A new approach for applying the in-situ Schmidt hammer test on a coal face

The indirect Schmidt hammer test is used to determine the mechanical behavior of rock materials. The method has so far been widely applied to intact rock, and therefore researchers have developed procedures for its use on rock cores and blocks. However, there is currently little information about using the Schmidt hammer for in-situ testing. The purpose of this study was therefore to evaluate the application of the Schmidt hammer test in-situ on a coal face. In this study, a measurement area of 72 m2 was selected in the center of a 330 m2 longwall face. The main measurement area was divided into a grid system, with each grid section having an area of 0.375 m2. The tests were conducted as a single hammer impact at the center of each grid section. One thousand nine hundred and sixty-five records were constructed using the data obtained from 10 face positions, and these were used for statistical analyses. The statistical results suggested that the total number of tests carried out on the main measurement area was more than the minimum required. An equation was then developed that not only gives the appropriate test number, but also provides information about the grid system. Hence, a new approach is proposed for determining the optimum grid system and test number for in-situ testing of coal faces.