DISTINCT ELEMENT SIMULATION OF ROCK MASS DEFORMATION NEAR TUNNELS IN COMPLEX GEOLOGICAL CONDITIONS, GUIDED BY STATISTICAL EXPERIMENTAL DESIGN

The mechanics of a flysch rock mass is determined by its complex discontinuity, heterogeneity, anisotropy, and diverse deformation modes. This study proposes a new methodology to simulate the deformation of Carpathian flysch in the vicinity of tunnels, employing the distinct element method (DEM), global-local modelling approach and a hybrid representation of discontinuities. The methodology enables the simulation of a wide range of structural models and properties of Carpathian flysch and reduces the computational complexity of numerical models. A global model reflects the initial stress field. Local models detail the properties of joint sets separating rock blocks and the properties of the ubiquitous joint model material inside the discrete blocks. Both direct and indirect representations of discontinuities contribute to the model response. The numerical model is addressed as a multiparameter system and examined through statistical design of experiments (DOE). The model is calibrated and validated using field measurements of displacements and convergences. The factors contributing to uncertainty in the simulation results are considered. A parametric analysis was conducted on the deformation of flysch rock mass surrounding a tunnel, evaluating the impact of bedding orientation, depth, and support stiffness. Bedding dip direction explained the asymmetry in sidewall convergence and its changes. Discontinuity stiffness and dilation, rarely studied model parameters, were found to have a significant effect on simulation error.