Abstract

Seismic-wave velocities have been measured on 37 unconsolidated permafrost samples as a function of temperature in the range -16 to +5 °C. The samples, taken from a number of locations in the Canadian Arctic islands, the Beaufort Sea, and the Mackenzie River valley, were tighty sealed immediately upon recovery in several layers of polyethylene film and maintained in their frozen state during storage, specimen preparation, and until they were tested under controlled environmental conditions. During testing, the specimens were subjected to a constant hydrostatic confining stress of 0.35 MPa (50 psi) under drained conditions. At no stage was a deviatoric stress applied to the permafrost specimens. The fraction of clay-sized particles in the test specimens varied from almost zero to approximately 65%. At temperatures below -2 °C the compressional-wave velocity was observed to be a strong function of the fraction of clay-sized particles, but only a weak function of porosity. At temperatures above 0 °C the compressional-wave velocity was observed to be a function only of porosity, with virtually no dependence upon the fraction of clay-sized particles. Calculation of the fractional ice content of the permafrost pore space from the Kuster and Toksöz theory showed that for a given fraction of clay-sized particles the ice content increases with an increase in porosity. It is concluded that the compressional-wave velocity for unconsolidated permafrost from the Canadian Arctic is a function of the water-filled porosity, irrespective of the original porosity, clay content, or temperature.

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