Mechanical Properties And Acoustic Emission Characteristics Of Weakly Cemented Sandstone Under Uniaxial Compression

The coal seam roof and floor of coal-rich area in Western China are mostly weakly cemented rock. Highly intensive mining of coal resources has produced a series of serious geological disasters and environmental damage issues. But the current research on weakly cemented rock properties can’t meet the needs of geological disaster prevention and environmental protection under highly intensive mining. A clear understanding of mechanical properties and failure mechanism of weakly cemented rock has some significance to restrain geological disasters and reduce environmental damage.The typical weakly cemented rock-weakly cemented sandstone is selected as the research object in this paper, and its mechanical properties and acoustic emission (AE) characteristics has been analyzed through the method of a combination of experimental investigation, theoretical analysis and numerical simulation. The main research work and main conclusions are drawn as follows:(1) On the basis of figuring out the mineral composition and cemented structure of sandstone, the experiment of calcareous argillaceous fine sandstone and argillaceous medium sandstone was carried out under uniaxial compression, then their deformation and failure characteristics are analyzed and compared. Uniaxial compressive strength and elastic modulus of calcareous argillaceous fine sandstone is higher. There are no significant plastic deformations before its failure, and its failure mode is mostly splitting failure. What’s more, it has the burst potential. As for the argillaceous medium sandstone, its uniaxial compressive strength and elastic modulus is lower. There are the significant plastic deformations before its failure, and its failure mode is mostly single inclined plane shear failure.(2) Two-part Hooke’s model can be used to depict the mechanical properties appropriately, and the compression stage of the weakly cemented sandstone can be concluded as nonlinear deformation of soft elements including primary porosity and micro-crack under low stress level.(3) Through the comparative investigation of AE and damage evolution during the failure process of two kinds of weakly cemented sandstone, the results are drawn as followed: the AE catastrophically occurs before the failure of weakly cemented sandstone, and this phenomenon can be used to judge sandstone failure. When compared to calcareous argillaceous fine sandstone, the damage of argillaceous medium sandstone occurs mainly during the crack stable propagation stage, and the AE represents the process of gradual accumulation before the failure of argillaceous medium sandstone, which can explain the obvious plastic deformation.(4) The PFC2D numerical model was built using parallel-bond to represent the cemented properties of weakly cemented sandstone, in order to study the failure process of weakly cemented sandstone and the effect of bond strength on mechanical properties and acoustic emission characteristics. The simulation results include:the specimen with higher bond strength shows higher compressive strength and more obvious brittle features, and the AE is concentrated after the peak strength. With the decrease of bond strength, the AE becomes more active in both early stage and end stage of load. The results of simulation is basic anastomotic with the laboratory experiment and consummate the deficiency of laboratory experiment.