Experimental Study On The Relationship Between Fine Sand Liquefaction And Construction Process Parameters Of CFG Pile

Liquefaction of saturated sand in the construction of long auger CFG pile composite foundation is a very serious engineering problem.The liquefaction of saturated sand will lead to the engineering environmental problems such as ground sand blasting,CFG pile top subsidence,perforation of CFG pile,so that the quality of CFG pile composite foundation cannot meet the design requirements,resulting in labor waste and economic loss to the project.In order to avoid the problem of saturated sand liquefaction during the construction of long auger CFG pile,it is of great significance to deeply study the relationship between the construction of long auger CFG pile and the liquefaction of saturated sand.Through the design of indoor using long auger CFG pile driver,the construction model test of long auger CFG pile in saturated sand was simulated in the laboratory,the influence of two construction parameters of pipe rotating speed and pile spacing on the liquefaction of saturated fine sand was studied,the causes of liquefaction of saturated fine sand by rotating speed and pile spacing are analyzed,the relationship model between construction parameters and liquefaction of saturated fine sand is established.The research conclusions are as follows:(1)The cyclic shear disturbance caused by the long auger pipe to saturated fine sand is the main reason for the liquefaction of saturated fine sand,pipe rotating speed and pile spacing are two important factors affecting the liquefaction of saturated fine sand.Under the condition of the same pile spacing,the degree of liquefaction of saturated fine sand increases with the increase of the pipe rotating speed.Under the condition of the same pipe rotating speed,the degree of liquefaction of saturated fine sand increases with the decrease of the pile spacing.(2)The increase of the pipe rotating speed and the decrease of the pile spacing lead to the larger fluctuation range of excess pore water pressure,the larger the peak value,and the smaller the valley value.The larger the peak value,the larger the degree of liquefaction of the saturated fine sand,the smaller the valley value,the larger the pumping action.(3)The fluctuation range of excess pore water pressure of saturated fine sand is larger than that of excess pore water pressure of saturated silty sand.The degree of liquefaction of saturated fine sand is heavier,the liquefaction of saturated fine sand is more obvious,the appearance of CFG pile in saturated fine sand is worse.(4)The degree of liquefaction of saturated sand becomes larger,the shape of saturated sand in the test process becoming worse,the phenomenon of water spillage will be aggravated,the concrete on the pile top will sag,the pile body will be connected through the holes.At the same time,the appearance of CFG pile will become worse after the test,the pile length will become shorter,and the pile diameter will be enlarged.(5)The ratio of pipe rotating speed to pile spacing has a functional relationship with the degree of liquefaction of saturated sand.With the increase of the ratio,the degree of liquefaction of saturated sand increases rapidly,while the ratio continues to increase,the degree of liquefaction of saturated sand increases slowly,when the ratio reaches a certain value,the degree of liquefaction of saturated sand remains unchanged.