Seismic Response Analysis On Karst Foundation- Pile Raft Foundation-Shear Wall Structure Interaction

With the development of economy, some of the buildings inevitably built in Karst foundation, but the special seismic action would have an impact on production and construction. Therefore, the seismic study on interaction of high-rise building and foundation in karst area is significance.A 3-D finite element model of karst foundation-pile raft foundation-shear wall structure interaction is established by using the finite element software ABAQUS in this thesis, and by the means of earthquake simulation to analyze the interaction model. The main contents and conclusions are as follows:(1) The adopted constitutive models of the shear wall structure and pile raft foundation and karst foundation are affirmed. Appropriate unit and size of foundation soil and the treatment of foundation boundary are selected. By selecting suitable seismic wave, the software of EduShake is used to invert the seismic wave, it shows that the seismic wave has certain effect to enlarge in karst foundation. Therefore the reasonable seismic wave input method is loading the inversion wave on the bedrock.(2) When the pile raft foundation is adopted, considering the effect of contact and friction coefficient value of pile-soil influence on interaction system. Research shows that, when the pile-soil contact is considered, regardless of the size of seismic action each layer of high-rise shear wall structure displacement were increased. The changes of the firiction coefficient have a little effect on the upper shear wall structure.(3) The foundations of the presence of karst cave-pile raft foundation-shear wall structure interaction under the action of the earthquake are compared. Two models of the upper structure under stress, displacement, acceleration had analyzed detailedly, besides, the force of three representative piles are analyzed. Research shows that the existences of karst cave weaken the stiffness of the foundation soil, the deformation in the upper structure increase. For each representative pile, the shear force and bending moment value which distribute along the pile body is greater than the shear force and bending moment value when there is no cave. The pile and raft junction is a weak link when they are in the seismic action, because most horizontal shear has been carried by pile top. Shear force and bending moment value occurs when pile in different soil layer interface when using the layered soil. Therefore, on the basis of considering dynamic load, the weak parts of pile foundation should be strengthened and more attentions should be taken to the pile when it in the layered soil junction which is easy to occur horizontal shear failure by stiffness mutation.