The Long-term Strength And Analysis Of Stability Of Surrounding Rock Of Underground Tunnel

According to the fact that our country is widely covered by mountains and plateaus, tunnel engineering has always been an important part of infrastructure construction in our country. With the improvement of the economic level of our country, the state is actively building a variety of tunnel engineering, to ease the traffic pressure and meet the needs of energy, environmental protection and other aspects. Therefore, the stability of tunnel engineering is an important research topic.The stability of surrounding rock of underground tunnel relates to many factors, and the long-term strength of surrounding rock is one of the important factors. In this paper, we use the numerical analysis software FLAC3D to calculate the displacement, stress and plastic zone distribution of surrounding rock at different time points and different long-term strength from the aspect of time and micro crack damage, the main research results are as follows:(1) According to the Moore Kulun criteria, the relationship between the friction angle, cohesion andcompression, tensile strength of rock mass are derived, combined with function relation between creep strength of rock and time, the sequence of rock strength parameters in different time are calculated. The strength parameters of different time points in the numerical model are calculated in turn and the displacement, stress and plastic zone distribution of the tunnel surrounding rock are obtained respectively, the stability of tunnel surrounding rock is judged.(2) By analyzing the variation of crack volume during the development of micro cracks in rock, combined with the volume data at different stages of the development of micro cracks obtained from the uniaxial compression test,the relationship between the ratio of the crack volume to the total volume of rock and the damage variable D function of rock strength is established. According to the long-term strength of different stages in the development of micro cracks, the displacement, stress and plastic zone distribution of surrounding rock in tunnel are calculated and a judgment about the stability of tunnel surrounding rock is made.(3) According to a method for predicting failure time of tunnel surrounding rock based on MSDPu strength criterion and subcritical crack growth theory, the failure time of tunnel apex is calculated after completion of tunnel excavation when taking the long-term strength as crack initiation strength σci and crack damage strength σcd. A conclusion of the larger the long-term strength of rock mass, the more late the damage occurs is draw along with the smaller original crustal, the later to rupture.