Study on the influence law of spray layer cavity on the main reinforcement of grid steel frame

Abstract The field monitoring data showed that a small amount of main reinforcement of lattice girder at the arch of a tunnel was under tension, and the calculation showed that the initial support structure should be under circumferential compression. In order to find out the reason for the tension of the steel frame main reinforcement, the geological radar was used and detected the cavity in the spray layer at the tension position. In order to further clarify the tension mechanism of the main reinforcement and the influence of factors such as the position and size of the cavity on the main reinforcement, numerical simulations were carried out, the results show that the cavity causes the eccentric compression of the shotcrete layer, resulting in the local bending moment of the lattice girder and the change of the stress distribution of the main reinforcement, when the size of the cavity exceeds 3m × 0.2m will cause local tension of nearby main reinforcement; The position of the cavity has a significant impact on the stress condition of the main reinforcement. Compared with the arch crown and arch waist, the cavity at the arch foot is more likely to produce large tensile stress on the main reinforcement, the size of the cavity is 6m × 0.2m causes 81MPa tensile stress in the main reinforcement. The research results provide a theoretical basis for the interpretation and analysis of tunnel lattice girder monitoring data.