Session Start Date

6-1-1988

Abstract

As the northern regions of Canada are developed, there is an increasing need to protect the fragile ecology as well as to maximize usage of local construction materials. The construction of earth dykes to retain liquid wastes is a common requirement in municipal and industrial developments. Frozen core earthfill dykes provide an effective technique to cut off seepage in cold permafrost areas (Sayles, 1984). The seepage of water through an unfrozen overburden or fractured bedrock foundation can occur and accelerate the thermal deterioration of an earth embankment. The development of the active layer during the summer reduces the dam's ability to retain water if the freeboard is inadequate. Several earthfill dams were built at the Lupin mine near Contwoyto Lake in the Canadian Arctic to form a mine tailings pond. Even though design forecasts indicated 9 m high structures would remain frozen after impoundment of the reservoir, very few case histories were found to support the design. Several earth dams have been monitored since 1982. Initially, ground temperature measurements were taken with thermistor strings in short boreholes. More recently, deep boreholes were instrumented with thermistor strings and the ground probing radar has been used to confirm and locate unfrozen zones within the dams. Specifically, the performance of three dams is reviewed here. The first dam, the base case, was built over virgin cold permafrost. The complete dam section froze during the first winter after construction. Part of the second dam was built over a 5 m deep talik associated with a seasonal creek and possibly a fault zone. The talik is apparently mostly refrozen and continuing to cool, however, geophysical surveys indicate a possible unfrozen remnant. The third dam was built across the reservoir after impoundment and during the winter. The internal nature of that dam and its thermal behaviour are quite different from the above two. The thermal regime of the dams and underlying foundation has changed considerably over the five years following construction. The results of the ground temperature and radar profiles are compared for various seasons to reconstruct the transient thermal regime at uninstrumented sections. The findings are significant for the design and monitoring of future water retaining structures in the North.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Second Conference

Publisher

University of Missouri--Rolla

Publication Date

6-1-1988

Document Version

Final Version

Rights

© 1988 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Design and Monitoring of Earth Embankments over Permafrost

As the northern regions of Canada are developed, there is an increasing need to protect the fragile ecology as well as to maximize usage of local construction materials. The construction of earth dykes to retain liquid wastes is a common requirement in municipal and industrial developments. Frozen core earthfill dykes provide an effective technique to cut off seepage in cold permafrost areas (Sayles, 1984). The seepage of water through an unfrozen overburden or fractured bedrock foundation can occur and accelerate the thermal deterioration of an earth embankment. The development of the active layer during the summer reduces the dam's ability to retain water if the freeboard is inadequate. Several earthfill dams were built at the Lupin mine near Contwoyto Lake in the Canadian Arctic to form a mine tailings pond. Even though design forecasts indicated 9 m high structures would remain frozen after impoundment of the reservoir, very few case histories were found to support the design. Several earth dams have been monitored since 1982. Initially, ground temperature measurements were taken with thermistor strings in short boreholes. More recently, deep boreholes were instrumented with thermistor strings and the ground probing radar has been used to confirm and locate unfrozen zones within the dams. Specifically, the performance of three dams is reviewed here. The first dam, the base case, was built over virgin cold permafrost. The complete dam section froze during the first winter after construction. Part of the second dam was built over a 5 m deep talik associated with a seasonal creek and possibly a fault zone. The talik is apparently mostly refrozen and continuing to cool, however, geophysical surveys indicate a possible unfrozen remnant. The third dam was built across the reservoir after impoundment and during the winter. The internal nature of that dam and its thermal behaviour are quite different from the above two. The thermal regime of the dams and underlying foundation has changed considerably over the five years following construction. The results of the ground temperature and radar profiles are compared for various seasons to reconstruct the transient thermal regime at uninstrumented sections. The findings are significant for the design and monitoring of future water retaining structures in the North.