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 experi- ment,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 be- tween 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 de- struction of cementation matters,and that the fracture is located the interface between the particles,or between the par- ticles 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 sprea- ding 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.