Guidelines For Geotechnical Investigations of Dams, Their Foundations And Appurtenant Structures (May 2020)
Dam safety requires a thorough understanding of the characteristics of the foundation and the materials that will be used, or have been used, for construction of a dam. These guidelines aim to improve practice to benefit dam owners through more effective and targeted investigations required to answer key questions about dams and their foundations.
Guidance is provided to owners, those preparing briefs for site investigations and for consultants carrying out the work. The Guidelines have been prepared to cover all types of water storage and tailings dams, both new and existing.
Common issues and objectives are described along with the steps required to undertake the investigations and appropriate methods.
These Guidelines are the culmination of extensive voluntary work by the Chairman, Emeritus Professor Robin Fell, and his Working Group. It is a significant development for dam engineering in Australia and will be a valuable resource.
In Australia we have a very diverse portfolio of dams, some regarded as being designed and constructed before there was a good understanding of the loading conditions that could apply. Sometimes there is limited knowledge of the actual details of construction and always there is a desire to ensure that the community’s resources are properly applied. The difficulty facing those who allocate funds for the benefit of the community measure the cost against the benefit achieved and to compare that with opportunities available.
Risk Assessment gives us the tools to estimate the likelihood of a circumstance occurring and of its consequences. It also gives us the tools to estimate what these will be after any improvement. These tools are diverse and can be imprecise. As time goes on our methods will improve but chance and circumstance will always be with us. But, if we use consistent methods, we will generally be able to rank the possible outcomes and compare them, in scale, with others.
ANCOLD is aware of the diversity of dams and the circumstance associated with them and offers this document merely as an indicator of the approach that may be taken. Nevertheless we hope that its adoption will lead to greater comparability between individual workers.Learn more
The application of risk assessment involves a major philosophical addition to, and enhancement of the deterministic standards developed over many years for appropriate safety of dams. These guidelines are issued to provide more appropriate and consistent guidance within a risk process, for dam safety evaluation under floods. In applying them, it must be remembered that they are guidelines only to what is considered current acceptable practice and allow owners and practitioners flexibility to exercise professional judgment in all aspects. Indeed, without the application of such judgment, the procedures themselves could lead to results that have serious shortcomings.
This is a rapidly developing area with ongoing research in many related aspects. In view of this ANCOLD will review the guidelines periodically and, to that end, seek comments from users at every opportunity.Learn more
These dam safety guidelines are intended to apply to what might be termed conventional dams (eg. for water supply, irrigation, power and flood mitigation). Guidelines for dam safety management of tailings dams are published separately.
These guidelines have been developed by ANCOLD with the aim of promoting appropriate dam safety management practices in Australia. It is recognised that circumstances vary enormously from dam to dam and different administrative frameworks apply in each state. Some states have specific dam legislation while other rely on more general provisions. For these reasons, ANCOLD puts this guideline forward as an advisory document that must be interpreted by appropriately qualified and experienced professionals in each case. In no sense is it intended that they should be regarded as a standard.
The guidelines will again be reviewed when knowledge and practice have developed to the point where an upgrade is required. With this in mind, comment from users and others is welcomed.Learn more
Within about ten years of the 1991 edition of the ANCOLD Guidelines on Design Criteria for Concrete Gravity Dams being published the Limit State design approach it proposed fell out of favour with Australian dam engineers. The ANCOLD Executive recognised this situation and resolved that the Guidelines be revised to reflect the preferred design approach amongst Australian dam engineers. A Working Group and a separate Expert Review Panel were formed in 2005 to review the Guidelines with the intention of preparing a document that was not only more in line with the current thinking but would also be widely adopted and used by practicing dam engineers.
It has not been an easy task for the Working Group and the Expert Review Panel. Although the working stress method, with associated Factors of Safety, approach was agreed amongst the team, it took considerable time and effort to reach consensus on the details, in particular chapters four through to six. The issue that took most effort to resolve was how the Factors of Safety relate to the level of certainty of the inputs, including knowledge of the foundations, loads, strength of materials and assumed mechanically feasible failure surfaces. The notes to Table 6.4.1 and the discussion in Appendix A highlight this issue.
One thing the drafting team agreed on early, and unanimously, was the importance of the concrete gravity dam design team having a thorough understanding of the foundation conditions, the development of a detailed geological model of the foundations and an understanding of the kinematically feasible failure mechanisms. In keeping with this principle, this revision of the guidelines has the section on foundations at the front of the document. There is a strong recommendation that the design team has expertise covering foundation geology and rock mechanics as well as the dam engineer.
These Guidelines provide a basis for design of concrete gravity dams in most situations. However, they require that the user will be a professional dam engineer with significant experience who is able to use sound engineering judgement in the application of the guidelines. It is recommended that less experienced dam engineers using these guidelines do so under the advice and guidance of an experienced dam engineer. It is the dam engineer who is responsible for the design.
On behalf of ANCOLD I would like to thank the members of the working group and all the other contributors that persevered in developing and bringing these Guidelines to fruition. They will be of great assistance to dam engineering professionals both within Australia and internationally.Ian Landon-Jones Chairman, ANCOLD Learn more