Mechanical response features and failure process ofsoft surrounding rock around deeply buried three-centered arch tunnel

ZHAO Yu(赵瑜)^{1, 2}, ZHANG Zhi-gang(张志刚)^{3, 4}

(1. Key Laboratory of New Technology for Construction of Cities in Mountain Area of
Ministry of Education (Chongqing University), Chongqing 400045, China;
2. School of Civil Engineering, Chongqing University, Chongqing 400045, China;
3. National Key Laboratory of Gas Disaster Detecting, Preventing and Emergency Controlling,
Chongqing 400037, China;
4. China Coal Technology Engineering Group Chongqing Research Institute, Chongqing 400037, China)

Abstract:Due to the extreme complexity of mechanical response of soft surrounding rock (SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties (PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model (PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load (HL) was in the range of 130 kN to 170 kN, the vertical load (VL) was in the range of 119 kN to 153.8 kN), rapid crack coalescence (the HL was in the range of 170 kN to 210 kN, the VL was in the range of 153.8 kN to 182.5 kN) and residual strength (the HL was greater than 210 kN, the VL was greater than 182.5 kN). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC^3D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Key words:deeply buried tunnel; physical model (PM); surrounding rock (SR); failure process