Research On Consolidation Of Composite Ground With Impervious Pile Under Vacuum-surcharge Preloading

The Soft soil foundation,Because of its low strength,high sensitivity,slow consolidation,and other characteristics will endanger engineering safety,it must be reinforced.Some engineering accidents are caused due to improper handling of soft ground,so the research must pay attention to the reinforcement of soft ground.The composite foundation method and drainage consolidation method are two common measures to deal with soft soil foundations,and they are widely used in various projects such as ports,bridges and highways.Because of poor permeability of impervious pile,it should be distinguished from ordinary sand well foundations.For the solution of the degree of consolidation of impervious pile composite foundation,scholars have made some studies,mostly concentrated on the condition of surcharge preloading,and the problem of using vacuum preloading to solve the impervious pile composite foundation has not yet been developed.This paper intends to study the consolidation of composite foundations with impervious pile under vacuum and vacuum-surcharge preloading conditions.The main tasks are as follows:(1)Aiming to the consolidation of impervious pile composite ground under vacuum preloading,which considering the vacuum preloading loading process and influence of ground with partially penetrated pile,simplifying the calculation process with equivalent-double-layered.And the simplified solution of the average consolidation degree of the reinforce layer and underlying soil under the vacuum preloading condition is deduced.Based on the simplified solution.Considering the influences of penetration,pile diameter ratio,vacuum change rate,permeability coefficient and compression modulus on the consolidation are plotted by programming.The results show that the influence of the penetration ratio and the compression modulus of the reinforce layer and underlying soil consolidation is significant,while the other factors are relatively small.The higher the vacuum loading rate,the faster the consolidation rate.When the vacuum rate increases to a certain extent,the consolidation rate is no longer obvious.(2)In order to solve the consolidation problem of undrained pile composite foundation under vacuum combined loading condition,the composite foundation of impervious pile is simplified by the method of double-layered soil.The simplified consolidation solution of impervious pile which under vacuum combined loading preloading is derived.Consider the influence of pile penetration,compression modulus of pile and soil,soil permeability coefficient on consolidation,and use the simplified solution to draw the image.The results show that the consolidation rate of impervious pile composite foundation increases with the increase of the penetration,ratio of compressive modulus of piles and soils,and the ratio of compressive modulus of soils in the upper and lower layers.Among all the influencing factors,the ratio of the permeability coefficient has no obvious effect on the consolidation rate,and the penetration degree has the greatest influence on the consolidation rate.(3)The numerical analysis of vacuum preloading undrained pile composite foundation is carried out by using ABAQUS.The study shows that the effect of vacuum preloading on the consolidation of foundation weakens with increasing depth.In the partially penetrated impervious pile composite foundation,the influence of the stress concentration of the pile on the soil consolidation of the pile should be considered because the modulus of the pile's elastic modulus is larger than the surrounding soil.By comparing with the simplified solution in the second chapter of this paper,it is found that the simplified solution is slightly less than the finite element simulation results,but it has enough accuracy to verify the applicability of the simplified solution.(4)ABAQUS was used to numerically analyze the composite foundation of vacuum-surcharge and preloaded undrained piles.The results show that the consolidation law of the ground is the same under both vacuum and vacuum-surcharge combined conditions.The consolidation effect of vacuum-surcharge preloading is more effective than that of vacuum preloading.By comparing the results of finite element simulation and simplifying solution,it is verified that the simplification solution given in this paper has sufficient accuracy and has certain applicability to the actual project.