Triaxial compression testing of frozen soils for the determination of rheological parameters

Detailed investigation of mechanical, deformation and rheological properties of frozen soils is an actual issue, as they are basis of civil-engineering survey for underground constructions in permafrost holding more than 50% of the territory of Russia. The majority of modern software packages which calculate structures stability considering stress state of soils massive, demand knowledge of mechanical and rheological parameters defined by triaxial compression tests. The current article presents: estimation method of frozen soils rheological parameters by triaxial compression testing; required equipment and the research results. The samples of frozen soil 10 - 50 m depth from Kharasavey gas field were used as test material. Mostly they are presented by loam, clay and sand. The experiments were run at the range of temperature from -3 oC to -6 oC. Triaxial compression testing was provided by the laboratory equipment which allows to run experiments in the mode of automatic load, maintenance and deformation processes registration. Test procedure of rheological parameters identification under conditions of long-term triaxial compression considered incremental load Stage duration was equal to 24 hours. The experiments were run until th specimen’s failure. As a result of the testing, mechanical, deformation and rheological parameters for frozen soils are defined at temperatures -3 oC  -6 oC. The achieved results can be interpreted in different models (Mohr-Coulomb, Drucker-Prager, Tresca etc.). The described experiments were carried out at LLC Gazprom Geotechnology for the design of underground drill cutting s storages in permafrost.