Relationships between the petrographic, physical and mechanical characteristics of sedimentary rocks in Jurassic weakly cemented strata

Physical and petrographic properties of sedimentary rocks have great influence on their mechanical behavior. Numerous laboratory tests were conducted on intact sandstones and mudstones obtained from Jurassic weakly cemented coal-bearing strata. Several physical and mechanical parameters, particularly the rock material constant mi and the brittleness coefficient BRIT−T, were determined. The microfabric of these sedimentary rocks was also analyzed to quantify their mineral compositions and to determine quantitative relationships among mineral compositions, physical and mechanical parameters using the regression analysis. Overall, both bulk density (ρ) and P-wave velocity (Vp) exhibit positive power relationships with uniaxial compressive strength (UCS) and Young’s modulus (E), respectively. The UCS of sandstones increases with increasing quartz content and decreasing feldspar content, and the brittleness of mudstones increases with the increase of quartz and feldspar contents. In addition, the rock material constant mi presents a logarithmic correlation with the ratio of feldspar-to-quartz content for sandstones and a polynomial correlation with the ratio of clay minerals to the quartz and feldspar contents for mudstones.