Research On CFG Pile Composite Foundation In Vertical Resistance Based On Field Experiment

In the recent several years, composite foundation using and developing rapid in our country, many kinds of composite foundation processing methods appear. The CFG pile composite foundation is used in projects widely because of its economic timber, rapid construction, good reinforcement effect. Meanwhile, it has obtained good economic benefits and social benefits, but the theory analysis still falls behind the engineering practice. The thesis based on CFG pile composite foundation of the housing buildings of Chuanbei Medical College subsidiary hospital in Nanchong city Sichuan province, analyze and study the bearing character and mechanism of action of the CFG pile composite foundation.The paper reviews the application and development of the CFG pile composite foundation, introduces briefly the formation condition and action mechanism, at the same time, makes some analysis and discuss in field experiment and theory.①Some load test on site are conducted, including 3 group natural foundation,13 group single piles and 6 group composite foundations .The bearing capacity of CFG pile composite foundation are researched.All the results provide the reference for foundation design. According to the result, this paper obtains three kinds of p～s curve pattern for CFG pile, and has made the analysis and the discussion on each pattern;At besides, contrastive analysis has carried on results between the composite foundation and the natural foundation,the single pile, some meaningful conclusions are obtained.②The vertical loads on CFG pile composite foundation are beared by co-action among pile capushion, pile and the earth. Because of the multi-influencing factors, the action mechanism of CFG pile foundation is in lack of exploration. The stress between pile and soil and pile-soil stress ratio following with load are observed and analyzed through buried steel strain gauge on the piles and buried soil pressure cell on and under cushion layer, meanwhile the reduction factor of soil bearing capacity between piles is obtained.According to the force on the pile and surface of cushion, which is orresponding to the pile, the roles and significance of the cushion is studied. The character of the stress distribution is knowledged.③As the elastic modulus of CFG pile is between cement-soil pile and conventional pile, there is a certain amount of compression under the load, but not numerical, which make a different between CFG pile and cement-soil pile and conventional pile on load transfer.The change laws of axial force,lateral friction and end resistance along with the load are observed and analyzed through buried steel strain gauge on the piles. In addition, The analysis has been made on the law of load-sharing for lateral friction and end resistance.At last, theload transfer mechanism of CFG pile composite foundation is very obvious.④A few of comparison and research are carried on three computational methods, namely: standard method, stress ratio method and negative friction force method, according to the computational model of bearing capacity. Some discuss is done on parameter selection. At last, confirmation is taken on the all kinds of computational methods according to data reached through the load test on site.