Rigid Length Of The Flexible Foundation Pile Composite Foundation Pilot Study

The composite foundation has been extensively applied in the civil engineering , and this promotes its theories and techniques to develop fast. The rigid pile composite foundation developed from the industrial and civil buildings, has already come into being relatively complete theory system and design calculation method. And that guide effectively engineering practice of composite foundation. In the construction of the high grade highway, composite foundation is mainly applied to handle the soft soil foundation that the structure, such as highway and abutment and passage etc. links up a segment. Thus we can control its post construction settlement and the stability of foundation. Because the rigidity of embankment is comparatively smaller, it can be called composite foundation under flexible base. At present, the research is not still mature for composite foundation under flexible base at home and abroad, such as its load transfer behavior, additional stress distribution, the method of bearing capacity determination, settlement calculation method and failure mode.This article researches on the working characteristic of rigid pile composite foundation under flexible base mainly through field tests, and the test schemes mainly have: (1) natural foundation loading test and single pile with static load test, which adopts high-strength pre-stressed concrete pipe pile (PHC pile), two kinds of pile length (short pile is 4 ms, long pile is 6 ms) to carry on the single pile bearing capacity test; (2) long-short-pile 4 piles composite foundation static load test under flexible base; (3) determination of pile-soil stress ratio.From the former analyses of test results, this artical mainly gets some following conclusions:(1) The force bearing mechanism of rigid pile composite foundation under flexible base differs from that of under rigid base, so while carrying on the calculation of bearing capacity and settlement, the calculation formula under rigid base can't be adopted directly, and related coefficient need to be imported to adjust the formula.(2) As the pile-soil stress ratio of composite foundation under flexible base is smaller, soil shares more loads and that causes soil body attain limit load to break than pile body first. The failure mode of composite foundation under flexible base completely differs from that of under rigid base. (3) The pile-soil stress ratio under flexible base is small, and the variety tendency and rule defers from that of under rigid base. The measured result indicates that the pile-soil stress ratio in the initial loading stage is big. And the value raised gradually with the load increasing.(4) The pile-soil stress ratio under flexible base is small, soil body shares more loads and as a result the deformation is bigger. So the design of composite foundation under flexible base should be according to deformation control(5) The stress at the top of long-pile is greater than that of short-pile under loading. So the long-pile can spread loads to the lower part better soil layer, reducing the settlement. And it can make the bearing capacity and deformation of long-short-pile composite foundation mutual coordination.