Abstract: To investigate the proper value of unloading in the unloading collapse process of loess between piles, a correlation between pile-soil interface shear strength, shear displacement, and pile-soil interface normal force under collapse was studied by interface shear test. In the range of neutral points, the results indicate that the shear strength of the pile-soil interface under different vertical stresses and water contents can represent the pile side negative friction resistance. Using the mechanical principle of the mutual action and reaction force between the unloading amount and the negative frictional resistance, we proposed a method to calculate the unloading amount based on the unloading variation laws during loess collapse. The rationality of proposed method is verified via the comparison between the calculated unloading values and the field measured results of pile side negative friction resistance in different loess areas. This method provides a quantitative means of unloading effect to promote loess unloading collapse evaluation and optimize the relevant loess engineering design theory.

Key words: unloading collapse, collapsible loess, collapse potential, collapse process