Vol18 No.5: 1371-1390
【Title】Time-dependent squeezing deformation mechanism of tunnels in layered soft-rock stratum under high geo-stress
【Author】CHEN Zi-quan1,4; HE Chuan1; WANG Jun1,3; MA Chun-chi1,2*
【Addresses】1 Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China; 2 State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China; 3 Sichuan Highway Planning Survey Design and Research Institute Ltd, Chengdu 610041, China; 4 Key Laboratory of Engineering Structures of Heavy Haul Railway, Ministry of Education, Central South University, Changsha 410075, China
【Corresponding author】MA Chun-chi
【Citation】Chen ZQ, He C, Wang J, Ma CC (2021) Time-dependent squeezing deformation mechanism of tunnels in layered soft-rock stratum under high geo-stress. Journal of Mountain Science 18(5). https://doi.org/10.1007/s11629-020-6356-0
【Abstract】Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior. In this paper, we studied the deformation mechanism during the construction period of deep-buried soft-rock tunnel by means of a combination of field observations and a numerical method. First, a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed. Then, the initial damage tensor reflecting the bedding plane (joint) distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method, i.e., a new rheological damage model (RDL model) of layered soft rock is established consisting of elastic, viscous, viscoelastic, viscoplastic and plastic elements. A field test was conducted on the Maoxian tunnel in Sichuan province, southwestern China, which is in broken phyllite (layered soft rock) under high geo-stress. The tunnel has experienced large deformation due to serious squeezing pressure, thus we adopted double primary support method to overcome the supporting structure failure problems.The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization, and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress. Thus, the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method. Compared with the single primary support method, the surrounding rock pressure, secondary lining force, surrounding rock deformation, and the depth of the damage to the rock mass was reduced by 40%-60% after the double primary support method was used.
【Keywords】Deformation mechanism; Layered soft rock tunnel; High geostress; Large squeezing deformation; Rheological damage model