干湿环境下膨胀土力学性能劣化的多尺度效应

doi:10.13722/j.cnki.jrme.2020.0170

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摘要为探索干湿循环作用下膨胀土力学性质与其结构损伤的多尺度效应，首先对重塑膨胀土试样进行0～6次干湿循环并记录开裂过程，而后分别展开三轴强度试验、核磁共振测试及扫描电镜试验，进而研究土体宏观力学行为与微细观结构损伤规律。研究结果表明：(1) 干湿作用参与下，土体应力–应变曲线软化显著，抗剪强度劣化，其中黏聚力在前3次干湿循环期间骤减，4次后趋于稳定，内摩擦角变化较小；(2) 土体裂隙在干湿循环作用下经历了启裂期、传播期和平衡期，平均裂隙率及平均隙宽均先后经历了增长期和稳定期，且平均隙宽在稳定期末略有收敛；(3) 土体微观结构受干湿循环影响显著，孔隙总体积增加，微孔不断粗化、贯通，形成介孔或大孔；土体微观结构破碎、疏松，颗粒和孔隙间界限模糊；颗粒丰度稍有增加，但整体处于平衡互馈状态；颗粒定向频率整体呈各向同性，但局部存在最优取向；粒径分布表现为黏粒稍减、粉粒稍增、砂粒相对稳定。综合分析上述结果，对干湿循环下膨胀土的微细观损伤过程进行描述，从而得到土体力学性能劣化的多尺度机制：湿度交替变化引起土体内亲水性黏土矿物循环胀缩，诱发膨胀势、基质势，反复作用于土体微细观结构，造成疲劳损伤，导致土体黏聚力骤减、抗剪强度损失；加之土体不均匀干缩产生张拉应力并驱动裂隙扩展、贯通，继而造成土体完整度退化、力学性能降低。研究成果为半干旱区膨胀土力学行为及结构损伤演化的认知提供有益参考。

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	刘宽1
	叶万军1
	高海军2
	董琪3

关键词 ：土力学, 膨胀土, 干湿循环, 力学性能, 微细观结构, 核磁共振, 扫描电镜, 多尺度效应

Abstract：To explore the multi-scale effects of mechanical properties and structural damage of expansive soils under the action of dry-wet cycles，the remolded expansive soil specimens were subjected to 0–6 dry-wet cycles with recording the cracking process and then，the triaxial strength(CU) test，nuclear magnetic resonance(NMR) test and scanning electron microscope(SEM) test were carried out separately. Furthermore，the macroscope mechanical behavior and micro- and meso-structure damage of the soil were studied. The results indicate that, due to the dry-wet action，the stress-strain curve softens significantly and the shear strength deteriorates. Specifically，the cohesion decreases sharply during the first three dry-wet cycles and tends to be stable after four cycles，while the internal friction angle changes little. Under the action of dry-wet cycles，soil cracks experience the initiation stage，the propagation stage and the equilibrium stage. Both the average crack rate and the average crack width increase at first and then maintain stable. Besides，the average crack width converges slightly at the end of the stable phase. The micro-structure of the soil is significantly affected by the dry-wet cycles，mainly illustrated by the increased total volume of pores and the continuous coarsening and penetration of micropores to form mesopores or macropores. The structure of the soil is broken and loose，and the boundary between particles and pores is blurred. The particle abundance slightly increases，but at a whole in a state of balanced mutual feed. The particle orientation frequency presenting the global isotropic feature has a local optimal orientation. The particle size distribution is characterized by slightly reduced clay particles，moderately increased powder particles and relatively stable sand particles. Based on the above results，the micro- and meso-damage process of the expansive soil under the action of dry-wet cycles was described，and the multi-scale mechanism of soil mechanical performance degradation was obtained. Alternating wet and dry changes first cause the cyclic swelling and shrinkage of hydrophilic clay minerals in the soil，and thus induce the expansion potential and matrix potential. Such potentials repeatedly act on the micro- and meso-structure of the soil，causing fatigue damage and thus a sudden decrease in the cohesion of the soil and a loss of the shear strength. Additionally，the uneven shrinkage of the soil produces tensile stress and drives crack propagation and coalescence，resulting in the degradation of soil integrity and reduction of mechanical properties. The research results may provide a useful guidance for the understanding of mechanical behavior and structural damage evolution of expansive soils in semi-arid areas.

Key words： soil mechanics expansive soil dry-wet cycles mechanical properties micro- and meso-structure nuclear magnetic resonance scanning electron microscope multi-scale effect

引用本文:

刘宽1，叶万军1，高海军2，董琪3. 干湿环境下膨胀土力学性能劣化的多尺度效应[J]. 岩石力学与工程学报, 2020, 39(10): 2148-2159.
LIU Kuan1，YE Wanjun1，GAO Haijun2，DONG Qi3. Multi-scale effects of mechanical property degradation of expansive soils under drying-wetting environments. , 2020, 39(10): 2148-2159.

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http://rockmech.whrsm.ac.cn/CN/10.13722/j.cnki.jrme.2020.0170 或 http://rockmech.whrsm.ac.cn/CN/Y2020/V39/I10/2148

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