PHYSICAL AND HYDRAULIC-PROPERTIES OF WEATHERED GRANITIC ROCK IN SOUTHERN CALIFORNIA

Weathered granitic rock is a material with properties intermediate bet ween soil and hard rock. It retains structural features of the hard ro ck, including joint fractures, but also has porosity generated as a re sult of weathering of primary minerals, clay formation, and root invas ion. This study evaluated the physical and hydraulic properties of mod erately and highly weathered granitic rock (class 5 and 6, respectivel y, of the classification scheme of Clayton and Arnold (1972)) in the S an Jacinto Mountains of southern California. Class 5 and 6 samples exh ibited comparable bulk densities (approximately 1.94 g cm-3), porosite s (27%), and particle size distributions. Saturated hydraulic conducti vities were also similar for both weathering classes (approximately 5. 5 cm h-1). Water retention data indicate that about 50% of the water h eld at saturation is drained at -100 cm head. Effective pore size dist ributions calculated from water retention data indicate that 25% of th e total porosity was associated with pores >100 mum in diameter.