ABSTRACT
The Older Volcanics occur in extensive sheets over some relatively large areas of the Melbourne region, a large proportion is covered by younger sediments and sometimes the Newer Volcanics. Weathering of the Older Volcanics can be very variable, depending on such factors as number and composition of flows present, presence of tuffaceous phases, and history of exposure. The residual soils formed on the Older Volcanics are either high plasticity clays or silts, usually with a low sand and gravel content, but with occasional coarse fractions up to approximately 40%. Reactivity data on the clays within the study area are limited to the North Melbourne area, where a number of buildings supported on shallow footings founded in residual Older Volcanics material have experienced shrink/swell damage. Fresh, intact Older Volcanics rock can have very high strength and correspondingly high modulus values. The Older Volcanics can exhibit a wide range of transmissivity, depending on thickness and rock mass weathering characteristics.
