Experimental study on interface properties between crushable soils and pile materials

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Direct shear tests between soils and steel materials were conducted in this research to investigate influential factors on coefficient of friction. Diatomaceous mudstone known as a soft rock, and Shirasu sand that is a typical crushable soil were used as soil specimen. Steel plates having different surface roughness, Rmax, of 10, 30, 40gm, were prepared as pile materials. Other experimental parameters were normal pressure, cm, shear displacement rates of 2mm/mm and 20mm/mm, and number of repeated loading.Principal findings from this research are as follows :1)The shear strength at the pile-soil interface is dominated by Mohr-Coulomb criterion where shear strength is proportional to effective normal stress siguma_n.2)Coefficient of friction m is increased with number of repeated loading toward internal coefficient of friction of soil.3)This phenomenon is associated with crush of soil particles. It is presumed that finer soil particles produced by particle crush bury ditches on the pile surface so that pile-soil slip mode changes to soil-soil slip mode as crush of soil partilces is progressed.