Effect of surface roughness on interface shear strength parameters of sandy soils

Understanding the interface shear strength is crucial for the design of geotechnical structures. This study investigates the effect of surface roughness on the interface friction angle, peak interface friction coefficient, and interface shear strength through direct interface shear tests. The experiments were performed on 10 samples of concrete and steel with the level of roughness varying and soil. The objective is to provide soil parameters for a site that is located around 6 km away to the south of Al-Amarah city, Southeast of Iraq where earthquakes hit frequently. The research is intended to investigate the effect of earthquakes on objects that are built in that particular region, by putting emphasis on the interaction between the soil structure and the roughness of the contact surface between the structural parts and the soil. In order to evaluate the roughness nature of structural materials, a test program was conducted using the SRT-6210 Digital Surface Roughness Tester. The average roughness parameter (R a) had the strongest association with shear parameters, and so it is the indicator to explain the shear behavior of sand-concrete and sand-steel interfaces. The direct shear box test was employed to find out the soil's shear strength parameters as well as the interface shear strength parameters. The test shows a profound change in the shear strength characteristics of sand-concrete and sand-steel indispensable interfaces. As the roughness index increased. It depicted an upward slope of apparent shear strength and friction coefficient taken at the interface. The shear strength had increased by 25.13% when the roughness of the concrete was below 20 mu m 20{\rm{\mu }}{\rm{m}} and by 36.26% when the roughness of the steel was below 30 mu m . \hspace{0.25em}30{\rm{\mu }}{\rm{m}}.\hspace{0.25em} Moreover, sand-steel samples interface friction angle increased by approximately 31.5% with increasing surface roughness and sand-concrete samples by 21.54%. The results also revealed that the peak interface friction coefficient ( mu p ) \left(\mu p) increased with the increase in R a.