Development of a Core Barrel for an In Situ Measurement of the Thaw Consolidation Behavior of Permafrost

摘要

In permafrost areas, environmental changes, such as infrastructure, building, and climate change, have effects on the thermal regime of soil and can initiate permafrost degradation. As a result, this will lead to the degradation of the mechanical properties of the soil. Thus, good knowledge of permafrost characteristics is essential to make the right decisions during the design and construction phases of a project and to anticipate potential problems related to climate change. The goal of this project was to improve our capacity to characterize thaw-sensitive permafrost by developing a drilling tool that is able to carry out in situ tests. In partnership with the Mechanical Engineering Department of Laval University, an oedometric core barrel was designed, and a prototype was built. As the core barrel is modular, it is easy to clean and maintain. Once the barrel has penetrated frozen soils, thawing is initiated by an electric heating element. A pneumatic cylinder then allows the user to set a consolidation pressure, and drainage occurs radially along the first 20 cm of the core. The drained water is discharged at the top of the drill hole, and information on the thaw consolidation behavior is recorded during the test. The complete testing procedure can be made during the in situ drilling operation. In order to validate the testing procedure, laboratory tests were made in pure ice and synthetic permafrost reconstituted in barrels. The testing program has allowed improvement of the initial design of the equipment as well as the test procedure. The reliability of the thaw settlement/consolidation tests was evaluated for fine and coarse soils.