Analysis Of The Mechanical Effects Of Hydraulic Tunnel Plug Based On Coupled Fluid-solid Theorem

Although the amount of hydraulic tunnel plug works in general little, but as one of the the main control of the conditions, the demands of their schedule are more urgent. There is an extremely important meaning for the the construction of the latter part of the project whether completed the plug work smooth and timely. At present,《Specification for design of hydraulic tunnel》(SL279—2002)gives only general principles for the design of plug, however, there wasn't one certain principles for the construction projects,and in fact, they developed their own design principles and selected parameters for one project. As the plug is very important for the safe of the hydro project and the design principles is not quite rational and any other reasons, the length of some plugs is too large to wasting, not only make the already relatively short duration lasted more tension, but also increased the project cost unnecessarily. Therefore, there are some theoretical significance and practical value in engineering for establishing the optimization method of plug design of plug by the analysis of the mechanical effect of the plug comprehensively.In this paper, based on the general principles of design of the hydraulic tunnel plug at home and abroad, firstly, with the JingJia dam's hydro diversion tunnel project, simulated diversion tunnel's rock mass and plug's stress field and rock mass's three-dimensional seepage field by finite element method using ANSYS10.0 software, and researthed the force characteristics of the rock mass and the plug based on the coupling of the seepage field and stress field. Secondly, enduced the correction formula of design of plug to consider the rock's additional flexibility resistance by theoretical analysis. The main contents are as follows:1.) Based on analysis of the principles for some hydraulic tunnel's plugs, summarized the problems of the current design method of plug and the factors that affect the stability of the plug;2.) With the JingJia dam's hydro diversion tunnel project, established the three-dimensional elastic-plastic finite element model of the surrounding rock and pug of the diversion tunnel using ANSYS10.0 software, and researched the deformation and stability of the surrounding rock and the plug under the stress field;3.) With the JingJia dam's hydro diversion tunnel project, established the three-dimensional seepage field model of the the impact of regional of surrounding rock in the Diversion tunnel plug running period. Analysed the the surrounding rock deformation by the influence of the seepage field,and then established the coupled model of seepage field and stress field;4.) By researthed the force characteristics of the rock mass and the plug based on the coupling of the seepage field and stress field, enduced the correction formula of design of plug to consider the rock's additional flexibility resistance by elastic-plastic theoretical analysis.Through the above work, summarized the main conclusions and engineering experience are as follows:1.) In general, the plug was under pressure,and the tension and compression stresses are smaller and no more than the strength of plug concrete itself.;2.) Water pressure mainly beared by the friction on Contact surface of the plug and surrounding rock,and the friction gradually weakened from the upstream to downstream;3.) The tail of plug formated local plastic zone because of formed the invading surface as no water pressure inside the tunnel and the rock beared the elastic deformation of the plug itself;4.) Consider the beneficial effects by the additional elastic resistance of the surrounding rock, we can amend the plug's conventional design methods,and the optimization of the formula can improve the stability against sliding plug to a certain extent;5.) Improved the rock elastic modulus is conducive to the stability against sliding of the plug, therefore, tunnel excavation should not only consider the characteristics of plug size but also to take into account the stability of the plug, to avoid to block the tunnel in the complicated cross-section shape and geological conditions;6.) It can not improve the stability of the plug by improving the strength level of concrete of plug, and the plug itself was too safe, therefore, there was no practical effect by improving the plug concrete's strength grade for the safety of the plug;7.) To play the beneficial effects of the additional elastic resistance of the surrounding rock fully, the plug should be designed into the upstream section of large and small, wedge-shaped body of the downstream section, but the wedge angle of wedge-shaped body size should be appropriate, not the bigger the better.