Design and experimental application of a direct shear test apparatus for the pile-soil interface

Abstract:

To investigate the mechanical properties of the pile-soil interface， this study addresses the limitations of conventional direct shear tests in inadequately accounting for the curved surface morphology and actual roughness of pile bodies by designing a novel direct shear test apparatus capable of simulating the curved surface morphology and roughness characteristics of engineering piles. The apparatus features a nested dual-shear box configuration， wherein independent control of normal stress and tangential displacement is achieved through the synergistic operation of a bolt loading system in the upper shear box and a hydraulic actuation unit in the lower shear box. Using field-measured data， curved-surface concrete pile models were fabricated using spatial model scanning technology and 3D printing techniques， and direct shear tests were conducted on silty clay to systematically analyze the effects of moisture content， interface roughness of the curved surface， and normal stress on the mechanical properties of the pile-soil interface. Experimental results demonstrate that the interfacial bearing capacity exhibits a biphasic trend （initially increasing and subsequently decreasing） with rising moisture content， significantly increases with interface roughness， and shows a positive correlation with normal stress， all of which align with practical engineering conditions. These findings validate the applicability and scientific rigor of the apparatus design， demonstrating its practical engineering significance.