Research On Water Level For Prevention Of Up-foating Of Topical Stations In Metro Line One Of Changchun

Changchun is the capital city of Jilin Province, belongs to the high plain ofeastern Songliao plain. It is a north temperate continental semi-humid monsoonclimate zone. There is pore water in Quanternary unconsolidated deposits and porefissure water in clastic rocks. The two main groundwater dynamic types areinfiltration–runoff, evaporation, infiltration and runoff-runoff and evaporation. TheChangchun metro project shows us that the starting station is the North round-road ofRenmin Street and the line alongs the north to south Renmin Street, throughing theQingfeng Road, Yikuang street, North Renmin Square, and the South Square station,to the south across Beijin Street, Renmin Square, Jiefang Road, Freedom Road, SouthLaker Road, prosperity road, Weixing Square, South-round road, Centre businessstation and Southern Red tusi station. The landscape type is a wavy terraces of thealluvial flood plain in this project. The surface lithology is artificial stacked ofQuanternary, and its underlying lithology is silty clay of Pleistocene alluvium. Theproject area is located in Jilin and Heilongjiang fold system (gradeⅠ), the Songliaointerrupt trap (level II) Southeast Uplift (III level) with the eastern edge of raised nineChangchun, the southeastern part of the (IV class).According to the borehole data and geological and hydrogeological data, severalmethods are used in compute the water level for prevention of up-floating. In dynamicanalysis method, we can choose those methods which are ratio coefficient plot curvemethod and frequency analysis to analysis the relationship between rainfall andgroundwater dynamic, and then draw the year groundwater dynamic curve andinter-annual groundwater dynamic curve. Hydrogeological parameters were calculated by field pumping tests. Including water balance method, all above methodsare used in inquiring into the highest water level of groundwater as references todetermine the water level for prevention of up-floating.Basing on the above methodology and data, the numerical simulation ofgroundwater model was established for the forecasting of groundwater level by GMSsoftware. The numeric groundwater model is identified and validated firstly by usingthe dynamic data of groundwater level from November2010to November2011. Thegroundwater level is overall fitted well， showing the generalization of the structureand boundary of aquifers and the setting of hydro-geologic parameters are proper,which can truly reflect the characteristics of aquifers. The model can be used topredict the water level，such as The highest mixed water level in the region of twolayers of aquifers connected by the middle construction. It can be the reasonablereference of the anti-uplift fortified water lever. On all the methods, it comes toconclusion that the minimum water depth for prevention of up-floating is2.37m, andan average water depth is2.62m.With the typical station site conditions, the buoyancy analysis of Renmin Squarestation and the South Lake road station is carried out. Buoyancy of the South LakeRoad station is not necessary to reduction, because the station building’s excavationdepth have reached the confined aquifer. The piezometer tube head Hz in the stressanalysis figure is not the confined water level. It’s the mixed water level. Because inthe construction, the permeable bed is drilled to confined water, result phreatic aquiferwater and confined water mix together. The excavation depth of some station isreached to clay aquitard. According to analysis the impacted by basal water pressure,a reasonable reduction factor can carry out. Buoyancy calculation required to select adifferent reduction factor and methods according to different site conditions. One caseof South Lake road can explain the building basement without reduction in theconfined aquifer, but another case of the one with basement in the clay aquitard isconsidered the reduction. It is given a propery reduction coefficient. Only Changchunconditions can reduction factor in this study be directed. Using the numericalsimulation method to select the up-floating can be verified by the calculation result,both the security and stability in the building and economy and reasonability in this project can be ensured.