| When the natural foundation can't meet the requirement of engineering construction, we must adopt some measures, one of them is to reinforce the foundation. The purpose of ground treatment is to reinforce the foundation soil, to improve the engineering characteristic of the foundation soil, to increase the shear strength of the foundation, to lower the compressibility of the foundation,to improve the hydraulic permeability of the foundation, to improve the dynamic characteristic of the foundation ,to ameliorate the bad foundation characteristic of the special soil etc, by making use of filling, tamping, compaction, drain, cementation, adding tendons and thermal methods etc.. There are many methods of foundation treatment in common use. According to the principle of reinforcement, they can be divided into the compaction method, displacement, composite foundation, adding tendons and grouting etc.. Each kind of method has different principle of reinforcement and field of application.As a kind of high bond strength pile composite foundation, CFG pile composite foundation is a new kind of composite foundation constituted of CFG piles, subsoil among piles and cushion mat, piles and soil connect with foundation through cushion mat and undertake the load together。This technology has many advantages that the applicability is wide, the bearing capacity can increase greatly, and it can be constructed easily in short time and cheap cost. It developed very fast since 70's, now it's very popular and applied nation widely.This paper introduces the design method and the superiority of CFG pile and the problem of the given engineering design, illustrates the applied research of CFG pile in specific project finally.Composite foundation of CFG pile has different engineering characteristic from other composite foundations. Its pile length can range from several meters to more than 20 meters, can make use the side resistances of the whole pile. The load undertaken by CFG pile can variety from 40% to 75% of the total load that occupies the total load, so, the bearing capacity of composite foundation can increase in large extent, and have great adjustability. In regard to foundation form, CFG pile can apply to not only strip footing and isolate footing, but also raft foundation and box foundation. In regard to soil, CFG pile can apply to filled soil, saturated or unsaturated cohesive soil, and the soil with good compaction or bad compaction. CFG pile can make use of the side resistances of the whole pile as rigid piles, and has obvious effect of end bearing when the pile stand on firm stratum. CFG pile is a good drainage pipeline, the water can drain up alone the pile, and it is propitious to increase the compactness of soil among piles and reduce swelling of ground caused by the slowly dissipating of bore pressure. In addition, composite foundation of CFG pile has time effect, with the convalescent period increasing and the instauration of construction strength, the bearing capacity of soil among piles can increase to some extent.The cushion mat constituted with of grading stone-sand, coarse sand, macadam etc., is a key of the composite foundation of CFG pile. It can guarantee the piles and the soil undertake the load together, and reduce the stress concentration of the bottom of the foundation. The cushion can adjust the horizontal and vertical load ratio of pile and soil. To rigid pile, if the cushion is too thin, the pile will produce remarkable stress concentration on the foundation, which will certainly result in the thick foundation, if the cushion is thick, the bearing ability of soil around the piles can develop well. but if the cushion is too thick, it is equal to replace the soil and fill back, it is waste and makes the stress ratio on piles and soil become small, it means that the shallow foundation soil undertakes more load, and the piles in composite foundation are out of use. Many of engineering practices and experiment indicate that the proper thickness of cushion is 15-3...
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