| Foundation pit engineering is a system engineering integrating geological engineering,geotechnical engineering,structural engineering and geotechnical testing technology.In the process of deep foundation pit excavation,the design and construction of foundation pit supporting structure is of great significance to ensure the safety of underground structure construction and surrounding environment of foundation pit.However,in conventional design,the supporting structure of the foundation pit is usually calculated under the action of Rankine active earth pressure,which is often different from the actual situation.At the same time,when the elastic foundation beam method is used to analyze the deformation of foundation pit supporting structure,it is a common method to calculate the horizontal resistance coefficient of soil by m method.However,the value of the proportional constant m of the horizontal resistance coefficient of the soil is very random,which has a great influence on the calculation results.In order to improve the above two shortcomings,this paper studies the design method of foundation pit support considering the initial stress state and m-method optimization parameters.This paper takes the foundation pit engineering of the entrance and exit of Beidajie station of Taiyuan Metro Line 2 as the engineering background.Firstly,in order to study the relationship between the deformation of the supporting structure and the earth pressure in the process of foundation pit excavation,the design method of foundation pit support starting from the initial static earth pressure and considering the excavation process is proposed.Using this method,with the aid of finite element software(implemented by ANSYS software programming),the excavation process analysis and calculation of the foundation pit support structure of the 1st entrance and the 3rd entrance are carried out.The change of horizontal displacement of supporting structure from initial static earth pressure is obtained,and compared with the calculated value of horizontal displacement under the action of traditional Rankine active earth pressure(obtained using Lizheng deep foundation pit software)and on-site monitoring value,the analysis result proves the correctness and rationality of the method.The horizontal resistance coefficient of the soil in this analysis adopts the constant K method.Then select the No.2 entrance and exit foundation pit,the equivalent m value of the scale constant of the horizontal resistance coefficient of the multi-layer soil in the foundation pit engineering under the typical geological conditions is obtained by back analysis according to the horizontal displacement monitoring value of the supporting structure in the excavation process of the foundation pit,The m value is applied to the previous design method of foundation pit support starting from the initial static earth pressure and considering the excavation process.The change of horizontal displacement of foundation pit support structure at No.1 entrance is calculated again,and the calculation results are compared with the field monitoring values.The analysis results show that the accuracy of calculation can be further improved by applying and optimizing the parameter m.The specific conclusions are as follows:(1)Considering the initial stress state and excavation process,the maximum horizontal displacement of the support structure calculated is close to the actual monitoring value,while the maximum horizontal displacement obtained under the action of Rankine active earth pressure is quite different from the monitoring value,which indicates that the numerical simulation analysis method in this paper is reasonable and reliable.(2)During the excavation of the foundation pit,the displacement of the supporting structure gradually increases,and the earth pressure it bears gradually develops from the initial static earth pressure to the active earth pressure.(3)When the equivalent m value is 1.2MN/m~4,the horizontal displacement of the supporting structure is closer to the field monitoring value,which is more suitable for the deep foundation pit soil under the typical geological conditions of Taiyuan.The equivalent m value obtained by the displacement back analysis method can well reflect the stress and deformation of the supporting structure in the excavation process of Taiyuan foundation pit.(4)Compared with the horizontal displacement of foundation pit support structure obtained by K method,the horizontal displacement of foundation pit support structure obtained by m method is closer to the actual field monitoring value. |
PDF Full Text Request