Discussion On The Correlation Between The Permeability Of Surrounding Rock And The External Water Pressure Of Tunnel

In the 21st century , with the rapid development of economic construction and the implementation of the western development strategy ,watershed tunnel scheme is adopted in great quantities and towards deeper lying,extra-large direction in hydropower engineering, transportation engineering,inter-basin diversion project. Along with the increase of buried depth, the high external water pressure problem becomes more and more serious .The existence of high external water pressure often leads large-scale landslide, water gushing and lining fracture event. Once happen, it will influence the construction, damage machinery, increase the cost and even cause heavy casualties. Now the high external water pressure has become an important and unavoidable problem in the design and construction of the tunnel, and has evoked enormous attention.Based on the previous research, it is found that the permeability of surrounding rock largely influences the external water pressure of the tunnel. Until now the correlation studies between permeability of surrounding rock and the external water pressure of tunnel are mostly empirical, not comprehensive. So the topic"Discussion of the correlation between permeability of surrounding rock and the external water pressure of tunnel"is selected.Concentrated on the question of external water pressure , the basic influence mechanism and the theory of influencing degree about the permeability of surrounding rock to the external water pressure of non-pressure tunnel is systematically studied in this paper. Compared to the previous research achievement, the corresponding relationship between the permeability of surrounding rock and the external water pressure of non-pressure tunnel has been initial established. The main conclusions are as follows: (1) In the homogeneous rock , when the tunnel structure is determined and the total head is the same , the smaller the permeability coefficient, ,the smaller the external water pressure and its reduction coefficient.(2) In the homogeneous rock, when the tunnel structure and the permeability coefficient is determined, the smaller the total head, ,the smaller the external water pressure and its reduction coefficient.In the heterogeneous rock,(1)The rule in the homogeneous rock is suitable to the heterogeneous rock.(2)When the permeability coefficient changes regularly, the reduction coefficient of external water pressure is different to the coefficient in equivalent permeable rock .(3) When lenticle exists in the rock, as the head increases, the effect of different permeability of the lenticle to external water pressure is different.