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Shock compression and dynamic fragmentation of geological materials



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Kirk, Simon 


This thesis investigated the shock compression and fragmentation of ge- ological materials with application to blast mining. Two geological materi- als were investigated; Lake Quarry Granite and Gosford Sandstone. Lake Quarry Granite was fully dense, while Gosford Sandstone was porous. The composition and microstructure of the materials were quanti ed and this information was later used in the analysis of their mechanical properties. The elastic sound speeds were measured for each material, from which their elastic moduli were derived. Gosford Sandstone had a reduced sound speed compared to its component minerals, which was analysed using geometric grain models and Hertzian contact theory. The shock Hugoniot of each ma- terial was measured though a series of plate impact experiments using a light gas gun. The experiments focused on the stress region of interest for blast mining, 0 to 12 GPa. The, fully dense, Lake Quarry Granite was found to have a constant shock speed, which agreed with the elastic longitudinal sound speed measured previously. As the material remained elastic, its Hugoniot was shown to be predictable using composite theory and the chemical com- position. The, porous, Gosford Sandstone underwent shock compaction and resulted in large variations in shock speed. The Hugoniot of Gosford Sand- stone was found to remain partially porous, even to high stresses, and was analysed using a P-a shock compaction model. Explosively-driven expanding ring fragmentation experiments were performed on Lake Quarry Granite to observed its fracture response under loading similar to those in blast mining. The experiments established that the fragment size reduced with loading strain rate until it reached the grain size. After this point the fragment size remained constant with increasing strain rate, a phenomenon not previously observed. The rock was found to be dominated by intergranular fracture, so the minimum achievable fragment size was the size of the grains with this failure mechanism.





Shock, Fragmentation, Geological material, Sandstone, Granite


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
This work was sponsored by Orica.