Behavior Of Hydraulic High Pressure Tunnels

With the increase of load of the Power Grid and the load difference between peak and valley load, the power system will be seriously lack of peaking capacity. To meet the peaking need of the Grid and improve the source structure of the system, it is necessary to construct the mass pumped storage power station. And more high pressure tunnels will be constructed. The change in stresses in the rock mass generated by the internal loading of a pressurized tunnel, has traditionally been estimated assuming that the rock mass is impermeable and that the internal pressure in the tunnel can be treated as a mechanical load applied to the walls of the opening. The deleterious effects of pressurized seepage, percolating through the natural discontinuities in the rock mass, have generally been ignored, resulting in tunnel alignments with inadequate lateral and vertical cover. Therefore, the study of the behavior of pressure tunnels should be based on the coupled seepage-stress model in order to guide the practice in reason.In this thesis, the rock mass is treated as a continuous porous elastic medium, on the basis of the seepage field of the rock mass, the pore-water-pressure distribution in the rock mass around the tunnels is evaluated. Then, the seepage-induced stresses in the rock mass is studied. Based on the analysis of stress field in the rock mass around the excavation, the stresses behavior of the pressure tunnel with the internal pressure is studied using the coupled seepage-stress model. On the basis of the stresses analysis, the existed design rules of pressure tunnels are discussed.First, The pore-water-pressure distribution in the rock mass around the pressure tunnel is evaluated using the image well method proposed by Harr(1962). The seepage-induced stresses in the rock mass is analyzed, and several conclusions are gained.Second, The influence of angle was analyzed in the stresses analysis in the rock mass around the excavation. The stress field around pressure tunnels using the coupled seepage-stress model to evaluate, and the stability of the slope with impermeable surface is analyzed. The result indicates that the seepage field, slope angel, and the boundary condition is influence the stress field. And several conclusions are gained from this analysis.Finally, Based on the stresses analysis of the rock mass, the existed design rules are discussed, and a new method to predict the safe location of the pressure tunnels is developed.