Practical ground response curve considering post-peak rock mass behaviour

Abstract

Analysis of stresses and displacements around circular opening excavated in rock mass has been one of the significant issues in tunnelling. A plastic zone is formed around underground opening as a result of high induced stress magnitudes. The ground response curve is one of the best methods to investigate the tunnel stability that represent the relationship between the decreasing of inner pressure and the increasing of radial displacement of tunnel wall. In recent years, several methods have been suggested for analysis of ground response curve by many researchers, however, some of the analytical solutions that have been presented, are relevant to elastic-perfectly plastic or elastic-brittle-plastic behaviour of rock. But real behaviour of plastic zone is strain softening with variable dilatancy. In this study, it is attempted to take into account the post-peak rock mass behaviour (drop modulus and variable dilation angle) in the stress-based finite difference approximation numerical procedure, so an algorithm is suggested to analyse the tunnel stresses and convergences. In order to verify the proposed algorithm, the results were compared with FLAC numerical solution. For showing the applicability of the proposed algorithm, the Ghomroud tunnel convergence was calculated based on the proposed algorithm and compared with the monitored tunnel convergence. At the end, the effect of various parameters including dilation, critical softening parameter and rock mass quality (GSI) was studied on the tunnel convergence and plastic zone thickness. Based on the obtained results, the higher quality of the rock mass surrounding the tunnel has, the narrower plastic zone forms and the lower tunnel wall converges. Also, the rock mass with higher brittleness means more convergence and wider plastic zone. Furthermore, constant dilation in plastic zone overestimates the tunnel wall convergence.

Parametric Evaluation of Simultaneous Effects of Damaged Zone Parameters and Rock Strength Properties on GRC

“…In this study, the same data sources used in Ghorbani and Hasanzadehshooiili [26] were gathered as the database and then were used as the training data in the evolutionary polynomial regression (EPR) via the framework of genetic algorithm (GA). e summary of the data sources is as follows: a case of field measurements regarding the Hanlingjie tunnel in Hunan, China, at a depth of 146 m [17], two cases of Elastic-plastic rock mass considering strain softening [4,9], a case of strain softening rock mass considering exponential decaying post-peak dilation parameter [52], and a case of elastic-perfect-plastic behavior of a rock mass considering EDZ [43]. Besides, Ghorbani and Hasanzadehshooiili [26] utilized the problem originally solved by Zareifard and Fahimifar [43] in order to cover the effects of new features of their proposed algorithm, such as the effects of the intermediate principle stress (b), the weight of the damaged rock mass and existence of a softening zone, and the exponential decaying dilation behavior.…”

Heterogeneous Rock Simulation Using DIP‐Micromechanics‐Statistical Methods

“…In (6), μ represents one of the strength parameters φ, and C and the subscripts p and r denote the peak and residual values, respectively [27]. e rock is assumed to be a heterogeneous material, and its mechanical properties are considered to conform to the Weibull distribution function.…”

A New Numerical Finite Strain Procedure for a Circular Tunnel Excavated in Strain-Softening Rock Masses and Its Engineering Application

“…and GhorbaniHadi et al [21] proposed a series of new semi-analytical solutions and numerical procedures for calculating the stress and displacement around a circular tunnel excavated in strain-softening Mohr-Coulomb, generalized Hoek-Brown, or three-dimensional nonlinear Hoek-Brown rock mass. Although these methods were applied well on the mechanical analysis and the tunnel design [16,[22][23][24][25][26][27], they are based on the small deformation hypothesis and not applicable to analyze a tunnel with a high risk of large deformation.…”