Rate-controlled cone penetration tests in permafrost

Abstract

Cone penetration tests (CPTs) were carried out in the summers of 1999 and 2000 in a permafrost mound near Umiujaq, in northern Quebec, Canada, to study the cryostratigraphy and assess the creep behaviour of permafrost. A new linear pushing system using an actuator technology was specifically designed and developed to accurately control the penetration rate of the cone in the permafrost. This system has a load capacity of about 113 kN at a maximum penetration rate of 1.5875 cm/s and a stroke of 120 cm and can provide constant penetration rates as low as 4 × 10–6 cm/s. It can be disassembled in pieces for easy hand transport and use in remote locations. Two different types of CPT were performed in the permafrost mound: stratigraphic profiling and creep test. The first type is a quasi-static CPT at a penetration rate of 0.1 cm/s, providing a stratigraphic profile of permafrost in terms of the measurement of penetrometer sensors as a function of depth. The second type is a series of quasi-static CPTs at incremental rates of penetration, from 10–4 to 10–2 cm/s, carried out in a homogeneous layer to study the creep behaviour of permafrost. Five distinct zones (unfrozen and frozen active layer, permafrost, cryotic but unfrozen ground, and perennially noncryotic ground) can be identified in the stratigraphic profiles. The creep exponents calculated from the creep tests range from 12 to 35 for the ice-poor frozen active layer and from 4 to 11 for the ice-rich permafrost. Key words: cone penetration test, permafrost, rate-controlled, creep behaviour, cryostratigraphy.