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Climax Mine - CAVR Asbestos Disposal Shaft; Closure Plan <br />November 15, 2012 <br />105 pounds per cubic foot (pcf) plus a 1.6 factor of safety. <br />Construction details for the concrete shaft cap are presented on Sheets 2 and 3, attached. The <br />shaft cap will be a two -foot thick cast -in -place reinforced concrete 'plug' constructed within the <br />conical section of the existing shaft collar. Wood formwork will be constructed and placed near <br />the bottom of the conical section (Sheet 3). The formwork has been designed to fully support <br />the weight of the wet concrete plus a 100 pounds per square foot (psf) live load. Wood <br />formwork was selected in favor of corrugated metal formwork for ease of construction and <br />installation within the circular opening. Three steel reinforcement bars (rebar), or shear studs, <br />will be embedded into the existing concrete at six locations around the circumference of the <br />conical section. Three rebar hoops will be placed at the locations of the shear studs near the <br />perimeter of the concrete cap section, as illustrated on Sheet 2. In addition two rebar mats will <br />be placed near the top and bottom of the concrete cap. The rebar mats will resist flexural <br />stresses within the concrete, and the purpose of the hoops is to prevent the transfer of <br />unacceptable stresses into the existing concrete slab and shaft collar. Because of the <br />placement within the conical section of the shaft collar, and with the aid of the rebar hoops, the <br />cap will act similar to an arch structure, allowing it to safely withstand the loading associated <br />with up to 100 feet of overburden soil. Also, as shown on Sheet 2, the top of the concrete cap <br />will extend a minimum of one foot beyond the outside edge of the existing shaft collar, with the <br />surface of the cap five to eight inches higher than the existing concrete slab. This overlap <br />feature, with the upper rebar mat included, will minimize the potential for surface water to enter <br />the shaft and create an air flow barrier. The surface of the cap will be sloped to shed water off <br />of the cap. <br />To meet the design criteria, a concrete mix design with a 28 -day minimum compressive strength <br />of 4,000 psi is required. The mix has been designed with Type V Portland Cement that is <br />resistant to sulfates that could be present in the overburden fill material. To provide an <br />additional factor of safety and to create a concrete surface less susceptible to weathering and <br />degradation a mix design with a 28 -day compressive strength of 6,000 psi has been specified, <br />and the concrete will be sealed with an epoxy coating. The rebar used will have a minimum <br />yield strength of 60,000 psi and the shear studs will be epoxy coated to reduce the risk of <br />corrosion. Material specifications will meet or exceed those included in the DRMS IMR General <br />Bid Specifications, where applicable. In addition, form placement, reinforcing steel installation, <br />and concrete pouring will be conducted in general conformance with the IMR General Bid <br />Specifications. <br />Construction activities will be observed under the direction of the project engineer. Construction <br />observations will include an inspection of all materials delivered to the project to ensure they <br />meet or exceed the project specifications, as well as observations of the execution of all work <br />elements. Field quality control testing will be performed in general accordance with the DRMS <br />IMR General Bid Specifications, and will include field testing of slump and entrained air and the <br />preparation of a minimum of four test cylinders to verify the compressive strength of the <br />concrete. One cylinder will be tested at seven days after placement, two at twenty -eight days, <br />2 <br />