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UBC Theses and Dissertations

Design and construction best practices for dugout earth dams in northeast British Columbia Smith, Kalie


In the Peace River Region in northeast British Columbia, dugout reservoirs, which classify as dams under the Water Sustainability Act, are used to store fresh water for oil and gas activities. These dams are constructed using native silt and clay soils with low strength properties and susceptibility to erosion and freeze-thaw. Site visits were conducted in August 2018 and May 2019 at seven dams. Soil samples were collected for laboratory testing to determine material properties for the soils used to construct the dams. Aerial images were captured with drones for topographic analysis using photogrammetry to determine as-built conditions. Numerical modelling was conducted to analyze seepage and stability under steady-state conditions. Probabilistic and sensitivity analyses were used to assess the impact of strength properties and dam geometry. Observed as-built conditions were compared with designs and existing best practices for construction. Where recommended best practices are not followed, the methods used were evaluated. The objective is to make recommendations for best practices for design and construction of dugout earth dams storing fresh water for oil and gas activities in northeast BC. Seven key areas of dam performance were analyzed at each of the seven dams: embankment stability, hydrotechnical considerations, internal seepage, surface erosion protection, construction, appurtenant structures, and maintenance. Embankment slopes were typically designed to follow recommendations but were often constructed steeper than designed. Erosion protection blankets are not as effective as riprap for protection against wave action. The value of cohesion varies for similar soils, and embankment stability is very sensitive to this parameter. Blanket drains are effective for managing seepage and preventing piping. Existing guidelines for freeboard and spillways are typically followed and are found to be appropriate. Lift thickness and compaction equipment varied, and dams should be overbuilt to ensure that adequate freeboard is maintained after consolidation settlement.

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