Quantification of Surface Roughness Using Laser Scanning with Application to the Frictional Resistance of Sand-Timber Pile Interfaces

Still commonly used today, timber piles represent a cost-effective deep foundation alternative for carrying structural loads or densifying liquefaction-susceptible soil deposits. However, the range in interface shear friction angles between common timber pile types and sand is unknown, and little data exist for wood specimens in the range of normal stresses typically encountered in the field. This study evaluates the use of laser-scanning techniques for the quantification of surface roughness and presents the results of interface shear tests conducted on untreated Southern Pine, treated Southern Pine, and untreated Douglas Fir. The surface roughness of the timber pile specimens was found to be anisotropic, with surface roughness approximately three to four times larger in the circumferential direction than the longitudinal direction, presenting implications for torsional and axial load transfer. The peak and constant volume effective interface friction angles and interface friction ratios were relatively insensitive to relative density for the range in relative densities investigated, whereas the interface response was sensitive to normal stress. The role of surface roughness and surface hardness on the interface response was determined to be statistically significant and confounded by the inverse relationship observed between hardness and roughness for the species of timber pile investigated.