Research On Deformation Characteristics Of Main Tower Rock Deep Foundation Pit Of Steel Truss Suspension Bridge In Jinsha River Canyon In Li Jiang-Shangri-La Railway

In recent years,with the expansion of the construction scale,the application scope of deep-rooted projects has also become more and more extensive,including not only middle and high-rise or super high-rise buildings,subways,but also mountain bridges and super bridges.The study on the stability of deep excavation of deep foundation in the construction of bridge is very important,especially the deep foundation pit excavated on the rock slope is directly related to the safety of the whole bridge.Therefore,how to analyze similar super-deep pits with pure rock and find out the deformation rules in the process of excavation and support becomes an important task at present.This paper takes the deep excavation of the main tower of the Jinsha River Bridge of Lixiang Railway as the research object,and studies the deformation characteristics of the excavation and supporting in the whole process of the excavation.The main research results are as follows:?1?The support system scheme for the deep foundation pit of the main tower of the Jinsha River Bridge and the on-site construction monitoring program are worked out,and the on-site monitoring work is completed.The monitoring results show that the deformation curve of the deep rock mass in the rock foundation pit is forward lean,the maximum displacement occurs at the top of the foundation pit;the surface settlement curve presents a flute shape,and the maximum settlement occurs at about 2m from the foundation pit,instead of the foundation pit.The smaller the distance from the foundation pit is,the smaller the settlement value is.The supporting structures such as anchor piles and steel supports have obvious limitations on the deformation of deep foundation pits.The deformation of deep foundation pits is very different from the lithology of the foundation pit where the foundation pit is located.The deformation of rock foundation pit is relatively small compared with the soil foundation pit of the same size.The measured value of the deformation of the foundation pit is far less than the warning value,indicating that the design of the envelope structure is conservative.?2?Numerical simulation of the whole process of deep foundation pit construction is carried out by using finite difference software FLAC^3D.The deformation law and the stress of deep foundation pit are obtained.The prestressed anchor cable is mainly subjected to tensile force,and the steel support is mainly subjected to pressure;the simulated deformation of the foundation pit deformation curve and the actual measured curve are basically the same,and the measured value is larger than the simulated value.?3?From the results of simulation calculation,it can be seen that the excavation of deep excavation has obvious spatial effect,the displacement of the side wall in the middle of the foundation pit is the largest,and the closer to the corner of the foundation pit,the smaller the horizontal displacement of the sidewall of the foundation pit;The axial force of the steel support depends on the position,and the closer the axial force is to the slope,the greater the axial force.The results show that three-dimensional numerical simulation is an effective method to analyze the spatial effect of deep foundation pits.Based on the previous researches of many scholars,this paper analyzes and summarizes the deformation laws of deep rock foundation pits,providing valuable experience for the design and construction of similar rock foundation pits in the future,and it is very.significant for the improvement of the entire deep foundation pit theory.