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Elastic Solution of Rock Stress and Displacement in a High-Pressure Hydraulic Tunnel Adjacent to a Karst Cavity
(1 Institute of Geotechnical Engineering, Huaqiao University, Xiamen 361021; 2 State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221008)
Abstract The stability of surrounding rocks in hydraulic tunnels under the effects of excavation and seepage is an important subject, for which the study on rock stress and displacement in high-pressure hydraulic tunnels adjacent to karst cavities is tough. In this paper, based on the elastic hypothetical theory, the karst cavity action coefficient and the complex potential theory are used to solve problems during excavation of the hydraulic tunnel adjacent to a karst cavity so that the analytical formula of rockmass stress and displacement is obtained. Each influential factor of water seepage out of the hydraulic tunnel is simplified to an axisymmetric case, and the effects of seepage fields are taken as a seepage body force acting on the stress fields. The plane strain theory is used to obtain a calculation formula to solve the water-filling problem during a normal operation period. Finally, an elastic solution is obtained by using the superposition principle. Based on the prerequisite of being in conformity with the Norway Criterion, the effects of the karst cavity action coefficient, rock-pore water pressure, and overburden are successively discussed by comparing the calculation results before and after water seeping out the tunnel. The analytical results show that the initial water filling plays a decisive role in rock stability; the increment of the karst cavity action coefficient and depth contributes to rock stability; under the influence of rock-pore water pressure, the circumferential stress field adjacent to the karst cavity presents a phenomenon of alternating higher values and lower values, which is not the case for the radial stress field; and the rock bias effect of the hydraulic tunnel adjacent to a karst cavity decreases with the increasing of the karst cavity action coefficient.
Abstract：
The stability of surrounding rocks in hydraulic tunnels under the effects of excavation and seepage is an important subject, for which the study on rock stress and displacement in high-pressure hydraulic tunnels adjacent to karst cavities is tough. In this paper, based on the elastic hypothetical theory, the karst cavity action coefficient and the complex potential theory are used to solve problems during excavation of the hydraulic tunnel adjacent to a karst cavity so that the analytical formula of rockmass stress and displacement is obtained. Each influential factor of water seepage out of the hydraulic tunnel is simplified to an axisymmetric case, and the effects of seepage fields are taken as a seepage body force acting on the stress fields. The plane strain theory is used to obtain a calculation formula to solve the water-filling problem during a normal operation period. Finally, an elastic solution is obtained by using the superposition principle. Based on the prerequisite of being in conformity with the Norway Criterion, the effects of the karst cavity action coefficient, rock-pore water pressure, and overburden are successively discussed by comparing the calculation results before and after water seeping out the tunnel. The analytical results show that the initial water filling plays a decisive role in rock stability; the increment of the karst cavity action coefficient and depth contributes to rock stability; under the influence of rock-pore water pressure, the circumferential stress field adjacent to the karst cavity presents a phenomenon of alternating higher values and lower values, which is not the case for the radial stress field; and the rock bias effect of the hydraulic tunnel adjacent to a karst cavity decreases with the increasing of the karst cavity action coefficient.
CAI Yan-Yan-1,
2 ,
ZHANG Jian-Zhi-1 etc
.Elastic Solution of Rock Stress and Displacement in a High-Pressure Hydraulic Tunnel Adjacent to a Karst Cavity[J] MODERN TUNNELLING TECHNOLOGY, 2015,V52(1): 45-54
2015, Vol. 52 