Dr. Villalobos-Jara, Felipe

The study of materials with large particle size has been a great challenge in geotechnical engineering. Despite the current work around the world using coarse-grained materials CGM in rockfill dams and mining waste rock dumps, for instance the geotechnical characterization of these materials is still an important issue in geotechnical engineering practice which deserve more research. There are standards covering CGM in a few particular applications and scaling methods have been proposed to deal with large particle sizes. However, scaling methods are appropriate only under certain conditions. The scalping techniques consist in a simple approach for the geotechnical characterization of CGM. In this article, the scalping techniques analysed are divided in: the scalping method, the matrix method and the scalping/replacement, which are studied in detail in terms of its effectiveness, focusing on the geomechanical characterization of CGM. As a main conclusion, these three techniques are limited in its use under small scalping ratios (3 < r < 8) which is the ratio of maximum particle size of both original and scalped gradation. Finally, recommendations for the use of percentages and ratio of scalping are provided.

The geotechnical characterization of coarse granular materials such as very coarse-grained soils, rockfills, mining waste rocks and related materials is one of the key themes in geotechnical engineering but least studied and developed. Although there are some geotechnical standards and accepted geotechnical practice, there is not a standard for size-scaling, which is a critical step in advanced stage engineering (i.e. detailed design) on large structures involving this kind of materials. Several size-scaling techniques are available for use, with advantages and disadvantages. Among these, the parallel gradation method PGM (also known as homothetic grain size distribution), is one of the current practices and used for more than 50 years, but surprisingly just a few studies have corroborated its capability, and under specific material types. This work assesses a detailed database covering the development of this method from its first uses up to now. The application of this method is analysed based mainly on the material maximum internal friction angle and the Marsal’s particle breakage index (Bg).