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Western Dam Engineering <br /> <br /> <br /> <br />14 <br />done both at the source and after placement to <br />evaluate particle breakdown. QC of large diameter <br />(i.e. > 12-inch) materials, such as rockfill and riprap, is <br />generally limited to visual inspection. <br />Many regulatory agencies require a “Construction <br />Observation Plan” as part of the pre-construction <br />submittals for review and approval. Consistency <br />should be maintained between the project <br />specifications and the Construction Observation Plan <br />to avoid confusion among the project team. <br />Seasonal Shutdown Considerations <br />Cold weather placement of earthfill materials is <br />undesirable as it can lead to frost, heave, voids, <br />difficult moisture control, lenses that may lead to <br />seepage, and an overall weakened mass. A limited <br />amount of cold weather earthfill placement may be <br />unavoidable. In these cases provisions may include soil <br />heaters, blankets, 24-hour work schedules to keep fill <br />“alive” and avoid frost buildup, more intensive QA/QC, <br />and removal of any fills negatively impacted by <br />weather. <br />Any dam construction project that will require more <br />than one construction season to complete to avoid <br />adverse weather conditions will need to have <br />specification provisions for shutdown of the site to <br />protect the work that has already been completed. It <br />will generally be left to the discretion of the engineer <br />to decide when the seasonal shutdown is necessary, <br />based on conditions experienced at the site. In cold <br />weather climates, this will involve protecting the work <br />from the effects of freezing temperatures and excess <br />moisture in the form of snow. Exposure of compacted <br />earth materials can lead to the formation of frost and <br />ice lenses within the material, altering its density and <br />structure to an unacceptable state. <br />Specifications should require that all placed and <br />compacted fill materials, at least those within the <br />impervious zone(s) of the dam, be protected from <br />freezing by the placement of sacrificial loose soil <br />materials to a depth sufficient to insulate the fill from <br />freezing. Surfaces should be sloped to drain to prevent <br />rainfall and snowmelt from saturating placed soils. <br />Exposed filters and drains should be capped with fine- <br />grained sacrificial materials (usually separated with <br />geotextile), to be removed when construction <br />resumes. Concrete work must be protected from <br />freezing temperatures during the initial curing period, <br />and so may require the use of blankets and/or heaters, <br />or accelerants in the mix, during cold weather leading <br />up to winter shutdown. <br /> <br />Poor weather can often mean lower quality and <br />higher cost. <br />Maintaining river diversions and necessary dewatering <br />of the worksite can be problematic during seasonal <br />shutdowns, and these issues should be considered and <br />discussed within the specifications. The specifications <br />should also discuss what provisions are required to <br />verify and validate the adequacy of previously <br />completed work at the re-initiation of construction at <br />the end of the shutdown period. <br />Contractor Qualifications <br />For many construction projects, it is difficult to <br />anticipate what contractors might bid on the job and <br />just what their qualifications are, let alone who the <br />winning contractor might be in an open-bidding <br />scenario. Since dam construction projects tend to be <br />unique in their requirements and challenges versus <br />other heavy civil construction, having a contractor who <br />is experienced in dam construction is nearly always <br />advantageous, if not crucial, for success. <br />Requirements for contractor qualifications should be <br />incorporated in the bidding package to ensure they <br />demonstrate familiarity and experience with dam <br />construction upon bidding. This includes minimum <br />required qualifications for the general contractor as <br />well their proposed key subcontractors (i.e. grouting, <br />blasting, and manufacturers assigned to design certain <br />components). Qualification requirements should <br />include the key staff (Superintendent, Construction <br />Engineer) and not just the overall company. In some