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Recent physical model studies have refined designs for high-flow air diffusers for managing accumulations of broken ice at navigation projects. Although these solutions are successful in the model, implementing them in the field can be difficult because of uncertainties in airflow scaling. This study uses field and laboratory data to test theoretical relationships between airflow from the diffuser and the resulting near-surface water velocity. In the experiments, water velocities were measured adjacent to bubbler plumes for depths ranging from 0.52 to 6.5 m and airflow rates ranging from 0.015 to 0.68 standard cubic meters per minute/meter. The observed vertical and horizontal water velocity data compared moderately well to theoretical curves based on the equations of Kobus and Ashton. In addition, a reasonably linear relationship was found between the average velocity of the horizontal, near-surface flow field V and unit airflow from the diffuser [Q.sub.a] CE Database subject headings: Validation; Bubbles; Diffusion; Velocity; Air flow.

This paper describes a study undertaken at Umiujaq, in northern Quebec, on laterally loaded piles in permafrost subject to a constant displacement rate. Test results of bending moments, shear load, soil reaction, and pile displacements demonstrate the complex nature of creep of frozen soils. FEM simulations show a good concurrence with field test results and confirm a clear distinction between stationary and nonstationary creep. CE Database subject headings: Lateral loads; Piles; Permafrost; Canada; Creep; Displacement.

The analysis and design of buried chilled pipelines in frost heaving soils warrants a study of the complex pipe-soil interaction. Stress gradients are generated at the interface between frozen and unfrozen ground because of differential heave, produced as the chilled pipe crosses from the unfrozen, heave-susceptible terrain to the frozen, nonheaving one, resulting in the generation of uplift forces acting on the pipe portion buried in the frozen ground. The present paper characterizes the load-resistance response of the uplift-resistant side of the pipe section as it is pulled upward at a constant displacement rate through the frozen ground. Crack patterns in the frozen soil around the pipe section were observed in uplift tests. In view of this, a theoretical assessment of tension-fractured and compression-crushed zones, developed in the vicinity of the pipe, producing a reduced peak uplift resistance is discussed.

The construction and maintenance of structures subject to subzero (

The middle Mississippi River, which extends from the mouth of the Missouri River near St. Louis to the confluence with the Ohio River at Cairo, Ill., is a critical navigation route throughout the year. During cold periods, the ice accumulations and ice jams that form on this reach can delay or suspend winter navigation, incurring great costs to industry as well as cities and towns whose economies depend on river commerce. Much of this ice originates in the Missouri River. With the onset of warmer air temperatures, the rapid release of these ice accumulations can result in substantial damage to river structures such as dikes, revetments, and levees. This study analyzed historical data and used numerical hydraulic models to assess the possibility of structural solutions to these ice problems. The study identified reach locations where structural ice control might be possible. A simple computer model then simulated the upstream progression of ice covers on the middle Mississippi to assess the feasibility of various ice control alternatives. An ice retention structure located on the Missouri River near its mouth was found to be the most favorable of the structural ice control options considered.