Abstract: With the development of mineral resource exploitation in western China， the seasonal freezing-thawing effect has become more and more important to the stability of mine dump in high-altitude and cold regions. Taking a polymetallic mine in Tibet as the object， a series of shear tests on coarse-grained soils from dump of the mine at a freeze-thaw interface and under full thawed state were carried out using a large direct shear apparatus with temperature control. The effect of gravel particles content on shear strength of coarse-grained soils was considered during the test design. The results show that the shear stress-shear displacement curve of coarse soils under full thawed state performs as strain hardening， while that at freeze-thaw interface shows strain softening characteristics. Under the same content of gravel particles， the shear strength of freeze-thaw interface is approximately 2 times as much as that of full-thawed soils. The reason of this phenomenon lies in tow aspects. Firstly， the ice cementation increases the cohesive strength of the soil interface. Under the test condition， the cohesive strength increased by ice cementation is approximately 50~60 kPa. Secondly， the lubrication of water at the freeze-thaw interface is weakened， which leads to the increase of sliding friction. Moreover， the ice encapsulation on the surface of coarse particles enhances the occlusal friction between particles， so the internal friction strength of coarse particles at freeze-thaw interface is also greater than that of the thawed soils. With the increase of gravel particles content， the cohesive forces at both the freeze-thaw interface and the thawed soils decrease， while the internal friction angles increase. Compared with the thawed soils， the cohesive force of the freeze-thaw interface decreases relatively slowly and the internal friction angle increase quickly.

Key words: Mine dump, Coarse-grained soils, Freeze-thaw interface, Large-scale shear test, Seasonal frost regions