Abstract: Particle shape is one of the key factors that affects the mechanical responses of calcareous sands. Different calcareous sands in terms of the characteristic particle shape(block, strip, and disc) were manually selected. A new particle shape descriptor(deviation factor α)was introduced to quantitatively describe the particle shape by using microscopic image acquisition and processing techniques. Meanwhile, a series of undrained triaxial tests were carried out on calcareous sands of different combinations of particle shape. The effects of particle shape on the shear strength of the calcareous sands were examined. It was found that:(1)the deviation factor(α)can be used as an effective method to distinguish calcareous sands of different particle shapes; (2)the undrained shear strength of calcareous sands yields good correlations with the deviation factor(α):the undrained shear strength decreases with the addition of disc-shaped calcareous sands(α increases), whereas it increases with the addition of strip-shaped calcareous sands(α decreases). The outcomes of this study provide insight into the particle shape characteristics of calcareous sands, and it also offers a promising method to accurately evaluate the shear strength of calcareous sands.