Research On The Tunnel Excavation Impact Assessment On The Adjacent Reservoir Of Water Diversion Project In Kun Ming

In recent years,with the rapid development of China’s social and economic, the tunnel project is widely used in the aspects such as highway,railway, mining, irrigation, municipal and national defense. Simultaneously,the tunnel andunderground engineering rapiddevelopment increased the geological environmental problems. During the present tunnel construction,karst subsidenceand suddenly gushing water, surface water loss are common geological disaster problems. The gushing water was caused by tunnel construction leads to falling water tables. If the groundwater have contact by the hydraulic gradient with surface water through some connectivity way, then groundwater levels drop due to the tunnel construction will affect the surface water environmental by dewatering the surface water.There are many surface reservoirs near the diversion of central Yunnan province(Kunming Section), the tunnel excavationis likely to affect them. The analysis revealed the main controlling factors affect to the reservoir caused by the tunnel are permeability coefficient K and the hydraulic gradient J.Permeability coefficient K is mainly determined by the geological structure of the body between the reservoir and the tunnel. Summarizing the communicationstructure between the reservoir and tunnel. Compilating field investigation and laboratory data, and combining with the geological background conditions,karst features and hydrogeological conditions of the study area. Then use the inductive structure model prediction and evaluate the tunnel excavation’s impact to Jin Dian reservoir, Dong Baisa river reservoir, Xi Baisa river reservoir impact. This study draws on the research results as follows: 1、 According to the geological conditions and hydrogeological conditions in the study areato judge if the tunnel located the same media with reservoirs, to know the relationship between their elevation and which hydrogeologic units the reservoir located. The Long Zhaba reservoir located in Long La River Reservoir-Ma La River hydrogeological unit, the Tuo Dan Reservoir located in the Qing Shui river hydrogeological unit, the Huang Po reservoir is located Tang Lang hydrogeological unit, the Hong Po reservoir located in the Long Qing river hydrogeological unit, the Xi Baisa river reservoir located in Xi Baisha river hydrogeological unit, the Jin Dian reservoir is located Jin Zhi river hydrogeological unit, Dong Baisa river reservoir, Ba Baoshanbai river reservoir is located Dong Baisa river hydrogeological unit, the Guo Lin reservoir located Wu Jiaying hydrogeologic unit. 2、 The main controlling factors affect to the reservoir caused by the tunnel are permeability coefficient K and the hydraulic gradient J. The size of the permeability coefficient between tunnel and reservoir depends on the geological structure and lithology. The size of the hydraulic gradient between tunnel and reservoir is mainly determined by the difference in elevation and horizontal distance. According to the lithology between the reservoir and tunnel divide them three types as karst karst, karst not developed karst and hard rock, soft rock and mudstone. In the homogeneous medium, it has the greatest impact when the connectivity media between the reservoir and tunnel is karst karst,and when it is the soft rock have the minimize impact. In the inhomogeneous media, reservoirs and tunnel constructed by water flowing fault zone have the greatest impact, followed by water conductivity syncline structure communicated. When there is relatively impermeable layers between the reservoir and the tunnel have no impact. 3、 According to the previous analysis of the structure between the reservoir and tunnel, and predicted the impact of tunnel on the Jin Dian reservoir, Dong Baisa river reservoir, Xi Baisa river reservoir. Jin Dian reservoir basin mostly in ?2d purple gray thin siltstone, shale, sandy shale formations, is relatively impermeable layer.The underlying karst formations ?1l. But there is a connectivity fault near the reservoir connect the reservoir and tunnel. The field investigation found that this area’s?1lkarst formations was cracked structure, karst medium,mainly are dissolve corrosion holes and fissures. But because the large hydraulic gradient between the reservoir and the tunnel, it is believe that the tunnel influence huge to the reservoir. Xi Baisa river reservoir and tunnel are located in J2 non-karst mudstone, and the tunnel will not affect the reservoir. Dong Baisa river reservoir and tunnel located Chiang Jiang Jiafen-Shi Toushan syncline fold wings, communicating via ?1l karst, karst medium, but due to the smaller hydraulic gradient between the reservoir and the tunnel, the tunnel have less impact on the reservoir. 4、 The mirage reservoir are calculated by using the modflow by the amount of leakage fault.