Abstract: In order to study the effect of shear rate (less than 100 mm/min) and fine grains (less than 0.075 mm) content on residual
strength of the slip zone of a landslide in the Xiangjiaba reservoir area, ring shear tests were conducted on remolded slip zone soil using
the DTA-138 ring shear apparatus, the fine grains content and microstructure of slikensided surface of undisturbed samples and shear
surface of remolded samples were comparatively analyzed. It was found that the fine grains content obtained from undisturbed
slikensided surface are larger than that from the slip zone, and the fine grains content obtained from shear surface of remolded samples
are larger than that from area adjacent to the shear surface. With an increase of the rate of shear from 0.109 mm/min to 98 mm/min, the
residual strength stress ratios exhibit a concave pattern, ie. decrease at first and then increase with the lowest mobilized stress ratio at
the 1.09 mm/min (the lowest mobilized stress ratio of Rr-1#, Rr-4#, and Rr-5# remolded samples are 0.34, 0.42 and 0.39 respectively) .
The residual strength first increases and then decreases with increasing fine grains content, exhibiting a quadratic polynomial relation
with a critical value about 56%, and with increasing fine grains content, the range of variations in residual strength increases with
normal stress.

Key words: slip zone soil, shear rate, fine grains content, residual strength