Monitoring Analysis Of Soil Pressure And Internal Force Of Building Envelope Of The Deep Foundation Pit In North Qingdao Railway Station

Due to the development of urbanization, traffic pressure in the city becomes biggerand bigger, so the metro constructions are inevitable. Because of the limit of urban land,many metro stations have to go through the complicated geological soil, which increasesthe investment and risk of the construction. To the open excavation station, although manyhidden danger can be found in time, but some geological factors cannot be found easily.We take North Qingdao railway station of Qingdao Metro for example, by the means ofmonitoring Analyses of soil pressure and internal force of building envelope of thefoundation pit’s complicated geological conditions. We can get some variationcharacteristics of soil pressure and internal force of building envelope in the the landfillarea. No matter for engineering practice or theory development, this research and analyseswill be so meaningful.The research of the text mainly focuses on two parts monitoring data analyses, one issoil pressure around the pit, the other is internal force of retaining piles. With the analysesof the soil pressure monitoring data of two pits in District A and C1. We get the variationrelationship between the soil pressure and time as well as the depth and the law betweensoil pressure and displacement. We calculate the coefficient of active soil pressure anddistribution characteristics by Rankin’s theory, and analyses the change law and trend ofsoil pressure going with the time. The analysis of internal force of retaining piles is basedon stress of the string wire gauges, bending moment and support axial stress.With the calculation we get the developing degree of the bearing capacity in thebuilding envelope.The main conclusion of the study is as follows:（1）Active soil pressure with foundation pit excavation decreases at first thenbecome stability. The change rule of coefficient of active soil pressure by Rankin’s theory is basically the same as the soil pressure. The range of coefficient of active soil pressure is0.02~0.94. The average range of ka in different soil layers is: construction waste:0.32~0.45; life rubbish:0.12~0.29; soft silty clay:0.31~0.47; silty clay:0.38~0.57.（2）The characteristic of coefficient of active soil pressure of pit in garbage soil area,soft soil area and rich in sand area is:①soil pressure with foundation pit excavationdecreases at first then increases with different range ability;②Coefficient of active soilpressure in different layer is not same, as well as with the change of time trend. The valueof Ka in the shallow layer is always little, the trend becomes little then big with the pitexcavation. In deep layer it is bigger. The value of ka increases with the increase of thedepth, always little than0.8;（3）Its value increases with depth in vertical direction of pit. Soil pressure in eachsoil layer is different from the one calculated by Rankin’s theory. Design must be doneunder vary soil layer to make good use of the capacity of the building envelope. The fittingcurve of soil pressure show, soil pressure in vertical direction between0m and7m of pitchange little. Under the depth of7m, soil pressure changes more. When pit excavatebetween5m to10m, soil pressure decreases fastest, the range is near to the50%of the totalreduction. In vertical direction, displacement of building envelope has much fluence onsoil pressure with the increasing in depth.（4）The result of monitoring indicate, internal force of retaining piles increase withpit excavation, stress of the string wire gauges on both sides of the pile has a symmetricgrowth, stress suddenly increase when approach to the pit bottom, become steady aftercasting foundation pit bottom. During the process of excavation, the ratio of the maximumhorizontal displacement actually occurred and the biggest controlled displacement is68.4%. The playing degrees of bearing capacity of both the soil meeting surface andexcavation surface are about30%to40%. The ratio of support axial stress and maximumdesign value is53%, the bearing capacity of building envelope play small degrees.