A rockburst intensity criterion based on the Geological Strength Index, experiences learned from a deep tunnel
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ORIGINAL PAPER
A rockburst intensity criterion based on the Geological Strength Index, experiences learned from a deep tunnel Wei Zhang 1 & Xia-Ting Feng 1 & Ya-Xun Xiao 2 & Guang-Liang Feng 2 & Zhi-Bin Yao 1 & Lei Hu 1 & Wen-Jing Niu 1 Received: 7 February 2019 / Accepted: 9 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The occurrence of rockburst is related to the surrounding rock stress and geological rock mass strength. Rockburst occurs frequently during the construction at a deep tunnel in southwest China (a tunnel with a depth of approximately 2080 m, and a length of 13 km), leading to casualties, damage to construction equipment, and schedule delays. The application of the rockburst criteria based on the stress-strength/strength-stress ratio shows that they are not suitable for the construction stage. This paper suggests a simple and feasible rockburst intensity criterion based on the Geological Strength Index (GSI) for the construction stage. In this criterion, the strength of the rock mass exposed during excavation is estimated by the Hoek-Brown criterion and is used to reflect the geological conditions of the surrounding rock, considering the influences of the joint conditions and engineering disturbance. The maximum principal stress along the tunnel is obtained by the in situ stress inversion. The ratio of the rock mass strength to the maximum principal stress (σcm/σ1) is taken as the evaluation index. The criterion is as follows: σcm/σ1 > 1.2, none rockburst; 0.75 < σcm/σ1 ≤ 1.2, slight rockburst; 0.4 < σcm/σ1 ≤ 0.75, moderate rockburst; and σcm/σ1 ≤ 0.4, intense rockburst. The engineering applications show the reliability of this rockburst intensity criterion. The results of this paper provide a reference for rockburst intensity evaluation during the construction stage of deep tunnels. Keywords Rockburst intensity evaluation . Construction stage . Rock mass strength . Stress-strength ratio of rock mass . GSI
Introduction Rockburst is a common geological disaster during excavation in deep projects and threatens the safety of construction workers and equipment, delays the construction schedule, and destroys the support infrastructures. Rockburst is a sudden release of the elastic energy accumulated in rock mass under excavation or other disturbance (Feng et al. 2014; Hu et al. 2020). In recent years, rockburst disasters have frequently occurred in underground projects in China with the increase in burial depth and stress level (Feng et al. 2020; Jiang et al. 2019a; Jiang et al. 2019b; Zhao et al. 2017). For example, the “11.28” extremely intense rockburst occurred in the drainage * Xia-Ting Feng [email protected] 1
Key Laboratory of Ministry of Education for Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110004, China
2
State Key Laboratory of Geomechanics and Geotechnical Engineering, Chinese Academy of Sciences, Institute of Rock and Soil Mechanics, Wuhan 430071, China
tunnel at the Jinping II hydropower station. Seven workers were
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