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Western Dam Engineering Technical Note 19 Photo 2.Prefabricated concrete armoring mats for the crest of an overflow spillway. 6.Concrete and Soil Cement Mix Designs – Mix designs are often allowed to be proposed by the contractor or supplier of the product, subject to meeting the specification requirements. Specification requirements generally include strength and durability criteria, cement content or water/cement ratio, air content, workability, alkali reactivity, etc. For critical applications the engineer may want to specify the mix design, allowing the contractor to propose modifications or alternatives. 7.Temporary Construction Facilities (field offices, erosion control during construction, water quality protection, traffic control, temporary utilities, site fencing, temporary foundation pads, access roads, etc.) – These types of facilities are usually left to the discretion of the contractor, subject to general parameters established by the engineer and permit requirements. Be sure to keep in mind the owner’s use of the site during construction and include that information in the specifications if necessary. 8.Specialty Geotechnical Work – Specialty geotechnical work, such as mechanically-stabilized earth walls, liner designs (whether geosynthetic or asphalt), slurry trenches, dynamic deep compaction, temporary shoring, etc., may benefit from the contractor’s or subcontractor’s particular expertise associated with the specialty work. The specification would state any relevant design criteria, but the actual specifics of the system may be best developed by the specialty contractor. The engineer can always weigh-in when reviewing a submittal. 9.Prefabricated Structures – prefabricated structures such as small box culverts, small bridges, and abutments, may also be good candidates for design by others. Some items are not particularly well-suited to team effort specification approaches. These would include those elements where rigid design criteria must be met, such as with designation of appropriate materials for filters and drains, dam core material, or any other item that the engineer has identified as being either critical to the overall design intent or needing to meet narrowly- defined design criteria. For example, gradation limits for filter and drain materials are determined by using established, documented engineering procedures, and should not be left open to contractor input. Similarly, the use of specific borrow materials available on site for dam core material and embankment shells is best understood by the engineer and should not be placed in the team- effort realm. What about Value Engineering? Value engineering, where the contractor suggests changes to the approved design or allowed methods of construction with the goal of reducing costs, can be a useful tool in the right setting, but must be approached with caution. The engineer must be certain that the proposed change fits within the overall design and does not compromise the original design criteria or intent. Contractors may propose alternatives that are not consistent with standard dam safety practice (i.e., proposing the use of geosynthetic drainage materials in lieu of sand filters). Value-engineered proposals can also result in construction delays while the proposal wends its way through the required regulatory review channels. QA/QC Responsibilities: Owner/Engineer or Contractor? In a team effort environment, whose responsibility should it be to conduct quality control / quality assurance activities? This can be set up several ways. Traditionally, “quality control” (QC) was deemed the responsibility of the contractor to demonstrate that the work product met the specification requirements, and “quality assurance” (QA) was the responsibility delegated to the owner’s representative to review and independently verify the contractor’s QC results.