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http://dx.doi.org/10.7474/TUS.2019.29.5.346

Application of Strength Reduction Method to Evaluation of Pillar Safety Factor in very Closely Spaced Tunnels  

Jun, Sung-Kwon (Taeyoung Engineering & Construction)
Yoon, Dong-Ho (Department of Energy Systems Engineering, Seoul National University)
Song, Jae-Joon (Department of Energy Systems Engineering, Seoul National University)
Kim, Se Hyung (Korea Expressway Corporation)
Publication Information
Tunnel and Underground Space / v.29, no.5, 2019 , pp. 346-355 More about this Journal
Abstract
When evaluating pillar stability in very closely spaced tunnels, a local safety factor (strength/stress ratio) at the minimum width has been widely used. Tension bolts have been frequently applied as reinforcement for the cases where safety factors are less than 1.0 from FEM stress analysis. However, the local safety factor shows a constant value irrespective of the change in pillar width/tunnel diameter (PW/D) and the safety factor of the pillar is underestimated because the variation of deviation stress is relatively small even when the pre-stressing is applied to the tension bolt. In addition, the average safety factor proposed by Hoek and Brown(1980) was reviewed, but the pillar safety factor was relatively overestimated when the width of the pillar was increased. As an alternative, the SRM safety factor using shear strength reduction method shows the effect of changing the safety factor in the case of no reinforcement and tension bolt reinforcement as the pillar width/tunnel diameter(PW/D) changes. The failure shape is also similar to the previous limit theory result. In this study, the safety factor was evaluated without considering rock bolt and shotcrete to distinguish reinforcing effect of tension bolt.
Keywords
Closely spaced tunnel; Pillar width/tunnel diameter (PW/D); Pillar safety factor; Tension bolt; Strength reduction method(SRM);
Citations & Related Records
Times Cited By KSCI : 1  (Citation Analysis)
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