干湿循环作用下原状黄土宏-微观参数关系研究

Study on macro-micro parameter relationship of undisturbed loess under dry-wet cycle

为探明不同干湿循环条件对原状Q_(2)黄土宏观力学性能与微观结构的影响,明确宏观力学参数与微观结构参数的定量关系,开展了干湿循环试验、三轴压缩试验和扫描电镜试验,分析了干湿循环过程中原状黄土宏观强度和微观结构的变化规律,基于综合结构势思想,利用宏观力学参数定义了原状黄土可变性参数表达式,推导了用以描述黄土微观孔隙结构特征的孔隙特征参数,建立了原状黄土宏-微观参数关系表达式。结果表明:干湿循环作用下,原状黄土孔隙面积比和分形维数呈增长趋势,黄土峰值偏应力和黏聚力持续减小,干湿循环幅度越大,下限含水率越高,黄土孔隙结构的扩张和宏观强度的衰减越快,但内摩擦角变化不大;原状黄土的可变性可用宏观峰值偏应力与土体黏聚力的比值表征,即可变性参数,随着干湿循环次数的增加,原状黄土可变性参数整体呈非单调增长趋势变化;原状黄土的微观孔隙结构特征可用孔隙面积比和孔隙分形维数的乘积表征,即孔隙特征参数,其与可变性参数的变化关系和三角函数接近;原状黄土峰值偏应力与孔隙特征参数的比值随黏聚力的变化规律服从指数函数关系,经验证,该函数关系可较为合理地描述原状黄土宏观和微观参数间的数量关系。

In order to explore the effects of different drying-wetting cycles on the macroscopic mechanical properties and microstructure of undisturbed Q_(2) loess,and to clarify the quantitative relationship between macroscopic mechanical parameters and microstructure parameters,drying-wetting cycle tests,triaxial com-pression tests and scanning electron microscope tests were carried out.The change rules of macroscopic strength and microstructure of undisturbed loess during the drying-wetting cycle were analyzed.Based on the idea of comprehensive structural potential,the expression of variability parameters of undisturbed loess was defined by using macroscopic mechanical parameters.The pore characteristic parameters used to de-scribe the microscopic pore structure characteristics of loess were deduced,and the expression of macroscop-ic and microscopic parameters of undisturbed loess was established.The results show that under the action of dry-wet cycle,the void area ratio and fractal dimension of undisturbed loess show an increasing trend,and the peak deviatoric stress and cohesion of loess decrease continuously.The larger the amplitude of dry-wet cycle and the higher the lower limit moisture content,the faster the expansion of loess pore struc-ture and the attenuation of macroscopic strength,but the internal friction angle changes little.The variability of undisturbed loess can be characterized by the ratio of macroscopic peak deviatoric stress to soil cohe-sion,that is,the variability parameters.With the increase of drying and wetting cycles,the variability pa-rameters of undisturbed loess show a non-monotonic growth trend.The microscopic pore structure characteris-tics of intact loess can be characterized by the product of pore area ratio and pore fractal dimension,name-ly,the pore characteristic parameters,which are close to the variation relationship and trigonometric func-tion of variability parameters.The ratio of peak deviatoric stress of intact loess to pore characteristic parame-ters follows an exponential function with the variation of cohesion.It is proved that this function can reason-ably describe the quantitative relationship between macro and micro parameters of intact loess.