北疆白砂岩力学特性及其微观机制试验研究

Experimental study on mechanical characteristics and microscopic mechanism of white sandstone in northern Xinjiang

为深入分析北疆白砂岩的力学特性,通过开展不同因素条件下白砂岩的直剪、压缩、渗透以及SEM扫描电镜试验,从宏观、微观角度分析了其力学特性并揭示了其微观机制。试验结果表明:直剪试验中,黏聚力随含水率增大呈二次抛物线变化规律,在最优含水率附近达到峰值,内摩擦角随含水率增大呈线性下降趋势;随着干密度的增大,黏聚力与内摩擦角均呈线性上升趋势。压缩试验中,随着含水率增大,压缩指数逐渐增大,回弹指数呈波动变化;随着干密度的增大,压缩指数与回弹指数逐渐减小,函数关系可用指数函数表示;微观方面,随着竖向压力增大,粒径增大,圆度、孔径及微观孔隙率减小,颗粒与孔隙有明显定向性,其中微观孔隙率是影响压缩指标的主要因素。渗透试验中,渗透系数随着干密度增大呈指数趋势下降,在1.60~1.84 g/cm^(3)范围内渗透系数量级从10^(-4)降至10^(-6);微观方面,随着干密度增大,架空孔隙减少,土体渗透性降低,各项微观参数中平均孔径与渗透系数有显著的相关性,是影响白砂岩渗透性的重要因素。

In order to analyze the mechanical properties of white sandstone in northern Xinjiang,the direct shear,compression,permeability and SEM tests of white sandstone under different factors were carried out to analyze the mechanical properties from the macro and micro perspectives and reveal its microscopic mechanism.The test results show that in the direct shear test,the cohesion changes parabolically with the increase of moisture content,reaching a peak near the optimal moisture content,the internal friction angle decreases linearly with the increase of moisture content,and the cohesion and internal friction angle both show a linear upward trend with the increase of dry density.In the compression test,the compression index gradually increases and the rebound index fluctuates with the increase of moisture content,the compression index and rebound index decrease exponentially with the increase of dry density,the particle size increases and the roundness,pore size and microscopic porosity decrease with the increase of vertical pressure,the particles and pores have obvious orientation,and the microscopic porosity is the main factor affecting the compression index.In thepermeability test,the permeability coefficient decreases exponentially with the increase of dry density,the magnitude of permeability coefficient decreases from 10^(-4)to 10^(-6)when the dry density increases from 1.60 g/cm^(3)to 1.84 g/cm^(3,)the trellis pore and permeability decrease with the increase of dry density,there is a significant correlation between the average pore size and permeability coefficient,and the average pore size is the key factor influencing the permeability of white sandstone.