Study On The Stress And Support Timing Of The Retaining Structure Of Soft Soil Foundation Pit At Dongle Road Station

The research on the deformation stress and supporting time of the retaining structure of soft soil foundation pit is a hot topic at present.The difficulty and key point of the research are to effectively control the deformation of the retaining structure and reduce the local stress concentration,which is closely related to the problem of the supporting time of the foundation pit.In this paper,based on the measured data of the retaining structure of the foundation pit of dongle Road Station of Metro Line 3 in Foshan soft soil area,the deformation law of the diaphragm wall and the influence of temperature on the supporting axial force during the whole excavation process of the foundation pit are discussed.With the help of the improved cubic spline difference method,the stress state of the retaining structure is analyzed,the modified earth pressure distribution mode is proposed,and the support of the foundation pit is optimized The scheme of protecting time can control the deformation and stress of the retaining structure.Firstly,based on the measured data of the ground connection wall of the foundation pit of Dongle Road,the overall deformation,local deformation and characteristic deformation of the ground connection wall during the entire excavation process of the foundation pit are analyzed,and the relationship between the maximum lateral displacement and the excavation depth is discussed.By analyzing the measured data of the support shaft force and its nearby temperature,the effect of temperature on the support shaft force of different materials,different depths,and different support types is discussed.A prediction method based on the temperature change near the support is proposed,and the temperature is eliminated.The influence of factors on the supporting axial force,the study found that the supporting axial force is positively correlated with the temperature near it.Dongle Road foundation pit temperature has a maximum value of 8.3%,which is less than the specification value of 10%.Secondly,with the help of the improved cubic spline interpolation back analysis method,the stress state of the retaining structure during the vertical excavation of the foundation pit was discussed,and the performance and safety margin of the ground connection wall and supporting system were evaluated.Combined with the measured data of the earth pressure in Guangdong and Shanghai,the earth pressure distribution model suitable for the foundation pit of Dongle Road Station was proposed and compared with two empirical earth pressure distribution diagrams.The revised earth pressure distribution model was found to be more accurate.It is recommended to adopt a modified earth pressure distribution model in the design of the foundation pit envelope structure in the soft soil area of Foshan.Finally,based on the deformation and stress state of the retaining structure of the foundation pit,combined with the modified earth pressure distribution mode,the scheme of the supporting time of the retaining structure of the foundation pit is optimized with the aid of the finite element software.The optimization of support time is mainly aimed at the optimization of support time and location.It is found that the exposure time of the excavation surface should not be longer than 7 days;the deformation of the diaphragm wall and the most unfavorable state of the stress or the position of the resultant force of the earth pressure can effectively restrain the deformation of the wall and adjust the stress state of the retaining structure.The modified earth pressure distribution mode and the optimization of support timing scheme can provide reference for the design of new foundation pit in Foshan area,and lay a certain foundation for the transformation mechanism of support structure force system.