Study On Behavior Of Composite Foundation With Geogrids And Rammed Soil-cement Tapered Columns Under Cyclic Loading

As a new kind of reinforcement approach for soft soil foundation, the composite foundation with reinforced gravel cushion and rammed soil-cement tapered columns has been proposed only in recent years. In order to reveal the working characteristics of this new technology under cyclic loading, this paper adopts a method that combines model experiments and numerical simulation, systematically research the working characteristics of composite foundation with reinforced gravel cushion and rammed soil-cement tapered columns under cyclic loading from five respects include the interface contact friction characteristics between cement-soil and soil, the working performance of geogrid reinforced cushion, the dynamic properties of the soil, the bearing features of the composite foundation under cyclic loading, the stress filed and displacement field of the composite foundation. The following conclusions have been reached.1. The friction resistance of the interface between cement-soil and soil increases with the increase of curing period, the decrease of the water content of soil and the increase of the cement content of cement soil. And suitable cement content of cement soil is existed.2. The cushion can reduce the foundation settlement by adjusting load distribution. The thickness of the cushion is not more thick more good and a suitable thickness is existed. The settlement is diminishing further when add the geogrids into the cushion. The more the number of layers is, the smaller the foundation settlement is.3. Damping ratio firstly increases and then decreases with dynamic strain increase, and remains stable at last. The dynamic elastic modulus decreases with the increase of the dynamic strain and increases with the increase of the confining pressure. When the dynamic strain is small, the effect of the confining pressure on the dynamic elastic modulus is remarkable. The dynamic strength decreases with the increase of the shaking. It reduces quickly when the number of vibrations is small and reduces slowly then the number of vibrations is big.4. Factors such as the peak value of cyclic loading, the cyclic number, cushion with or without geogrids and the size of wedge angle have significant influences on the settlement of composite foundation, pile-soil stress ratio and the strain of the pile. The special shapes of tapered pile can enhance the interaction between pile and earth, decrease the settlement of the foundation, increase the pile-soil stress ratio, decrease the pile-top stress, reduce the stress concentration, optimize the stress distribution of the pile and increase the bearing capacity of composite foundation. The bearing capacity is increasing further when add the geogrids into the cushion that form double direction reinforced composite foundation together with rammed tapered cement-soil column.5. The results of numerical simulation by using the finite difference method FLAC3 D are coincident with the results of the model experiments. By analyzing the stress filed and displacement filed of the composite foundation, the distribution characteristics of the stress and the rules of the settlement changes of the composite foundation with rammed tapered cement-soil column and geogrid reinforced gravel cushion are further studied and the fact that the bearing features of rammed tapered cement-soil column are better than equal section one is further confirmed.