Abstract In order to control the surrounding rock deformation of a tunnel in soft rock with high geostress and opti? mize the double-layer initial support structure, the Ningchan Tunnel is used as an example in this study. The numerical simulation method is used to analyze the deformation characteristics under different thickness combinations of double-layer initial support and at different construction time of the second-layer support. The field monitoring data is also used to analyze the surrounding rock deformation characteristics of single-layer and double-layer initial support, and to verify the accuracy of the numerical simulation. As the results indicate: If the thickness of the first-layer initial support is no more than 0.04 times the tunnel span, increasing the thickness of the first-layer the initial support is highly effective in controlling the deformation of tunnel crown and hance. As the thickness increases, however,the controlling effect is gradually diminished. If the thickness ratio between the first-layer and second-layer initial support is 0.8-2.7, the ratio between the surrounding rock deformation and thickness is indicative of an exponential function relation. Hance convergence is more sensitive to the construction time of the second-layer initial support than crown settlement is. If the first-layer and second-layer support are 35 cm and 20 cm in thickness, the surrounding rock deformation can be effectively controlled, and the onsite operability can be guaranteed. The period before excavation of the lower bench is completed is the period in which the surrounding rock intensively releases its stress, and the impact of the excavation-induced unloading is the dominant factor in deformation. After construction of the secondary lining, the surrounding rock rheology is the dominant factor in deformation.
Abstract：
In order to control the surrounding rock deformation of a tunnel in soft rock with high geostress and opti? mize the double-layer initial support structure, the Ningchan Tunnel is used as an example in this study. The numerical simulation method is used to analyze the deformation characteristics under different thickness combinations of double-layer initial support and at different construction time of the second-layer support. The field monitoring data is also used to analyze the surrounding rock deformation characteristics of single-layer and double-layer initial support, and to verify the accuracy of the numerical simulation. As the results indicate: If the thickness of the first-layer initial support is no more than 0.04 times the tunnel span, increasing the thickness of the first-layer the initial support is highly effective in controlling the deformation of tunnel crown and hance. As the thickness increases, however,the controlling effect is gradually diminished. If the thickness ratio between the first-layer and second-layer initial support is 0.8-2.7, the ratio between the surrounding rock deformation and thickness is indicative of an exponential function relation. Hance convergence is more sensitive to the construction time of the second-layer initial support than crown settlement is. If the first-layer and second-layer support are 35 cm and 20 cm in thickness, the surrounding rock deformation can be effectively controlled, and the onsite operability can be guaranteed. The period before excavation of the lower bench is completed is the period in which the surrounding rock intensively releases its stress, and the impact of the excavation-induced unloading is the dominant factor in deformation. After construction of the secondary lining, the surrounding rock rheology is the dominant factor in deformation.
CHEN Zhimin1 WANG Hong1 GONG Jun2 LI Zengyin2 PENG Yi1
.On Surrounding Rock Deformation Characteristics in a High Geostress Soft Rock Tunnel with Double-layer Initial Support[J] MODERN TUNNELLING TECHNOLOGY, 2024,V61(3): 85-95
2024, Vol. 61 