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Geomechanics and Engineering
  Volume 15, Number 3, June30 2018 , pages 869-877

Stress interactions between two asymmetric noncircular tunnels
You-Sung La, Bumjoo Kim, Yeon-Soo Jang and Won-Hyuk Choi

    The continually growing demand for underground space in dense urban cities is also driving the demand for underground highways. Building the underground highway tunnel, however, can involve complex design and construction considerations, particularly when there exists divergence or convergence in the tunnel. In this study, interaction between two asymmetric noncircular tunnels-that is, a larger main tunnel and a smaller tunnel diverging from the main tunnel, was investigated by examining the distributions of the principal stresses and the strength/stress ratio for varying geometric conditions between the two tunnels depending on diverging conditions using both numerical analysis and scale model test. The results of numerical analysis indicated that for the 0o, 30o, 60o diverging directions, the major principal stress showed an initial gradual decrease and then a little steeper increase with the increased distance from the left main tunnel, except for 90o where a continuous drop occurred, whereas the minor principal stress exhibited an opposite trend with the major principal stresses. The strength/stress ratio showed generally a bell-shaped but little skewed to left distribution over the distance increased from the left larger tunnel, similarly to the variation of the minor principal stress. For the inter-tunnel distance less than 0.5D, the lowest strength/stress ratio values were shown to be below 1.0 for all diverging directions (0o, 30o, 60o and 90o). The failure patterns observed from the model test were found to be reasonably consistent with the results of numerical analysis.
Key Words
    underground highway; noncircular tunnel; principal stress; diverging condition; strength-stress ratio
You-Sung La, Bumjoo Kim, Yeon-Soo Jang and Won-Hyuk Choi: Department of Civil and Environmental Engineering, Dongguk University, 30, Pildong-ro 1-gil, Jung-gu, Seoul, Republic of Korea

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