Investigate the effect of rock mass joint intensity on performance of support systems in the tunnel by using DFN-DEM numerical modeling (Case study: the access tunnel of Rudbar Lorestan Dam plant)

Abstract

Summary In this paper, a DFN-DEM simulation using PFC3D software has been carried out to evaluate the effect of joint intensity variation on tunnel support systems performance. The obtained results indicated more resistance of steel frame against change of rock mass fracture intensity in relation to shotcrete. Introduction The geometric properties of joint sets, especially joint intensity, may be changed by various factors such as explosion, earthquakes, faulting etc. Therefore, it is essential to study the performance of tunnel support systems under various conditions of joint intensities. In this paper, by focusing on the access tunnel to the gallery of Rudbar Lorestan dam as a real case study, simulation of tunnel support systems and its surrounding rock mass close to the real condition using the DFN-DEM approach and PFC3D software is provided. Also for the first time, the dependence of the performance of shotcrete and steel frame to change the intensity of fracturing of rock mass, at this level of accuracy in simulation of jointed rock mass, has been investigated. Three dimensional distinct element software, PFC3D is considered for numerical modeling in this paper. This software has many advantages such as ability to create three-dimensional distinct joints with limited size and with different statistical characteristics, flexibility in different conditions and ability to monitor a momentarily caving and falling during tunnel stability analysis. Methodology and Approaches In this paper, at the first stage, by using the discrete fracture network (DFN) modeling and based on the surveyed data from the access tunnel, existing fractures in this region have been simulated in the PFC3D software. Then the model is linked with the intact rock model. Finally, the performance of tunnel support systems of shotcrete and steel frame relative to changes of the rock mass fracture intensity is investigated. Results and Conclusions Serious damage to Shotcrete support system occurs by doubling the number of joints, while serious damage occurs in the steel frame by quadrupling the number of joints. Therefore, by increasing joint intensity due to various factors such as explosions, earthquakes etc., the steel frame support system has higher reliability.