南阳膨胀土在受荷的湿干循环过程中细观结构演化规律研究
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摘要
为了研究浅层膨胀土的细观结构在湿干循环过程中的演化规律,研制了可以进行CT扫描的CT-固结仪。在不同压力作用下对南阳膨胀土的原状样及其重塑土样进行多组多次湿干循环试验,并对每次烘干和增湿稳定后的试样进行CT扫描,跟踪观察湿干循环过程中试样的细观结构变化。结果表明:在湿干循环中,土样的膨胀量和收缩量都比较大,经历三次湿干循环之后,相同饱和度下土样体积基本不再变化;增湿和干燥都能使原状膨胀土及其重塑土的结构损伤,第一次烘干之后,土样即产生明显裂隙;随着湿干循环次数的增加,土样裂隙继续开展,土样结构损伤发生累积;上部荷载对裂隙开展有一定抑制作用,并影响裂隙的发育和裂隙网络的形状;原状膨胀土的裂隙围绕第一次形成的主裂隙发育,而重塑膨胀土的裂隙呈龟背状或辐射状;原状膨胀土及其重塑土在湿态(饱和度S_r=85%)时的CT数M_E值均较干态(饱和度S_r=25%)时的M_E值大;湿态和干态的M_E值均随湿干循环次数呈近似线性变化,前者的坡度比较平缓,后者则较陡;基于CT数据定义了膨胀土的细观结构参数,提出定量描述湿干循环过程中膨胀土细观结构参数与试样饱和度、湿干循环次数及所受荷载的数学表达式,预测结果与试验资料比较接近。
In order to study the meso-structural evolution of expansive soil during wetting-drying cycles, the CT-consolidation apparatus was developed; A number of tests of wetting-drying cycles were carried out for intact and remolded expansive soil under loading condition, and CT scanning was taken on samples after each wetting and drying finished.The research results indicate that during wetting-drying cycles the amount of shrinkage and swell of samples are large. After three times of wetting-drying cycles, the volume of soil samples under the same saturation is no longer changed. Both wetting and drying can induce the structural damage of expansive soil samples. After first drying, cracks generate on expansive soil samples obviously. Along with the experiment, cracks continue to expand, soil damage accumulate. The upper load has some inhibitory effect on the crack development and influences the development of the crack and the shape of the crack-network. The crack of undisturbed expansive soil is developed around the first formation of main crack while remolded expansive soils crack is a turtleback. The CT data M_E of samples are bigger in saturation of 85% than in saturation of 25%. The CT data M_E of samples in both wet and dry states are all approximately linear with the number of wetting-drying cycles and the slope of the former is relatively flat, while the latter is steeper. Meso-structural evolution parameters are defined, and the relationship between meso-structural evolution parameters and saturation, wetting-drying cycle times is proposed, the predicted results are close to the experimental data.
In order to study the meso-structural evolution of expansive soil during wetting-drying cycles, the CT-consolidation apparatus was developed; A number of tests of wetting-drying cycles were carried out for intact and remolded expansive soil under loading condition, and CT scanning was taken on samples after each wetting and drying finished.The research results indicate that during wetting-drying cycles the amount of shrinkage and swell of samples are large. After three times of wetting-drying cycles, the volume of soil samples under the same saturation is no longer changed. Both wetting and drying can induce the structural damage of expansive soil samples. After first drying, cracks generate on expansive soil samples obviously. Along with the experiment, cracks continue to expand, soil damage accumulate. The upper load has some inhibitory effect on the crack development and influences the development of the crack and the shape of the crack-network. The crack of undisturbed expansive soil is developed around the first formation of main crack while remolded expansive soils crack is a turtleback. The CT data M_E of samples are bigger in saturation of 85% than in saturation of 25%. The CT data M_E of samples in both wet and dry states are all approximately linear with the number of wetting-drying cycles and the slope of the former is relatively flat, while the latter is steeper. Meso-structural evolution parameters are defined, and the relationship between meso-structural evolution parameters and saturation, wetting-drying cycle times is proposed, the predicted results are close to the experimental data.
引文
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[12]朱国平,陈正汉,韦昌富,等.浅层红粘土的细观结构演化规律研究[J].水利与建筑工程学报,2016,14(4):42-49.Zhu GP,Chen ZH,Wei CF,et al.Microstrcture evolution of red clay during wet-dry cycles[J].Journal of Water Resources and Architectural Engineering,2016,14(4):42-49.(in Chinese).
[13]朱元青.基于细观结构变化的非饱和原状湿陷性黄土的本构模型研究[D].重庆:后勤工程学院,2008.Zhu YQ.Constitutive model of undisturbed collapsible loess based onmeso-structure change[D].Chongqing:Logistic Engineering University,2008.(in Chinese).
[2]卢再华.非饱和膨胀土的弹塑性损伤本构模型及其在土坡多场耦合分析中的应用[D].重庆:后勤工程学院,2001.Lu ZH.A elasto-plastic damage constitutive model for unsaturated expansive soil and its applications in multi-field coupling analysis of slope[D].Chongqing:Logistical Engineering University,2001.(in Chinese).
[3]胡波,龚壁卫,程展林.南阳膨胀土裂隙面强度试验研究[J].岩土力学,2012,33(10):2942-2946.Hu B,Gong BW,Cheng ZL.Test study of shear strength of fissure-plane in Nanyang expansive soil[J].Rock and Soil Mechanics,2012,33(10):2942-2946.(in Chinese).
[4]袁俊平,丁巍,蔺彦玲,等.浸水历时对裂隙膨胀土渗透性的影响[J],水利与建筑工程学报,2014,12(1):83-86.Yuan JP,Ding W,Lin YL,et al.Influence of soaked period on permeability of cracked expansive soil[J].Journal of Water Resources and Architectural Engineering,2014,12(1):83-86.(in Chinese).
[5]崔颖,缪林昌.非饱和压实膨胀土渗透特性的试验研究[J].岩土力学,2011,32(7):2007-2012.Cui Y,Miu LC.Testing study of permeability characteristics of unsaturated compacted expansive soil[J].Rock and Soil Mechanics,2011,32(7):2007-2012.(in Chinese).
[6]Elkady TY,Abbas MF.Shear strength behavior of highly expansive soil[J].Geo Congress,2012:2532-2541.
[7]卢再华,陈正汉,蒲毅彬.膨胀土干湿循环胀缩裂隙演化的CT试验研究[J].岩土力学,2002,23(4):417-422.Lu ZH,Chen ZH,Pu YB.A CT study on the crack evolution of expansive soil during drying and wetting cycles[J].Rock and Soil Mechanics,2002,23(4):417-422.(in Chinese).
[8]姚志华,陈正汉,朱元青,等.膨胀土在湿干循环和三轴浸水过程中细观结构变化的试验研究[J].岩土工程学,2010,32(1):68-76.Yao ZH,Chen ZH,Zhu YQ,et al.Meso-strutural change of remolded expansive soils during wetting-drying cycles and trixial soaking tests[J].Chinese Journal of Geotechnical Engineering,2010,32(1):68-76.(in Chinese).
[9]杨和平,张锐,郑健龙.有荷条件下膨胀土的干湿循环胀缩变形及强度变化规律[J].岩土工程学报,2006,28(11):1936-1941.Yang HP,Zhang R,Zheng JL.Variation of deformation and strength of expansive soil during cyclic wetting and drying under loading condition[J].Chinese Journal of Geotechnical Engineering,2006,28(11):1936-1941.(in Chinese).
[10]吕海波,曾召田,赵艳林.干湿交替环境下膨胀土的累计损伤初探[J].自然灾害学报,2012,6(21):119-123.Lv HB,Zeng ZT,Zhao YL.Preliminary study on accumulative damage of expansive soil in alternation of wetting-drying environment[J].Journal of Natural Disasters,2012,6(21):119-123.(in Chinese).
[11]曾召田,刘发标,吕海波,等.干湿交替环境下膨胀土变形试验研究[J].水利与建筑工程学报,2015,13(3):72-76.Zeng ZT,Liu FB,Lv HB,et al.Experimental study on deformation of expansive soil in alternation of wet-dry environment[J].Journal of Water Resources and Architectural Engineering,2015,13(3):72-76.(in Chinese).
[12]朱国平,陈正汉,韦昌富,等.浅层红粘土的细观结构演化规律研究[J].水利与建筑工程学报,2016,14(4):42-49.Zhu GP,Chen ZH,Wei CF,et al.Microstrcture evolution of red clay during wet-dry cycles[J].Journal of Water Resources and Architectural Engineering,2016,14(4):42-49.(in Chinese).
[13]朱元青.基于细观结构变化的非饱和原状湿陷性黄土的本构模型研究[D].重庆:后勤工程学院,2008.Zhu YQ.Constitutive model of undisturbed collapsible loess based onmeso-structure change[D].Chongqing:Logistic Engineering University,2008.(in Chinese).