CGRG Bibliography of Canadian Geomorphology
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Author : Fortier, R.; Allard, M.; and Gagnon, O.
Date : 2004.
Title : Assessment of permafrost conditions at Salluit, Nunavik, using cone penetration tests.
Publication : Geo-Engineering for the Society and its Environment. 57th Canadian Geotechnical Conference and the 5th joint CGS-IAH Conference. Hilton Quebec Hotel, Old Quebec. October 24-27, 2004.
Issue :
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Abstract
The village of Salluit is located in the continuous permafrost zone along the southern shore of Hudson Strait, in Nunavik (Canada). The village lies in the bottom of a restricted valley and most village infrastructures are built on frozen saline and ice-rich marine sediments creating problematic ground conditions for the construction of civil infrastructures. The available terrain with proper ground conditions for stable foundation is therefore scarce and little is know on the permafrost conditions and occurrence in the valley. Proper assessment of available terrain for the village expansion in the valley taking into account the permafrost conditions is therefore a major concern for Salluit. Following the request of the provincial government of Québec and the Inuit community of Salluit, a thorough survey for mapping the permafrost conditions at a very large scale (1:2000) was carried out in summers 2002 and 2003. An integrated multi-technique approach was adopted for properly assessing all the soil types, permafrost conditions and lateral changes in conditions and stratigraphy. The techniques used in the field were deep and shallow sampling of permafrost, cone penetration tests (CPTs) and geophysical surveys. Penetration-rate controlled CPTs were carried out in permafrost at temperatures as low as -5 °C for stratigraphic profiling and assessment of creep behaviour of permafrost. Syngenetic ice-rich permafrost near the permafrost table in marine sediments and colluvial deposits, and saline ice-poor permafrost with few thick ice lenses in the marine sediments at depths larger than 2 to 4 m were investigated. The till in depth overlaid by the marine sediments was also penetrated over few centimeters during one CPT. The typical penetration rate used for the CPTs was 0.1 cm/s; it is a good compromise between the very high values of cone resistance of permafrost at a standard rate of 2 cm/s following the creep behaviour of ice in permafrost, and the lower values of cone resistance and the time needed for performing deep CTPs at 0.1 cm/s. The ice-rich permafrost and the ice lenses are characterized by cone resistance in excess of 20 MPa and friction ratio lower than 1%. The ice-poor permafrost has cone resistance lower than 20 MPa and friction ratio higher than 1%. The electrical resistivity is close to 10 ohm-m for the ice-poor permafrost and in excess of 1000 ohm-m for the ice-rich permafrost. Cone resistances higher than 80 MPa at a penetration rate of 0.01 cm/s were measured in the till. This very low penetration rate was used for decreasing the cone resistance and avoiding any damages to the pushing system and penetrometer. The creep exponents found from the creep tests are lower than 5 for the ice-rich permafrost and higher than 5 for the saline ice-poor permafrost. The difference in ice content can explain the difference in creep behaviour of frozen soils. The results of the CPTs are useful for assessing the creep parameters of permafrost and designing pile foundation as an alternative to shallow footing in a permafrost environment sensitive to climate warming.
Bibliography of Canadian Geomorphology