Technical Presentations and AGM

Associate Professors Jun-ichi Kodama and Atsushi Sainoki

Presentation abstracts

Mechanical behaviours of frozen rocks

In cold climates, the temperature of soil and rock that lies at or close to the earth’s surface can often fall below the freezing point of water. While the combined effects of low temperatures and the presence of frozen water on changes in the material properties and behaviour of soils has been extensively studied, there is less known of the effect of these sub-zero temperatures on partially and fully saturated rock. Its effects are no less important particularly in hilly and mountainous terrains where rock walls formed for culverts, cuttings and embankments for road and rail lines can contribute to their instability. The effects of water content, temperature and loading rate on the strength and failure process of rock at sub-zero temperatures were investigated and are presented in this paper. Over the range of temperatures studied there was little change observed in the properties of dry rock. The presence of water in the rock, however, resulted in a marked increase in rock strength and the fracture initiation stress. Rock strength increased with amount of water present and the rate of load application, with the effect being exacerbated at the colder temperatures. Interestingly, the changes in strength were not uniform as there was a greater rate of increase in the tensile strength of rock with temperature than compressive strength. It is postulated that these changes in mechanical properties may be explained in part by a reduction in the stress concentration within the interstitial spaces and cracks of the rock samples tested.

Simulating intense shock pulses due to asperities during dynamic fault-slip

Seismic waves arising from fault-slip that occurs in deep underground, e.g. tunnels for hydraulic power plants and underground excavations, could inflict severe damage to the underground openings. Experimental results have revealed that intense shock pulses could generate due to the unloading of fault surface asperities that move apart during the fault-slip. This study focuses on examining the effect of fault surface asperities on the seismic waves arising from fault-slip. By means of a 3D numerical model representing underground geological conditions, dynamic analyses are carried out in order to simulate collision and unloading of fault surface asperities. Saeb and Amadei’s model and Barton’s shear strength model are newly implemented into constitutive models of FLAC3D code for the analyses. Parametrical study is conducted with the dynamic analyses in order to examine the most influential factor on the generation of intense seismic waves. The results reveal that stress release due to the unloading of the asperities has a significant influence on the intensity of seismic waves, while the collision of asperities, stiffness of the fault, and asperity geometry have a much lesser influence. When the stress release is large, the peak particle velocity excited by seismic waves is found to increase threefold, compared to that for fault-slip occurring along a planar surface. It indicates that significant deterioration of rockmasses could be induced due to the high particle velocities. This study has numerically confirmed the hypothesis that intense shock pulses could occur due to the unloading of fault surface asperities.

About the presenters

Associate Professor Jun-ichi Kodama

Dr. Jun-ichi Kodama is Associate-professor of rock mechanics laboratory at Hokkaido University in Sapporo, Japan. His research and teaching activities focus on rock mechanics and mining engineering. His research interest is in mechanical behaviors of rocks under ultimate conditions, stability assessment of rock slopes and tunnels. He is also interested in development of new resources including underground coal gasification. He is a guest professor at Henan Polytechnic University in Jiaozuo, China. He is a board member of Japanese society for rock mechanics and an editor-in-chief of International Journal of Japanese society for rock mechanics.

Associate Professor Atsushi Sainoki

Atsushi Sainoki obtained a Bachelor degree in Mineral Resource Development Engineering in 2009 and a Master’s degree in Field Engineering for Environment in 2011 from Hokkaido University, focusing on the stability evaluation of a rock slope formed in an open-pit mine. Afterwards, he was enrolled in McGill University, Canada, and obtained a PhD degree in Mining Engineering in 2014 about dynamic modelling of mining-induced fault-slip. He has developed various numerical modelling techniques to simulate mining-induced fault-slip in dynamic conditions, especially considering the influence of fault surface asperities. Also, he investigated seismic activities in a deep underground mine with a numerical modelling approach employing the discrete element method, which gave an insight into the influence of a fracture network on rock burst potential. He has published more than 19 papers in SCI journals and is an associate editor of an international journal. He is now an associate professor at International Research Organization for Advanced Science and Technology, Kumamoto University, Japan. In Japan, he is conducting research on induced-seismicity in a broad range of field, such as geo-thermal reservoir, carbon sequestration site, and deep underground mine.

The AGM will be held together with these presentations.

Venue location

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.