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<br />14 <br /> <br />Feasibility Report for Dam Safety Modifications to DeWeese Dam <br />April 22, 1997 <br /> <br />intensive. This, combined with more difficult access to the exterior surfaces of the crest raise <br />sections, is expected to result in a substantial increase in the unit costs for demolition, compared <br />to those for Alternative No, I. <br /> <br />It is uncertain as to what extent the deteriorated concrete penetrates beyond the existing surfaces <br />of the crest structure, The depth of concrete removal required will not be known with certainly <br />until the time of construction, and will vary along the length of the crest. For the purposes of <br />this study, it was assumed that a uniform thickness of I foot would need to be removed from the <br />upstream and downstream faces of the dam as well as from the top surface, In addition, the top <br />2 feet ofthe crest would be removed to create a horizontal working surface for installation of the <br />passive reinforcement anchors, <br /> <br />Disposal of the concrete removed from the dam crest is an issue that will need to be addressed <br />during the final design phase of the project. Our estimates for this study indicate that about 530 <br />cubic yards of demolished concrete would have to be disposed of for this alternative. Similar <br />to Alternative No.1, two options available for disposal of the demolished concrete are: I) <br />disposal of the concrete in the reservoir, or 2) disposal of the concrete off-site. While disposal <br />of the crest concrete in the reservoir would be less costly, care would need to be taken to ensure <br />that the discarded concrete does not interfere with the operation of the outlet works or with <br />recreational boating during times of low reservoir levels. Our estimated costs for this alternative <br />assume the demolished concrete will be disposed of off-site. <br /> <br />Drainage/Seepage Provisions <br /> <br />Similar to Alternative No, I, relief of uplift pressures and control of seepage along the base of <br />the crest section will be an effective way to improve the structural stability of the rehabilitated <br />crest section. Accepted practice [5] allows for a reduction of uplift pressure if a drain system <br />exists within the dam, The proposed drain system for Alternative No.2 would consist of the <br />following components: <br /> <br />Expandable Waterstop: Construction of a new concrete cap over the existing crest raise sections <br />and on top of the original dam concrete would make the effective installation of conventional <br />PVC waterstop difficult. However, there are several expansive-type waterstops available, which <br />are effective in controlling seepage through concrete joints. <br /> <br />PVC Drains & Drilled Outlet Holes: The drainage system for Alternative No.2 consists of the <br />installation of 3-inch-diameter quarter-section PVC drain pipe at the upstream heal of the <br />existing crest section, Similar to Alternative No,l, the PVC drain pipe would extend along the <br />entire length of the crest and would include outlets drilled through the crest concrete at <br />approximately 40-foot spacing (the actual spacing of the drain outlet holes would be determined <br /> <br />~ GEl Consultants, Inc, <br /> <br />96006\REPORTS\FEAS\TEXT,NEW <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />