Spillway case study (continued)

In prior applications, 8 inch thick ABM has successfully withstood unit discharges in excess of 100 cubic feet per second/per foot, which is the approximate equivalent to the expected discharge of the spillway at this project site, however, as an added factor of safety, it was decided that intermediate anchoring would be necessary every 120 feet along the 10% slope section of the spillway to resist drag forces. A poured concrete “deadman” anchor, constructed approximately 5.5 feet below grade, will secure each 120 foot long section of ABM. Each subsequent ABM panel would then be positioned to provide a 5 foot minimum overlap of the previous panel to serve as an “expansion” joint. The panels along the sides of the spillway would be installed in a 3 feet deep terminal trench and subsequently buried to provide additional anchoring. The design analysis concluded that the 8 inch ABM, utilizing these methods of installation, would produce a factor of safety greater than the targeted 1.5 to 1. 

referencing each panel, identified numerically, with a panel layout plan prepared by ARMORFORM, Inc.

Construction

A local contractor, McGraw & Son Construction Company, Inc., Glen Daniel, West Virginia, was chosen to construct the spillway and install the ABM. The installation of the ABM panels commenced at the bottom of the spillway and proceeded upwards. This “reverse-order” of installation was necessary to properly construct the intermediate anchor trenches and overlaps. More than 70 custom made panels of ABM were shipped to the project via motor freight. Each panel, up to 3,500 sq. feet in size, was fabricated to fit a specific section of the spillway. Proper placement of the panels was facilitated by cross-

ABM panels were unrolled into position and joined together with a portable sewing machine prior to filling with concrete. The ABM was installed directly over a site specific geotextile filter to prevent the loss of underlying material through the openings around the perimeter of the blocks. For this project, a 5 ounce per square yard nonwoven geotextile was selected. A nonwoven geotextile was selected because it exhibited a higher angle of friction and greater hydraulic characteristics when compared to a woven geotextile. The fine aggregate concrete, supplied by a local ready mix plant, was injected into the panels, through a 3 inch diameter hose, utilizing a conventional grout pump. Once the ABM was filled with concrete to the required thickness and allowed to cure, coal refuse was utilized to backfill the terminal trenches along the sides of the spillway. The entire project required approximately 45 days to complete with more than 5,000 cubic yards of concrete being injected into the ABM panels.

For this high volume spillway, ARMORFORM ABM appeared to be the only practical solution. Riprap was not a viable option due to the extremely large diameter stone that would be required, and to properly install a poured concrete spillway would have been far too costly. This coal company is just one of several end users who have discovered the advantages of ARMORFORM. Coal refuse facilities operated by other firms have also benefited from this technology, as have the owners/operators of landfills and embankment dams.

This case study is a summarized version of an article “High Tech for High Volume” which appeared in the May 1998 issue of GFR magazine.

Summary