Study On The Influence Of Transverse Bracing System On The Deformation Of Enclosure Structure Of Foshan Daliang Foundation Pit

With the development of rail transit in China,the foundation pit engineering of metro station is increasing.At the same time,the station foundation pit is generally located in downtown area,and the surrounding environment is complex.Therefore,higher requirements are put forward for the foundation pit construction.It is particularly important to control the stress and deformation of the supporting structure during the excavation of the subway station foundation pit.Based on the foundation pit engineering of Daliang Station in Foshan of Guangdong Province,the stress and deformation of the supporting structure during the excavation of the foundation pit are studied.According to the field construction monitoring data,the deformation law of the retaining structure during the excavation of foundation pit is analyzed.Field tests were carried out to study the effect of ambient temperature on the internal support axial force.Finally,the finite element analysis software is used to simulate the excavation process of the foundation pit of Daliang Station,to study the stress and deformation of the supporting structure of the foundation pit excavation,and to analyze the influence of different supporting conditions on the deformation of the retaining structure.The main work and conclusions are as follows:(1)Based on the analysis of construction monitoring data,it is concluded that the wall deformation mainly occurs within the range of twice the depth of excavated soil.The maximum lateral displacement of underground diaphragm wall mainly concentrates near the excavation face and the maximum lateral displacement of underground diaphragm wall is0.02%~0.3% H(H is the excavation depth).All-concrete bracing system is more advantageous to control the horizontal deformation of enclosure structure.The overall deformation of the wall is negatively correlated with the cumulative value of the supporting axial force of the same section.The larger deformation of the wall,the smaller of the supporting axial force of the same section.(2)Through the analysis of the influence of temperature change on the supporting axial force,the concept of temperature coefficient of supporting axial force is put forward.Based on the measured data,the temperature coefficient of supporting axial force in the foundation pit of Daliang Station is obtained.The temperature effect of monitoring value of supporting axial force is corrected and the temperature effect value of supporting axial forceis predicted according to the change of ambient temperature.(3)The original foundation pit model is established by using numerical simulation software,and the reliability of numerical calculation results is verified by comparing with the measured data.The relationship between the internal force of support and the difference of water and soil pressure on both sides of diaphragm wall during excavation of foundation pit is studied.The results show that the internal support is the main stress component in the supporting structure,and at the end of excavation,the support bears 70% of the difference of water and soil pressure between the two sides of the diaphragm wall.(4)By studying the influence of different supporting conditions on the deformation of enclosure structure,it is found that: When adjusting the support to reduce the deformation of the retaining structure,priority should be given to shortening the spacing of the support layer near the bottom of the foundation pit and increasing the support erection density.In order to reduce the deformation of enclosure structure by adjusting the type of bracing material or increasing the prestressing force of steel bracing,it is considered that increasing the prestressing force of steel bracing should be given priority in the area where the seasonal temperature varies greatly.