Mechanical behaviors of cemented sand and gravel materials based on triaxial tests during unloading and reloading

Understanding the mechanical behaviors of cemented sand and gravel materials during unloading and reloading in the context of the unloading and reloading paths can help enhance the accuracy of predicting the stress and deformation of cemented sand and gravel dams during reservoir storage and discharge. To this end, a large shear triaxial instrument is used to conduct the triaxial unloading and reloading tests on the cemented sand and gravel materials under different confining pressures and stress levels with a cemented content of 100 kg/m³. The triaxial shear test results obtained under loading are systematically analyzed along with the stress and deformation of the materials obtained in the triaxial tests pertaining to the unloading and reloading paths. The results indicate that the increase in the internal friction angle and cohesive force enhances the peak strength of the cemented sand and gravel materials in the unloading and reloading paths. The stress levels do not considerably affect the unloading modulus of the materials. However, with the increase in the confining pressure, the resilient modulus first increases nonlinearly and later decreases gradually. Under different confining pressures, the ratio of the average of the resilient modulus to the initial modulus remains constant. The variation trend of the volume of the cemented sand and gravel materials at the loading stage of the triaxial unloading and reloading tests is the same as that during the loading tests, that is, it first increases and later decreases. With the increase in the same confining pressure under the stress level, the unloading carrier shrinkage of the specimen gradually changes to unloading carrier expansion. These findings may provide valuable experimental bases to construct a realistic constitutive model for cemented sand and gravel materials.