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

Weathered granitic rock is a material with properties intermediate between soil and hard rock. It retains structural features of the hard rock, including joint fractures, but also has porosity generated as a result of weathering of primary minerals, clay formation, and root invasion. This study evaluated the physical and hydraulic properties of moderately and highly weathered granitic rock (class 5 and 6, respectively, of the classification scheme of Clayton and Arnold (1972)) in the San Jacinto Mountains of southern California. Class 5 and 6 samples exhibited comparable bulk densities (approximately 1.94 g cm-3), porosites (27%), and particle size distributions. Saturated hydraulic conductivities were also similar for both weathering classes (approximately 5.5 cm h-1). Water retention data indicate that about 50% of the water held at saturation is drained at -100 cm head. Effective pore size distributions calculated from water retention data indicate that 25% of the total porosity was associated with pores >100 mum in diameter.