Abstract
When carrying out construction that underpasses existing subway tunnels, the surrounding rock is frequently disturbed. Therefore, it can loosen easily and become unstable, which makes its stability difficult to control. Here, we considered an existing subway tunnel in a certain subway section and used orthogonal experiments to design a simulation program as well as the UDEC (Universal Distinct Element Code) simulation software to determine the influences of four factors (i.e., grout density, grouting pressure, dynamic shear force, and viscosity) on the grouting reinforcement effect. The following results were obtained: (1) the combination of the construction method and the grouting parameters strongly influences the reinforcement effect on the surrounding rock of the tunnel. The grouting pressure is not directly proportional to the stability of the surrounding rock. The dynamic adjustment of the relationship between the grouting pressure and the grout density can effectively improve the stress state of the surrounding rock of the tunnel, control surface settlement and deformation, and reduce the section reduction rate of the tunnel. (2) The distribution of joints is closely related to the failure area and form of the surrounding rock of the tunnel. For surrounding rock with well‐developed joint fissures, an excessively high grouting pressure should not be used as they are unstable. (3) The effective bearing range of grouting‐reinforced surrounding rock is dependent on the pore pressure and principal stress difference. The area where the pore pressure is 70–80% of the initial grouting pressure is the effective bearing range of the grouting‐reinforced surrounding rock. The stability of the surrounding rock increases with decreasing principal stress difference and increasing range. (4) The actual monitored data show that the surface settlement can be effectively reduced by handling of grouting reinforcement parameters flexibly, which can meet the control standards.
Highlights
With rapid urbanization in China, the role of subways in alleviating urban congestion and facilitating travel is becoming increasingly important
Because the grouting effectively improved the mechanical properties of the surrounding rock, most measurement points subsided by 50–60 mm, and the surface settlement values were small; this was conducive to control the surface settlement
Random joints were added in the simulation process to restore the real formation state. e following main conclusions were obtained from this study: (1) e use of grouting to reinforce the surrounding rock stratum of the tunnel can effectively improve the stress state of the tunnel, control the surface settlement and deformation, and reduce the section reduction rate of the tunnels
Summary
With rapid urbanization in China, the role of subways in alleviating urban congestion and facilitating travel is becoming increasingly important. Erefore, studying the control of the surrounding rock when crossing existing subway tunnels is crucial for ensuring the safety of subway construction. Zhang et al analyzed the distribution pattern of a grout pressure field and fracture opening based on the grout-rock coupling effect [8] He et al simulated the steady flow in rough fractures using triangular, sinusoidal surfaces and the typical joint roughness coefficient (JRC) profiles [9]. A few studies have investigated the influence of construction methods and grouting parameters on the stability of the surrounding rock of the tunnel when crossing existing subway tunnels. In the engineering context of an existing crossing subway tunnel, this study used the UDEC discrete element simulation analysis software to simulate the factors affecting the grouting control of surrounding rock, analyzed and compared the results with actual measurement results, and determined a reasonable construction method and grouting parameters
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