Deformation Characteristics And Prediction Of A Foundation Pit In Wuhan

Based on the foundation pit engineering of a subway station in Wuhan,this thesis analyzes the monitoring data of diaphragm wall horizontal displacement,surface vertical displacement,wall top horizontal displacement and support axial force deformation,and then establishes the three-dimensional section model of foundation pit by combining with the finite element software MIDAS/GTS to calculate the diaphragm wall horizontal displacement,surface vertical displacement and wall top horizontal displacement under different excavation depths,Compared with the field measurement results,the deformation law of deep foundation pit is summarized.At the same time,combined with the grey system theory,based on the grey correlation analysis,the GM(1,n)model is established for the horizontal displacement of diaphragm wall,and the correlation prediction is carried out under the influence of pile top settlement,column settlement,surface settlement and other factors,and compared with the prediction results without the influence of relevant factors,the accuracy is verified.Finally,the results of short-term forecast and long-term forecast are compared.The main contents of this thesis are as follows(1)Deformation characteristics of retaining structure: This thesis selects several monitoring sections,analyzes the monitoring data of diaphragm wall,and summarizes the deformation law of diaphragm wall.The results show that the deep horizontal displacement curve of diaphragm wall is "bow",and the maximum displacement position moves down about 2.5m for each excavation layer,and the maximum deformation position is between the excavation line of the fourth layer and the excavation line of the fifth layer.(2)Surface vertical displacement and deformation characteristics: the surface settlement curve is "groove type".With the increase of excavation depth,the accumulated amount of surface settlement increases gradually.The maximum value of surface settlement generally appears at the vertical distance of 7-8m from the edge of foundation pit.When the distance exceeds 10 m,it gradually decreases.On the whole,the settlement of the long side of the foundation pit is larger than that of the short side,and the settlement of the long side is larger in the middle,and gradually decreases from the middle to both sides.(3)Variation characteristics of internal support axial force: the support axial force increases rapidly in the initial stage of excavation,and the value of support axial force almost maintains a stable stage after the completion of earth excavation.The axial force of concrete excavation increases with the increase of excavation depth,and fluctuates slightly.When the steel support is prestressed,the upper axial force fails in a short time,and then returns to the original axial force and remains stable.The steel support also fails in a short time after the pre axial force is applied,and then recovers and increases gradually.(4)Grey prediction of lateral deformation of retaining structure: grey correlation analysis is used to calculate the grey correlation degree between horizontal displacement of diaphragm wall and six related factors.The results show that the higher the correlation coefficient is,the higher the accuracy of the model is.Finally,the horizontal displacement of diaphragm wall is predicted in the next 10 time points.The results show that the prediction time of the model should not exceed 5 time points.