ABSTRACT: Being based on sedimentary rocks of coal measures, this paper systematically analyses mechanical properties of sedimentary rocks and their influencing factors such as confining pressure, temperature and the content of water by using triaxial mechanical tests. The mechanical behaviours of different lithological rocks under different confining pressures, temperatures and moistures have been studied. As a result the qualitative and quantitative relationships between the mechanical properties of sedimentary rocks of coal measures and confining pressure, temperature, and moisture are respectively established. It is shown that sedimentary rocks of coal measures are commonly weak, and the strength and stiffness of the rocks reduce rapidly from sandstone to mudstone. The stiffness and strength of different rocks increase with the increase of confining pressures. Behaviour of the strain softening and failure mechanism on different rocks transforms with the increase of confining pressures. Temperatures and moistures mainly influence the mechanical properties of rocks. Under the circumstance of dryness, low moisture and/or low temperature, the rocks demonstrate attributes of brittle and shear fracture after the peak strength. From the stress?strain curves the strain softening characters is obviously shown. With the increases of temperature and/or moisture, the values of the uniaxial compression strength and elastic modulus of the rocks decrease remarkably. In case plastic failure is dominant, however, the properties of strain softening is not so remarkable.
Coal measures are the system of sedimentary rocks that have an intergrowth relationship based on alike genesis and being contained coal seam. Paleogeographical environment, paleo-tectonic condition, paleoclimate and paleo-plant condition are important controlling factors of the formation of coal measures. The formation of coal-bearing is the result of fillings at the edge of sedimentary basin under the condition of tropical climate, which is mainly composed of terrigenous detrital rocks and coal seam. Sedimentary rocks of coal measures are mainly sandstones, siltstones, sandy mudstones and mudstones. For example, coal measures of Permian period in Huainan coalfield of China were formed from delta plain environment [1]. It contains 33.66% of sandstones, 8.7% of siltstone, 50.38% mudstone and 7.23% of coal seam. Sedimentary rocks of coal measures occur within the shallow crust and their formation and geological environment are distinctly different from magmatic rocks or metamorphic rocks. Because of their relatively weak lithological character, and their complex component and variation within wide limits, coal measures rocks show particular mechanical properties. Hence, when the rock quality and stability of rock slope and mining engineering are evaluated, it is necessary to study the mechanical properties of sedimentary rocks of coal measures and their control factors [2].
