基于4D显微成像的非饱和颗粒土微观力学与渗流试验研究

An experimental study of micro-scale mechanics and water retention characteristic of unsaturated granular soil based on 4D micro-tomography

非饱和土力学水力-力学相关的微观机制尚不明确,目前缺乏准确的微观试验分析。针对非饱和土试验无损化观测的研究需求,研发了适用微焦点CT(computed tomography,简称CT)扫描系统的微型非饱和三轴试验装置与微型土-水特征曲线试验装置,研发的装置均主要包含压力控制系统、数据采集系统和装置主体,体积轻巧、兼容性高,可分别实现对小型化颗粒状土试样在非饱和三轴剪切试验与非饱和渗流试验的无损动态三维成像。与常规试验设备结果进行对比分析,验证了自研的微型试验装置的精度与可靠性。开展三轴剪切与非饱和渗流的原位CT扫描试验,均获得微米级分辨率三维图像,图像分析所得参量的多尺度演化趋势准确反映了原位试验的宏观应力-应变关系及全局持水能力特性。

The micro-scale hydraulic-mechanical mechanism of unsaturated soil is still unclear,and the relevant microscopic experimental researches are insufficient.Aiming at the experimental requirements of observing the microscopic behavior of unsaturated soil,we developed a miniature triaxial test apparatus and a miniature soil-water characteristic curve test device for unsaturated granular soil,which bases on the similar experimental principle of conventional unsaturated soil test device and suits for μ-CT scanning system.Two devices have a miniaturized size,light weight,and high compatibility,which are able to achieve the non-destructive and dynamic high-resolution 3D tomography of unsaturated granular soil samples under unsaturated triaxial shear test and SWCC test respectively.The experimental accuracy and reliability of these two developed mini-devices were verified by comparing with the results of conventional triaxial test and conventional SWCC test devices respectively.We carried out in situ CT scanning tests of triaxial shear and unsaturated seepage,and obtained micrometer resolution 3D images.The multiscale evolution trends of the parameters obtained from the image analysis accurately reflect the macroscopic stress-strain relationships and global water-retention capacity characteristics of the in situ tests.