[1] A grain-based Universal Distinct Element Code model was developed to generate a deformable polygonal grain-like structure to simulate the microstructure of brittle rock. It takes into account grain-scale heterogeneity including microgeometric heterogeneity, grain-scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and Ä spö Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack-initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.Citation: Lan, H., C. D. Martin, and B. Hu (2010), Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading,

Geomorphic study on Wujiahe segment of Serteng piedmont fault, Inner Mongolia is made. Through analysis of the available data in combination with the results of predecessors' studies it can be obtained that average vertical displacement rate is 0.48-0.75 mm/a along the Wujiahe segment since the late Pleistocene (14.450~22.340 ka BP) and 0.56--0.88 mm/a since the early-middle Holocene (5.570--8.830 ka BP). Analyzing paleoseismic phenomena revealed in the excavated 5 trenches in combination with the results of predecessors' studies of paleoearthquakes on the fault, we determine five paleoseismic events on the Wujiahe segment of Serteng piedmont fault since 27.0 ka BP and the recurrence interval to be about 4.300~4.400 ka. A cluster of paleoearthquakes occurred probably during 8.000-9.000 ka BP and two paleoseismic events in 10.000-20.000 ka BP may be missed. A comparison between height of fault scarps and sum of displacement caused by paleoseismic events revealed in trenches, and recurrence interval of paleoseismic events obtained from average displacement rate along the fault and the dislocation by one event suggest that three paleoseismic events are absent in Alagaitu trench. Two paleoseismic events may be absent on the whole active fault segment.

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Abstract:Triaxial compressive creep tests were conducted on red sandstones after different thermal treatments. Subsequently, the thermal influence on the axial, lateral and volumetric creep curves under various stress levels was analyzed. The results show that both the instantaneous and time-based deformation behaviors depended largely on the stress and temperature conditions. The instant axial strain increases linearly with increasing deviator stress and the instant deformation modulus decreases non-linearly with temperature. An interesting phenomenon was observed whereby the lateral creep strain had an apparent linear correlation with the axial creep strain. Furthermore, the fitting lines' slopes of lateral and axial creep strain increase gradually with the increasing deviator stress at identical temperature and first decreases and then increases as temperature is elevated. Then, on the basis of the Burgers creep model and the concept of strain energy, a creep damage model implemented in FLAC 3D (Fast Lagrangian Analysis of Continua 3D) is presented, and this model was able to describe the entire creep process completely including primary creep stage, secondary creep stage, and tertiary creep stage comparing with the experimental and theoretical results based on test data and numerical calculations. The influence of two damage parameters on creep curves and the thermal influence on creep parameters are subsequently discussed. Under the same stress level, the parameters K, G M and G K and η K of creep model decrease with temperature, while the parameter η M first augments as temperature rise to 300 • C and then decreases as temperature at above 300 • C. The higher is the temperature, the smaller the critical stress ratio (CSR).

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