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Stability Analysis of a Rectangular Tunnel in Granitic Rocks at a Depth of 205 m, Bhima Basin, Karnataka
The stability of underground excavation in hard rock at depth is significantly controlled by the direction and magnitude of the prevailing in-situ stress field and existing fracture patterns within the rock mass due to anomalous stress concentration and wedge formation. In this paper stress concentration and displacement around a rectangular tunnel of 4 × 3 m size and 20 m length excavated in granitic rocks at a depth of 205 m in the vicinity of a reverse fault has been analyzed using Phase-II FEM Code. The study area forms a part of Bhima basin in the district of Yadgir in Karnataka. The important rock types exposed in the area include proterozoic limestone in contact with basement granites. A total of 56 rock samples obtained from the rock mass around the excavation were tested for various rock mechanical parameters for their use as input in the numerical analysis. A total of 40 rock fractures measured in the rock mass around the excavation reveal the presence of two major joint sets strike direction N55° E & N330° W with dips of 90 & 45° respectively. The analysis using Hook and Brown failure criteria for the rectangular tunnel in fracture free granites shows a maximum 21.85 MPa tensile stresses at corner with maximum 0.3 mm vertical displacement at crown and 0.4 mm horizontal displacement at side wall. The stability index at corners thus reduces to 1.83 which in case of side walls is of the order of 4.32. The same rock mass with two joint sets reveal increase in vertical displacement (0.7 mm) in crown and sidewalls. The same excavation in reverse fault zone set up shows extremely unstable structure with Stability Index of <1. However, in-situ measurements of displacements match with case of normal stress field and no indication of high stress field typical of reverse fault set up is noticed.
Stability Analysis of a Rectangular Tunnel in Granitic Rocks at a Depth of 205 m, Bhima Basin, Karnataka
The stability of underground excavation in hard rock at depth is significantly controlled by the direction and magnitude of the prevailing in-situ stress field and existing fracture patterns within the rock mass due to anomalous stress concentration and wedge formation. In this paper stress concentration and displacement around a rectangular tunnel of 4 × 3 m size and 20 m length excavated in granitic rocks at a depth of 205 m in the vicinity of a reverse fault has been analyzed using Phase-II FEM Code. The study area forms a part of Bhima basin in the district of Yadgir in Karnataka. The important rock types exposed in the area include proterozoic limestone in contact with basement granites. A total of 56 rock samples obtained from the rock mass around the excavation were tested for various rock mechanical parameters for their use as input in the numerical analysis. A total of 40 rock fractures measured in the rock mass around the excavation reveal the presence of two major joint sets strike direction N55° E & N330° W with dips of 90 & 45° respectively. The analysis using Hook and Brown failure criteria for the rectangular tunnel in fracture free granites shows a maximum 21.85 MPa tensile stresses at corner with maximum 0.3 mm vertical displacement at crown and 0.4 mm horizontal displacement at side wall. The stability index at corners thus reduces to 1.83 which in case of side walls is of the order of 4.32. The same rock mass with two joint sets reveal increase in vertical displacement (0.7 mm) in crown and sidewalls. The same excavation in reverse fault zone set up shows extremely unstable structure with Stability Index of <1. However, in-situ measurements of displacements match with case of normal stress field and no indication of high stress field typical of reverse fault set up is noticed.
Stability Analysis of a Rectangular Tunnel in Granitic Rocks at a Depth of 205 m, Bhima Basin, Karnataka
Lecture Notes in Civil Engineering
Verma, Amit Kumar (editor) / Mohamad, Edy Tonnizam (editor) / Bhatawdekar, Ramesh Murlidhar (editor) / Raina, Avtar Krishen (editor) / Khandelwal, Manoj (editor) / Armaghani, Danial (editor) / Sarkar, Kripamoy (editor) / Kumar, Binu (author) / Bajpai, R. K. (author) / Singh, T. N. (author)
International Conference on Geotechnical Challenges in Mining, Tunneling and Underground Infrastructures ; 2021
Proceedings of Geotechnical Challenges in Mining, Tunneling and Underground Infrastructures ; Chapter: 19 ; 317-329
2022-06-04
13 pages
Article/Chapter (Book)
Electronic Resource
English
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