Prediction of Large Deformation and New Classification of Soft Rock Based on FDEM Simulation

The prediction and classification of large deformation of the soft rock tunnel in the field of tunnel engineering are important and complex. The limitations of previous predictions and classifications of large deformation of soft rock tunnels were summarized. Considering its advantages in simulating the fracture of the tunnel surrounding rock mass, the combined finite-discrete element numerical method (FDEM) was used to simulate the deformation and failure process of soft rock with different strength-stress ratios. The large deformation mechanism of the surrounding rock under high in-situ stress as well as the deformation or failure mode of surrounding rock under different in-situ stresses were revealed. In addition, the tunnel deformation prediction equation and new classification of tunnel deformation based on the strength-stress ratio were proposed. The following findings were obtained from the present study. ① Critical hysteresis damping can be adopted to simulate the progressive large deformation process of soft rock tunnel, which can yield the final deformation of the unsupported tunnel and prevent a dynamic response. ② As the strength-stress ratio decreases, the deformation or failure modes of surrounding rock can be divided into four categories: elastic-plastic deformation, closed fracturing, shear dilation, and broken expansion. In addition, new classification of rock deformation based on different surrounding rock failure modes, as well as the corresponding support measures, were proposed. ③ A prediction equation for tunnel deformation based on the deformation of surrounding rock obtained from different strength-stress ratio was proposed; compared with previous prediction models, this prediction equation can improve prediction accuracy and applicability, and makes up for the deficiency of the previous models that the prediction error is great at low strength stress ratio, which indicates that this equation is particularly suitable for the prediction of large deformation of surrounding rock with low strength-stress ratio, and can predict the total deformation of unsupported tunnel surrounding rock, which is essential for guiding the design of the support scheme, selection of support parameters, and prediction of the tunnel boring machine (TBM) jamming state. © 2024 Chang'an University. All rights reserved.