Concrete Rehabilitation Work On the Uncompahgre Project
A. B. Reeves
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The South Canal extending from the outlet of Gunnison Tunnel to the Uncomphagre River in westernColorado is one of the principal features of the Uncompahgre Project of the Bureau of Reclamation. Most of the concrete lined channel had ‘/2 t o I side slopes, 6 in. thick. Approximately one half of the lining was reinforced. This canal was constructedin 1906 and 1907, and specifications for the concrete work were in accordance with standards of that period. This resulted in a permeable and low grade of concrete as compared to present day requirements. During 30 years of operation a good many failures had occurred due to (I) disintegrating action of alkali, believed to be contributed by the under-lying shale material; (2) settlement of foundation; (3) swelling of shale under the lining; (4) hydro- static pressure under the lining; and (5) weather-ing including frost action. This canal was rehabilitated during the nonirriqation seasons, (November to March) from 1934 to 1937. In places where the old concrete was badlybroken up, a new lining of reinforced concrete approximately 6 in. thick was placed inside the old channel, care being taken to secure bond and anchorageto the old lining wherever possible. Modern standards of concrete construction were carried out resulting in compressive strength averaging 5500 psi for test cylinders 2 8 days old. Particular attention was given to finish to secure a low frlc-tion coefficient thus maintaining the capacity. Where the lining was badly cracked but still in place and held together by the reinforcement, the method of repair was to cover the entlre surface with shotcrete. The shotcrete layer is from 0 to 4 in. thick reinforced with bars at I2 in. both ways. Care was exercised to insure a clean surface for the shotcrete, and to secure a bright glazed surface which has a good roughness coefficient. Bulged floors in the tunnels were repaired by re-placement of the old concrete by a new section with a curved invert, thus eliminating the necessity for reinforcement.