A no-tension elastic–plastic model and optimized back-analysis technique for modeling nonlinear mechanical behavior of rock mass in tunneling

In this paper, we present a no-tension elastic–plastic model and an optimized back-analysis technique for stability analysis of underground tunnels. A set of constitutive equations is presented to simulate the no-tension behavior and plastic yielding of jointed rock masses which yield according to the Drucker–Prager yield criterion and permits no-tension. A nonlinear 2-D finite element model is consequently formulated for the prediction of the behavior of the excavated rock mass. As for the model parameters, the genetic algorithm technique is employed to find the optimal rock mass properties by minimizing the discrepancy between the predicted results and field measurement. The nonlinear finite element model coupling with the genetic algorithm optimized back-analysis technique is then applied to a synthetic example of a deep tunnel in yielding rock. The results show that the forward and back-analysis system is capable of estimating the model parameters with stable and good convergence and give reasonable predictions. Numerical experiments are also carried out to check the influences of position and numbers of measurements to the reliability of the back-analysis results. Furthermore, the sensitivity analysis of the genetic algorithms optimization procedure is discussed in terms of identification of geo-material properties.