In between the many factors, which will influence the distribution character of initial stress, the slope angle of the mountain is important one. Therefore, stress distribution in mountains under different slope angles with considering different lateral coefficients of initial stress is studied using numerical method. The results show that the actual initial vertical stresses are usually 2–5 times of the gravitational stresses for some zones. The next part of this paper shows the remarkably different plastic zones distributions after excavating a cavern under different slope angles. Ultimately, a suggestive advice to determine the fitting areas of the in-situ stress is proposed.

1.1 Generally situation

Quite a number of hydropower stations will be built in southwest China in the few years, most of which poses underground powerhouse. These plants are generally located in high canyon regions. In the current engineering, the depth of the direct overburden rock is defined as the basis of calculating the vertical initial stress generally. However, according to some analysis, thus definition for the vertical component of the initial stress may cause a considerable error. The purpose of this article is to study the problem by comparing the two basic conditions: Firstly, assuming that the project is located under a slope with a angle; Secondly, it is under a flat surface of ground. The latter part of this paper, the rock stability will be studied when a cavern is excavated in the above models.

1.2 Influence of slope angle to initial stress distribution

At the design stage of hydropower project stress measurements are conducted, then the numerical method to fit out the initial stress field in the project areas will to do. But under normal circumstances the measured data are very limited, which poses discrete charater generally.

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