Impacts of geological conditions on instability causes and mechanical behavior of large-scale tunnels: a case study from
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ORIGINAL PAPER
Impacts of geological conditions on instability causes and mechanical behavior of large-scale tunnels: a case study from the Sichuan–Tibet highway, China Ziquan Chen 1 & Chuan He 1 & Wenbo Yang 1 & Wenqi Guo 1 & Zheng Li 1,2 & Guowen Xu 1 Received: 20 December 2018 / Accepted: 7 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Tunneling in complicated geological conditions frequently encounters problems with squeezing ground, large ground deformation, rockbursts, asymmetric deformation, non-linear rheology of surrounding rock, water inrush, and failure of supporting structures. In this paper, the Sichuan–Tibet highway, which is located at the north-west edge of the Sichuan basin and the eastern margin of the Qinghai– Tibet plateau, serves as a case study to investigate potential hazard sources for tunnels constructed in complex and difficult mountainous areas. Consideration first is given to the following 5 sets of conditions: crossing a fault zone, shallow tunnels in soft rock, crossing a landslide deposit, and deep tunnels in hard and soft rock formations. A program of field tests was performed to study the changes in rock pressure and the performance of support structures in different geological conditions. The results confirmed that the squeezing of rock depended upon a combination of the surrounding rock strength and the in situ stress field; fracture zones and water conditions reduced the integrity and mechanical properties of the surrounding rocks; topography and bedding structure can induce asymmetric mechanical behavior of the supporting structures during construction. Meanwhile, time-dependent rock deformation may have greater adverse impacts on the structural safety performance of tunnel during their operation. Keywords Sichuan–Tibet highway . Large-scale tunnels . Hazard sources . Complicated geological environment . Mechanical behavior . Supporting structures
Introduction After decades of rapid development, the transportation system in eastern China fundamentally has undergone improvement, but now, the focus on railway and highway construction is shifting gradually to the middle and western parts of China. However, as shown in Fig. 1a, due to the presence of mountainous areas in the west and the uplifted Tibetan Plateau in the south west, the geological hydrogeological environments are much more challenging (Fig. 1b).
* Wenbo Yang [email protected] 1
Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, Sichuan, China
2
Chongqing City Construction Investment (Group) Co., Ltd, Chongqing 400015, China
A large number of highway and railway tunnels have been or will be built in these mountainous areas of southwestern China where the land region at an average elevation of 1000–2000 m rises to the land region lying at an average altitude of 4500 m. These include the Chengdu–Lanzhou railway, Chongqing– Lanzhou railway, Dujiangyan–Wenchuan highway, Chengdu– Xian railway, Sichuan–T
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