EAGER: Exploratory Research on Rock Damage from Geologic and Induced Thermal Loading

Colorado School Of Mines, Golden CO

Investigators

Abstract

The behavior of rock under short- and long-term thermal excursions is a critical knowledge gap in rock science and engineering disciplines. Such advanced understanding will be important in many applications, including mined and civil excavations, in situ resource extraction or geothermal development for which excavations will be extended into rock masses at elevated temperatures. Most analyses have focused on rock stress as result of tectonics and depth. With insight into how thermal changes influence the fabric and structure of the rock, new excavation methods and technologies may be developed that lead to a truly engineered design of thermally-induced rock breakage. The most relevant questions to be investigated are: How does the PT (Pressure-Thermal) history of intact rock (and a rock mass) induce damage and influence behavior? Which mechanisms are most important in influencing the changes in mechanical structure of heated rock? How do these mechanisms influence excavatability, stability and strength? This EArly-concept Grant for Exploratory Research (EAGER) project involves geology, civil and mining engineering, and extractive metallurgy and mineral processing. This multi-disciplinary approach will help broaden participation of underrepresented groups in research and positively impact engineering education. The assessment of induced damage will involve rocks with well-defined thermal and stress history and composition. Rock samples will be subjected to additional selective heat-treatment (e.g., microwaves) in dry and saturated states, and the resulting damage and changes in properties will be evaluated using thin section petrography, optical cathodoluminescence, scanning electron microscopy and automated mineralogy. Investigations of geologic damage caused by thermal and stress history (e.g., skarns in the contact zone of local metamorphism, pegmatitic intrusions) will study samples from core and mined exposures. The temperature and pressure history will be evaluated using geothermobarometry of mineral pairs and placed in regional context based on existing thermochronology studies (e.g. U-Pb/He thermochronology of apatite and zircon). These results will be compared with those from experiment 1) to identify cracking behavior and generation of stresses and damage at grain boundaries as result of heating. Finally, numerical simulation of thermal loading of will be analyzed numerically and the results will be compared to the experimental observations.