No abstract

Deep-buried soft rock tunnels exhibit low strength and easy deformation under the influence of high ground stress. The surrounding rock of the soft rock tunnel may undergo large deformation during the construction process, thereby causing engineering problems such as the collapse of the vault, bottom heave, and damage to the supporting structure. The Chengwu Expressway Tunnel II, considered in this study, is a phyllite tunnel, with weak surrounding rock and poor water stability. Under the original design conditions, the supporting structure exhibits stress concentration and large deformation. To address these issues, three schemes involving the use of the double-layer steel arch to support, weakening of the steel arch close to the excavation surface, and weakening of the steel arch away from the excavation surface to support were proposed. Using these schemes, the inverted radius was varied to explore its influence on different support schemes. For simulation, the values of the inverted radius selected were as follows: 1300 cm, 1000 cm, and 700 cm. The proposed support plan was simulated using FLAC3D, and the changes in the pressure between the initial support and surrounding rock, the settling of the vault, and the surrounding convergence were investigated. The numerical simulation results of monitoring the surrounding rock deformation show that the double-layer steel arch can effectively reduce the large deformation of the soft rock well. When the stiffness of one of the steel arches was weakened, the support’s ability to control the deformation was weakened; however, it still showed reliable performance in controlling deformation. However, changing the radius of the invert had an insignificant effect on the deformation and force of the supporting structure.

The study investigates a new chemical grout by mixing the main agent, auxiliary agent, catalyst, foam stabilizer, solvent, and water, to treat the distress of railway tunnel. The orthogonal design was used to obtain 16 groups of grout proportion schemes, and reasonable proportion parameters were screened using laboratory and field tests. Additionally, this study included detailed research on the grout performance. The test results showed that the proportion schemes of groups 3, 4, and 15 grout were the most reasonable. In particular, for group 3, the viscosity is 663 MPa·s, the curing time is 119 s, the foaming capacity is 1589%, and the compressive strength is 20.16 MPa. For group 4, the viscosity is 663 MPa·s, the curing time is 137 s, the foaming capacity is 1809%, and the compressive strength is 17.76 MPa. For group 15, the viscosity is 281 MPa·s, the curing time is 98 s, the foaming capacity is 1173%, and the compressive strength is 26.79 MPa. Groups 4 and 15 grouts were used to treat the frost boiling and track bed subsidence in existed railway tunnels. Based on this, field monitoring showed that muddy water became clear water with an average depth of only 4 mm in the drainage ditch and that the irregular subsidence of the track bed was also solved after treatment. According to the aforementioned experimental research and analysis, it is proven that new grout not only exhibits a reasonable solidification time, high strength, and excellent waterproofing and impermeability with no pollution of the environment but also can be produced by a safe and convenient synthesis method. Group 4 is suitable for treating tunnel seepage, group 15 is suitable for structural reinforcement, and group 3 confers the advantages of seepage prevention, leakage stoppage, and reinforcement.