An overview on the determination of the shear strength of coarse grain materials (rockfills) from small scale laboratory tests

ABSTRACT: The shear strengths of rockfills are key parameters required in stability analysis of structures made of rockfills. Conducting laboratory tests using in situ materials and respecting the minimum ratio of specimen size to maximum particle size, dmax, specified by the well-established standards are very difficult if not impossible. To overcome this difficulty, several scaling down techniques were proposed in the past on samples preparation. Among them, parallel method is largely used. The analyses show that the methodology used in the past to validate or invalidate a scaling down technique through direct comparison between the shear strengths of modeled and field samples is inappropriate. The reliability of the scaling down techniques (including parallel method) in determining shear strength of field rockfill has never been demonstrated. Further analysis shows that applying the minimum specimen size to dmax, ratio required by the studied standards may result in unreliable results.