Primary Study On The Influence Factors On Underground Rock Cavern Under Earthquake

The response and safety of rock cavern (tunnel) under earthquake are the difficulties and hot pots for construction of hydraulic engineering in the intensive earthquake area of West China. In the present paper, the influences of overburden and cavern sectional shape as well as in-situ stress condition on the characteristics of rock cavern under earthquake are analyzed by using FLAC 3 D. It is reported that the cavern response (displacement and stress) will decrease with the increasing overburden. Whenλ≥1(especiallyλ>2), there is probably a critical depth (300m), when the overburden is less than the critical value, the responses of rock cavern under earthquake are changed significantly with overburden, while when the overburden is large than the critical value, the responses of rock cavern under earthquake are changed slightly with overburden, in addition, the critical depth tend to decrease with the increasingλ(side pressure coefficient). It is also suggested the response of circular shape cavern is less than that of triangular and hoof shape cavern under the same loading condition. As well, the cavern response will decreases with the increasingλ(side pressure coefficient), and the decreasing rates tend to decrease with the increasing overburden. It is further revealed that the cavern response and the decreasing rate with increasingλat the condition ofλ<1 are significant larger than that ofλ>1.The influences of earthquake amplitudes, frequency and duration time on the different rock caverns displacement are primarily studied by using FLAC 3 D in the present paper. It is reported that the displacements of rock cavern clearly increase with the increasing earthquake amplitudes and duration time as well as the decreasing frequency. The changing rates of displacements with the above earthquake parameters decrease with the increasing overburden and in-situ side pressure coefficient (λ). It is also indicated that under shallow overburden, the threshold earthquake intensity (0.13m/s, equal to the VII earthquake intensity) is probably existed. When the earthquake intensity reaches up to the threshold value, the cavern displacements significantly increase with the increasing earthquake amplitudes. In addition, it is revealed that the low frequency properties of earthquake have clearly influence on the cavern displacement, the cavern displacement under earthquake with low frequency is clearly larger than that of earthquake with high frequency.It is reported that the cavern displacement will decrease then increase with the increasing incidence angle(different incidence propagation from horizontal propagation to vertical propagation), and the influences of cavern incidence angle tend to decrease with the increasing depths and in-situ stress side pressure coefficient.The influence of spatial inhomogeneous on the displacement characteristics of underground rock cavern...