True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from t...True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.展开更多
Fist-sized iron nodules, extensively found on the ground of Western Australia, were investigated by element analysis(XRF, ICP-MS and ICP-AES), electron microscopes, X-ray diffraction and M?ssbauser spectroscopy. Loose...Fist-sized iron nodules, extensively found on the ground of Western Australia, were investigated by element analysis(XRF, ICP-MS and ICP-AES), electron microscopes, X-ray diffraction and M?ssbauser spectroscopy. Loosely-packed pisoidic structures of a few to >10 mm in size were observed in the cross-section of nodules. Chemically, the nodules are majorly made of O, Si, Fe and Al, and share similar REE pattern with the loess sourced Greatford concretions from New Zealand. Angular quartz particles, nano-sized goethite and hematite are found to be the major mineral phases. Other minerals, such as detrital zircon, barite and Ce-containing particles can also be observed but of very low abundance. No detectable carbonate or amorphous silica implies that these nodules have experienced little underground fluid alteration. The quartz particles showing particularly three sections of fractal size-distributions, together with their extensive broken features and conchoidal fractures, strongly suggest in situ fragmentation of the host rock with minimum later dynamic sorting. These observations indicate the genetic environment of those nodules is always close to the surface of the tectonically stable ground since their formation. Because of the similarity of climatic and geological features, the genesis and preservation environment of these nodules in Western Australia may provide clues on the formation of Martian iron concretions.展开更多
基金supported by the National Key Basic Research Program (No. 2010CB226800)the Innovation Team Development Program of the Ministry of Education (No. IRT0656)the Fundamental Research Funds for the Central Universities (No. 2010YL14)
文摘True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.
基金a General Research Fund (Grant No. HKU 703911P) provided by the Hong Kong Research Grants Council
文摘Fist-sized iron nodules, extensively found on the ground of Western Australia, were investigated by element analysis(XRF, ICP-MS and ICP-AES), electron microscopes, X-ray diffraction and M?ssbauser spectroscopy. Loosely-packed pisoidic structures of a few to >10 mm in size were observed in the cross-section of nodules. Chemically, the nodules are majorly made of O, Si, Fe and Al, and share similar REE pattern with the loess sourced Greatford concretions from New Zealand. Angular quartz particles, nano-sized goethite and hematite are found to be the major mineral phases. Other minerals, such as detrital zircon, barite and Ce-containing particles can also be observed but of very low abundance. No detectable carbonate or amorphous silica implies that these nodules have experienced little underground fluid alteration. The quartz particles showing particularly three sections of fractal size-distributions, together with their extensive broken features and conchoidal fractures, strongly suggest in situ fragmentation of the host rock with minimum later dynamic sorting. These observations indicate the genetic environment of those nodules is always close to the surface of the tectonically stable ground since their formation. Because of the similarity of climatic and geological features, the genesis and preservation environment of these nodules in Western Australia may provide clues on the formation of Martian iron concretions.
