膨胀土损伤变量不同表征方法评价的试验研究

Experimental study of assessment of different characterization methods of expansive soil damage

裂隙性是膨胀土的重要结构特征,裂隙损伤对膨胀土的变形、强度和稳定性有重要影响。岩土体损伤演化理论是当前研究的前沿课题,选择合理的损伤变量决定着损伤模型的正确性。为评价几种损伤变量表征方法的合理性,以南水北调中线工程陶岔引水渠坡的膨胀土为试验研究对象,通过控制净围压和吸力分别为100、50 k Pa下的CT-三轴剪切试验,定量研究了分别基于承载面积、CT数的均值ME和方差SD的损伤变量表征方法的合理性。研究发现,损伤面积相同而损伤部位不同的试样偏应力-应变曲线和强度基本一致;损伤面积和SD可以作为损伤变量表征参数,而ME不适合用来表征膨胀土的损伤变量,虽然ME可以很好地用来定义岩石的损伤变量。试验研究结果可以为建立考虑损伤的膨胀土强度理论和本构模型中损伤变量的选择、定义提供科学依据。

Cracking is one of important structural characteristics of expansive soils. The cracking damage has significant impact on the deformation, strength and stability of an expansive soil. In developing a damage model for soils, it is crucial to choose proper variable to describe the soil damage. To evaluate the applicability of several existing methods for characterizing the damage variables, a series of CT-triaxial tests was conducted on the expansive soil sampled from the site at the middle part of the South-to-North Water Transfer Project in Taocha, China. Damage variable characterization methods based on the loaded area, mean ME and variance SD of CT numbers are quantitatively examined by means of CT-triaxial shear tests under 100 kPa net confining stress and 50 kPa suction respectively. It is shown that the strength and the deviatoric stress-axial strain curves are almost the same for the soil samples with the same damage areas and different damage positions. It is appropriate for the damage variables to be defined using the damage area and the SD. However, the ME, is not suited for defining the damage variable of expansive soil, though it performs well in characterizing the damage of rock. The results can provide a starting point for defining damage variable, strength and the constitutive model of expansive soil.