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Water Inflow Quantity Evaluation and Prediction for Cimushan Tunnel
Abstract
Tunnel excavation breaks the original hydrological dynamic balance, promotes water cycle and influences the mountain groundwater system to some extent. Water inflow during construction not only threatens construction safety, but also affects surface vegetation’s growth. Taking tunnel 1 in Chongqing Cimushan area as the project background, and through analyzing the hydrological test results from tunnel exploration stage, counting the actual water inflow quantity in construction period, doing the 3-D finite element numerical modeling, we analyzed and evaluated the tunnel water inflow quantity, to provide reference for recognizing the harm of groundwater and making treatment measures.
Using the geological survey data of Nanshan, combined with numerical simulation, this paper studied the regional seepage characteristics of tunnels under the condition of tunnel construction (considering and not considering the waterproofing measures) in the karst trough area, and forecasted the water inflow of proposed tunnel and compared with the calculated value of the existing water inflow. The reason of the gap is discussed. The results show that the calculated results of groundwater runoff modulus [unit water inflow 10.10 m³/(d·m)] are similar to those of atmospheric precipitation [11.11 m³/(d·m)], and is close to the numerical simulation results [11.50 m³/(d·m)]. Under the influence of tunnel excavation, the water discharge of Tongluoshan Tunnel decreased by 2.4%; the left hole of Nanshan Tunnel dropped by 6.9%; the right hole dropped by 4.7%. The left hole of Nanshan Tunnel is the most affected by proposed tunnel, right hole is the second, and Tongluoshan Tunnel is the smallest. When the proposed tunnel is constructed in time for waterproofing and second lining, the waterfall of the left hole of proposed tunnel is reduced by 66.3% and the right hole is reduced by 66.2%. Under the condition of multiple tunnels in the karst trough area, the excavation of proposed tunnel has little effect on water inflow and seepage characteristics of the existing tunnels in a certain range, and has less influence on the deep tunnel.
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