Study On Working Behavior Of CFG Pile Composite Foundation

The purposes of ground treatment are strength-increase of soil ground compressive properties-decrease settlement and differential settlement reduce of foundation. As we know, composite foundation is widely used in engineering at present, theoretical study is far behind practice, most of the researches are based on the experiment and experience and can seldom study it with the method of numerical analysis. With the quick application of composite foundation technology in China, some problems concerning its characteristics' settlement are also produced.. The following questions are dealed with and the conclusions were given this paper: Problem study:1. This Paper presents single Pile and nine CFG Piles composite foundation by using of ANSYS FEM Program, characteristics of co-action among Pile cap-cushion-pile-earth in composite foundation of pile cluster under vertical loading are studied with three dimensional finite elementmethod; and load transmission characteristics and pile-soil stress ratio, settlement and their influence factors such as s/d, L/d and Ep/Es, in composite foundation are systematically analyzed. Furthermore, large area group Piles and single Pile composite foundation which analyzed by finite element analysis is expounded in this paper.2 .Compared with Pile foundation, settlement of composite foundation 15 much greater and easily to Produce crack or incline in upper structure. The design method based on the theory of settlement control 15 more rigorous and reasonable than that based on the theory of bearing capacity The composite modulus it is only used in Particular condition This Paper gives formula of calculating composite modulus that 15 more reasonable and Practical value of application , and combined with engineering examples to demonstrate its rationality. Conclusion: 1. Working behavior under the vertical loading of a single pileWith the loading increasing, the pile-soil stress ratio will increase gradually and the foundation settlement will increase too.With the thickness of cap-cushion increasing, the stress ratio declined ceaselessly but the degressive tend slower gradually; With the thickness of the cap-cushion increasing, the settlement of the pile top had a little decrease and the settlement of the soil surface are stable basically when the thickness of the cap-cushion exceeded 40mm.The reasonable thickness of the cap-cushion is 10 to 30cm. (3) With the modulus of the cap-cushion increasing, the stress ratio raised ceaselessly but the raising tend is lower gradually, and the settlement of the pile top increased but the settlement of the soils and the bearing dais declined. The changed grads of all become the small when the modulus exceeded numbers.(4)With the long-diameter ratio increasing, the stress ratio raised. With the length of pile increasing, the declined settlement is no obvious. The efficient length of the pile in thecomposite foundation exceeded the actual length in working even more.(5) With the piles-soils modulus ratio increasing, the stress ratio increased gradually. With the soils modulus declining, the settlement of the pile top, the surface and the bearing dais increased alt. The more big piles modulus, the lowest of the settlement of the above three.(6) With the replacement ratio increasing, the stress ratio declined gradually.(7) With the modulus ratio of the soils of the pile bottom and the soils between the piles increasing, the stress ratio increased too but the settlement of foundation along with declining. The settlement foundation inclined slowly when this ratio increased numbers.2. Working behavior under the vertical loading of the grouppiles(1) All of the contrary force of the pile's top distributed is big in the corner, the second is boundary and middle, and the smallest is center. It formed the shape of the converse basindistributing but the difference of the contrary force of the pile's top declined with the thickness of the cap-cushion increasing and increased with the underlay modulus, Ep/Es, L/d and Epile bottom soil/Esoils between piles i...