Abstract：The results of drained shear tests carried out on calcareous sand sample from the South China Sea were presented. The tests reveal that the relation between the stress and strain changes when the confining pressures are changed. Under low pressure，it is similar to the terrigenous sand；and under the medium confining pressure，the mechanical property of the calcareous sand is just analogous with that of the terrigenous sand under high stress level. The particle breakage results in liberation of the close interspace. Thus the volume of strain is much larger than that of quartz sand，which makes almost all the deformation irreversibly plastic during shear process. And the results also indicate that the dilatancy and ratio of stress are closely related to the confining pressures，they decrease as the confining pressures increase.
