Numerical Analysis Of Pile Anchors And Cantilever Piles Support In Foundation Pit Of Minglu Building

Based on a practical engineering,after consulting a large number of related literatures,collating engineering measured data and establishing a numerical analysis model,the stress and deformation characteristics of the pile-anchor and cantilever pile supporting structure are studied.Based on FLAC3 D software,the influence of relevant parameters,such as the embedded depth of pile,the free length of bolt,and the magnitude of prestress,on the stress of the pile anchor structure was investigated.According to the characteristics of deep-shallow pit in main-podium building,the depth-width ratio is introduced,the parameters of the pit toe coefficient and depth ratio are redefined.The excavation deformation of the deep-shallow pit in main-podium building is summarized.The main work and achievements are as follows:The working principle of prestressed pile anchored support system is summarized.Based on the monitoring data,the changes of building settlement,crown beam horizontal displacement,and axial force of anchor during excavation are analyzed.The results show: The maximum axial force of the prestressed anchor appears in the free section and is evenly distributed,and gradually decays to zero after entering the anchor section.The influence of excavation on the surrounding buildings is mainly related to the relative locations of the two and the structure of the building itself.The overall numerical model of the foundation pit was established and the stress characteristics of the prestressed pile-anchor retaining structure were discussed.The bending moment of the pile is in a "bow" shape distribution and decreases with the increase of the anchor prestress.The free length of the bolt should pass through the potential slip surface to reduce the loss of prestress.According to the results of analysis of shear stress and axial force of the anchorage section,the force at the end approaches zero,that is,there is a certain critical value for the anchoring length.For the deep-shallow pit in main-podium building,a targeted local numerical model is established.The two cases with different depths in the direction perpendicular to the pit wall or along the pit wall were studied.The concept of depth-width ratio was introduced to comprehensively consider the effect of shallow pit width and main foundation pit depth on the horizontal displacement of the support structure.When the depth-width ratio is less than 0.5,the shallow pit supporting structure can be designed in accordance with the current specifications and appropriate reinforcement measures can be taken.When the depth-width ratio is less than 0.3,the influence of the main building pit can be ignored.When the foundation pit has a depth difference along the direction of the pit wall,the maximum impact range of shallow pit on the main pit is about 10 m;the impact of the main pit to the shallow pit is mainly concentrated within the range of 2 times the depth difference.Affected by the deep difference between two sides of the deep-shallow pit,the horizontal displacement isoline of the surface shows an “S” distribution at the junction of deep and shallow pits,that is,there are two transitions in the affected area.