Abstract:

In order to study the interconnection between macroscopic and microscopic failure characteristics of different textured sandstones， three types of sandstones from Xianghualing mining area were analyzed using petrographic analysis， sedimentary phase discrimination， and uniaxial compression and shear tests to observe the microscopic structural characteristics. The results show that compressive strength of terrestrial sedimentary quartz sandstone is the largest， followed by feldspathic sandstone， and marine sedimentary glauconitic sandstone is the smallest. In uniaxial compression， quartz sandstone and feldspathic sandstone exhibit brittle failure on a macroscopic scale， while glauconitic sandstone shows ductile failure with softening characteristics. On the microscopic scale， quartz sandstone undergoes intergranular failure with a smooth surface， while feldspathic sandstone experiences intergranular and transgranular failure with a small scallop?shaped surface and minimal adhering debris， and glauconitic sandstone displays a flat?granular composite fracture surface with obvious grain crushing and pronounced scratches. The failure characteristics are jointly controlled by the grains， cemented material and structural weak planes. The shear test microscopically shows that the quartz sandstone occurs has transgranular failure first and then intergranular failure， with uneven surface， scrapes and debris， while the feldspathic sandstone occurs transgranular failure mainly and intergranular failure， with partially flat surface， scrapes and debris. The glauconitic sandstone simultaneously exhibits intergranular and transgranular failure， resulting in a smooth surface with almost no abrasion or debris. The microscopic failure characteristics are influenced by the grain strength and cementing materials.

Key words: sandstone, mineral composition, microstructure, failure characteristics, strength