Penetration rate-controlled electrical resistivity and temperature piezocone penetration tests in warm ice-rich permafrost in Northern Quebec (Canada)

摘要

Electrical resistivity and temperature piezocone penetration test (RTCPTU) was carried out in warm ice-rich permafrost formed in silty soil near Umiujaq, Northern Quebec, Canada, to study the cryostratigraphy of permafrost and adapt soil classification charts for the interpretation of RTCPTU in such environment. A linear pushing system based on an actuator technology was used to accurately control the penetration rate of the piezocone in permafrost. According to the interpretation of the RTCPTU logs, cryostratigraphic contacts and layers such as the thawing front, permafrost table and base, active layer, ice-rich permafrost and perennially noncryotic ground, layers of ice-poor frozen silt, and ice lenses were identified. Due to its reticulated cryostructure made of a sequence of centimetric thick ice lenses and frozen soil layers, ice-rich permafrost is characterized by extremely variable values of cone resistance and friction ratio corrected for pore pressure effects, pore pressure, and electrical resistivity between 5 and 50MPa, 0.01 and 2%, near zero and 10 MPa, and 0.01 and 20 kΩ-m, respectively. Cone resistance up to 50 MPa, friction ratio down to 0.01%, pore pressure near 10 MPa, and electrical resistivity close to 10 kΩ-m are characteristics of thick ice lenses. The layers of ice-poor frozen silt with high unfrozen water content have cone resistance lower than 10 MPa, friction ratio in excess of 1%, pore pressure lower than 3 MPa, and electrical resistivity lower than 1 kΩ-m. Based on permafrost behaviour types as characterized from the RTCPTU logs, new zones are proposed in soil classification charts to identify frozen soils. These adapted soil classification charts are helpful to practitioners for the interpretation of RTCPTU carried out in permafrost.