| With the rapid development of the city and subway construction,the urban underground space has been more and more developed and utilized,and the foundation pit engineering has emerged in the dense urban building areas.The impact of subway foundation pit excavation on the surrounding environment has become increasingly prominent.Subway foundation pit excavation and construction will inevitably encounter the pile foundation of adjacent buildings.In practical engineering,foundation pit excavation causes foundation and foundation deformation of adjacent buildings,and even leads to building cracking,tilt and other adverse consequences,such cases are not uncommon.As a form of deep foundation,pile foundation mainly depends on pile side resistance and pile tip resistance to transfer load to the soil around the pile and deep soil.The excavation of the foundation pit will inevitably cause the horizontal displacement and land subsidence of the soil outside the pit.The deformation of the soil in the pile body will have a certain impact on the pile side resistance and pile tip resistance,thus affecting the safety performance of the building pile foundation.Therefore,it is possible to analyze the main influence factors of foundation pit excavation on the deformation of pile foundation of adjacent buildings,and to predict the deformation of pile foundation of buildings according to certain engineering conditions,which is of great significance for the smooth construction of deep foundation pit engineering and prevention of building damage.How to predict and analyze the influence of deep foundation pit excavation on the pile foundation of adjacent buildings is one of the hot issues in the field of geotechnical engineering.1.The influence of pile foundation deformation of adjacent buildings during foundation pit excavation is analyzed by MIDAS.Taking the excavation depth of foundation pit,the distance between building pile foundation and foundation pit,the vertical load and stiffness of building pile top,the number and location of braces in foundation pit,the buried depth andstiffness of supporting piles as variables,the influence of these factors on the horizontal performance of pile foundation of adjacent buildings is studied.And the main influencing factors are analyzed.2.According to the conclusion of MIDAS model,the pile top displacement of building pile is taken as the result of six factors,such as excavation depth of foundation pit,stiffness and diameter of building pile,stiffness of supporting pile,number of internal bracing,vertical load of building pile top and so on.Several models are established by MIDAS software,and 270 sets of data of pile top displacement corresponding to six different factors are obtained.After normalizing the data,using the BP neural network of MATLAB neural network toolbox,using 6 variables as input layer and pile top displacement as output layer,240 groups of data are randomly selected to build neural network model,and then the neural network model is used to predict the pile top displacement of the remaining 30 groups of data.Through the comparison between the predicted value and the actual value,it is known that the trained neural network can well predict the pile top displacement of the construction pile,and its error is controlled within 7%,which can meet the requirements of the project.3.After analyzing the possible horizontal displacement of the pile foundation during the foundation pit excavation,this paper studies the influence of the horizontal deformation on the superstructure when the pile foundation of the main building of Guang Dong Science Center is in different positions by ANSYS.By applying the same deformation to the foundation in different positions,it is analyzed that the horizontal displacement of the pile foundation at the most corner of the building has the greatest impact on the superstructure,while the horizontal deformation of the pile foundation in the middle position has little effect on the superstructure. |
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