Dams of local materials with shields and cores of cohesive impervious soils and shoulders of coarse-fragmental materials, such as gravel, rubble, and stone, with a comparatively small quantity of fine fractions (sand, grit, and clay) have gained popularity lately. Such dams in the USSR are: Nurek, Charvak, Vilyui, Sarsang, V. Tobol, Khantai, etc., and abroad --Oroville, Portage Mountain, Benmor, Cougar, Infiernillo, Gepaeh, and Shimen. The outlines of such dams and hence the volumes of materials needed for their construction are usually determined by their slopes, which are a function mainly of the shear strength or angle of internal friction of the coarse-fragmental materials.Since the volumes of modern dams are quite appreciable, even small variations of the angle of internal friction can cause substantial changes in the volume and cost of the structure. For instance, for the Nurek dam with a volume of about 60 million m3,a change of the angle of internal friction of the pebbles of the shoulders from 35" to 38 ~ i.e, by about 8%, will cause a decrease in the volume of the dam by about 4 million m 3 and of its cost by 10 million rubies.Despite the importance of this characteristic, until recently there were no reliable data on it here or abroad, as a consequence of which the angle of internal friction was often underestimated in designs, which led to an overestimation of the volumes of structures.Furthermore, it was noted that slopes of 1 : 1 and even 1 : 0.7 were used in rockfill dam construction, although the angle of repose of the fill was 36~ ~ to which corresponds a slope of I : 1.3-'1 : 1.4.Large instruments for the determination of the shear strength of coarse-fragmental materials were first used in the design and construction of the Svir, Dar'yal, and Ortotokoi dams in the USSR and the Fort Peck dam in the USA. However, these investigations were carried out tximarily With rubbly soils with a high content of clay fractions on instruments whose sizes and Ioads were far from sufficient. For this reason it was impossible to make any general conclusions on the basis of these investigations.