Open Access

ARTICLE

Laboratory Model Tests and DEM Simulations of Unloading- Induced Tunnel Failure Mechanism

Abierdi¹, Yuzhou Xiang², Haiyi Zhong², Xin Gu², Hanlong Liu^{2, 3}, Wengang Zhang^{2, 3, *}

1 School of Hehai, Chongqing Jiaotong University, Chongqing, 400074, China.
2 School of Civil Engineering, Chongqing University, Chongqing, 400045, China.
3 Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Chongqing, 400045, China.

* Corresponding Author: Wengang Zhang. Email: .

Computers, Materials & Continua 2020, 63(2), 825-844. https://doi.org/10.32604/cmc.2020.07946

Received 14 July 2019; Accepted 19 August 2019; Issue published 01 May 2020

Abstract

Tunnel excavation is a complicated loading-unloading-reloading process characterized by decreased radial stresses and increased axial stresses. An approach that considers only loading, is generally used in tunnel model testing. However, this approach is incapable of characterizing the unloading effects induced by excavation on surrounding rocks and hence presents radial and tangential stress paths during the failure process that are different from the actual stress state of tunnels. This paper carried out a comparative analysis using laboratory model testing and particle flow code (PFC^2D)-based numerical simulation, and shed light upon the crack propagation process and, microscopic stress and force chain variations during the loading-unloading process. The failure mode observed in the unloading model test is shear failure. The force chains are strongly correlated with the concrete fracture propagation. In addition, the change patterns of the radial and tangential stresses of surrounding rocks in the broken region, as well as the influence of the initial stress on failure loads are revealed. The surrounding soil of tunnel failure evolution as well as extent and shape of the damage zone during the excavation-induced unloading were also studied.

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