Numerical analysis of symmetric and asymmetric rock-bolting pattern on stability of underground fractured structures, using DFN and DEM method (case study CLAB2 cavern, Sweden) Nooshin Senemarian Isfahani Date of submission :Sep 20, 2020 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Persian Supervisor: Dr. Hamid Hashemolhosseini (Hamidh@iut.ac.ir) Supervisor: Dr. Amin Azhari (aazhari@iut.ac.ir) Advisor: Dr. Alireza Baghbanan(bagh110@iut.ac.ir) The stability of underground structures excavated in jointed rockmass, has been challenging for geotechnical engineers. This is mainly due to the erratic geometry of fractures causing complexity for analyzing the interaction between blocks. Discrete fracture network (DFN) is a reasonable method probabilistically defining and evaluating the irregularity of fracture networks, including spacing, length, size, and orientation. In this study, the stability of a large excavated cavern located in south Sweden (CLAB2) in a jointed rock mass, including six fracture sets, is evaluated by the discrete element method (DEM) in three dimensions (3DEC, Itasca) and utilizing DFN method. The goal of this research is to suggest a suitable pattern for the rock-bolting support system that guarantees the stability of this large cavern. In this regard, various rock bolting support systems are proposed, iired by Canadian, Australian, and African rock-bolting systems. The evaluated patterns include 3,6 or 9-meter rock bolt length with 1.5, 2, and 5 meters spacing. Totally,190 rock-bolting patterns, containing symmetric patterns with equal rock bolt lengths and asymmetric patterns with 2 and 3 different rock bolt lengths, in various DFNs were simulated. Both technical and economic criteria are investigated to suggest the best patterns, based on the volume of unstable blocks and the used rock bolt length, respectively. It was concluded that the asymmetry bolt patterns with three different rock bolt lengths were the most suitable patterns based on technical and economic criteria. The ultimately recommended pattern for CLAB2 cavern was an asymmetric pattern with 3, 6, and 9 meters for bolt lengths and spacing of 2 meters. Key words: CLAB2 cavern, rock bolting system, Discrete fracture network (DFN), discrete element method (DEM), probabilistically defining
