Fragment shapes resulting from loading at different peak pressures and rise times.
PFC3D is used to investigate the response of rock blocks to chemically induced pressure pulses. Numerical experiments are conducted on 25 cm cubes of rock with 3.8 cm diameter cylindrical cavities (holes). The holes extend the length of the cube or are limited to the middle 7.8 cm of the cube. The cavities are filled with a chemical mixture in which the reaction is initiated. The pressure resulting from the reaction fragments the rock block. Itasca's discrete element software PFC3D is used to represent the rock and model the fracturing process. The Itasca material-modeling support package (Potyondy, 2016) is used to create specimens of spherical-grain parallel-bonded synthetic material, which are subject to explosive loading. Three specimens are created, a coarse-grained 25 by 25 by 10 cm box, a fine-grained 25 by 25 by 10 cm box, and a coarse-grained 25 cm cube. The coarse models have an average particle diameter of 8.5 mm and the fine model has an average particle diameter of 4.25 mm. The coarse model particle diameters were chosen to result in a specimen with approximately 10,000 particles.
Each specimen consists of a packing of spherical particles connected by parallel bonds. Table 1 gives the material microproperties. The essential micro properties are density (1960 kg/m3), modulus (1.5e9 Pa), normal to shear stiffness ratio (1.5), cohesion (20e6 Pa) and tensile strength (1e6 Pa). A full description of all the microproperties in Table 1 is given in (Potyondy, 2016). These microproperties give rise to the following macroscopic properties: a Young’s modulus of 1.82e9 Pa, a (static) direct tensile strength of 0.74e6 Pa and an unconfined compressive strength of 3.4e6 Pa. The material specimens are created without a hole. The material specimens are initially under zero stress.
These data files use a combination of the PFC material modeling support package and the PFC Python programming environment. Python is a programming environment which is embedded in PFC3D. More information about Python can be found in the PFC3D manual in the scripting section.
Running master.p3dat creates all the material specimens and runs all the cases described in the report.
The data files in the folder coarse_box/ are used to generate the coarse specimen for this parameter study. The folder fine_box/ contains the files that create the fine specimen, and the folder cube/ contains the files for the dimensional specimen. In these folders the specimen geometry is defined in mvParams.p3dat and the material properties are defined in mpParams.p3dat. Running the file myMatGen.p3dvr in these folders creates the model save.
The folder fistSrc/ contains the files which define the material modeling support package. Changing these files is typically unnecessary. Note that this work was conducted with a development version of the material modeling support package: version fistPkg21b. The release version, fistPkg21, should have identical behavior.
The file load.py is a Python module which defines the hole excavation and pressure loading procedure. It is not necessary to call load.py directly, the Python files described below import functions from this module.
The file parameter_study.py runs the 25 case parameter study. The files base_fine.py and base3d.py run the fine model and 3D model. These files define the hole radius, peak pressure and pressure decay time.