Research on bearing behaviors and negative friction force for filling piles in the site of collapsible loess with big thickness

Large scale field tests of filling piles were performed in a collapsible loess site with a thickness of 35m under natural content and immersion states.The diameter and length of test piles were 0.8 m and 40 m,respectively.4 types of test piles were designed and several measuring methods were adopted.It was shown by test results that the positive frictional resistance measured from pile ZH2 and the negative frictional resistance measured from pile ZH5 were smaller than those measured from pile ZH3 and pile ZH4;The negative frictional resistance measured from test piles was far greater than the numerical value recommended by ? Code for Building Construction in Collapsible Loess Regions ?(GB50025-2004);The locations of neutral points measured from several pile tests in-situ exceeded the range proposed by ?Technical Code for Building Pile Foundations ?(JGJ 94-94);The collapsible settlement of loess could be decreased with pile group.The results obtained in this paper might be useful for the similar project and to revise GB50025-2004 and Code JGJ 94-94.