Influence of Microstructures of Rock on Its Whole Deformation and Failure
Geo-Energy Division
Mining and Geotechnology Department |
- Objectives
- An enough theoretical basis has not been given to an influence of microstructures, such as composition grains, on a characteristic of failure and deformation of rock. This study was planned to clarify experimentally a relation between the change of grains and grain boundaries and the change of characteristic of failure and the deformation of rock. A surface of the rock specimen was observed in a tensile test which induced microscopic damages on it. The change of characteristic of the deformation of rock was measured using strain foil gauges under hydrostatic compression.
- Results
- A tensile test using a stress feedback method was effective to inducing damages in a rock specimen without destroying a whole body of it. In the tensile test, strange phenomena were measured on the rock specimen. It showed the specimen inflated to perpendicular directions to a tensile axis. This behavior of the specimen was different from that of an elastic body, therefore a simulation analysis of the tensile test using a distinct element method (DEM) was conducted to examine the influence of the grain and grain boundary behavior. Fig.1 shows examples of lateral strain behaviors of the rock specimen in the tensile test and that of a computed DEM model. The lateral strain behaviors of DEM model are similar to that of the rock specimen qualitatively. A DEM analysis showed that this strange increases of lateral strain in the tensile region were local phenomenon and the lateral strain of the whole specimen increased in a compressive region and that if properties of the weak plane which was imitated a mineral grain boundary became easier to deform, a tendency for the lateral strain to increase in the tensile region was strengthened.
- The damage which was induced by the tensile test changed a deformation characteristic in case of a hydrostatic pressure loading on the specimen but the relation between the change of the deformation characteristic and the induced damage didn't agree with an expectation. On the other hand, an observation with optical microscope could not catch the fracture during the tensile test but an observation of a replica film which was impressed on the surface of the specimen after experiment could show a failure fracture. Therefore, it is suitable for the purpose to measure the failure fracture in the way of failure.
| National Institute for Resources and Environment |
