Experimental Analysis Of CFG Pile Composite Foundation Under Embankment Load

The technology of CFG pile composite foundation has such characterisitics of rapid-construction speed, short-period project, easy quality control and economically.The bearing behavior and deformation properties of flexible composite foundation has large difference between the case of rigid composite foundation; so under the great environment of current construction of passenger dedicated lines in the soft soil foundation treating in large-scale use of the technology of high-strength pile in China,the study on the bearing behavior and deformation properties of flexible composite foundation has important project value and theoretical significance.This paper mainly discusses the engineering characteristics of CFG pile composite foundation under embankment,the mian work and the main conclusions are as follows:Selecting a typical cross-section,burying various sensors on test field to test bearing behavior and deformation properties of flexible composite foundation,using the data to analysis the actual treatment of test field such as the deep lateral deformation,the settlement deformation,the Pile's strain distribution along the depth,the change law of pore water pressure during the period of construction,the pile-soil stress ratio and the mobilization factor of soil between piles and so on. Mainly in the following conclusions: (1)The change of excess pore water pressure is proportional to the construction speed of embankment filling, the construction speed is faster,then the excess pore water pressure is larger, otherwise smaller. (2) The growth rate of lateral deformation is proportional to the construction speed of embankment filling; In addition,we can use the curve's change tendency of lateral deformation to determine the influence depth of composite ground, use the curve's change linear of lateral deformation to evaluate the lateral stability of composite ground.(3) under the load of embankment,the maximum pile strain of reinforcement area generates approximately at the place from the pile top 1/3 of the pile length.(4)The settlement of composite foundation and the tension of geotechnical grille are proportional to the depth of soft foundation,the depth is deeper,the settlement and the tension are larger.(5)The change of earth pressure is closely related to the load fluctuation, the greater load,the greater value of earth pressure.Because of the construction quality of the pile of composite foundation on site is poor, the change law of pile-soil stress ratio following the load filling appeared abnormal situation.Using the equipment of Southwest Jiaotong University to do the geotechnical centrifugal model test of high strength pile composite foundation under the load of embankment,3 times the distance of pile diameter between piles (Ml) group and 5 times the distance of pile diameter between piles(M2) group were set, according to the test data, The bearing behavior and deformation properties of flexible composite foundation is analysed. Main conclusions are as follows: (l)The foundation deformation increases with the distance of piles,the pile distance affects markedly the lateral deformation of foundation. The reinforce areas of two models' foundation was not subjected to shearing failure.(2) The ground settlement of the center of embankment increases with the distance between piles. In addition,the settlement of M2 was not controlled in effect.(3)The growth rate of earth pressure does not increases with the loading rate ad infinitum,the earth pressure on the piles and the soil changes during the coordination and development.The composite foundation of Ml is in stable status, the composite foundation of M2 is at the limit state of destruction.(4)The reinforced band of model shows "M" distribution law along the transverse position of railway,this is related to the good results and the greater rigidity of high strength pile composite foundation.(5)The Pile's strain distribution along the depth of two models increases then decreases, the maximum is found in the place which distance is 21.5 mm from the pile top. Further, as the distance between the larger pile, pile strain also showed growth trend.Through comparativing analysis of the treatment effect of two models, we draw a conclusion: When the substratum of high-strength pile composite foundation is harder, 3 times the distance of pile diameter between piles shouled be set; in addition,if the distance between two piles is not only larger,but also the bearing capacity of composite foundation perform stably, adding cap on the pile top is a good choice.Finally,the current research achievements of the calculation analysis of composite foundation are summarized, the united method of Mindlin's solution and Bousinesq's solution is also discussed in brief,the basic thinking of calculation is then given. The united method features clear concept,the actual loading and the deformation features are fully considered; Although the calculation parameters are less, but the support of large number of tests and theory is still needed to reasonably determine them.