Numerical Analysis Of Working Properties Of The Rigid Long-short-pile Composite Foundation

Rigid long-short-pile composite foundation, a new type of foundation treatment, is increasingly used to solve engineering problem. What engneers concern most is whether this foundation treating method can meet engineering requirements, at the same time, can obtain optimal economy. The present studies of rigid long-short-pile composite foundation is still at the initial stage. Its behaviors and working mechanism need to be studied deeply. The design theories need to be improved furtherThree-dimensional long-short-pile composite foundation analyzing model is established based on finite element analysis software ABAQUS. In the process of changing compression modulus of the bearing stratum for the piles, the changing regularity of pile settlement, the axial force of pile, pile-soil load share ratio, and the frictional resistance of the pile in four aspects was summarized. The working mechanism of the long-short-pile composite foundation was further analyzed.The preliminary conclusions are shown as follows:(1) In the rigid long-short-pile composite foundation, the pile settlement is nonuniform under the cushion cap. The relationship for the settlement is king-pile> siding-pile> comer pile. Because the long-pile bearing layer was set on the hard soil, the overall settlement was limited. The long pile settlement and the long-pile bearing layer are closely related;(2) In the rigid long-short-pile composite foundation, Loads from the superstructure are shared by the pile body and the soil. The bearing capacity of composite foundation comprises two parts:pile and soil. With the increase of the soil stress between the piles, the axial force of pile will be reduced. Therefore, the pile axial force and the short pile bearing stratum are closely related;(3) In the rigid long-short-pile composite foundation, the cushion can adjust the pile-soil stress ratio. Based on the concept of composite foundation, Short piles bear most of the soil stresses. Therefore, pile-soil stress ratio and short pile bearing stratum is closely related;(4) In the rigid long-short-pile composite foundation, with the compression modulus of the bearing stratum increasing, the pile-sharing loads increases gradually. This will cause the pile axial force to increase gradually. The final result is that pile side friction resistance increasing gradually. After the side friction of piles reaches the ultimate value, pile side friction decreases gradually. Therefore, the pile side friction and the size of the pile layer strength are closely related;(5) In the rigid long-short-pile composite foundation, piles can stab into the soil upward and downward. It will lead to the difference type of stress between composite foundation and ordinary pile. The pile stabbing into the cushion changes the positions of the maximal axial force. The pile stabbing into the soil downward causes the change of the friction resistance of the pile end:(6)In this paper, based on the existing theory of composite foundation, the settlement deformation and the bearing capacity calculation method is summed up.