Experimental research on characteristics of the ultrasonic p-wave velocity of coal-based paste filling materials

The research aims to explore changes in the ultrasonic p-wave velocity of coal-based paste filling materials, which is used for recovering standing pillars in the closed/closing coal mines, under influences of multiple material factors. To this end, orthogonal tests were designed and coal grains were taken as main materials to evaluate the influences of four factors (particle size of coal grains (A), high-water material content (B), cement content (C), and water content (D)) on ultrasonic p-wave velocities of samples. Test results show that (1) Ultrasonic p-wave velocity of coal-based paste filling materials is in the range of 1.596 to 2.357 km/s and these are listed (in descending order) as D, B, C, then A according to their influences on the ultrasonic p-wave velocity. (2) Ultrasonic p-wave velocity is positively correlated with the compressive strength and shear strength, with correlation coefficients separately of 0.82 and 0.69. (3) Formulae for changes in the ultrasonic p-wave velocity under influences of different factors were fitted. The ultrasonic p-wave velocity of coal-based paste filling[1] materials has a quadratic polynomial relationship with factor B while having exponential relationships with factors A, C, and D. Based on fitting equations for changes in single factors and the ultrasonic p-wave velocity, a predictive model for comprehensive parameters of characteristics of ultrasonic p-wave velocity of coal-based paste filling materials under joint action of the four factors was established, and the predictive model was verified.