In underground construction in permafrost zones covering more than 50% of the territory of Russia, it is of the high concern to comprehensively study deformation, strength and rheological characteristics of frozen ground to make a framework for engineering designs. Majority of the modern analysis programs for underground structure stability with regard to stress state of surrounding rock mass require strength and rheological parameters to be determined by three-axial testing. This article presents a laboratory-scale procedure for three-axial compression of frozen soil, equipment and testing results. The test materials were specimens of frozen ground taken in Kharasavay gas-condensate field at a depth of 10 to 50 m, mostly, loam, clay and sand. The three-axial compression tests were performed on equipment of Geotek Science and Production, Russia. This triaxial-compression testing equipment allows automated loading, maintenance and recording of deformation processes for a long time. The long-term three-axial compression procedure included step-by-step loading. The step to step interval was 24 hours. The tests proceeded until failure of a specimen. As a result of the tests, the strength, deformation and rheological characteristics of frozen ground were determined under the temperatures of 30°C and 60°C. The test results conform with different models, e.g. Mohr–Coulomb, Drucker–Prager, Tresca, etc. The described three-axial compression test schemes for frozen ground were trialed by GAZPROM Geotechnologies in design projects of underground waste disposal in permafrost rocks.

Keywords

Frozen ground testing, triaxial compression, theological characteristics, geomechanics.