红层软岩遇水作用的孔隙结构多重分形特征

红层软岩内部孔隙具有随机、多样化的分布特点,孔隙结构的变化是影响其宏观力学性能的关键所在。由SEM扫描电镜获取岩样不同饱水时间下的细观结构图像,根据盒维数法计算出孔隙的分形维数,发现随着饱水时间的加长,孔隙的分形维数呈现增大趋势。同时对孔隙的数量、大小进行统计分析,得出不同饱水时间下岩样内部孔隙的分布特征。基于多重分形理论,采用统计矩的方法对孔隙结构进行定量表征。结果表明,孔隙结构的分配函数与q阶次趋于线性关系,验证了该结构的自相似性与无标度性,由广义分形维数D(0)>D(1)>D(2)说明了孔隙具有多重分形特征,由多重分形谱参数分析了孔隙结构的不规则性与复杂程度,更好地表征孔隙大小各异的分布情况。结合孔隙结构的多重分形特征与岩样抗压强度,建立起孔隙结构变化与其力学性能的关联性,对研究红层软岩的损伤过程具有一定的指导意义。

MULTIFRACTAL CHARACTERISTICS OF PORE STRUCTURE OF RED BEDS SOFT ROCK AT DIFFERENT SATURATIONS

The internal pores of red beds soft rock are random and diversified. Their changing characteristics can affect the macroscopic mechanical properties of the soft rock. The mesoscopic structure images of the rock samples at different saturation time are obtained by Scanning Electron Microscope and are used to calculate the fractal dimension by box dimension method. It is found that the fractal dimension of pores increases with the increase of saturation time. Basing on the quantity and size of pores,the distribution characteristics of pores in the rock samples at different saturation times are obtained. The multifractal theory is used to quantitatively evaluate pore structure. The results show that the distribution function of pore structure tends to be linear with q order,which verifies its self-similarity and scale-less property. The generalized fractal dimension of D(0)>D(1)>D(2) reveal the multifractal characteristics of pores,and the irregularity and complexity of pore structure are analyzed by multifractal spectrum parameters,which can characterize the distribution of different pore sizes. Combining the multifractal characteristics of pore structure with the compressive strength of the rock samples,the relationship between the change of pore structure and its mechanical properties is established,which has certain guiding significance for studying the damage process of the red beds soft rock.