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Static Ice Loads at Dam Face and at Far Field

Author(s): Alain Cote; Andre Taras; Georges Comfort; Brian Morse

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Abstract: Ice thrust is an important factor for properly designing safe dams. A 4-year field program on 4different dams was undertaken from 2008 to 2011 to measure the ice loads against the dams and in the ice sheet both near and far from the dam. Three different types of pressure sensors (2 types of flat-jack and a biaxial) were used and good agreements were observed between them. The largest spatially-average (25 m) line load recorded was 145 kN/m at the dam face and 105 kN/m in the far field (i. e., 27 m from the dam face). Environmental conditions (temperature, snow precipitations, wind) and forebay water level fluctuations were also recorded. Ice sheet warming and water level variations are the main contributors to the developments of ice loads. A predictive model of ice loads was developed and the results were in good agreement with measurements. During a thermal rise event within the ice, the space/time ice load profile was very variable along the wall face. The temporal peak of average loads from 11 vertical pressure panels distributed over 25 m against the dam wall, shows higher average amplitude than at far field. The higher time frequency components of load variations at the wall were attenuated, as measured in the ice sheet 27 m away from the dam. The loads may have possibly been dampened by ice creep. The “Indentation” factor presented by Carter (2003) for dams has been confirmed by the load measurements along the wall. We have observed systematically higher maximum line loads as we considered shorter spans. Maximum average loads can increase by 30% from a 25 m to a 10m instrumented span of wall. The maximum average load at the wall tends to match the one measured at far field as we increase the number of measurement points along the wall, given homogeneous conditions of the ice field. This notion is in complete agreement with the design concepts used for ice loads on off-shore structures (ISO-19906).

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Year: 2016

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