Research on Wetting-Deformation Regularity and Microstructure Evolution Characteristics of Remoulded Loess in Triaxial Soaking Tests
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摘要: 为了研究填土在三轴浸水过程中的湿化变形规律及其细观结构演化特性，用改进的非饱和土CT-三轴仪对延安新区的重塑Q2黄土做了3组共17个偏压固结浸水试验. 在三轴浸水过程中对试样的两个断面进行了多次CT扫描，得到了固结和湿化过程中土样的宏观变形以及土样内部细观结构演化的CT图像和相应的CT数据，基于CT数定义了土的结构性参数和结构演化变量. 研究结果表明：干密度、净围压、基质吸力和偏应力均对试样的湿化变形特性有显著影响；提高干密度可有效减小湿化变形量和降低湿剪破坏的风险（干密度1.52、1.69 g/cm3的试样浸水过程中体应变分别为–0.58%～4.66%、–0.58%～2.43%，干密度1.79 g/cm3的试样体应变为0.019%）；湿化过程中试样越来越密实，试样的CT数均增大；浸水初期，试样原有结构发生破坏，CT数变化较剧烈，均能达到总变化量的60%；同时干密度、净围压、基质吸力、偏应力及含水率对土的结构性参数和结构演化变量有显著影响. 研究成果对填土工程的设计具有重要参考价值，为建立非饱和重塑黄土的结构损伤演化方程与结构性模型提供了科学依据.Abstract: To explore the wetting-deformation regularity and microstructure evolution characteristics of filled soil, three groups, 17 samples, of immersed anisotropic consolidation tests of reshaped Q2 loess in the Yan’an new district were studied using the improved unsaturated soil triaxial apparatus with computed tomography （CT）. The CT scanning was applied to the two sections of the samples in the triaxial soaking studies. The macroscopic deformations, soil samples’internal mesoscopic structure evolution CT images and the corresponding CT data were obtained in the consolidation and the wet process of the soil sample. Structural parameters and structural evolution variables of the soil were defined based on the CT data. The results show that the dry density, net confining pressure, matrix suction, and deviatoric stress have a significant influence on the wetting deformation characteristics. Increased dry density can effectively reduce the wetting deformations and the risk of wet shear failure. （The strains of the dry density specimen at 1.52 g/cm3 and 1.69 g/cm3 during immersion were –0.58% to 4.66% and –0.58% to 2.43%, respectively, and the strain of the dry density specimen of 1.79 g/cm 3 was 0.019%.）The CT data of all samples increased, indicating that the specimens become more and more compacted due to humidification deformation. In the early stage of immersion, the original structures of the soil samples were destroyed, and the change of CT data was more severe, reaching 60% of the total change. Meanwhile, the result is affected by the dry density, net confining pressure, suction, deviatoric stress, and moisture content. These results are valuable for the design of filled soil engineering and provide a scientific basis to establish the structure of the unsaturated remoulded loess damage evolution equation and the structural model.
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图 1 改进后的CT-湿陷三轴仪及其底座
Figure 1. Collapsible triaxial apparatus with improved CT and its base
图 2 4号试样浸水过程中的CT图像
Figure 2. Images of CT scanning of the fourth sample in soaking tests
图 3 干密度为1.52 g/cm3试样浸水量与CT数、浸水量与CT方差之间的关系曲线
Figure 3. Curves M and S vs. quantity during wetting of the sample with
$\rho_{\rm d}=1.52\; {\rm g/cm^3}$ 
图 4 16号试样浸水过程中的CT图像
Figure 4. Images of CT scanning of the 16th sample in soaking tests
图 5 干密度为1.69 g/cm3试样浸水量与CT数、浸水量与CT方差之间的关系曲线
Figure 5. The curves M and S vs. quantity during wetting of the sample with
$\rho_{\rm d}=1.69\; {\rm g/cm^3}$ 
图 6 17号试样浸水过程中的CT图像
Figure 6. Images of CT scanning of the 17th sample in soaking tests
图 8 试样体应变与结构演化变量之间的关系
Figure 8. Curves
${{\varepsilon }_{\text{v}}}$ vs. D of the sample表 1 扫描参数
Table 1. Scanning parameters
电压
/kV电流
/mA时间
/s层厚
/mm重建矩阵 空间分辨率
/mm120 165 3 3 512 × 512 0.38 
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表 2 土样的基本物理指标
Table 2. Physical parameters of soil samples
相对密度 ${d_{\rm{s}}}$ 塑限
${w_{\rm{p}}} $/%液限
${w_{\rm{L}}} $/%最大干密度
${\rho _{_{\rm{d}\max} }}$/（g•cm–3）最优含水率 ${w_{{\rm{op}}}} $/% 2.71 17.3 31.1 1.92 12.9
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表 3 试验研究方案
Table 3. Experimental programs
试验分
组编号干密度ρd/（g•cm–3） 试样 净围压/kPa 基质吸力/kPa 偏应力/kPa Ⅰ 1.52 1号 50 150 100 2号 50 150 200 3号 50 300 100 4号 50 300 200 5号 100 150 100 6号 100 150 200 7号 100 300 100 8号 100 300 200 Ⅱ 1.69 9号 50 150 100 10号 50 150 200 11号 50 300 100 12号 50 300 200 13号 100 150 100 14号 100 150 200 15号 100 300 100 16号 100 300 200 Ⅲ 1.79 17号 100 300 100
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表 4 干密度为1.52 g/cm3的试样在试验过程中的参数
Table 4. Control conditions of test sample with
$\rho_{\rm d}$ = 1.52 g/cm3试样 固结过程 浸水过程 轴向应变 饱和度 轴向应变 饱和度 体应变 1号 0.19 59.3 0.08 97.7 –0.58 2号 1.22 60.1 11.80 71.1 3.08 3号 0.26 55.5 0.73 96.2 0.64 4号 3.38 54.3 10.92 68.8 3.30 5号 0.25 57.9 0.51 97.2 2.49 6号 0.62 59.6 4.99 97.9 4.45 7号 0.49 53.8 1.63 94.1 3.62 8号 1.31 57.0 23.30 96.6 4.66
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表 5 干密度为1.69 g/cm3的试样在试验过程中的参数
Table 5. Control conditions of test sample with
$\rho_{\rm d} $ = 1.69 g/cm3试样 固结过程 浸水过程 轴向应变 饱和度 轴向应变 饱和度 体应变 9号 0.19 78.9 0.03 98.6 –0.58 10号 0.24 79.6 21.87 99.2 1.8 11号 0.14 74.4 0.08 99.2 1.18 12号 0.89 68.5 0.88 93.3 1.65 13号 0.13 72.3 0.05 96.6 1.04 14号 0.16 79.5 0.09 97.7 1.78 15号 0.20 78.3 0.05 95.4 1.67 16号 0.53 79.0 0.10 98.5 2.43
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