| In recent years,with the continuous development of city construction,subway spring up in many big city.In the course of the construction,deep foundation pit engineering is the primary problem which engineers been facing with,especially for subway construction,in water-rich thick sandy stratum with high underground water level,brings many problems to design and construction.As everyone knows in order to meet people's travel convenient,the subway station often in the city center,which will be faced with dense surrounding buildings,and complicated underground municipal pipeline.The study shows that underground water is the main factor affecting the stability of foundation pit,improper handling may cause serious accidents,and foundation pit reinforcement as a measure to control groundwater has been successfully applied to the deep foundation pit engineering in various fields,however,relevant research for the thickness of reinforcement in the foundation pit is rare.And the code not made clear formula yet.This article will use the theory calculation and numerical simulation to put forward calculation formula for critical thickness of reinforcement,and optimize analysis the thickness of reinforcement in the yang hu yuan foundation pit reinforcement engineering.Based on foundation Pit Engineering of yang hu yuan Station on the Changsha Metro Line 3,this thesis employ theoretical calculation and numerical simulation to make research on groundwater seepage in water-rich thick sandy stratum in the building intensive area,to optimize the thickness of reinforcement body and to study the stability of foundation pit.Research contents and conclusions are as follows:(1)Describing the purpose of reinforcement in the foundation pit,commonly used methods and the reinforcement technology advantages and disadvantages,summarizing the achievements of predecessors in foundation pit reinforcement and critical thickness of foundation pit bottom,focusing on the analysis of taking reinforcement measures in water-rich thick sandy stratum and the significance of studying on the thickness of reinforcement.(2)Relying on foundation pit engineering of yang hu yuan Station on the Changsha Metro Line 3,to establish finite element simulation of dewatering and excavating in water-rich thick sandy stratum,and analysis in the process of dewatering,the effect of groundwater seepage on foundation pit.The results show that the effect of groundwater seepage can not be ignored.At the bottom of the retaining structure groundwater seepage,groundwater seepage effect reaches maximum point.The action of seepage increase effective stress in soil and compress aquifer,resulting in uneven settlement to surface soil.Taking reinforcement measures to cut off the hydraulic connection between the inside and outside of the foundation pit,to prevent seepage flow effect,is applicable to the water-rich thick sandy stratum in dense surrounding buildings.(3)In the foundation pit reinforcement project,considering the whole reinforcement scheme and the reinforcement range,reinforced the undisturbed soil has been transformed for the cement soil,and cement stabilized soil's shear-bearing capacity and capacity of resistance to gushing in foundation pit surge has been greatly improved.Considering strength of reinforcement body and using theoretical calculation method,the thickness of reinforcement body were analyzed and optimized.Considering shear-bearing capacity,the thickness of is only 32% of actual engineering.(4)Employing finite element analysis software to establish a theoretical model to calculate the thickness of reinforcement body,using phi/c(computation module)in the software to obtain under the critical thickness of reinforcement body's safety factor,and adopting anti uplift calculation methods to compare,the two safety factor are close,and both of them meet the safety requirements.With the thickness of reinforcement body,cohesive strength and internal friction angle increasing,safety factor increase. |
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