ArticlesHow Healthy Are Your Dams?
So, how healthy are your dams? Whether you are a municipality, industrial complex, sawmill, conservation authority, water commission, mine operator, institution, etc. if you design, operate or otherwise maintain a dam you should be aware of the CDA requirements. The above comments are meant only as an overview. For more detail on the CDA requirements regarding safe dam management, contact your provincial director or a consulting firm that specializes in dam safety and design.  “The Four Pillars of Dam Safety”
Dams have been around for millennia and are common throughout the world. Originally, earth dams consisted of little more than earthen embankments while concrete dams tended to be mortar and rock structures. These structures evolved into reinforced concrete, timber and other core type earth dams in the nineteenth century. In the past half century, dams have been developed as part of the hydroelectricity and mining industries, using improved technology to become much larger and more sophisticated. With increased sophistication in construction came a parallel requirement for sophistication in engineering and management. Semi-probablistic Design Methodologies for Earth Dam and Foundation DesignAuthor: Perry Mitchelmore ABSTRACTPresently, a geotechnical assessment of dams is expressed as a factor of safety, the ratio of resistance to demand. The capacity is established using deterministic methods that are influenced by engineering judgment, a degree of conservatism in material parameter selection and assessment of the structure. While different absolute values are used for different load combinations, safety factors are not a suitable measure of relative reliability for geotechnical structures. An alternative approach, increasingly adopted in other fields of geotechnical engineering is the probabilistic approach. In a probabilistic analysis, uncertainty in material parameters and loading conditions is quantified through statistical analysis or by the engineer exercising their judgment. A probabilistic analysis provides a measure of reliability of the structure that can be applied to economic analysis for both capital and maintenance decision analysis. Recent publications of the National Building Code of Canada and the Canadian Bridge Design Code include Load and Resistance Factored Design (LRFD) methodologies for foundation design. These methodologies are semi-probabilistic and may eventually provide the technological bridge that transforms geotechnical analysis from deterministic to full Probabilistic analysis methods. Despite this evolution in foundation and earthwork design methodologies, dam design and foundation design for dams still relies exclusively on the Working Stress Design (WSD) method. This paper examines WSD, LRFD and reliability based design approaches, their development, fundamentals, advantages and limitations. The objective of the paper is to learn from the experiences of the foundation engineering community in introducing LRFD and reliability methods to learn how theses methodologies can be introduced in dam design and assessment. Perry Mitchelmore, P. Eng., of Meco (Mitchelmore Engineering Company Ltd.), can be reached at (902) 444-3131 or email at: info@mecoengineers.com. Geotechnical Characteristics of Sediments on the Western Central Scotia SlopeAuthor: Kevin MacKillop, Kate Jarrett, Perry Mitchelmore, Dave Mosher, Calvin Campbell ABSTRACTRecent oil and gas exploration in Eastern Canada has included deep water regions of the Scotia Slope. The Geological Survey of Canada in collaboration with non-government agencies, has undertaken a program to understand deep water margin geologic processes and potential geohazards. Short (<10 m) piston cores have been analyised to assess the geology, geotechnicial properties, stress history, and static failure potential. These geotechnical data indicate that the sediment is overconsolidated near the surface to normally to slightly underconsolidated with depth. A slope stability analysis of near surface sediments was evaluated using the infinite slope method of analysis. A limited comparison of results using wedge analysis techniques was completed using XSTABL software. This slope stability analysis shows that surficial sediments are stable (FS>1) under undrained static conditions. Earthquake loading was evaluated by calculating the earthquake-induced horizontal acceleration required to cause failure. The horizontal acceleration required to cause failure varies from 0.013g to 0.046g.
Kevin MacKillop, GSC (Atlantic), Nova Scotia, Canada Perry Mitchelmore, P. Eng. of Meco (Mitchelmore Engineering Company Ltd.), can be reached at (902) 444-3131 or email at: info@mecoengineers.com. Seismic Design Considerations for Atlantic CanadaAuthor: Valerie Latour, EIT and Perry Mitchelmore, P. Eng. of Meco (Mitchelmore Engineering Company Ltd.) The Canadian Dam Association (CDA) Dam Safety Guidelines - Technical Bulletin for Dam Safety (CDA 2007) recommend a progression of steps for the design or assessment of safe dams under seismic loading. Initially, each design should start with simplified analysis, such as pseudo-static analyses. If the preliminary assessment indicates a potential problem, or if there is some doubt about the simplified assessment, the designer should progress to a amore detailed method. More detailed analysis includes Newmark - Type deformation analysis, dynamic response analysis, or non-linear deformation analysis. The application of seismic design criteria is different in the Atlantic and Western Regions of Canada (Adams 2007). This paper presents an extensive review of the available literature with the focus directed toward practical design techniques available to design professionals - with particular consideration of solutions for the unique challenges present in Atlantic Canada. The available methods presented in the literature will be applied directly to a Nova Scotia case study of a small concrete gravity dam to evaluate their applicability from a consulting engineer's perspective. Valerie Latour, EIT and Perry Mitchelmore, P. Eng. of Meco (Mitchelmore Engineering Company Ltd.), can be reached at (902) 444-3131 or email at: info@mecoengineers.com. Small Dams in CanadaLarge dams are significant engineering achievements and their profile with the public is justifiably high. This has resulted in the perception that the majority of dams in Canada are large dams. However, it is intuitively known in the dam safety community across Canada that small dams outnumber large dams by a wide margin. Small dams frequently have Consequence classifications of High; however, their lower profile with the general public often results in dam safety programs for these structures being a lower priority. Several Canadian provinces maintain databases on dams in their jurisdiction, compiling data on physical parameters, types, classification, owner, etc. Databases from selected provinces were used by the authors to develop descriptive statistics on dam features, distribution of risk, purpose and other pertinent data. The distribution of various consequence classifications for varying heights of dams are discussed with focus on small dams and small dam owners.
Chris K. Grapel, P. Eng., EBA Engineering Consultants Ltd., Edmonton, Alberta, Canada Perry Mitchelmore, P.Eng. of Meco (Mitchelmore Engineering Company Ltd.), can be reached at (902) 444-3131 or email at: info@mecoengineers.com. |
