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II I I I I I I I I I I I I I I I I I I Concrete Pipe - The concrete pipe was assumed to be capable of withstanding a pressure head of between 160 and 2DO feet of water. Apparently, higher class concrete pipe is not readily available. Therefore, if additional strength is needed, concrete pipe may not be practical. The concrete pipe was assumed to have bell and spigot joints. Concrete Pipe Installation - The outside diameter of the concrete pipe is only 5 inches less than the width of the tunnel. Therefore, the concrete pipe will have to be installed sequentially from one end with a specialized system. A rail line could be used to slide or roll the pipe into the tunnel and would aid in aligning the segments. The rail line would be sacrificed and left in place at the end of the project. Special care would be required to align and connect the segments. Pipe Bedding - All three alternatives were assumed to require six inches of pipe bedding to cushion the pipe on the tunnel invert. It is anticipated that this material will be two inch minus, well graded, clean gravel. Pipe Cradles and Supports for Alternative I - The purpose of the pipe cradles in alternative I is to prevent lateral movement of the pipe. It was assumed that the pipe would rest on the pipe bedding with the cradles used only for lateral restraint. The cradles could be relatively simple consisting of curved concrete or wooden blocks. For the purposes of cost comparison, it was assumed that the cradles would be placed every I DO feet along the length of the pipe. Sand Backfill for Alternative II - The annulus between the pipe and the tunnel should be filled with a relatively stable material. For the purposes of this study it was assumed that a clean sand material would be sufficient for this purpose. At this time, grouting is not anticipated to be necessary. The sand could be placed pneumatically from the end of the tunnel with two or more air lines. The sand would not be compacted. The sand would be uniformly graded clean material. The cost presented in the table includes both materials and placement of the sand. Granular Backfill for Alternative m - The granular backfill for alternative III was assumed to be 2 inch minus, well graded, clean gravel. It is anticipated that this material will be moderately compacted using hand operated equipment. The costs presented in the cost table include both materials and labor. Although the material is similar to the pipe bedding, the cost of installation for the granular fill is expected to be greater because of the tighter working conditions and need to work around the pipe. 22