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ailure Mechanism and Excavation Method for Soft-Rock Tunnels with Large Deformation under Complex Geological Conditions
(1 Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031;2 China Communications Construction Company Ltd., Beijing 100088)
Abstract By analyzing the large deformation events that occurred in the Zhegushan tunnel of the WenchuanMaerkang expressway, the rock failures are divided into three categories: plastic flow of soft rock, bending deforma? tion of the plate girder and slipping of the structural surface. A comparison of the two-step excavation method and three-step excavation methodwas performed for a 50-meter-long test section with a typical rock mass. The results show that for the two-step excavation method, the advance rate and construction space between the left and right side of the lower bench have a significant effect on tunnel stability. Based on a comparison of the tunnel′s peripheral displacement, contact pressure between the surrounding rock and the initial support (as well as the internal force of the steel arch) for the two-step and three-step construction methods, it is found that for the two-step excavation method, the tunnel′s peripheral deformation, the pressure between surrounding rock and the initial support are relatively large since the one-pass excavation section is very large and the pressure of the rock mass increases too quickly, and the safety reverse of the steel arch is not enough. For tunnels in complex regions or environments, the re? served deformation volume of the rock mass should be adjusted for the actual situation at the site, a reasonable construction method and tunnel advance rate should be chosen and the three-step construction method can effectively control the occurrence of large deformation in cases of unfavourable rock masses.
Abstract：
By analyzing the large deformation events that occurred in the Zhegushan tunnel of the WenchuanMaerkang expressway, the rock failures are divided into three categories: plastic flow of soft rock, bending deforma? tion of the plate girder and slipping of the structural surface. A comparison of the two-step excavation method and three-step excavation methodwas performed for a 50-meter-long test section with a typical rock mass. The results show that for the two-step excavation method, the advance rate and construction space between the left and right side of the lower bench have a significant effect on tunnel stability. Based on a comparison of the tunnel′s peripheral displacement, contact pressure between the surrounding rock and the initial support (as well as the internal force of the steel arch) for the two-step and three-step construction methods, it is found that for the two-step excavation method, the tunnel′s peripheral deformation, the pressure between surrounding rock and the initial support are relatively large since the one-pass excavation section is very large and the pressure of the rock mass increases too quickly, and the safety reverse of the steel arch is not enough. For tunnels in complex regions or environments, the re? served deformation volume of the rock mass should be adjusted for the actual situation at the site, a reasonable construction method and tunnel advance rate should be chosen and the three-step construction method can effectively control the occurrence of large deformation in cases of unfavourable rock masses.
.ailure Mechanism and Excavation Method for Soft-Rock Tunnels with Large Deformation under Complex Geological Conditions[J] MODERN TUNNELLING TECHNOLOGY, 2017,V54(5): 146-154
2017, Vol. 54 