Laboratory Measurements of Rock Under Approximate Blast-Strain Loading Paths

Blasting for rock breakage produces high amplitude and rapid compressive loading of the rock near the blasthole, with rapidly decreasing compression with distance into the rock. Compression from the blast is followed by rapid unloading, leading to extension or even tensile loads in some cases at certain times and distances from the blasthole. Blast modeling considering linear-elastic / elastic-brittle rock behavior is well advanced, as is actual field blast experience. However, rocks are not completely linear elastic-elastic brittle, thereby leading to limitations of modeling and interpreting the field experience. To better comprehend rock behavior during blast induced loadings, an investigation of intact rock failure under theoretically ideal blast loading and unloading stress-strains has been made. Unique quasi-static laboratory stress-strain controlled rock tests are presented, along with discussion of the results. These unique tests provide knowledge of rock failure in shear or tension - i.e. rock breaking and coming apart into fragments - versus rock yielding and subsequent rock stiffness change and strength damage caused by the high-compressive loadings. These tests provide the potential for improved control of rock-blast fragmentation, heave, and microfracture generation for reduced crushing and milling energy, and improved control of blast vibrations. This could be accomplished by blast modeling using the strain-controlled loading path rock behavior identified by the laboratory tests.