Abstract: Generally, the pervasive joint model in FLAC3D and the simulation calculation using MohrCoulomb strength criterion are used to evaluate the stability of rock accurately. However, the layered rock mass is essentially regarded as isotropic, leading to a large error between simulated results and monitoring values. Based on a revised HoekBrown criterion, the instantaneous equivalent and best onetime approximation are performed on the I1-J2 plane and MohrCoulomb strength criterion, respectively, and the corresponding equivalent strength formula is derived. The formula is used to calculate the equivalent strength parameters of rock masses with different inclination angles, and the FLAC3D pervasive joint model is imported to study the stability of the surrounding rock in the Gonghe tunnel of the ChongqingHunan expressway. The results show the following. (1) The methods are used for modifying the rock mass parameters. The deformation of key points after the tunnel excavation is greater than that before the modification, which is closer to the measured value. (2) The value of deviatoric stress σ1-σ3 obtained from the instantaneous equivalent modification is smaller than that before the modification. The value of σ1-σ3 obtained from the best onetime approximation modification is greater than that before the modification, and the change in trend with inclination is the same as that before modification. (3) The instantaneous equivalent modification and best onetime approximation modification methods can be used for rock mass parameter modification; the latter one has a better effect.

Key words:

Hoek-Brown criterion, numerical simulation, equivalent strength parameters, layered rock mass, pervasive joint model, surrounding rock stability