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Acta Geotechnica - This paper presents a novel conceptual approach for evaluating the mechanical effect of pore liquids on the overall geotechnical behavior. The approach is based on empiric... 相似文献
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Manuel Raith Matthias Ebert Katja Pinkert Christian U. Grosse 《Meteoritics & planetary science》2018,53(8):1756-1772
Since the 1960s, hypervelocity impact experiments have been conducted to study the complex deformation mechanisms which occur in the subsurface of meteorite craters. Here, we present ultrasound tomography measurements of the damage zone underneath seven experimentally produced impact craters in sandstone cubes. Within the framework of the Multidisciplinary Experimental and Modeling Impact Research Network and the NEOShield Project, decimeter-sized sandstone targets were impacted by aluminum and steel projectiles with radii of 2.5, 4, and 5 mm at velocities between ~3.0 and ~7.4 km s−1. The 2-D ultrasound tomography clearly shows a correlation between impact energy and the damaged volume within the target blocks. When increasing impact energies from 805 to 2402 J, a corresponding increase in the damage radius from ~13.1 cm to ~17.6 cm was calculated. p-Wave velocity reductions up to 18.3% (for the highest impact energy) were observed in the vicinity of the craters. The reduction in seismic velocity decreased uniformly and linearly with increasing distance from the impact point. The damage intensities correspond to peak damage parameters of 0.4–0.51 compared to undamaged target blocks. In addition to the damage zone below the crater, we could identify weakened zones at the sandstone walls which represent precursors of spalling. The volume of the damaged subsurface beneath experimentally produced craters determined through ultrasound tomography is larger than that obtained from previously reported p-wave velocity reductions or to microscopic and microcomputed tomography observations of crack densities in experimentally produced craters. 相似文献
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This paper suggests a new method for obtaining steady‐state solutions for ‘full‐flow’ penetrometers. The method is based on the numerical solution of the small strain plastic‐flow problem (i.e. rigid plastic material) with an inhomogeneous strength field, which is determined by converting changes of material properties over time in a stationary frame of reference into spatial distribution of strength in a moving frame of reference. Rather than building streamlines from back integration of soil element distortion, as previous methods have suggested, the method treats the domain as continuous with the associated field equations. The method employs an upstream weighting technique for the determination of information flow within the domain. The execution order for the calculation is based on topological ordering. This results in the calculation having a complexity of O(N), as compared with O(N1.5) for the strain path or streamline methods (N is the number of discretized points), which significantly reduces the calculation time. The formulation is presented for the cylindrical (T‐bar) penetrometer, and includes aspects of soil strength degradation, strain rate effects, strength anisotropy, and interface strength law. Comparison to previously published values, based on large displacement finite element simulations with remeshing, showed good agreement, indicating on the correctness of the suggested approach. Investigation into the soil rigid‐body rotation and the remolding effect on anisotropy characteristics showed an interesting behavior, where the decrease of strength anisotropy due to remolding has a greater influence when the soil strength is higher in the vertical direction. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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