Research On Stability Of Diversion Tunnel Under Complex Geological And Dynamic Conditions In Yunnan

Total water resources in our country is not rare,but due to the large population base,per capita availability is very low,and the regional distribution of water resources is obviously unbalanced,specifically reflected in that southeast has much more water than northeast.With the improvement of the underground tunnel construction technology in our country,numerous inter-basin diversion project started to build,and it needs to build long tunnels because of the long distance.Due to the long distance,water diversion lines will cross different stratums like soft soil shallow buried segment?soft rock section and fault fracture zones,in which the complex geological environment can cause many problems.These problems can have extremely disadvantageous influence on the stability of the underground tunnel.So this article depends on the long distance water diversion tunnel project in kunming,using numerical analysis software FLAC3D,which is commonly used in geotechnical engineering,studying on the tunnel stability problems of the long distance water diversion tunnel in kunming under special geological conditions such as soft soil shallow buried segment?soft rock section and fault fracture zones.The main contents are as follows:(1)Constructing a three dimensional calculation model based on the imported soft soil shallow buried segment of the water diversion tunnel in Yunnan province(Kunming).Because the Duncan-chang model is unable to consider the inherent defect of principal stress,so after improving the Duncan-chang model in FLAC3D and validating its rationality and practicability,it is used to simulate the soil.By analyzing the effect of different excavation methods?small duct grouting reinforcement and different excavation footages on the stability of underground tunnels.It is concluded that for the shallow buried tunnel in soft soil in Kunming,it is better to choose the method of CRD excavation?using the small duct grouting reinforcement method in advance and take the excavation footage for 2 meters.Seismic load has extremely adverse effect on the stability of tunnel under earthquake condition,so more effective support measures should be taken to prevent tunnel from instability destruction.(2)Constructing a three dimensional calculation model based on the soft rock section of water diversion tunnel in Yunnan province(Kunming).Using FLC3D contact elements to build a contact face in the area between lining and surrounding rock and FLC3D seismal calculation module to load seismic wave.This chapter focuses on studying the difference between with and without the contact surface under dynamic loading,the difference between the dynamic response of the lining and surrounding rock with the contact face,and the influence of changing the interface cohesion and the peak of seismic wave on the dynamic response of the interface.The results show that after setting up the contact face,the interaction between the lining and surrounding rock becomes much stronger,coming up with the release slip phenomenon.The connection between the lining and surrounding rock is not as close as the rigid connection,which makes the dynamic response of lining structure reduced.Under earthquakes,the contact surface shows stress concentration and relative sliding phenomenon,which can Easily cause cavity local buckling problems,so anchor reinforcement measures should be taken to support.With the increase of contact surface cohesion,the relative sliding on contact surface decreases obviously,and with the increase of seismic wave peak,relative sliding on contact surface increases obviously.(3)The water diversion tunnel in Yunnan(Kunming)goes through the fault fracture zones,which lies in the earthquake areas.Establishing a three dimensional calculation model with fault fractures based on the section where tunnel surrounding rock is class ?,then using FLAC3D seismal calculation module and loading the seismic wave.This chapter focuses on sdutying the influences of fault fracture zone's position,thickness and strength on the stability of underground tunnels.The results show that the existence of fault fractures will weaken the stiffness and strength of the surrounding rock near them.These differences make the fault fracture zone show more intense shear effects under seismic load,which makes the seismic reflection more intense,leading to unstability at locations near the fault fractures.It shows that situations when fault fractures cross the tunnel is much more dangerous than situations when there are no fault fractures crossing the tunnel.Fault fracture zone's thickness and strength are important factors which influence the seismic stability of tunnels.When the fault fractures are thicker or weaker,the tunnels are more likely to be unstable.In this case,dealing the surrounding rock near the fault fractures with reinforcement measures like grouting and setting shock absorption layer and aseismatic joint is necessary.