基于核磁共振及分形理论预测非饱和土石混合体SWCC

Predicting soil-water characteristic curves of unsaturated soil-rock mixtures based on NMR and fractal theory

【目的】土石混合体的物理力学特性与土—水特征曲线(SWCC)关系紧密,直接或间接测量SWCC费时耗力,且所得结果具有离散性,因此建立预测非饱和土石混合体SWCC的理论模型具有现实意义。【方法】采用NMR技术反演得到横向弛豫时间T_(2)图谱,将之转化为累计孔隙体积曲线,从而结合Young-Laplace′s理论及分形理论,以T_(2)为纽带建立起体积含水率与基质吸力的理论模型,并对模型进行验证。【结果】结果显示:土石混合体具有多重分形特征,对其进行分区研究,可由体积含水率与基质吸力在双对数坐标中的斜率换算得出不同孔隙半径范围内的分形维数;体积含水率与基质吸力的对数值存在强烈的线性关系,其相关系数均≥0.995;初始含水率与模型中的拟合参数具有线性关系,且相关系数均≥0.990,模型中的参数均可通过初始含水率进行求解。【结论】结果表明:模型预测结果与实测SWCC吻合程度较高,可以很好地应用于非饱和土石混合体的SWCC预测中。

[Objective]The physical and mechanical properties of soil-rock mixtures are closely related to the soil-water characteristic curve(SWCC),which is time-consuming and labor-intensive to measure directly or indirectly,and the test data are discrete.Therefore,it is of practical significance to establish a theoretical model to predict the SWCC of unsaturated soil-rock mixtures.[Methods]The experimental results of NMR were processed to obtain transverse relaxation time T_(2) profiles,which were transformed into cumulative pore volume curves,thus combining Young-Laplace′s theory and fractal theory to establish a theoretical model of volumetric water content and matric suction using T_(2) as a link,and to validate the model.[Results]The soil-rock mixtures have multiple fractal characteristics,and the fractal dimensions in different pore radii can be obtained by converting the slope of the volumetric water content and matric suction in double logarithmic coordinates;the logarithmic values of volumetric water content and matric suction have a strong linear relationship,and their correlation coefficients are all ≥ 0.995;the initial water content has a linear relationship with the fitted parameters in the model,and correlation coefficients are all ≥ 0.990,and all the parameters in the model can be solved by the initial water content.[Conclusion]The model has a good predictive performance and can be applied to predict SWCC for unsaturated soil-rock mixtures.