Deeply weathered rock at victorian damsites

Two major features of weathering at Victorian damsites are joint controlled weathering and sub-basaltic weathering. These features have received attention in the literature from geologists generally engaged on engineering projects. The author has been fortunate to have been associated with geologic investigations at more than fifteen damsites where the features have been exposed.

Weathering at Australian sites is typical as it tends to occur where water is most often present. Barriers within or above the subject rock direct percolating waters to some locations and protect others.

The significant feature of joint controlled weathering is that the relevant barriers, the limonite-coated joints, are themselves the product of earlier weathering and provide the avenue for water penetration into the rock mass bound by the joints.

Sub-basaltic weathering appears to be due to the effect of the basalt cap in concentrating percolation through vertical joints.