Effects of diagenetic stage and burial depth on the microstructure and mechanical properties of coal-bearing sandstones

The mechanical behavior of sandstones within coal-bearing strata exerts a critical influence on roof stability during coal mining, while their microstructure and porosity fundamentally determine the physical and mechanical properties. This study investigates the diagenetic and mechanical evolution of six medium-grained sandstones from the Bultai Coal Mine, Shendong Mining Area, spanning the Cretaceous (A) to Jurassic (B-F) periods with varying burial depths. Microstructural analysis reveals that the pore system, comprising intergranular and intragranular pores, cement-internal pores, and microfractures, becomes increasingly cemented with depth. The deeply buried Yan'an Formation (D-F) exhibits markedly superior mechanical properties compared to shallower units: porosity is reduced by 45.9-52.1%, while tensile strength, compressive strength, and elastic modulus are enhanced by 582-1134%, 552-656%, and 13.3-19.7 times, respectively, accompanied by a 60.6-69.2% lower peak strain. These results demonstrate that depositional period and burial depth jointly control microstructural and mechanical evolution. This study establishes a quantitative correlation between porosity, strength, and modulus. The results elucidate the coupled influence of diagenesis and burial depth on sandstone mechanics, thereby providing a more reliable framework for assessing geomechanical risks in the Shendong mining area.