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Andrew Pattle and Bram Knoop
This paper provides an outline of a process that can be used to optimise regular dam surveillance and monitoring activities. The process is applicable for a wide range of dam types that an owner/operator may be responsible for. Basic assessments are made of inherent reliability and potential consequences of failure using key factors such as construction features, foundation conditions and observed performance. The key factors are combined to give a relative risk ranking for each dam. These rankings are used to determine specific dam monitoring schedules. The process focuses the monitoring effort on those dams that are perceived to constitute the greatest portion of the overall risk. The methodology is simple and provides a cost-effective framework for setting appropriate resourcing levels for dam monitoring.
A safety review of the Corin dam has identified several deficiencies including an inadequate spillway capacity. A hydraulic model test, included in the review indicated that the construction of a 1.3m wave wall along the top of the dam was required to prevent overtopping during the flood of 10,000 years.
The original post tensioning anchors installed along the spillway crest were also identified as unreliable due to inadequate corrosion protection measures.
This paper presents safety assessment and aspects of the construction of the remedial works for Corin Dam. As part of the safety review, the condition of the dam was reviewed against the risks of piping, slope instability, flood and seismic forces. The paper also discusses the long term effects of the acidic leakage on the grout curtain and on the integrity of the core.
The risk associated with the flooding during anchor installation and the discovery of a gap formation between the clay core and the concrete spillway wall are also considered.
Over the last 30 years, the demand for water storages in Queensland’s Mary’s River has grown significantly. As a result of this growth in demand it was decided to raise Borumba Dam, the major storage on the system, in two stages The first stage was to be approximately 2 metres in I997 and the 25 metre raising be required in about 2010.
Borumba Dam was completed in 1964. It is a 43 metre high concrete faced dam with a 32 metre long on the left abutment. The first proposal for initial raising was to install a two metre high air-inflated rubber dam on top of the existing crest. However, it was determined that this method of raising presented a number of prob and a new solution was sought.
Leonard A McDonald and Chi Fai Wan
A risk assessment has been undertaken as part of a comprehensive review of the safety of Hume Dam. Use of risk assessment techniques, to assist in evaluating the safety of existing dams, is a relatively recent trend. Hume Dam was a particularly challenging subject for the application of risk assessment techniques at their present stage of development. The challenge lay in the number and diversity of dam elements to be analysed, in the number and complexity of the potential failure modes and in the fact that there were significant safety issues under normal operating conditions.
This paper outlines some of the key lessons learned from that phase of the risk assessment that was concerned with estimating the chance of dam failure. Some of the issues discussed have not previously been addressed in the literature and some demonstrate a clear need for improved analysis procedures.
Raymond A. Stewart
On I7 June 1996 while investigating a small pothole on the crest 183 m high Bennett Dam an unexpected crest collapse occurred resulting in a large sinkhole. Following this incident the safety status of the dam was uncertain. The reservoir was lowered by 2 m over a six week period by spilling up to 5,000 m 3 over the spillway and through the turbines.
An unprecedented dam investigation commenced immediately and was completed December 1996. During drilling a second sinkhole was discovered at another location on the dam.
A sophisticated compaction grouting technique was developed to remediate the sinkholes to the depth of 5 m and the work was successfully completed by 1997. -The reservoir was returned to service in time to collect the freshet in spring 1997. This event was the most dam safety concern in the history of BC Hydro operations.
This paper describes how B.C. Hydro managed the crisis, and the subsequent safety assessment.