Negative Friction Test On Bored Pile Foundation Of Collapsible Loess Area

As one of the most original and basic plile forms, pile foundation is widely applied in modern engineering and plays an irreplaceable orle compared with other piles forms because of its great adapatability to foundation soil, high intrigity stability, strong foundation bearing capacity, small settlement and other advantages. Correspondingly, the research on pile technology theory and construction techniques, espencially the pille negative friction, are constantly.Pile negative friction is a harmful effect to the construction which strethened. is equivalent to the drop-down load imposed on the pile, and it reduces the pile bearing capacity of piles and would lead to the occurrence of excessive settlement. It will produce more heavey settlement in the same depth of the pile when the ground soaked. Therefore, the effect of negative friction must be taken into account in designing pile foundations. And according to our nation’s standard requirements, in the process of the design,not only the positive friction in self-weight collapse loess, but also the negative one should be eliminated. So the calculation of the nagative friction is crucial to a pile fundation. There are formula method, theoretical and field test method in calculating the negative friction. And in the field soaking test, suspension method and electrometric are the common choice which, though the obtained dates much accurate and reliable, have not so much experimental date because of its high cost and long time.Based on the test of bored pile negative friction in collapsible loess site, the paper pretend to conclude the characteristics and basic law of negative friction by testing the positive and negative friction in two uplift piles and two empty end anti-stress pile to find the pile neutral position with balancing theory.