Experimental Study on the Reliability of Scaling Down Techniques Used in Direct Shear Tests to Determine the Shear Strength of Rockfill and Waste Rocks

The determination of shear strength parameters for coarse granular materials such as rockfill and waste rocks is challenging due to their oversized particles the minimum required ratio 10 between specimen width (W) maximum particle size (dmax) tested samples direct tests. To overcome this problem, a common practice prepare test by excluding particles. This method called scalping scaling down technique. Making further modifications on scalped achieve specific distribution curve (PSDC) leads other techniques. Until now, parallel technique has been most popular commonly applied, generally because it produces PSDC similar that field material. Recently, critical literature review performed authors revealed methodology used previous researchers validate or invalidate techniques in estimating inappropriate. validity remains unknown. In addition, W/dmax 10, stipulated ASTM D3080/D3080M-11 tests, not large enough eliminate effect (SSE). authors’ recent experimental study showed 60 necessary avoid any SSE study, series tests were with different dmax values, prepared applying All specimens had equal larger than 60. results scaled values smaller those establish predictive equation effective internal friction angle (hereafter named “friction angle”) dmax, which was then predict angles samples. Comparisons measured predicted demonstrated equations based correctly samples, whereas failed validated, invalidated presented study.