Abstract: Freeze-thaw cycling is an important factor affecting the safety of high earth-rock dams in severe cold regions. This paper presents the results of freeze-thaw cycling tests on the rockfill materials of the Rumei project, a high core wall rockfill dam on the Lancang River, Tibet. We conducted the tests using rockfill weathering test apparatus developed by Tsinghua University, together with direct shear tests under the conditions of different normal stress. Deformation and strength characteristics of the rockfill materials under freeze-thaw cycling were then examined. Test results show that during a given freeze-thaw cycle, a rockfill sample undergoes three typical stages: thaw shrinking, frost shrinking, and frost heaving. On completion of the freeze-thaw cycles, the sample starts a large back expansion deformation, reducing its compactness and shear strength. The reduction in shear strength is about 11.5% to 15.4% in the case of 20 freeze-thaw cycles.

Key words: weathering, rockfill material, freeze-thaw cycle, deformation properties, shear strength