| China is a country which has rich hydropower resources, with the developing strategy of the western part, and at present China is in high tide of hydropower constructions. To establish hydropower stations, much excavation on rock masses needed to be done, the influence of the seepage of underwater is necessarily concerned. Because of seepage, the shear strength decreased, and the specific gravity of rock mass is increased, and seepage load is produced, these all are bad to the stability of rock mass.Based on the stability of the large underground caverns of Shuangjiangkou hydropower station under excavation, first using regression approach of multi-element, the initial ground stress is inversed, and then according to the seepage condition and the calculation parameters, the stability of caverns without seepage, under natural seepage (without anti-seepage facilities) and the seepage control design (with anti-seepage facilities) is calculated systematically. The field of displacement,stress and plastic zone under the three conditions is compared, and suggestions and conclusions having guiding significance to engineering design and construction can be got. As follows:(1)Without seepage, after excavation, the displacement of surrounding rock mass faced to excavation surface. The displacement of boundary wall is larger, and horizontal deformation is primary, vault crown settled down, bottom plate springed back. Radial stress of surrounding rock mass released and tangential stress increased. As the distance to tunnel wall increasing, the effect of excavation to stress state of surrounding rock mass smaller. Different plastic zone appeared on vault of main power house,main-transformed cavern and tail-adjusted cavern, upstream and downstream of boundary wall, the cross position of main power house and bus tunnel, main-transformed cavern and bus tunnel, main power house and tailrace corridor, tail-adjusted cavern and bus tunnel.(2)Under natural seepage, the rule of the field of displacement,stress and plastic zone did not change. But, because of underwater, compared to without seepage condition, the displacement increased generally, the radial stress released more, the tangential stress increased more, the volume of the plastic zone increased largely.(3)Under seepage control design, the rule of the field of displacement,stress and plastic zone did not change too. But, because of the seepage control facilities such as anti-seepage curtain and drainage curtain, compared to natural seepage condition, the displacement decreased obviously, the radial stress increased; the tangential stress decreased, the volume of the plastic zone decreased.(4)Under seepage control condition, earthquake load using pseudo-static method is considerd. The calculation suggests that: the effect of earthquake load on the stability of caverns is not much.(5)Comparing natural seepage and seepage control conditions, conclusions can be got: under natural seepage, because of seepage load, the magnitude of displacement and the volume of plastic zone increased, the distribution of stress got worse, but under seepage control, the anti-seepage curtain and drainage curtain changed the seepage path of underground water and decreased seepage load, so the he magnitude of displacement and the volume of plastic zone decreased, the distribution of stress reformed, seepage control improved the stability of surrounding rock effectively.(6)The calculation reveals that: anti-seepage curtain and drainage curtain can low the level of underwater, prolong the seepage path of underground water, decrease seepage load and improve the stability of surrounding rock effectively, so the construction quality of seepage control facilities should be monitored and managed availably.(7)On the whole, the surrounding rock mass of underground caverns of Shuangjiangkou hydropower station under present excavation scheme and support form and seepage control design is safe and stable.
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