Vacuum Stack Preloading The Theory And Practice Of Dealing With Soft Subgrade

Along with the rapid development of economy, many higway projects need to be built on the flabby groundsill in the area of Pearl River Delta of Guangdong Province.This kind of soft soil has the characteristic of rich-watercontent, high compressibility, lower in permeability and bearing capacity. Such soft groundsill should be treated with first while the highway is to be constructed. The conventional stack-preloading method which we use at present can not meet the requirement of stabilization, time limit of construction and the settlement after completion of works, so a new kind of technique is to be introduced to soft soil treatment.This paper introduces in detail the mechanism of consolidation in the preloading method combining vacuum with stack-load, and puts forward the calculating model. Because settlement after completion of works is the key index of soft soil treatment, it is so important to calculate the final settlement accurately during the construction period. Criterion method of settlement calculating is also introduced in this paper.After comparing the calculating value of criterion method with the data which measured in-site, this paper points out:(1)Settlement brought by side deformation should be taken into account among the super soft silt groundsill in Pearl River Delta Area; (2)stress history has a great deal influence to the settlement, but the pre-consolidation pressure PC for the judgement of consolidation state of soil has no credibiliy which is gotten in laboratory.Moreover, the conventional method and finite elements method were adopted to analyze and validate the theory of stabilization and deformation. This paper introduces the method of design and construction, and presents the relational control parameters which used for designation and construction based on measured data.Finally, this paper detailedly introduces the application of preloading method combining with vacuum stack-load in the practice of a freeway project. Three sorts of experience calculation method of final settlement which based on the settlement data measured in-site are contrastively analysed, and points out the hyperbola method be recommended for settlement predicted because it accord with the actual instance of Guangdong Pearl River Delta Area, and bring up the range of settlement correcting coefficient corresponds to the characteristic of the region.