AbstractThe deformation of a primary support is one of the difficult problems often encountered in the excavation of a deep-lying soft rock tunnel. Directed against the problems of the large deformation of the primary support, the cracking of the lining, and the sinking of the vault in the Kalumoqi Tunnel that is being built, the classification of surrounding rock and deformation monitoring are carried out, and the causes of the disease are analyzed. On this basis, the measures for changing the supporting parameters are proposed. Finite-element software is used to verify the supporting effect of the changed parameters by numerical simulation, and the construction effect is evaluated by on-site monitoring. The results show that: (1) part of the vault is peeling and the cracking phenomenon of the sprayed concrete when disease occurs, the deformation of parts has obviously sustained growth, the deformation velocity value is larger, longitudinal connecting steel bar and steel arch shelf of primary support show strong tensile deformation, steel arch shelf of primary support at the arch foot has broken, and the deformation of the primary support of the tunnel is larger, showing an extruded deformation as a whole. The convergence value and rate at the arch foot are greater than those at the arch top, and the maximum convergence value of the arch foot is 50 mm, and the maximum convergence rate is 29 mm/d. The convergence of the arch foot has a sudden change, and the deformation shows a trend of continuous increase. (2) The numerical simulation results show that the displacement of the subsidence of the sinking vault, the arch waist, and the arch foot decreases by 80%, 90.8%, and 96.2%, respectively, compared with the original support parameters. The changed SVa support parameters produce less displacement deformation, and the deformation at the vault, the arch waist, and the arch foot all meet the requirements of the design code, which can ensure the safety of the tunnel construction and the stability of the structure. (3) By comparing the numerical simulation with the field measured data after the parameter changes, it is found that the sinking vault, the convergence of the arch waist, and the displacement of the arch foot is significantly reduced, the problem of the large deformation of the primary support is solved, the overall deformation of the surrounding rock tends to be stable, and the shape of all the supporting forms of the tunnel is intact without obvious damage phenomenon.

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