弱胶结砂岩遇水软化过程细观结构演化及断口形貌分析

对西部鄂尔多斯红庆河矿区的弱胶结砂岩采用饱水实验、SEM扫描电镜、QEMSCAN扫描电镜和力学实验等试验手段,分析其软化过程细观结构演化及其细观断裂形貌和断裂机理。研究表明:弱胶结砂岩的成岩特性决定了其遇水软化、崩解的特性与其矿物组成和结构特征密切相关;证实了弱胶结砂岩遇水软化过程中细观结构破坏的主要方式为胶结物质的破坏,且发生破断的位置为物颗粒与颗粒的接触界面或者颗粒与胶结物质之间界面;弱胶结砂岩的宏观力学行为主要由颗粒间接触决定,当边界荷载发生变化时,砂岩的最终断口发生在黏土胶结物上及其与矿物颗粒的交界处,少数发生在矿物颗粒上,颗粒体系内部结构的变化总体上可以分为颗粒破碎、颗粒或颗粒簇脱离母体结构、沿颗粒裂纹扩展及微裂隙呈弥散分布、胶结物质破坏等四大类;胶结物质力学性质是其破坏形式的关键因素,为进一步研究弱胶结砂岩变形破坏机理奠定基础。

Analysis on the microstructure evolution and fracture morphology during the softening process of weakly cemented sandstone

The microstructural evolution,the fracture morphology,and fracture mechanism of the weakly cemented sandstone in the Hongqing River ore area of the Ordos,western China,are studied through water saturation experiment,SEM scanning electron microscopy,QEMSCAN scanning electron microscopy,and mechanical experiments etc.The results show that the diagenetic characteristics of weakly cemented sandstone determine the close correlation between their features (specifically,softening with water and disintegration) and their mineral composition and structural characteristics.The study confirms that the destruction of meso-structure during the softening process is due to the destruction of cementation matters,and that the fracture is located the interface between the particles,or between the particles and the cementation matters.The macroscopic mechanical behavior of the weakly cemented sandstone is mainly determined by the contact between the particles.When the boundary load changes,the final fracture of the sandstone occurs in the clay cementation matters,or in the interface between them and the mineral grains,with only a little of fracture occurring in the mineral grains.The changes in the internal structure of the granule system can be divided into four types,namely,particle breakage,particles or particle groups breaking away from the matrix structure,the spreading along the grain fracture and the dispersed distribution of microfracture,and the damage of cementation matters.The mechanical properties of cementation matters constitute a key factor in the forms through which damage occurs,which lays a foundation to further study the deformation and damage mechanism of weakly cemented sandstone.