Design criteria for remedial works for a 75-year old earthfill dam

摘要

The safety of existing dams is a major issue faced by today's dam engineers not only in Australia but also in other countries, both developed and developing. Churchman Brook Dam is a 26m high earthfill dam with a puddle clay core and impounds a reservoir of 2.2 GL. Various remedial works have been undertaken since completion of construction in 1928. In September 2000, a sinkhole in the right abutment was observed during a routine dam inspection. Following this incident, detailed site investigations were carried out. These investigations revealed that there are soft zones and possibly voids formed in the upper part of the clay core. A comprehensive dam safety study and a risk workshop undertaken in 2002/2003 showed the dam to be deficient in aspects associated with piping, spillway adequacy and outlet works condition. It was agreed at the early stages of the design phase that a rational set of design criteria be developed considering both safety and economical aspects. A rational geotechnical model was developed for the foundation utilising triaxial test data from 1980s and recent investigations. The existing spillway chute will be upgraded with a concrete liner attached to the existing chute incorporating no-fine concrete as a free-draining medium. This paper presents the various aspects of the remedial works with main emphasis on the development of the design criteria considering both safety of the dam and economy of the proposed remedial works.