Abstract: In order to further study the effect of shear rate on the strength and deformation characteristics of calcareous sand, direct shear tests are carried out on dry calcareous sand under different shear rates in this paper. With the increase in shear rates from 0.1 mm/min to 2.4 mm/min, the shear strength of calcareous sand decreases at first and then increases in the tests, and a similar change trend of the internal friction angle is also found. Meanwhile, the measured critical shear rate is 1.6 mm/min for dry calcareous sand. Under a low normal stress condition, the shear dilatancy phenomenon in calcareous sand sample is more likely to occur with an increase in the shear rate. Under a relatively high normal stress condition, overall shear shrinkage decreases gradually with the shear rate increases from 0.1 mm/min to 1.6 mm/min. When the shear rate continues to increase from 1.6 mm/min to 2.4 mm/min, the maximum shear shrinkage increases gradually. The micro-mechanism of loading rate effect of calcareous sand varies under different normal stress conditions. Under the low stress conditions, the loading rate effect of calcareous sand is mainly caused by the dislocation, displacement and rearrangement of particles, while the particle breakage plays an important role at higher stress levels.

Key words: calcareous sand, shear rate, direct shear test, strength index