Research On The Anti-heavy Stability Of The Foundation Pit Bottom Of Kunming City Of Charm

In recent years,the rise of high-rise buildings is accompanied by the problem of anti uplift stability of deep foundation pit bottom.Excessive upheaval at the bottom of the foundation pit will affect the internal force distribution of the supporting structure and the overall stability of the foundation pit,affecting the normal operation of the surrounding buildings and underground pipelines.Therefore,how to correctly and reasonably solve the problem of anti upheaval stability at the bottom of the pit in the foundation pit engineering has always been a concern of geotechnical engineers.It can be seen from previous scholars' research that when there are engineering piles at the bottom of the pit,it is bound to have a restraining effect on the uplift deformation of the pit bottom after the excavation of the deep foundation pit.Therefore,it has a certain engineering value to study how to control the uplift of the pit bottom by engineering piles.In the analysis method of anti heave stability of deep foundation pit bottom,this paper improves the limit equilibrium method of circular sliding mode,and discusses the contribution of soil physical and mechanical parameters and support structure parameters to the anti heave stability of foundation pit bottom by using the improved formula;combined with the actual project,ABAQUS numerical simulation is used to analyze the different pile length,pile spacing and pile length respectively Different response effects of diameter on anti heave of pit bottom.The main work and achievements of this paper are as follows:(1)This paper improves the limit equilibrium method based on circular sliding mode in the limit equilibrium analysis method of anti heave stability of deep foundation pit bottom.In this method,the influence of soil anisotropy and pile reinforcement in passive area is added,and the application range of the formula is improved.(2)Based on the improved stability analysis formula of anti heave at the bottom of the pit,the influence of soil gravity,internal friction angle of the soil,cohesion of the soil,the depth of the support structure into the soil,the height of the lowest internal support,the rigidity of the support structure and the overload outside the pit on the stability of anti heave at the bottom of the pit is discussed.The results show that the decrease of soil weight,the increase of cohesion,the increase of internal friction angle and the increase of anisotropy ratio will increase the safety factor of anti heave stability of the pit bottom,and the change of internal friction angle has the most obvious response to the anti heave stability of the pit bottom among the above parameters;secondly,the increase of the depth of the wall,the decrease of the height of the inner support of the lowest tunnel and the decrease of the ground overload All of them can increase the safety factor of anti heave stability of the pit bottom,and the change rate of the safety factor of the pit bottom stability caused by the change of the above parameters decreases in turn.(3)The results of ABAQUS numerical analysis show that the heave deformation of the pit bottom is affected by the length of the engineering pile.The influence depth range of the soil heave deformation near the edge of the foundation pit is shallow,and the influence depth range of the soil heave deformation near the corner and center of the foundation pit is deep.Near the edge of the foundation pit,the influence depth of soil uplift deformation is about 20~30m.Near the corner of the foundation pit,the influence depth of soil uplift deformation is about 30~40m.Near the center of the foundation pit,the influence depth of soil uplift deformation is relatively deep.The change trend of safety factor of anti uplift stability at the bottom of the pit is approximately nonlinear with the amount of uplift at the bottom of the pit.With the increase of pile length,the maximum amount of uplift at the bottom of the pit decreases,so the required safety factor of stability decreases,that is to say,when the pile length of the project increases,the stability can be achieved by providing a smaller safety factor;With the increase of the pile diameter,the axial force of the central pile body has hardly changed,the axial force of the angle pile body has increased by about 3%,the axial force of the short side pile body has hardly changed,and the axial force of the long side pile body has decreased by about 6%.It shows that when the diameter of the engineering pile changes in the range of 0.6~1.2m,the axial force exerted by the soil on the pile body is less affected by the change of the diameter of the engineering pile.The change trend of the safety factor of anti uplift stability at the bottom of the pit is approximately nonlinear with the amount of uplift at the bottom of the pit.With the increase of the diameter of the engineering pile,the maximum amount of uplift at the bottom of the pit decreases,and the required safety factor of stability decreases,that is to say,when the diameter of the engineering pile increases,the stability can be achieved by providing a smaller safety factor;With the increase of pile spacing,the maximum axial force of center pile has been increasing,but for angle pile and side pile,with the decrease of pile spacing,the change range of axial force of pile shaft is smaller.When the pile spacing is 6m,the axial force of angle pile and side pile is the smallest,and the pile spacing is better at this time.At this time,the pile spacing is more appropriate and can also better inhibit the deformation and uplift of soil.The change trend of the safety factor of anti uplift stability at the bottom of the pit is approximately nonlinear with the amount of uplift at the bottom of the pit.With the increase of the distance between piles,the maximum amount of uplift at the bottom of the pit increases,the required safety factor of stability increases,that is to say,when the distance between piles increases,a greater safety factor can be provided to achieve stability.