Sawing a Dam in Half (on Purpose)

Quick Overview

The Fontana Dam, built by the TVA between 1942 and 1945, was intentionally sawed in half along its central axis by cutting a 1.5-inch thick, 100-foot-long slot into the concrete to relieve internal compressive stress caused by Alkali-Silica Reaction (ASR) in the concrete's reactive aggregates.

Key Points: The Fontana Dam, completed in 1944, is the tallest dam east of the Mississippi River, standing at 480 feet high and 2,365 feet long. The dam began showing signs of deterioration due to Alkali-Silica Reaction (ASR), which causes concrete to swell and crack, necessitating intervention. TVA engineers implemented a novel solution in 1976: cutting a 1.5-inch thick, 100-foot-long slot through the dam's center to relieve internal stress. The slot cutting process involved using a diamond-wire saw to cut vertically through the concrete block, managing the slurry byproduct by pumping it to holding tanks. The design of gravity dams like Fontana inherently relies on their weight for stability, but ASR expansion countered this, making the slot necessary to relieve internal compressive stress. The GAA (Grout, Aggregate, Alkali) reaction requires reactive silica aggregates, which are present in about 90% of the Earth's crust, making ASR a widespread concern. TVA continues to monitor the structure regularly, measuring movement and strain to ensure the long-term integrity of the dam after the slotting procedure.

Context: This video explains the unique structural challenge faced by the Tennessee Valley Authority (TVA) regarding the Fontana Dam, a massive concrete gravity dam completed in 1944. The issue stemmed from Alkali-Silica Reaction (ASR), a chemical reaction between reactive silica in the aggregates and the alkaline cement paste when water is present, causing the concrete to expand, crack, and threaten structural integrity. Because gravity dams rely on their mass for stability, any internal expansion that counters this weight is a serious concern.

Detailed Analysis