Study On The Mechanical Characteristics Of CFG Pile Under The Action Of Base Rebound

With the rapid development of the construction industry,CFG piles have been widely used.Excavation of the foundation pit will cause the rebound of the soil at the bottom of the foundation pit.The rebound of the soil will cause upward pulling force on the pile body.When this pulling force reaches a certain level,the pile may be pulled off,which will affect the CFG loading.Normal use.In this paper,soil compression,rebound test,soil-concrete interface friction test and finite element simulation are used to systematically study the mechanical characteristics of CFG piles during excavation of foundation pits.The main research contents are as follows:(1)Using indoor compression and rebound test to study the law of springback in excavation of excavation.The test found that when the unloading amount is small,the springback amount is small;when the unloading amount reaches a certain level,the springback amount is only Significantly increased.And the recompression curve is close to a set of parallel lines.Before reaching the pre-consolidation pressure,the recompression curve is close to a straight line.This phenomenon becomes more and more obvious as the pre-pressure increases.After the recompression curve reaches the pre-consolidation pressure,the trend of the curve is consistent with the consolidation curve.Due to different pressures,the unloaded rebound pressure is inconsistent at a certain pressure.The specific performance is as follows: the greater the preliminary pressure,the smaller the rebound amount.This leads to the difference in displacement of the rebound of the foundation pit in different depths,which in turn causes the uneven stress of the pile foundation in the foundation pit and the upward tension of the pile foundation.(2)Set up concrete blocks with different roughness,and use the shearing instrument to complete the interface friction test between concrete and soil.It is concluded that the relative displacement of concrete,silty clay and silty clay reaches20-30 mm,the shear force reaches the maximum.(3)The finite element analysis software ABAQUS is used to simulate the influence of different soil conditions and different stress history on the springback ofthe foundation pit.Different cohesion and different internal friction angles will affect the springback of the foundation pit.The finite element analysis software ABAQUS was used to simulate the stress characteristics of the pile during the excavation of the foundation pit.The study found that the pulling force received by the pile body has a great relationship with the length of the pile.The soil around the foundation pit has an extruding effect on the bottom of the foundation pit,resulting in a further increase in the degree of tensile strength of the CFG pile.During the excavation process,the excavation progress can be effectively controlled,and the excavation sequence can be reasonably arranged to help reduce the pulling force on the pile.During the resilience of the foundation pit,the pulling force on the pile gradually increases with the excavation depth,and does not increase after reaching a certain depth.(4)For a specific building foundation pit project,calculate the springback of the foundation pit and compare it with the simulated value.It is found that the calculated value is larger than the simulated value,and the curve trend of the two is more consistent.Using low strain testing for CFG piles in the foundation pit found that the integrity of the pile body found that the piles arranged around the foundation pit had more broken piles,and the broken piles were concentrated between 3-4m from the pile head.This result is basically consistent with the finite element simulation results.