 0.68 times the diameter from the rock wall. Conversely, the rotation angle of the major principal stress on the side walls decreases with the distance, where dip angles/azimuths change from 56°/58° to the initial state, rotating by 34° and 32°, respectively. The stress rotation amplitude in the roof surrounding rock is greater than those in the bottom and sides. An asymmetric coupling support technology was proposed. Furthermore, numerical simulation analysis and on-site industrial tests verified that this asymmetric coupling support technology can significantly enhance the stress state of surrounding rock, effectively reduce the plastic zone, and provide better control over the deformation of roadways in weakly-cemented soft rock.