基于核磁共振技术的水泥改良膨胀土抗剪强度参数分析

Analysis of Shear Strength Parameters of Expansive Soil Improved by Cement Based on Nuclear Magnetic Resonance Technology

从两个方面研究水泥对膨胀土抗剪强度的影响。在宏观方面,通过室内直剪试验,水泥掺量比例范围为0%~6%时,分析水泥改良膨胀土抗剪强度的黏聚力和内摩擦角的变化特性。试验表明:水泥可有效提高改良膨胀土的黏聚力和内摩擦角。水泥掺量比例较低时,改良土的黏聚力增加幅度不超过15 kpa,水泥掺量比例在3.5%~4.5%时,黏聚力增加幅度最大,达到37.25 kpa。内摩擦角一直在逐渐增加,增加幅度较小。水泥改良膨胀土的最佳掺量比例为4.5%。在微观层方面,采用核磁共振技术对改良膨胀土的孔径分布图、T~2谱分布图进行分析研究,结果显示:不论是素土还是改良膨胀土,孔径分布曲线呈单峰变化趋势,孔径峰值集中在0.02μm。随着水泥掺量比例的增加,中孔集中孔径减小;T~2谱信号强度呈峰值先降低后升高,弛豫时间先缩短后增长,孔隙度先降低后增大的变化趋势。

The influence of cement on the shear strength of expansive soil is studied from two aspects.In the macro aspect,through the indoor direct shear test,the proportion of cement content ranges from 0%to 6%,increasing by 0.5%,and the variation characteristics of cohesion and internal friction angle of the shear strength of expansive soil improved by cement are analyzed.The test shows that cement can effectively improve the cohesion and internal friction angle of the expansive soil.When the proportion of cement content is low,the increase of cohesion of the modified soil is no more than 15 kpa;when the proportion of cement content is 3.5%~4.5%,the increase of cohesion is the largest,reaching 37.25 kpa.The internal friction angle has been increasing gradually,with a small increase.The optimum proportion of cement to improve expansive soil is 4.5%.In terms of the microscopic layer,nuclear magnetic resonance(NMR)technology is used to analyze and study the pore size distribution diagram and T2 spectrum diagram of the improved expansive soil.The data results show that the pore size distribution curve of both plain and improved expansive soil show a single-peak variation trend,with the peak of pore size concentrated at 0.02 m.As the proportion of cement content increases,the concentrated pore diameter of mesopore decreases.The signal strength of T2 spectrum decreases first and then increases,the relaxation time is long first and then short,and the porosity decreases first and then increases.