Simulation Analysis For Organization Scheme Of Kuncheng Tunnel Construction Crossing Groundwater Sensitive Area

Water diversion project of the central Yunnan province attach great importance solving the short of water resource and the crisis of water environment in city Kunming.The main construction of the whole project is outlet tunnel,for instance Kuncheng tunnel in the eastern Kunming basin with of 56.2km and N-S-striking direction.The southern end of Kencheng tunnel is through the Heilongtan and Bailongtan karst river systems that are both sensitive areas of groundwater in the Chenggong district,Kunming.Soluble rock is widely distributed in the area,and the elevation of the tunnel is lower than the underground water level,tunnel excavation will inevitably affect the groundwater dynamic conditions Hence,it is possible that tunnels will be flooded by groundwater.Even worse,it may result in the die out of Heilongtan and Bailongtan springs.Except the traditional geological prediction,strengthening construction methods and water plugging measures to reduce the effect of tunnel construction on the groundwater environment,as for Kuncheng tunnel’s 8#and 9#branch holes are located at two different hydrogeological units,in the meanwhile,the Heilongtan and Bailongtan springs belong to two individual karst systems,so the main purpose of this paper is to reduce the influence of tunnel construction on groundwater from the perspective of construction organization.Based on the results of field geological survey and relevant data,this paper analyzes the geological background of the research area,divides the hydrogeological structure of the research area in detail,combines its hydrogeological characteristics,takes uses of two branch holes to make the construction plan,It includes three kinds of construction orders.This paper discusses respectively from different time and space to reveal two sub-systems:Heilongtan and Bailongtan springs,the change of the groundwater flow system,through groudwater numerical simulation,the comparison and analysis to seek the best construction organization plan.The specific research contents and main achievements are shown as follows:（1）Diameter and discharge characteristics in the study area belongs to monophyletic and multiple exchange type.The recharge area is as same as the soluble rock development banding named Yiduoyun.It was separated by water barrier of Permian p₁d in the south of Daqingyan,then,two water system come into being,and finally the groundwater excretes to Heilongtan and Bailongtan springs.（2）The tunnel elevation is lower than the groundwater level and the elevation of the Heilongtan and Bailongtan springs,so the tunnel excavation will affect all the aquifers of the system.During the absence of any measures,the tunnel construction may cause the die out of Heilongtan and Bailongtan springs,which will have a certain effect on the groundwater environment.（3）When the 8^#hole is excavated to the 9^#branch,the Heilongtan subsystem is exposed first.The tunnel has the greatest influence on the water level of Heilongtan;and when the 9^#hole is excavated to the 8^#branch,the Bailongtan system is exposed first,and the tunnel has the greatest influence on the water level of the Bailongtan;and the influence of the tunnel to the water level of Heilongtan and Bailongtan springs is more balanced when the two holes are simultaneously excavated in opposite direction.Under three construction sequence,the influence range of the tunnel to the underground seepage field is gradually expanded.When the tunnel is excavated to the dark river pipeline in Heilongtan and Bailongtan springs,the water gushing amount increases abruptly.（4）Taking into account the size and area of water inrush,and the changes of water level in the Heilongtan and Bailongtan springs,and in order to protect the water source of the Heilongtan and Bailongtan springs and reduce the influence of tunnel on the groundwater environment,it is considered that the order of the two tunnels to be excavated at the same time is more reasonable.Under the construction order,the influence range of the tunnel to the underground seepage field is minimal,and the Heilongtan has the lowest water depth and the shortest construction period.（5）Compared with non-supporting excavation,the simultaneous supporting excavation of two holes can make the maximum depth of the Heilongtan and Bailongtan springs be small,and the water level of the Heilongtan and Bailongtan springs can recover gradually,and the influence area of the tunnel to the seepage field gradually decreases,and the maximum impact area is the same as the minimum impact area in the non-supporting open excavation.After comprehensive comparison,it is concluded that the simultaneous supporting excavation of two holes in opposite direction is the best construction organization plan.