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Limit variation analysis of shallow rectangular tunnels collapsing with double-layer rock mass based on a three-dimensional failure mechanism

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Journal of Central South University 2019年第7期26卷 1794-1806页

作者： ZHAO Lian-heng HU Shi-hong YANG Xin-ping HUANG Fu ZUO Shi School of Civil Engineering Central South University Changsha 410075 China Key Laboratory of Heavy-Haul Railway Engineering Structure (Ministry of Education) Central South University Changsha 410075 China School of Civil Engineering and Architecture Changsha University of Science and Technology Changsha 410004 China

In the framework of upper bound theorem of limit analysis, the progressive collapse of shallow rectangular tunnels with double-layer rock mass has been theoretically analyzed based on the three-dimensional (3D) velocity discontinuity surfaces. According to the virtual work principle, the difference theorem and the variation method, the collapse surface of double-layer rock mass is determined based on the Hoek-Brown failure criterion. The formula can be degenerated to a single-layer rock collapsing problem when the rock mass is homogeneous. To estimate the validity of the result, the numerical simulation software PLAXIS 3D is used to simulate the collapse of shallow tunnels with double-layer rock mass, and the comparative analysis shows that numerical results are in good agreement with upper-bound solutions. According to the results of parametric analysis, the potential range of collapse of a double-layer rock mass above a shallow cavity decreases with a decrease in A1/A2,σci1/σci2 and σtm1/σtm2 and an increase in B1/B2,γ1/γ2. The range will decrease with a decrease in support pressure q and increase with a decrease in surface overload σs. Therefore, reinforced supporting is beneficial to improve the stability of the cavity during actual construction.

关键词： shallow tunnels three-dimensional collapse double-layer rock mass Hoek-Brown failure criterion variation analysis upper bound limit analysis

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The role of dilatancy in shallow overburden tunneling

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Underground Space 2019年第3期4卷 181-200页

作者： Muhammad Shehzad Khalid Mamoru Kikumoto Ying Cui Kiyoshi Kishid Department of Urban Management Kyoto UniversityNishikyo-KuKyoto 615-8540Japan Department of Civil Engineering Yokohama National UniversityYokohamaKanagawa 240-8501Japan

The mechanical behavior of sandy ground during shallow circular tunneling is explored for various overburden heights H(=0.5D,1.0D,1.5D and 2.0D;D is the diameter of the tunnel)and various dilatancy coefficients(w//=0,1/3,1/2,and 1;/and w are the internal friction angle and dilation angle,respectively)through finite difference *** ground is modeled as a linear elastic-perfectly plastic material that employs the Mohr-Coulomb yield criterion and obeys the non-associated flow *** ground reaction curve is applied in conjunction with the stress path as a conceptual tool for interpreting the mechanical response of the ground to *** is revealed that,at a certain relaxation value,a yield zone develops during tunneling and extends to the *** relaxation value increases with increases in the overburden and w//values for the cases of less shallow tunnels(i.e.,H=1.0D,1.5D and 2.0D),while for the shallowest case(H=0.5D),the extent of the yield zone to the ground surface is not sensitive to the w//*** shear strain due to tunneling also increases with an increase in the w//***,the w//value affects the radial displacement and the surface settlement due to *** magnitudes of the surface settlement and the radial displacement at the tunnel crown both decrease with an increase in the w//*** relative difference in the displacement at the tunnel crown between the upper bound and lower bound values,w//(at the last computed stage),increases with an increase in the overburden *** is recommended,therefore,that careful consideration be given to the dilatancy angle in the case of relatively less shallow tunnels.

关键词： shallow tunnels Dilatancy Overburden Ground reaction curve Stress path

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