Study On The Behavior Of Rigid Pile Composite Ground With Different Cushion Thickness

In the late years, rigid-pile composite ground has been in great use in thefield of civic building. Many scholars and engineering technician have beenparticularly studied on the composite ground and rigid-pile composite ground.And its theory has been consummated gradually. But studying on the cushion istoo little, because the failure mechanics of the cushion is complex and it is hard tosimulate the working fettle of the cushion. The cushion is the core technique ofcomposite ground. Many characteristics of composite ground are related to thecushion. Based on the comprehension of the roles of cushion, cushion is analyzed.When the cushion is on the two kinds of extreme conditions, they aredisadvantageous on the ratio of the sharing load between the pile and the soil. Onone hand, if the cushion is absolutely rigid, it will be one part of foundation;onthe other hand, if the cushion is absolutely limber, it will be one part of the soilamong the piles. The cushion can make the pile and the soil to bear the loadtogether. But correspondingly how much bearing capacity can the pile exert andwhether to enhance the bearing capacity of the pile in the composite ground is notbeen confirmed. In practical engineering, when the soil among the piles is soft,underneath the pile head is often set some cushion, which corresponds to the pilehead entering into the cushion, whereupon the influence on the interact amongthe pile-the soil the cushion is not studied. And the influence on the load, whichthe pile and the soil based on the analysis above, the author designed the modeltest of rigid-pile composite ground with large vertical-rigidity pile (simulating thelong-pile) and with different thickness of cushion, was performed to investigatethe behavior of cushion of rigid-pile composite ground under vertical load. In oneof the tests, pile head was embedded in the cushion for a certain length. Testresult shows that the rigid pile for the composite ground even with100mm-thickness cushion only can bear the fewer loads and hardly exert itsbearing capacity. Some cushions underneath the pile head can increase loadcarried by the pile head in the meantime reduce the pile head penetration intocushion. At last, a discussion is made on the effect of cushion thickness on thepile head stress, soil stress and settlement and pile head penetration by usingFinite Element Method.