Inspecting concrete dams: interpreting data and visual signs of change

Abstract

The inspection of concrete dams, generally on rock or other hard foundations, requires the understanding and interpretation of visual signals and often small movements and behavioural changes. The visual signals may be cracks or perhaps seepages. Behavioural changes may be signalled by measured data such as surveyed movements or measured changes in seepage flows. But in terms of causality, the seepage changes may have resulted from deterioration of the dam concrete or erosion within the rock foundation. Reduced seepage flows may be from beneficial reservoir siltation or may indicate blocked drains and higher uplift pressures adversely affecting sliding safety factors for the dam. Dimensional changes and movements of the dam may be due to imposed loading, chemical reactions or temperature. A key role which any inspection requires is the interpretation of such observations and measured data in terms of what they mean for the safety of the dam. This can be a detective exercise. In this paper, the writer draws on many years of experience designing and inspecting such works to give examples of such signs and changes and what they signalled in terms of dam behaviour.