Study On The Effect And Mechanical Mechanism Of Uplift Pile In Large Deep Foundation Pit

With the rapid development of underground space exploitation in recent years,the size and the number of deep excavation are increasing.Unloading from large-scale excavation will cause soil resilience,whereas overrun of the upheaval in the bottom will lead to instability or even destroy of the foundation pit,thus affecting the surrounding environment,endanger the normal operation and use of adjacent buildings and pipelines.Though,in actual engineering project,the usage of uplift pile is an effective method in inhibiting the upheaval in the foundation pit bottom.Therefore,the study of influence of uplift pile on the bottom and optimize the arrangement of the pile groups program could have important instruction on practical engineering.In this paper,using the finite difference program(FLAC3D),uplift pile effect on deep foundation in soft soil area and its mechanical mechanism have been systematically studied.First,the actual project case to verify the rationality of simulation method,model and parameter selection is carried out.Then they are used for the analysis of influence of single pile and further pile on the bottom rebound in deep excavation.There are the following:Through the establishment of single pile on anti-uplift model to simulate uplift resistance characteristics of single pile under different excavation stages.The results show that constraints of single pile exist only within a certain level range.At the same time,interaction mechanism between pile and soil around the pile is deeply studied,concluding that the position of the neutral point moves down as pile length increases,and with the same pile length,with the increase of the internal friction angle,the position of the neutral point shift upward.Neutral point depth ratio and pile length and internal friction angle can be related by power law.Soil elastic modulus change is not obvious influence the position of neutral point etc.Based on the single pile model simulation results,a three-dimensional model of pile group is expanded to simulate the effect of anti-uplift effect of pile group in the excavation.By changing the parameters of pile group(pile length,pile diameter and the pile spacing,etc.),comprehensive analysis of effect of pile groups in anti-uplift in the deep excavation and the pile-soil interaction mechanism in pile group are carried out.The results show that pile group can be effectively suppressed the bottom uplift,and improve the anti-uplift factor of deep excavation.As the pile spacing decreases,the pile length and pile diameter increases,the displacement restriction effect of pile group is enhanced.The pile group provide a great pullout resistance on the soil below the bottom and by sharing the force to each pile,an overall anti-bump effect is formed.Pile group would produce a soil compacting effect,increasing the shear strength of the surrounding soil,so the soil part of the upper portion of the critical stress point has a greater side friction on the pile groups,which produce more resilient on the shallow soil.From single model to pile group model,the uplift mechanism and optimization scheme of the uplift pile in deep excavation engineering are deeply analysed,which can provide a useful reference for the actual engineering.