Dynamic FEM Analysis On Composite Foundation Under Blasting Seismic Action

Composite foundation is widely used in Foundation Treatment. The application process of composite foundation has developed greatly in recent years. For instance, the strength and length of the pile has improved greatly. The bearing capacity of the composite foundation gets a significant raise, the height of the building has reached one hundred meters. However, the original theroy is lag behind. Therefore, the aseismicity of the composite foundation is demanded more, and the dynamic analysis of composite foundation becomes hotspot. This paper is based on the dynamic experiment of the composite foundation under the blasting seismic action. Through developing 3D finite element model, the model parameteres have selected according to the investigation report of the field trial and the results of dynamic experiment. Then the dynamostatic characteristics of natural foundation, soil-cement and CFG composite foundation under the effect of blasting seismic and the time-response curve of the correlation are discussed in the paper.The main conclusion can be abtained as follows.(1) Through modeling static settlement and modal analysis, it shows that spring boundary presents the effect of external soil to ststic settlement somehow, and model the hypothetic artificial boundary preferably.(2) Contrasting numerical calculation and field trial results shows that the foundational natural frequencies, which are calculated by spring damping boundry, is close to the practical situation. The natural frequencies of the cement-soils composite foundation and CFG composite foundation are more frequent than the natrual foundation slightly and dynamic response varying law of numerical calculation is in accordance with to the experiment results.(3) According to the analysis of CFG composite foundation, the changing regularity of acceleration, displacement and stress about horizontal and vertical can be reached. The horizontal acceleration and displacement will decrease with the decrease of the depth, and will decrease with the increase of the distance from the blasting source. The vertical acceleration and displacement will increase with the decrease of the depth, and will decrease with the increase of the distance from the blasting source. In the view of vertical acceleration, composite foundation has a better aseismicity than natrual foundation, and CFG composite foundation is better than cement-soils composite foundation.(4) The maximum horizontal stress and stress ratio distribute at both ends. The stresses distributing both in the middle of the pile body. The maximum vertical stress and stress ratio distribute at half of the pile depth.For different composite foundations, the maximum stress and dynamic stress ratio is different.