Application And Deformation Analysis Of Vacuum Preloading In Soft Foundation Treatment

With the rapid development of our economy, the construction activities are more and more.The engineer often encountered in soft soil foundation, especially in the coastal areas, whichbring troubles to engineering, so it is needed that soft soil foundation treatment. The soft soilis widely distributed in China, there are many genetic types, from north to south, from east toWest has the distribution of soft soil, the distribution of soft soil show that the soft soil innorth is stronger than in south.Based on the previous work of investigation and the engineering cases, the Degree thesisresearch the deformation of soft soil foundation treated by vacuum preloading method. Toexplore the reasonable calculate method of the foundation settlement under vacuumpreloading, and using the finite element simulate the deformation, the main contents andresearch results are as follows:(1) This paper introduces the treatment method of soft soil foundation of existing, they canbe divided into two categories from the mechanism. one category is the soil improvementmethod, another is the composite foundation method. Soil improvement method is improvingsoil material properties, improve soil strength and compression and so on, for instance,drainage consolidation, soil replacement cushion etc.. Composite foundation is not to changethe original soil, but construct composite foundation in the foundation, the soil and the pilebear the load together.(2) Basing on the above content, introduce the design, construction and monitoring schemeof a port engineering case of vacuum preloading method, according to the nature of the site ofthe soft soil, select of method of treatment, finally chose the vacuum preloading method andmonitoring data of foundation deformation.(3) The research of deformation find that the foundation has a large settlement, and faster inearly stage, slower in the later stage, the most settlement occurred in the first three months.The compression of silt layer accounted for the70%~89.3%proportion of total settlement,and the shear strength is greatly increased, the pore water pressure in different depth of thefoundation have different degrees of decline. Around the Foundation reinforcement zoneoccurred the ring cracks, the because of contraction of foundation in the process of vacuum preloading. Properties of the soil within the depth of plastic drainage plate has been greatlyimproved, especially the mud layer is improved greatly.(4) Based on the measured data, calculate the settlement by means of the equivalent loadingmethod, the logarithmic curve method, negative pressure seepage field, effective stressmethod, vacuum degree difference method, and the finite element method. Compare thecalculated results with the measure date find that the equivalent loading method is relativelypractical, but smaller than the measured results. The vacuum preloading foundationdeformation is analyzed by plane strain finite element method, the results is close to measured,this method has certain reliability so can be used as a kind of calculation method. At the sametime,research the effect of different factors affecting the vacuum preloading,and results showthat the vacuity under the membrane, the size of plastic drainage plate depth, spacing havegreat influence on engineering. Through the hyperbolic fitting settlement observation data, getthe finally foundation settlement, and the calculation of consolidation degree above80%,which meet the design requirements. So the depth of plastic drainage board should passthrough the soft soil layer, spacing should not be too large. However, because of the wellresistance effect, the effect of vacuum degree is limit, excessive depth of plastic drainage willcause unnecessary waste.