Simulation of real tunnel convergences in soft rock using Discrete Element Method with Rate Process Theory

Creep deformation of soft rock caused by tunnel excavation can produce significant safety and construction challenges. In this study, a Discrete Element Method (DEM) numerical model combining the Rate Process Theory (RPT) is developed, in conjunction with the Support Characteristic Curve (SCC) approach, to simulate creep-induced convergences of a tunnel excavated in soft rock. To achieve this, two-dimensional (2D) DEM tunnel models are constructed using particles, and their interactions are simulated by a hybrid combination of the linear and flat-joint contact models. The RPT is integrated into such models through a user-defined Visual C++ script, which adjusts their friction coefficients during the DEM simulation based on the relative velocity between particles. The micromechanical parameters of completely weathered granite were calibrated by uniaxial compression multi-stage creep tests (UCMCTs) and applied to the tunnel excavation simulation. The support forces, as computed using the SCC approach, are applied to the tunnel particles using a used-defined FISH function. The displacements of the tunnel linear particles change over time, the time-dependent behavior of the simulated support system is accounted for in the analysis. Numerical results obtained with the developed model were validated using field monitoring data collected from a tunnel case study. Results indicate that computed convergences align well with the monitoring data, both in terms of values and of deformation trends.