Checking Concrete Growth

by Vann A. Newell, (M.ASCE), Lead Structural Engr.; Tennessee Valley Authority, 11101 Market St., Chattanooga, TN 37402,
David T. Tanner, Lead Instrumentation Engr.; Tennessee Valley Authority, 11101 Market St., Chattanooga, TN 37042,
Charles D. Wagner, (M.ASCE), Manager; Civil Engrg., Tennessee Valley Authority, 11101 Market St., Chattanooga, TN 37042,


Serial Information: Civil Engineering—ASCE, 1994, Vol. 64, Issue 1, Pg. 70-72


Document Type: Feature article

Abstract:

When the Tennessee Valley Authority built its dams in the 1930s, instrumentation installed in the massive concrete detected a defect that would later cause major problems: concrete growth from alkali-aggregate reaction. At Hiwassee Dam, a 307 ft high, 1,287 ft long concrete gravity structure, such growth has squeezed the spillway openings and caused significant structural cracking in the abutments. Cutting four slots completely through the concrete is expected to control the damage. Two slots adjacent to the spillway, ½ in. wide and 50 ft deep, were cut in January 1993. Two slots in the abutments, cut a year later, are 8 in. wide at the top, tapering to 3 in. at depths45 and 60 ft. For the abutment cuts, permanent blister cofferdams aretalled before any actual cuts are made in the concrete. Cutting is done from inside the cofferdams, which are steel plate structures with a 4 ft internal radius, extending from foundation rock to above maximum headwater. Additional seals are installed after the slots have been completed. The remediation project included post-tensioning the dam against possible earthquake damage, using 140 tendons placed in two rows parallel to the axis of the dam.



Subject Headings: Concrete dams | Earthfill dams | Gravity dams | Concrete structures | Drop structures | Spillways | Concrete | Cofferdams | Tennessee | United States

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