Abstract
Stress and deformation around circular tunnel are crucial for optimizing the support system and evaluating the tunnel stability. The damage zone induced by blasting or mechanical excavation can dramatically influence the support design and methods because the self-weight of broken rock mass at the roof of the tunnel can exert a high pressure on the support system, leading to the support system instability due to the overload. This paper presents a new closed-form solution for analyzing the stress and deformation of deep circular tunnel excavated in elastic-brittle rock mass with the consideration of the rock gravity and damage zone by using the unified strength criterion. A new modified equilibrium equation in the fracture zone is used to determine the stress and the radius of fracture zone. The correctness of the solution is also verified by comparison with the numerical simulation results. The results illustrate that the rock gravity, damage zone radius, and intermediate principal stress have an extremely important influence on the ground response. The tunnel surface convergence and damage zone radius with the consideration of the gravity are obviously larger than those without consideration of the gravity. The rock gravity effect under the high intermediate principal stress gradually weakens, illustrating that the intermediate principal stress is beneficial to tunnel stability. Large deformation instability of the tunnel is dependent on the extension of damage zone. The larger the radius of damage zone, the larger both fracture range and tunnel surface deformation. The proposed solution in this study is novel and can be used to assess the ground convergence for different scenarios and to optimize the support system during the early design stage of the tunnel.
Highlights
The extent of damage zone varies with the tunnel shape, excavation method, and rock mass properties. e distribution of damage greatly impacts the ground response and support design. is damaged zone can be considered a rock failure zone in which the rock mass properties are seriously weakened due to the disturbance caused by the excavation. e extent of the damage zone near the tunnel surface in blasted tunnels is far more significant owing to the impact wave and stress redistribution [1, 2]. e damage can range from a few centimetres in tunnels with tunnel boring machine (TBM) to several decimetres and several meters in drilling and blasting [3, 4]
A new elastic-plastic solution of deep circular tunnel excavated in elastic-brittle plastic rock mass is presented by using unified strength criterion. e new solution considers the effect of intermediate principal stress, rock gravity, and damage zone on ground response
Associated and nonassociated flow rules are considered in the solution. e correctness of the solution is verified by comparison with the numerical simulation results. is study demonstrates that the intermediate principal stress, rock gravity, and damage zone can dramatically influence the stress and deformation of surrounding rock
Summary
The extent of damage zone varies with the tunnel shape, excavation method, and rock mass properties. e distribution of damage greatly impacts the ground response and support design. is damaged zone can be considered a rock failure zone in which the rock mass properties are seriously weakened due to the disturbance caused by the excavation. e extent of the damage zone near the tunnel surface in blasted tunnels is far more significant owing to the impact wave and stress redistribution [1, 2]. e damage can range from a few centimetres in tunnels with tunnel boring machine (TBM) to several decimetres and several meters in drilling and blasting [3, 4]. Some researchers have investigated the response behaviour of circular tunnel considering different rock materials and flow rules based on USC [15,16,17,18,19] Those researchers ignored the effect of rock gravity in the damage zone on stresses and deformation of the tunnel. The previous study did not consider the effect of gravitational load in rock masses that follow a uniform strength criterion Both intermediate principal stress and gravitational force exert considerable influence on the equilibrium and should be evaluated using the governing equations for accurately predicting the stresses and deformation around the tunnel.
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