Study On Soil Compacting Effect Of Open Pipe Pile

In this paper,through the model slot test,particle flow simulation,engineering case analysis and other methods,the relationship between the soil plug effect and the soil compacting effect of prefabricated pipe piles with the same diameter and different wall thickness is studied.The main research results are as follows:(1)The results show that when the outer diameter is 5cm and the wall thickness is 2mm,6mm,10mm and 14mm,the larger the wall thickness is,the more cumulative blows are needed to complete the pile sinking,and the higher the wall thickness is,the smaller the soil plug height will be,and the IFR value will decrease in a zigzag line during the pile sinking,The smaller the height of soil plug is,the smaller the IFR(the ratio of the increment of soil core length to the increment of pile sinking depth)is.The smaller the height of soil plug is,the greater the lateral earth pressure is.With the increase of the distance between measuring points,the value of lateral earth pressure decreases exponentially.The soil compacting effect of open-ended pipe pile driving will cause different degrees of uplift of adjacent piles and the generation of axial force of adjacent piles.The smaller the height of soil plug is,the higher the uplift of embedded piles is.The axial force of embedded piles increases with the decrease of the height of soil plug.The section position of the maximum axial force caused by the soil squeezing effect of driven piles is 0.45M deep,about 3/5 of the pile length Depth.(2)Based on the particle flow software PFC2D,the model test is simulated,and the results of the model test are verified mutually.The results show that the piles with the same diameter and smaller wall thickness need longer length and deeper penetration depth to achieve the complete closure effect.The lower the height of soil plug,the greater the pile driving resistance,and the faster the internal friction increases when the pile is nearly completely blocked.When the open-ended pipe pile is driven,due to the embedded pile on the right side,the pile plays a similar role as the retaining wall,and the particle displacement on the left and right sides of the pile is significantly different.The difference between the left and right sides is about 10%.The smaller the height of the soil plug,the more obvious the soil effect and compacting effect on both sides of the pipe pile,the greater the average lateral displacement of particles around the pile.The pile sinking of the pipe pile will cause displacement and rotation of the adjacent pile.The rotation angle is first clockwise and then anticlockwise,and the clockwise rotation angle is smaller than the anticlockwise rotation angle.The adjacent pile inclines towards the driven pile.The smaller the height of the pipe pile soil plug,the greater the rotation angle of the adjacent pile,and the more obvious the soil compacting effect.(3)Combined with a project in Yangzhou,the influence of pile driving and soil compacting effect on pile body is compared under the condition of direct driving and first driving and then driving.It is found that the soil compacting effect produced by pile driving can be effectively reduced by first driving before driving.Before pile driving,the hole should be introduced first,and the soil reduced due to the hole introduction provides a large gap for pile sinking.This is similar to the pile sinking of open-ended pipe pile with small wall thickness.Because of its small volume,the required clearance for pile sinking is relatively small,resulting in smaller soil compacting effect.It is the application of this principle to make the pile sinking more smoothly before driving.