Journal of Cold Regions Engineering

A Swedish full-scale pilot plant employing all-year-round natural sewage sludge dewatering is presented in this paper. The treatment includes three different types of outdoor ditches: a freezing ditch for the winter months, a drying ditch for the early summer months, and a combined drying-freezing-thawing-drying (DFTD) ditch for sludge produced in late summer and early autumn. The test period included two consecutive winters. Complete freezing of the sludge was achieved in the first winter in contrast to the second when incomplete freezing of the sludge occurred due to an unusually warm winter. The dry matter content for the freezing ditch was, at the harvest in August, 30–70 of the first test year. The second test year yielded a sludge with a dry matter content of 20–40 in the freezing ditch. The final dry matter result for the DFTD ditch was 20–40. The summers included were similar to the extent that both late summers were unusually warm, helping to produce sludge of high final dry matter content. The first summer, being somewhat warmer and with a lower sludge loading, yielded a sludge of 60–90 dry matter in the drying ditch. The second summer, when the sludge load was approximately double the preceding year, resulted in a sludge of 20–60 dry matter.

The thawing and drying process in full-scale sludge freezing ditches was studied. The ditches are located in northern Sweden. The treated sludge derived from a small wastewater-treatment plant with mechanical and chemical treatment. Due to the relatively warm winter of 1994–1995, it became possible to study the effect of incomplete freezing. The results show that frozen and thawed sludge has a porous and humus-like structure, whereas unfrozen sludge has a compact and smeary consistency. The study also shows that incomplete freezing decreases the dewaterability of the sludge, but that the result measured as solid content is satisfactory even if all the sludge is not well frozen. Moreover, the study indicates that the thawing depth could be estimated by a simple equation based on the number of positive degree-days.

This paper provides the results of two small-scale testing programs linked to large-scale field programs carried out by the writers and others. The large-scale in-situ sea ice testing program was part of the Office of Naval Research's (ONR's) Sea Ice Mechanics Initiative (SIMI). Three field trips to Barrow, Alaska, were completed to examine the seasonal evolution of the first-year sea ice growing on Elson Lagoon. Trips were made in November, March, and May, when significant changes in thickness and temperature profile were evident. The experiments were designed to determine the fracture behavior of sea ice in situ and make comparisons with small-scale lab tests. Due to the unique microstructure of the sea ice tested, it was necessary to complete small-scale (0.1 m) tests for comparative purposes. A detailed study of the ice fabric at the site revealed a very strong alignment of the c-axis. This prompted a study of the fracture properties parallel (hard-fail) and perpendicular (easy-fail) to the preferred c-axes orientation plane in both the largeand small-scale tests. The effects of c-axis alignment, temperature and microstructure on the fracture toughness and tensile strength are investigated.

In conjunction with Phase VI of the large-scale in-situ fracture test program undertaken during the Office of Naval Research (ONR) Sea Ice Mechanics Initiative (SIMI) project, three full-depth cores were collected from the first-year sea-ice sheet near Point Barrow, Alaska, and shipped back to Clarkson University for further analysis. A detailed study of the ice fabric at the site revealed that there was a very strong horizontal c-axis alignment. With this in mind, a set of fracture experiments using the Semi-Circular Bend (SCB) fracture geometry was developed to determine the effects of the alignment on the apparent fracture toughness, K_Q. The effect of crack orientation with respect to the c-axis on K_Q was also investigated by initiating fracture either parallel or perpendicular to it. To match the field conditions at the ice surface, the tests were performed isothermally at −10°C. Using closed-form solutions for the SCB fracture geometry, values for K_Q were determined directly from load and displacement data. Results show that there is a slight but recognizable decrease in fracture toughness as depth and c-axis alignment increase. Crack orientation has a more noticeable effect, with fracture toughness being measurably lower when the crack path is perpendicular to the c-axis. Overall, the results compare well with other small-scale experiments performed on ice with similar characteristics and temperature.

This paper deals with the interpretation of small-scale first-year sea ice strength and property test data collected in 1982 during several field trips at Tarsiut Island N-44 location in the Canadian Beaufort Sea. Measurements of flexural, horizontal, and vertical uniaxial compressive and confined plane strain and borehole jack strengths are presented. Mathematical relationships representing the variation of these mechanical properties with temperature; salinity; strain and stress rates; and crystal structure (depth) are analyzed. Uniaxial unconfined compressive strength data of horizontal sea ice samples are compared with triaxially confined borehole jack strength data. Flexural strength data obtained from laboratory tests are compared with full-thickness cantilever beam tests performed in the field. The measured flexural strength of first-year sea ice is also provided in a statistical format. The apparent elastic modulus of sea ice is presented as a function of salinity and temperature.