Study On Hydro-geological Characteristics Of Longquanshan Tunnel On Chengdu Metro Line Eigtheen

Based on the Longquanshan Tunnel Project of Chengdu Metro Line 18,in this paper,the engineering geological conditions of the study area are analyzed firstly,such as topography and geomorphology,meteorological characteristics,geological structure and stratigraphic lithology.It is regarded as the material foundation to control the spatial distribution and strength characteristics of groundwater seepage field system.Based on the occurrence,migration and dynamic characteristics of groundwater in the site,the regional hydrogeological conditions are analyzed.Based on the hydrochemical analysis of underground water samples collected from shallow holes and deep holes in tunnel,the types of water quality and the erosive ability of groundwater are clarified by the results of the analysis.According to the characterizing effect of chemical composition on geological environment characteristics,the changes of Ca²⁺/Mg²⁺ratio and HCO₃^-/SO₄^2-ratio are compared and analyzed,which further explains the hydrogeological conditions in the study area and provides a comprehensive basis for the division of hydrogeological units.Based on the hydrogeological conditions,the regional hydrogeological units are divided into six parts according to the geological structural characteristics of the study area.In combination with hydrogeological test,the relationship between the permeability characteristics of rock mass and the buried depth is discussed and analyzed.It is concluded that the permeability coefficient of rock mass in Longquanshan tunnel site presents a negative exponential decline with the deepening of the buried depth.The hydrogeological conceptual model of Longquanshan is established.Through the theoretical analysis of the similarity between the seepage field and the heat conduction temperature field,the numerical simulation is carried out by using the thermal analysis module of ANSYS software,and the water inflow of each unit of the tunnel is calculated respectively.Furthermore,the overall water inflow of the tunnel is obtained synthetically.According to the hydrogeological characteristics of the Longquanshan area,the conventional methods,such as atmospheric precipitation infiltration coefficient method and groundwater dynamics method,are used to predict and analyze the water inflow of each hydrogeological units in the tunnel area,and through comparison with ANSYS numerical simulation,the characteristics of water inflow in Longquanshan Tunnel of Chengdu Metro Line 18 are comprehensively evaluated.