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The area prepared for the concrete plug is shaped into a cone where a minimum of 3 sides are <br />competent rock. <br />Technical Specification Section 03320, 3.01 Installation addresses this procedure. <br />The 3 -foot thick concrete plug and 7 -foot thick cemented rockfill are placed according to Technical <br />Specification Section 03320 and Section 03310. <br />The intent of the conical shape of the concrete plug and cemented rockfill is to prevent the structure <br />from settling. <br />The coarse shaft backfill provides a platform similar to concrete forms that are removed after the <br />concrete has cured. <br />2) Has CC &V had any experience with underground workings caving in or collapsing after the <br />concrete plug has been installed? <br />We are not aware of any instances where the concrete plug has collapsed. <br />Please let us know if you have additional questions. <br />S rel <br />r - <br />Timm Comer <br />Manager, Environmental Resources <br />Cc. Ron Roberts — Project Management Consultant and Scott Redabaugh — Construction <br />Superintendent <br />