Quantitative estimation method for the excavation-induced weakening effect of rock mass parameters in deep tunnels

The excavation-induced weakening effect of rock mass parameters is detrimental to the stability of deep tunnels. This study presents a quantification method for the weakening effect of rock mass parameters. In this method, the weakening factor is introduced as a quantitative index of the weakening effect of rock mass parameters, which can be calculated by the acoustic P-wave velocity measured in the surrounding rock and the Hoek–Brown criterion. Taking three deep tunnels as examples, the weakening law of rock mass parameters is investigated. The results indicate that the weakening effect is most severe near the excavation outline and gradually decays with increasing distance. Significant differences in the weakening effect can be observed at different parts of the tunnel cross-section and under different excavation methods. The weakening effect can be further exacerbated by multiple excavation disturbances. Among the strength parameters of rock masses, the weakening effect of uniaxial compressive strength is the most obvious, followed by uniaxial tensile strength, cohesive strength, and equivalent internal friction angle. The FLAC3D software is utilized to reproduce different weakening effects and analyze the energy distribution around tunnels. It is found that as the weakening effect intensifies, the accumulated elastic strain energy within the surrounding rocks gradually diminishes, and the peak elastic strain energy is at the junction of damaged and undamaged rock masses.