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Experimental study on shear failure characteristics of weak expansive oxidized soil under atmospheric conditions
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摘要: 膨胀土体材料在大气环境下自然氧化，其黏粒的化学成分、矿物组分和颗粒结构将发生变化。通过XRF成分检测及室内土工试验方法，研究了不同围压条件下原状土样与氧化土样的剪切变形破坏规律，用硬化系数量化分析了土样从压缩硬化过渡到压剪混合破坏模态的非线性软化特征。结果表明：原状土样氧化后抗剪指标有所增强，内摩擦角变化是抗剪强度增加的关键因素。原状土样和氧化土样的剪切破坏机制较为复杂，在试验设定加载条件下，可能发生鼓曲状压缩、硬化压缩、压剪混合或剪切滑移等各类破坏模态。硬化系数可对土样加载过程中的剪切应力应变关系曲线进行量化，体现压缩硬化向压剪混合及剪切软化破坏模态过渡的非线性变化特征。可为膨胀土氧化效应研究及其土体稳定性分析提供一定的理论参考。Abstract: Under atmospheric environment conditions, the natural oxidation of expansive soil may occur, and the chemical composition, mineral composition and particle structure of clay particles may change. In order to study the effect of atmospheric oxidation on the physical properties of Liulin weak expansive soil, the chemical components of undisturbed soil and oxidized soil clay were compared by XRF component detection and laboratory geotechnical test methods. The shear deformation and failure modes of undisturbed soil and oxidized soil samples were studied under different confining pressures. The hardening characteristics of soil samples under compression and shear failure modes were analyzed by the principal stress-strain constitutive relation. The results show that the key factor is the change of the internal friction angle for the increase of the shear strength index. Under the experimental loading conditions, the failure modes of undisturbed soil samples and oxidized soil samples are different, and various failure modes may occur, such as buckling compression, hardening compression, compression and shear mixing, or shear slip. For soil materials with softening properties, the hardening coefficient can be used to describe the nonlinear characteristics of the sample transition from compression hardening to compression shear mixing and shear softening failure mode. This paper can provide a theoretical reference for the study of the oxidation effect of expansive soil and the analysis of its engineering stability.
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图 1 柳林弱膨胀土现场勘察取样
Figure 1. Field investigation and sampling of Liulin weak expansive soil
图 2 柳林弱膨胀土氧化过渡及三轴试样制样
Figure 2. Oxidation transition state of Liulin weak expansive soil and preparation of triaxial sample
图 3 原状土与氧化土颗粒分配曲线
Figure 3. Particle size distribution curve of undisturbed soil and oxidized soil
图 4 不同围压条件下原状土与氧化土轴向应变曲线
Figure 4. Axial strain curves of undisturbed soil and oxidized soil under different confining pressures
图 7 初始切线模量、硬化系数与围压关系曲线
Figure 7. Relationship of initial tangent modulus, hardening coefficient and confining pressure
图 8 硬化系数反演应力应变曲线
Figure 8. Inversion curve of shear strength and axial deformation by hardening coefficient
表 1 柳林弱膨胀土与氧化土物理性质指标平均值
Table 1. Average values of physical indexes of Liulin expansive soil and oxidized clay
土样 含水率/% 密度/(g·cm−3) 干密度/(g·cm−3) 液限/% 塑限/% 塑性指数 自由膨胀率/% 标准吸湿含水率/% 原状样 20.8 1.904 1.576 51 30 21 53 3.5 氧化样1 18.9 1.879 1.580 57 31 26 48 3.1 氧化样2 17.2 1.929 1.645 55 30 25 50 3.5 
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表 2 柳林弱膨胀土与氧化土黏粒的化学成分
Table 2. Chemical compositions of Liulin expansive soil and oxidized clay
单位：% 土样 黏粒化学成分及质量比 MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 MnO Fe2O3 ZnO Rb2O SrO ZrO2 原状样 1.20 14.52 51.60 0.10 6.51 2.46 2.13 0.18 20.90 0.06 0.09 0.10 0.14 氧化样1 1.22 13.46 49.78 0.25 6.13 3.88 2.07 0.33 22.46 0.11 0.12 0.16 氧化样2 0.91 15.02 51.26 5.90 2.52 1.84 0.39 21.67 0.08 0.11 0.11 0.19 注：质量比为烘干（烘箱控温105~110 ℃）状态下，各黏粒化学成分的质量占比。
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表 3 柳林弱膨胀土与氧化土最大主应力差及其均值
Table 3. Maximum principal stress difference and its mean value of Liulin expansive soil and oxidized soil
单位：kPa 土样类别 无侧限条件 50 kPa围压 100 kPa围压 200 kPa围压 主应力差 均值 主应力差 均值 主应力差 均值 主应力差 均值 原状土 191.0 193.0 222.1 224.7 278.1 290.9 344.9 370.8 181.3 241.5 296.4 394.9 206.4 210.4 298.2 372.6 氧化样1 213.2 201.2 229.2 250.9 319.2 319.1 431.4 417.1 197.1 268.5 303.8 430.1 192.7 255.1 334.3 389.9 氧化样2 184.1 198.9 218.1 234.8 304.3 299.2 386.9 385. 6 204.9 254.3 298.5 364.7 207.7 232.0 294.7 402.3
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