Static ice loads on dams

Abstract

A 9 year field program was undertaken from 1991–1992 to 1999–2000 to (i) measure the loads in the ice sheet near a dam, (ii) measure the load distribution between a gate and a pier, and (iii) compare the loads on wooden and steel stoplogs. Parallel work was conducted to develop analytical predictors for ice loads. Much progress has been made. One of the most significant findings has been to identify the importance of water level changes on the resulting ice loads. Ice loads are much higher and more variable (compared to purely thermal loads) when significant, but not excessive, water level changes occur. Methods have been developed to predict the ice load. The algorithms predict thermal loads well. They are less accurate for loads produced by a combination of water level and ice temperature changes. An environmental model was developed, and the predictions using the model compare well with the measured data. Hindcast analyses were carried out to evaluate the distribution of expected ice temperature changes and thermal events. With respect to the loads on gates and stoplogs, an analytical method was developed to extend the results obtained in this project to other stoplog or gate configurations (i.e., spans, flexural rigidities, etc.) and pier lengths.Key words: ice loads, dam(s).

Effects of Changes in Arctic Lake and River Ice

“…Changes in ice conditions can affect hydroelectric operations in a number of ways, both positively and negatively. For example, the estimation of ice loads on facilities such as dams, intakes, outlets, and gates is important both for engineering design and operations (Comfort et al 2003). A shorter ice season and thinner ice cover could reduce the static ice loads on dams, but on the other hand, a more unstable winter with mechanical ice break-ups could increase the dynamic loads on in-channel facilities.…”

Numerical studies for a better understanding of static ice loads on dams

“…Pressures in ice cover were measured with D r a f t 6 6 two BP sensor groups (Duckworth and Westermann 1989) at about m from the dam face (considered to be "far field" -FF). Comfort et al (2003) reported that the loads resulted from superposition of: (i) large ice temperature changes produced by very cold winter; and (ii) intermediate water level fluctuations (an especially important contributor). The thermal strain rate at the time of peak load was ~10 -9 s -1 .…”

“…Based on a nine-year field program at nine sites, Comfort et al (2003) found that thermal ice loads can be amplified by intermediate water level fluctuations (of about an amount equal to the ice thicknessh. Here and further, definitions of symbols and abbreviations are given in the Table 6).…”

“…Although, dams have been built and operated for many years, a considerable scatter in design ice line-load values (kN/m) exists (between 90•h and 300•h (m) according to Westberg 2007). To harmonize design ice loads, several field studies were conducted, suggesting that design loads could be substantially higher than the recommended values (Carter et al 1998;Comfort et al 2003;Taras et al 2011).…”

“…Ice loads are discussed from a numerical/deterministic point of view (Table 1) and the reader is encouraged to interpret results presented herein in light of other analytical methods that can also describe ice loading behavior, including empirical (e.g., Comfort et al 2003), stability (Carter et al 1998) and statistical/chaotic analyses (Sanderson 2010;Taras et al 2011).…”