Abstract: The particles of the calcareous sands are easily broken under the conditions of high stresses. Consequently, the mechanical properties of the calcareous sands will change under the action of different pressures. The shear breakage characteristics of the calcareous sand particles under different normal pressures are examined and analyzed in this paper. Several direct shear tests on the calcareous sands from Nansha's island of the South China Sea are conducted under different positive pressures. The particle breakage degrees of the sand samples under different positive pressures are studied through the sieving tests. The analysis results show that the calcareous sands can be broken to some extent after the direct shear tests under different positive pressures. The content of the coarse particles reduces and the content of the fine particles increases accordingly. As the positive pressures increase, the particle breakage becomes more and more serious. The grain grading properties of the calcareous sands change after the crushing of the calcareous sand particles. As the normal pressures increase, the gradation of the sand samples becomes poor gradually from its original gradation. The strength envelope of the calcareous sands is the peak strength instead of the residual strength. The friction angle of the residual strength of the calcareous sand is equal to or close to the natural repose angle of the sand. From the point of view of engineering safety, the internal friction angle of the calcareous sands should be equal to or close to the natural repose angle.