This paper presents a set of triaxial compression tests on partially saturated dense sands to clarify the microscopic characteristics and their link to the macroscopic responses. Constant suction tests (CS tests) and constant water content tests (CW tests) are conducted under low confining pressure to observe microscopic and macroscopic behaviors of the sands associated with dilative shear bands. X-ray micro-tomography and image analysis techniques are applied to investigate the continuity as a defined index to evaluate the morphology of the pore water, the number of liquid bridges and the principal curvature of the air–water interface. The number of liquid bridges decreases for both the CS and CW tests, particularly during the strain softening process, while it decreases greater in the CW test than in the CS test. The curvature of the air–water interface remains at almost the same value under the CS test, while it tends to decrease under the CW test. The tendency of decreasing curvature corresponds to that of decreasing suction in the CW test. The peak deviator stress is higher in the CS test than in the CW test when the pore water is initially discontinuous, whereas it is identical between the two tests when the pore water is initially continuous. The residual stress is lower in the CW test than in the CS test, independent of the initial water retention states. The macroscopic responses at the different initial water retention states are qualitatively identical between poorly graded sand and well-graded sand.

本文提出了一组在部分饱和的致密砂岩上进行的三轴压缩试验，以阐明其微观特征及其与宏观响应的联系。在低围压下进行恒定吸力测试（CS测试）和恒定水含量测试（CW测试），以观察与扩张剪切带相关的砂土的微观和宏观行为。X射线显微断层照相术和图像分析技术被用于研究连续性，将其作为评估孔隙水形态，液桥数和气水界面主曲率的确定指标。在CS和CW测试中，尤其是在应变软化过程中，液桥的数量都会减少，而CW测试中的液桥数量要比CS测试中的减少更多。气水界面的曲率在CS测试中保持几乎相同的值，而在CW测试中则趋于减小。曲率减小的趋势与CW测试中吸力减小的趋势相对应。当孔隙水最初不连续时，CS测试中的偏斜峰值应力比CW测试中更高，而当孔隙水最初连续时，两次偏斜应力相同。与初始保水状态无关，CW试验中的残余应力低于CS试验中的残余应力。在坡度差的砂和坡度好的砂之间，不同初始保水状态下的宏观响应在质量上是相同的。曲率减小的趋势与CW测试中吸力减小的趋势相对应。当孔隙水最初不连续时，CS测试中的偏斜峰值应力比CW测试中更高，而当孔隙水最初连续时，两次偏斜应力相同。与初始保水状态无关，CW试验中的残余应力低于CS试验中的残余应力。在坡度差的砂和坡度好的砂之间，不同初始保水状态下的宏观响应在质量上是相同的。曲率减小的趋势与CW测试中吸力减小的趋势相对应。当孔隙水最初不连续时，CS测试中的偏斜峰值应力比CW测试中更高，而当孔隙水最初连续时，两次偏斜应力相同。与初始保水状态无关，CW试验中的残余应力低于CS试验中的残余应力。在坡度差的砂和坡度好的砂之间，不同初始保水状态下的宏观响应在质量上是相同的。与初始保水状态无关，CW试验中的残余应力低于CS试验中的残余应力。在坡度差的砂和坡度好的砂之间，不同初始保水状态下的宏观响应在质量上是相同的。与初始保水状态无关，CW试验中的残余应力低于CS试验中的残余应力。在坡度差的砂和坡度好的砂之间，不同初始保水状态下的宏观响应在质量上是相同的。