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