Theory And Application Study Of The Composite Foundation Formed By Heavily Rammed Stone-piers

A new type composite foundation which is formed by heavily rammed stone-piers come to the advantages of both stone pile and dynamic compaction foundation. This new composite foundation can not be restricted by the complexity of the rock fill and earth fill in the construction, and is also quite suitable for soft areas'treatment. Especially, in the coastal area, where a large acreage of the silt class soft clay ground should be filled with jackstone, this composite foundation is very popular. Moreover, because of its advantages in the construction, dynamic compaction, and dewatering, this type of foundation has been successfully applied to most of economically developed cities, especially in Shenzhen province, are located in coastal areas.However, study of the strengthening mechanics of this composite foundation is still at an initial stage. Especially, there is no explicit settlement calculation in engineering practices, although many theories concerning the analysis of piled raft foundation have been proposed by numbers of researchers. Usually, in the project, the preliminary design is carried on by the project experience, and is confirmed through the field test and revises, the suitable design parameters are determined at last. From the above mentioned, to develop the theory and application study of the composite foundation formed by heavily rammed stone-piers has the extremely important theory and the project application value.Based on summing up the development of the dynamic compaction method home and broad at present, the engineering characteristics of the saturated soft soil (weak subgrade) and the strengthening mechanics of dynamic compaction techniques were fully discussed, and the working mechanisms of the composite foundation were discussed as well. Then, based on the Vesic cavity expansion theory, an ultimate bearing capacity calculation method for single stone-pier is developed. This method can consider the additional constraint reaction which is caused by the vertical load on the surrounding soil. In combination with the study in this paper, a complete design calculation method of dynamic compaction stone-piers composite foundation was developed. The design parameters such as effective depth of dynamic compaction, tamping energies, numbers of tamping passes, length of intervals, intervals of tamping points, and the incidence of the dynamic compaction were investigated in depth. Moreover, on the base of summing up a mass of engineering practices, a construction method and the quality monitoring program were developed.