Comparative Study On Deformation Characteristics Of Sand And Silt Around The Pile During The Jacked Pile Driving Based On PIV Technique

Based on the jacked pile model test and particle image velocity measurement(PIV)technique,a series of comparative model tests were conducted on the displacement field of the single pile driving in sand and silt with different water content.In the test process,high-speed industrial camera CCD(charge coupled device)and Davis 8.0 series of acquisition software were used to continuously take images on the test surface,then the post-processing software PIVview2 C was used to obtain the displacement field cloud image of the soil around the pile.The test results showed that:(1)In the process of the single pile driving in sand,the relationship between piling force(P)and depth of sinking(H)is divided into three stages.The change rates of pile pressure P and pile sinking depth H in different stages are different,and compared with the first two stages,the perturbation of soil in the third stage is the largest.With the pile end Pierce,the soil displacement fields around the pile are symmetrical oval ring distribution on both sides of the pile tip.The maximum horizontal and vertical displacement fields are about 6.3D and6.7D.(2)In the process of the single pile driving in unsaturated silt,the curves of relationship between piling force(P)and depth of sinking(H)and the characteristics of the displacement field during the pile driving influenced by the water content of the silt.The P-H curves and characteristics of the displacement field of the silts with different water content of 3.4% and17.3% are basically identical;similarly that of the silts with different water content of 7.4%,11.1% and 13.4% are basically identical also.In the first stage,under the same depth of sinking(H),the force(P)has a trend that of first increases and then decreases with the silt water content increasing,the force(P)of the pile is the largest when the silt water content of11.1%.The above phenomenon can be explained reasonably using the cohesive force of silt with different water content.The cohesive force of silt with different water content has a similar change trend.When water content is too high or too low,the effective surface tension decreases for shrinkage membrane of gas-water interface between the silt particles,and leading to the cohesive force decreased.Comprehensive analysis shows that the characteristics of displacement field determine the macro mechanical properties of soil around pile.The horizontal and vertical influence range of the displacement field is about the entire imaging surface.(3)Compare the process of the single pile driving in sand and silt.About the pile pressing force:The P-H curves of sand and silt with 7.4%,11.1% and 13.4% of water content are generally divided into three stages during the pile-driving processes,while the P-H curve divisions of silt with 3.4% and 17.3% water content are divided into two stages.As a whole,the pile pressing force of sand is higher than the silt.About the displacement field morphology:In the process of single pile driving in sand,firstly the elliptical rings are gradually formed at the short distance on both sides of the pile tip,and then gradually penetrate in the distance.Finally,the displacement field outside the two tips is an independent elliptical ring;In the process of single pile driving in silt,firstly an independent oval ring is formed directly below the pile tip.At the same time,two symmetrical elliptical rings are vertically formed on both sides of the pile ends.Finally,the lower end of the lower end of the pile-shaped elliptical ring is gradually moved down and merged with the elliptical rings on both sides into an independent ring.About the amount of displacement:With the penetration of the pile,the maximum displacement of soil around the pile is obviously larger than that of silt.Comprehensive analysis shows that the deformation field variation characteristics of the soil around the pile is a reflection of the macroscopic mechanical properties of the soil around the pile.The PIV deformation field test can help understanding the internal mechanism of the effect of squeezing soil due to the pile driving,and solving the problems related to geotechnical engineering.