The utilization of rockfill material for the construction of high dam, which in some cases reached 1000 ft (304.88 m) in height, has been greatly increased in recent years to meet the demand of storing large quantities of water and to generate more hydrauelectric power. Rock-fill materials are usually varies in size, shape, mineral composition, and capacity to allow the passage of water. Such variations are reflected. on its engineering properties as strength and compressibility under load, which ultimately dictate the size and shape of the rock-fill core section of a dam.
Laboratory test results reported by many investigators (Holtz and Gibbs 1956, Morris 1959, Vallerga et al 1957) indicated that the angle of internal friction increased with increasing angularity. On the other hand test by Marchi and coworkers (Marchi et al 1969) showed that at low confining pressure the shape of particle has no influence on 'the angle of internal friction; however, with increased confining pressure, rounded particles showed higher angle of internal friction than comparable angular particles.
Field and Laboratory studies have shown that the compressibility of granular and rock-fill material increased with increasing angularity (Kolbuszewski and Fredrick 1963, Lee and Farhoomand 1967, Robert and De Souza 1958), decreases with increasing coefficient of uniformity (Lee and Farhoomand 1967, Robert and De Souza 1958), and increases with maximum particle size (Kolbuszewski and Fredrick 1963, Lee and Farhoomand 1967).
As far as known the data available regarding the influence of particle shape on the strength and compressibility of granular and rock-fill materials are obtained using the conventional triaxial apparatus. However, the actual deformations of rock-fill dams and embankments are more closely simulated by plane strain conditions than axially symmetric stress condition. This study is concerned with the effect of particle shape on the strength and deformation of two granular materials sheared under plane strain conditions.
Two types of materials were used in the test program. The first is subrounded sandy gravel known as Painted Rock material obtained from Painted Rock dam in Arizona, U.S.A. The second material is called crushed Napa basalt obtained from Blue Rock Quarry at Napa California. Both materials were sieved, and particles larger than No. 3 and smaller than No. 30 U.S. standard sieve were discarted. Fractions of the remaining material were measured and mixed to obtain straight line grain size distribution extending from No. 3 to No. 30 U.S. standard sieve size. Other physical properties of the material tested, as obtained using ASTM standard procedure are presented as follows:
(Table in full paper)
Testing Equipment The plane strain apparatus used in the test has been described previously in detail (Al-Hussaini 1971). The present description will, therefore, be limited to the main features of the apparatus, which are shown in Figure 1. The apparatus was built to test prismatic specimens 16 in. (406.4 mm) long, 2 in. (50.8 mm) wide, and 5 in. (127 mm) high by subjecting it to three mutually independent principal stresses.
