Study On Consolidation Law Of Foundation Under Preloading Considering The Influence Of Vacuum Degree Transfer

As a common foundation treatment technology,vacuum combined surcharge preloading method is widely used in civil engineering.As a form of negative pressure,vacuum degree plays an important role in the process of foundation consolidation.However,due to the complex law of vacuum transfer,the lack of relevant test data and calculation theory,there are few reports on the consolidation law considering the influence of vacuum transfer.The research in related fields is of great significance to reveal the mechanism of preloading.Firstly,with the help of indoor model test method,a small-scale vacuum combined surcharge preloading foundation model is established,and the transfer law of vacuum degree and the correlation mechanism between vacuum degree and consolidation degree are studied.Under different working conditions,the vacuum degree is transferred along the foundation depth presents a nonlinear decreasing trend,and the change rate is fast firstly and then slow;the vacuum degree loading increases first with time,reaches a certain value and then changes to be stable.The transfer of vacuum degree is closely related to the displacement of foundation,and then affects the degree of consolidation of foundation.Secondly,the finite element software PLAXIS was used to build the calculation model to simulate the process of vacuum combined surcharge preloading method.Based on the analysis of the two main factors that affect the vacuum transmission,the vertical drainage parameters and the thickness of the reinforcement layer,the conclusion is drawn that different factors have different influence on the vacuum transmission and the influence on the foundation consolidation degree is also different.Regardless of the type of vertical drainage,the longer and closer the length of the vertical drainage plate is to the thickness of the reinforcement layer,the more favorable it is for the transfer of vacuum degree.The relationship between vacuum degree and consolidation degree can also be influenced by the parameters of vertical drainage and the thickness of reinforcement layer.When the length of drainage water changes,there is a good linear relationship between the vacuum degree and the consolidation degree,and the vacuum degree has a great influence on the consolidation degree in the middle stage.When the thickness of the reinforcement layer changes,the vacuum degree and the consolidation degree show a good linear relationship in the middle and later stages.The consolidation equation under the condition of vacuum combined with surcharge preloading considering the nonlinear loss of vacuum degree along the depth is established,which provides a theoretical basis for the calculation of the consolidation degree under the effect of vacuum combined with surcharge preloading,and is verified with the actual project.Lastly,this paper uses analytic hierarchy process to rank the influencing factors of foundation consolidation under vacuum combined surcharge preloading: vertical drainage type,multi-stage loading,vertical drainage length,permeability coefficient,single-stage loading and reinforcement layer thickness.The influence of various factors on the consolidation of foundation under preloading method is quantified to provide reference for practical engineering design.