Squeezing Soil Effect Of Precast Pile And Analysis Of Time-space Effect On Adjacent Foundation Pit Excavation

In industrial and civil buildings,foundation pit is often excavated near precast piles that have been constructed.The construction of precast piles in soft soil area will produce strong squeezing soil effect,which will inevitably have some impact on the excavation of the adjacent foundation pit.In order to solve this problem,based on the theory of circular hole expansion with plane strain of infinite soil,this paper uses circular hole expansion method to further study the squeezing soil effect of precast piles in the construction process,and further analyses the time-space effect of the existence of squeezing soil on the foundation pit excavation.Firstly,the squeezing soil effect of single pile,multi piles and pile group is analyzed in soft soil area.The distribution law and influence range of soil displacement field,stress field and excess pore water pressure field under different pile driving sequence,pile layout shape and pile number,and the dissipation law of excess pore water pressure with time after pile driving are analyzed.The soil around pile is divided according to the disturbance degree.The results show that under different pile shapes and pile driving numbers the radial displacement of the soil around the pile is extruded outward and the vertical displacement is mainly uplifted upward in soft soil area.The displacement,stress and excess pore water pressure decrease rapidly with the increase of the radial distance,and the excess pore water pressure and stress increase linearly with the depth,while the vertical displacement decreases rapidly along depth.When the piles are driven sequentially,the sinking pile has obstructing and restraining effect on the squeezing soil effect of the post construction pile,which leads to the increase of vertical uplift of soil between piles.When the number of piles is less than 400 to 500,the excess pore water pressure and the influence range increase with the increase of the number of piles,and the influence range increases from 10 D of single pile to 128 D of pile group.Based on the analysis of squeezing soil effect of large area precast piles,the influence of squeezing soil effect on the time-space effect of adjacent foundation pit excavation in soft soil area is further analyzed.The distribution law of stress and deformation of foundation pit under the condition of considering or not considering squeezing soil effect is compared and analyzed.The influence of dissipation time of excess pore water pressure,number of piles,distance between foundation pit and pile group and excavation depth on the stress and deformation of foundation pit is analyzed.Taking the relative increase of stress and deformation of foundation pit supporting structure when considering squeezing soil effect as an index,the influence degree of squeezing soil effect on adjacent foundation pit excavation is quantitatively expressed.It is found that when considering squeezing soil effect,the distributing disciplinarian of the horizontal displacement and bending moment of supporting structure,ground settlement,pit bottom uplift are similar to those without considering soil squeezing soil effect,but the numerical value is obviously increases.The degree of influence of squeezing soil effect on adjacent foundation pit decreases with the end time of piling,the distance between foundation pit and pile group,and increases with the number of piles.Under the working condition of this paper,when the end time of pile driving is less than one month,the distance between foundation pit and pile group is less than 10 m or the number of piles is more than 300,the relative increase of stress and deformation of foundation pit supporting structure is more than 50%,which is greatly affected by squeezing soil effect.