Analysis of the Stress Variation on Surrounding Rock during Large Diameter Shield Tunneling

Large-diameter shield tunneling technology is widely applied in urban rail transit construction. However, its advancement faces significant challenges, including large excavation cross-sections, great burial depths, high thrust and torque requirements, and pronounced disturbances to rock and soil masses. This paper proposes a real-time monitoring method for the surrounding rock stress during shield tunneling, enabling continuous surveillance of stress variations. Based on the test results, the study analyzes the variation patterns of additional stress in the surrounding rock when operating under balanced conditions in an Earth Pressure Balance (EPB) shield. Furthermore, the paper discusses the magnitude and extent of influence of this additional stress. The results indicate that: The stress in the surrounding rock at the tunnel face gradually increases as the shield cutterhead approaches, reaching its peak value when the cutterhead arrives at the monitoring point. This peak value is close to the theoretical value of the additional contact pressure at the tunnel face. Both the circumferential and radial stresses around the tunnel exhibit a trend of initial increase, followed by a decrease, and finally stabilization. Specifically, the circumferential stress reaches its maximum value before the cutterhead arrives at the monitoring point, whereas the radial stress peaks when the cutterhead is directly at the monitoring point. Analysis of the variation pattern of additional stress reveals that the influence range of shield tunneling on the surrounding rock ahead is approximately 0.8 times the cutterhead diameter. Furthermore, both the maximum total additional stress and the residual total additional stress in the surrounding rock show a linear relationship with the distance from the monitoring point to the tunnel wall. Based on the theoretical value of the additional contact pressure at the tunnel face, calculation formulas for the maximum and residual total additional stresses are proposed. These stress variation patterns were further verified using data from shield tunneling in other sections. The research findings can provide a basis for controlling the stability of surrounding rock during large-diameter shield tunneling in urban rail transit projects.