Comparative Study On Anti-frost Heave Performance Of Pile-supported Foundation Pits In Winter

With the increase of underground engineering scale and engineering cycle,the occurrence of overwintering foundation pit is more and more frequent,especially the deep foundation pit in the northern seasonal permafrost region will inevitably encounter the overwintering problem,and the anti-frost heave performance of overwintering foundation pit needs to be further studied and solved.Based on the theoretical analysis and numerical simulation analysis,the combination of different pile types(cantilever pile,pile anchor),the support,double row piles supporting of foundation pit,the comparative study on the negative temperature freezing condition and under the condition of normal temperature difference of stress and deformation of foundation pit,and the way the different types of pile supporting in antifreeze bilge the similarities and differences in terms of performance.The main research contents and conclusions are as follows:Firstly,the research status of soil mass frost heave and pile row foundation pit support at home and abroad is summarized and analyzed,and the soil mass frost heave mechanism and horizontal frost heave force are analyzed theoretically,and the basic principle of FLAC3 D finite difference software for foundation pit overwintering simulation analysis is introduced in detail.The simulation analysis results of cantilever pile support form show that: the frost heaving effect of soil has a very significant impact on the stress and deformation of foundation pit;with the increase of pile diameter,the peak value of horizontal displacement of cantilever pile decreases,but the frost heaving force of pile side increases rapidly;the change of pile insertion ratio has little impact on the horizontal displacement and frost heaving force of pile side.The simulation analysis results of pile anchor support show that compared with cantilever pile support,under the same geological and surrounding conditions,pile anchor support has stronger control ability of horizontal displacement of pile body,but the frost heaving force of pile side is relatively large;the control effect of anchor layer,anchor prestress and anchor length on horizontal displacement and frost heaving force of pile body is very significant,pile anchor support form has great influence on pile position.The displacement on the side of the pile can be controlled very well,so it is a better choice for overwintering foundation pit support.The simulation analysis results show that: compared with other types of foundation pit support,the peak value of the smallest and the deformation control effect is the best among the four types of support,but excessive deformation control also leads to very large frost heaving force of soil beside the pile.The simulation analysis results of double row pile support show that: in the negative temperature freezing state,the front row pile and the back row pile have basically the same change law in the peak horizontal displacement,frost heaving force and other aspects,the row spacing of double row piles has a greater impact on the internal force and deformation of row piles,and the influence of coupling beam section size is very small;compared with cantilever piles,double row piles have better effect in controlling frost heaving horizontal displacement,and the pile side displacement is smaller The horizontal frost heaving force increases little.The simulation results of anti frost heave measures show that adding unloading hole and insulation layer can effectively reduce the horizontal displacement of supporting pile and frost heave force of soil beside piles.