The Dynamic Characteristics Of CFG Pile Composite Foundation Research Under The High-speed Train Load And Fatigue Life Prediction Of CFG Pile

At present, China is vigorously developing high-speed railway undertakings, withthe continuous improvement of train speed, the dynamic response of subgrade andfoundation is more and more obvious, study the dynamic characteristics of high-speedrailway subgrade and foundation are very necessary. In this paper, aim at the currentcommonly used to handle high speed railway subgrade foundation of CFG pilecomposite foundation, established the three-dimensional finite element analysis modelby the actual project of the non-ballasted-track-subgrade-CFG pile compositefoundation,calculated by finite element software ABAQUS, analyzed subgrade andcomposite foundation settlement characteristics and stratification in the subgrade fillingprocess, the dynamic characteristics of composite foundation unders dynamic trainloading, and two methods to calculate the fatigue life of plain concrete CFG pile, themain innovations and achievements as follows:1.Combine the settlement with the measured actual project data with ABAQUSsimulation of using the birth-and-death elements, to prove the finite element simulationis reliable by comparing the two kinds of the data;2.As amended by the static load and a series of sinusoidal excitation forcesuperposition to simulate the train load, instead of simply converting the train load intostatic load;3. The direction of the stress generated at composite foundation caused by trains is mainly vertical; the faster increased peak dynamic stress of piles and soil along thelongitudinal directions of the subgrade by increasing the speeds, the faster it decays,andthe number of the line trains runns is related to the law; soil dynamic stress decay fasterthan the pile along depth of the pile, the distribution of pile dynamic stress along thelength of the pile depth presents more complex; the dynamic stress attenuation of pileand soil along the pile length is not obvious with train speed.4.Vibration on the site of the train running mainly in the scope of the embankment,but the vibration caused by the venues outside the embankment should also be givendue attention; as the depth increases, the vibration at composite foundation caused bytrains focused in the pile body; the influence depth of vibration caused by the impact ofthe train running increases because of CFG piles exist;5.With increasing height of subgrade, the peak dynamic stress on top of the pilecontinued to decline,which shows a linear relation between them; the increase in trainlines, dynamic stress growth rate of composite foundation pile is faster than soil; theheight of subgrade increases within a certain range for composite Foundation withreduced acceleration effect is more obvious, but with the increasing height of subgrade,this trend of decrease may gradually slow down;6.The fatigue life calculated with the method of combining the critical surface withenergy is larger than using the value of local stress-strain method; the method ofcombining the critical surface with energy is specifically clear by defining the damagevariable is applicable to the analysis of concrete fatigue life with multiaxial state, andcan give the location of fatigue failure.