The Study On Ultrasonic Experiment Of Unsaturated Coal Samples Of Water Immersion Softening

The article is based on coal and rock fracturing-softening theory, by analyzing the physical and mechanical parameters before and after watering of hard top coal samples, combined with ultrasonic testing, uniaxial compressive strength testing and simulation, the soaking and softening effect of various coal rock specimens is analyzed. The main work and results are as follows:(1) Based on the damage theory of water on the rock, the mechanics between water and rock strength is analyzed, and a new rock fracture strength criterion is described, which can quantificational reflect the effect of pressure water on strength of fractured rock.(2) Porosity, water absorption and moisture content of different coal rock specimens are tested. By ultrasonic device, the coal samples'wave velocity and elastic modulus with different soaking time are measured; and also the uniaxial compression tests are done of coal sample before and after watering.(3) The relationship between ultrasonic wave and water content, longitudinal waves and soaking time in the process of softening is analyzed, and then the ultrasonic monitoring mechanisms is established to judge the effect of softening, and it will be of great practice guidance to mining on-site of water softening to hard top coal field. According to the ultrasonic wave velocity monitoring on watering seam, we can judge that whether is it saturated seam and the uniform extent of water injection, combined with the pressure and water before and after mine coal strength comparison results, a reasonable top coal to release time can be determined.(4) Through the analysis of the relationships between moisture content and softening extent, we analyzed the relationships of the moisture content and longitudinal wave velocity, moisture content and elastic modulus, moisture variation and longitudinal wave velocity, uniaxial compressive strength of different moisture content specimen, and then we summarized the relationship between moisture and softening.(5) Through numerical simulation, we analysis the coal sample of before and after softening, the result shows that the ultrasonic test concluded is reasonable.