Tunnel excavation has significant disturbance on groundwater system and related geo-environment, especially in karst regions like southwestern China. The present research was conducted to quantitatively understand the negative impacts posed by tunnel construction on the karst groundwater system and reveal the behavior of karst groundwater system under the tunnel disturbance, with the aid of field survey, hydrogeological analysis, and numerical simulation. The results suggested that negative impacts such as loss of surface and underground water, ground collapse, and house deformation would be posed directly and indirectly to the karst groundwater system and its dependent geo-environment as the result of groundwater level drawdown by tunnel excavation. The degree and range of groundwater drainage impact were determined by the lithological and hydrogeological characteristics of strata. These negative impacts were dominantly distributed in the karst depressions valleys, and the direct ones occurred at first and followed by the indirect ones. Simulation results showed groundwater level drawdown would not occur synchronously in spatial, but always occurred around the tunnel axis at first and gradually expanded towards far away over time. The maximum disturbance on groundwater system can reach to approximately 25 m vertically and 3000 m horizontally for present modeling tunnel. With the aid of numeral simulation, three response stages were identified for the karst groundwater system behavior to the tunnel disturbance. The impacts of tunnel practice on groundwater and surface water bodies can be gradually eliminated since the second stage, but would continue if existing failure of tunnel waterproof until a new balance state achieved. The present research can improve the understanding of the impacts of tunnel excavation on karst groundwater system and dependent geo-environment, and provide reference to the protection of water resources and geo-environment in karst regions like Chongqing worldwide.
Limited by geological survey methods, processes, and cost, it has long been a difficult thing to accurately detect the position of landslide slip surface and monitor the landslide internal deformation. Fiber Bragg grating (FBG) sensing technology has been widely used in geological engineering and geotechnical engineering due to its high-precision property. In this research, FBG sensing technology was applied to the monitoring of landslide internal deformation in Toudu, Chongqing, China. The in situ monitoring by FBG accurately determined the position of the landslide slip surface. Based on the relationship between fiber grating strain and deflection, the formula between landslide internal deformation and fiber grating strain was obtained, and the rationality of the formula was verified by the monitoring data of surface displacement. Finally, the internal deformation at the monitoring point of the Toudu landslide was calculated and the mechanism of the landslide was analyzed.
When every parameter is properly scaled down in accordance with some similarity coefficients, it is possible to study the physical-mechanical properties of rock mass with a scale model. To identify the key mechanisms of soft rock in deep buried tunnels, the proper sand, binder and ratio were selected. During the process, the model manufacture technology was introduced and typical tests were done and the results were presented. The physical and mechanical properties effects caused by each composition were discussed. It is shown that the physical and mechanical properties of chosen ratio material such as uniaxial compressive strength tests, elasticity modulus, tensile strength, internal frictional angle, and Poisson's ratio meet with similarity relationship well. The physical and mechanical properties of deep soft rock are simulated successfully.
Combining the field monitoring results of a deep-buried tunnel in Chongqing, the dynamic characteristics of the surrounding rock system under high in situ stress was analyzed by phase space reconstruction, calculating correlation dimension, Kolmogorov entropy and largest Lyapunov exponents. Both the Kolmogorov entropy and largest Lyapunov exponents show that the surrounding rock system is a chaotic one. Based on this, a local model was applied to predict surrounding rock displacement, and a nonlinear dynamic model was derived to forecast the interaction of the surrounding rock and support structure. The local method was found to have an extremely small total error. Also, the nonlinear dynamic model forecasting curves agree with the monitoring ones very well. It is proved that the nonlinear dynamic characteristic study is very important in analyzing rock stability and predicting the evolution of rock systems.
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