Frictional characteristics of calcareous sand subjected to oscillatory normal stress

Abstract

Calcareous sand is commonly utilized in coastal and marine constructions, and dynamic stress disturbances caused by the natural environment or human activities make calcareous sand to exhibit different shear properties. Hence, it is important to understand calcareous sand’s frictional behavior under variable normal stress. A sequence of direct shear tests on calcareous sand sourced from South China Sea were conducted using a dynamic shear box device. Both constant and oscillatory normal stresses were considered. The frictional characteristics under oscillatory normal stress were investigated by applying a constant shear rate (1 ~ 20 mm/min) and a sinusoidal normal load with different normalized amplitudes (0% ~ 80%) and frequencies (0.1 ~ 2 Hz). Experimental findings indicate that the shear stress, apparent friction coefficient, and normal displacement varied periodically in response to oscillatory normal stress, with phase lags observed among the normal stress, shear stress, and apparent friction coefficient. Unlike constant normal stress, oscillatory stress can either increase or decrease the shear strength, and the frictional strengthening or weakening is dictated by critical rate–amplitude–frequency values. Additionally, the shear stress results are characterized using the rate and state friction law. These findings shed light on the frictional behavior of calcareous sand exposed to complex stress states and beneficial for the mitigation of relative geo-risks.