Study On Working Behavior And Engineering Application Of CFG Pile Composite Foundation

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 engineering characteristic of foundation soil, to improve 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 1990's, now it's very popular and applied nation widely.Composite foundation of CFG pile has different engineering characteristic from other composite foundations. It is 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, 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.Before the site and the design of CFG pile, the data of the construction building construction are necessary, we should consider the construction equipments and technology synthetically according to the bottom soil of the foundation environment, construction and arrangement of the building, the delivery of load and the purpose of foundation treatment.The main design of the CFG pile composite foundation is determine 6 design parameters: pile length, pile diameter, pile interval, intensity of pile, thickness and material of cushion. We always adopts design principle of long pile interval and long pile length, and put the end of pile on the relative firm layer. Pile length should determined first in the design of the CFG pile composite foundation, which is depended on the requirement of building to the load and distortion, soil condition and equipments ability etc. The pile interval should be determined according to the design bearing capacity, quality of soil, construct technology etc., which is always 3-5 times of pile diameter. The mixture ratio of pile should be determined by the strength of pile in principle, and should satisfy the requirements of related standard. A cushion must be established between the pile head and the foundation, the proper thickness of cushion is 10-30cm, and it is proper to take more thicker cushion when adopted big piles or long range interval, it is proper to use medium sand, coarse sand, grading stone-sand or angular cobbles etc. as material, with the biggest grain size not more than 30mm. CFG pile must be arranged within the range of foundation. The pile diameter is decided by the equipments adopted, which is proper to take 350-600mm.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.