Abstract: Spherical template indenter (ball mode device) has been widely used in the mechanical properties of permafrost soil testing in the former Union of Socialist Soviet Republics (USSR) and Russian Federation. In the past 60 years of engineering practice, the test method, test theory, etc. were improved. It is simple, easy to test. And the results reflected the mechanical properties of frozen soil better. So, it widely used in long-term strength’s evaluation and forecast of the cohesion for the frozen soil. This paper made a brief introduction to the equipment, the test theory, and test methods. Moraine clayey loam in the outskirts of Moscow city was used as the object of study. In constant temperature (from -7 ℃ to 20 ℃) conditions, in a closed state, the freeze-thaw cycle tests were conducted, 3, 6, 20, 40 times, respectively. Physical properties of soil were tested in different experimental stages; and strength was tested on the frozen soil with spherical template indenter after the freeze-thaw cycle. After freeze-thaw cycle test, soil’s physical properties indicators reduced in varying degrees. With the increase in the number of freeze-thaw cycle, soil strength decreases. The volumes of water in soil change in the freeze-thaw process, which caused soil density decreases and the porosity increases. This is the reason for the reduction of soil strength.

Key words: spherical template indenter, equivalent cohesion, morainic clayey loam, cycle of freeze-thaw