A brief description is made of the rockfill laboratory of the Comision Federal de Electricidad in Mexico. Equipment is available for large-scale (specimens 113 cm in diam) triaxial and compressibility testing of granular materials with maximum particle size up to 20 cm, under lateral pressures up to 25 kg per sq cm. Results of triaxial tests run with three different rockfill materials are presented. The influence of gradation, confining pressure and particle breakage are discussed.