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|Structural stability evaluation : Gull Lake Dam
|United States. Army. Corps of Engineers. St. Paul District.
Pace, Carl E.
Gull Lake Dam
Pile load tests
Mississippi River headwaters
|Structures Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; SL-81-16.
Abstract: A typical interior monolith at Gull Lake Dam was evaluated for adequacy stability for five load cases: (1.) Normal operation (2.) Normal operation with truck loading (H15-44) (3.) Normal operation with earthquake (4.) Normal operation with ice (5.) High-water condition. By using the conventional stability analysis (rigid body assumptions), the approximate magnitude of loads on the foundation piles were determined; but, without knowing the supporting characteristics of the foundation material, the adequacy of the structure's stability was inconclusive. The supporting characteristics of the foundation material were determined by in situ testing using a pressuremeter to predict the horizontal supporting characteristics of the pile-soil system. Two 4-in.-diam core holes were drilled through typical monoliths to obtain access to the foundation material. The pressuremeter tests were performed and in situ soils data obtained. The in situ data were used to obtain the supporting characteristics of the foundation material. The horizontal modulus of subgrade reaction was obtained for three test positions in both of the two test holes. It was obtained as a variation of horizontal pressure and depth within the foundation material. The horizontal modulus of the subgrade reaction was then used in a three-dimensional direct stiffness analysis of the piling foundation. A beam on elastic foundation analysis was performed and the pressure, moment, and deflection along the length of the most critically loaded pile was determined. It was determined that the horizontal and vertical forces on the piling were not excessive in relation to the material properties of the pile. The pile deflections were also adequate under all load conditions. Unconfined compressive tests on the concrete gave an average strength of 5550 psi, which is adequate for this type of structure. Core logs are presented that give evidence that the concrete is well consolidated. A petrographic analysis of the concrete showed that it was nonair-entrained; the voids were commonly filled with ettringite; and small amounts of alkali-silica reaction product were present. These characteristics are not considered detrimental for this structure and exposure conditions. The structure is adequate in stability; the concrete is of good quality, and with rehabilitation of the deteriorated surface, the concrete dam can be expected to perform satisfactorily for many more years.
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