胶结砂砾石料三轴卸载—再加载力学特性试验研究
Mechanical behaviors of cemented sand and gravel materials based on triaxial tests during unloading and reloading
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摘要: 了解胶结砂砾石坝坝料卸载—再加载路径下的力学行为,有助于提高水库蓄、泄水时该坝应力、变形预测结果的准确性。利用大型三轴剪切仪开展了胶凝掺量100 kg/m3的胶结砂砾石料在不同围压与应力水平下的三轴卸载—再卸载试验,并结合相应的一次加载三轴剪切试验结果,系统分析了胶结砂砾石料三轴卸载—再加载路径下的应力变形特征。结果表明:胶结砂砾石料受应力卸载—再加载作用后,其内摩擦角与黏聚力均有所提高,增强了该材料的峰值强度;在同一围压下,不同应力水平对胶结砂砾石料卸载回弹模量值的影响较小,随着围压的增大,卸载回弹模量增加且增幅逐渐减小,不同围压下平均回弹模量与初始模量的比值基本相同,直接取其平均值;不同围压下胶结砂砾石料在加载阶段的体积变化规律与一次加载试验的体积变形规律基本相同,均呈先增大后减小,试件出现先剪缩后剪胀现象;在同一应力水平下,随着围压的增大,试件卸载时发生的体胀现象逐渐变为体缩。研究成果可为构建更加合理的胶结砂砾石料本构模型提供了重要试验依据。Abstract: 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.