Study On Influenced Range Of Using Vacuum Preloading To Improve Soft Clay Foundation

Large deformation even cracks may be caused by Vacuum preloading in improvingthe soft clay foundation, which would bring negative impact to the surroundingenvironment. Now, there are many studies on the improving mechanism, the calculationof consolidation and displacement, and the influenced depth of vacuum preloading, butthe researches about the deformation law of the surrounding soil and the horizontalinfluenced range of vacuum preloading are few, the conclusions from experimental andtheoretical analysis are not very consistent.This paper gives a preliminary study on the deformation law of the surroundingsoil of vacuum preloading based on the present improving mechanism. the author thinkthat the deformation of the surrounding soil is just caused by the uneven verticalsettlement and the different lateral deformation, there are two reasons for it, one is thetransfer of the vacuum degree to the influenced area, the other is the dropping of theunderground water line.Biot consolidation theory can be used to describe the consolidation progress of softclay foundation under vacuum preloading, with the principle of virtual displacement, thefinite element method answer of Biot consolidation equation can be carried out. Basedon the finite element equation of Biot consolidation, the author uses Fortran to get afinite element analysis program. In order to get the calculating results, some measureddata of vacuum preloading projects need to be input, then the program will show thereinforced effect. By comparing with the measured results, it is proved that the finiteelement analysis program is correct and rational, therefore, the program can be used as atool for various studies on vacuum preloading.With the program, by comparing the calculated results and the measured results,some conclusions are be enumerated as follow:(1) using the Duncan-change model tocalculate the soil's deformation, for example the vertical settlement and the lateraldisplacement, is more suitable to the vacuum preloading practice than flexibilitymodel;(2) the calculated soil's deformation law of the surrounding area is consistentwith the measured result and the conclusion educed by theoretical Study;(3) Area ofpreloading, Vacuum degree, Depth and Distance of plastic drain, Soil properties are allthe influential factors of the influenced range of vacuum preloading.