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191.
考虑了正应力及剪应力联合作用在岩样的端部,而且,在正应力被视为变量,剪应力被视为常量这一特殊条件下,对剪切带的变形特征及剪切带-带外弹性体系统的失稳判据进行了分析.根据剪切虎克定律及梯度塑性理论,提出了剪切带内部弹性应变、塑性应变及总应变的解析式,对上述三种应变进行积分,提出了剪切带错动弹性位移、塑性位移及总位移的解析式.利用压缩虎克定律及几何关系建立了剪切带外弹性体的刚度的表达式.根据刚度理论,建立了剪切带-带外弹性体系统的失稳判据.考虑岩样端面的剪切应力后,在流动剪切应力相同时,剪切带内部的弹性剪切应变(均匀分布)将增加;剪切带内部的塑性剪切应变(不均匀分布)将减小;剪切带的弹性剪切位移(线性分布)将增加;剪切带的塑性剪切位移(非线性分布)将减小;剪切带错动位移要小一些.另外,剪切应力对剪切带-带外弹性体系统的失稳判据没有影响.失稳判据仅和岩石的本构参数、剪切带倾角及结构尺寸有关. 相似文献
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考虑应力水平的软土固结系数计算与试验研究 总被引:1,自引:0,他引:1
在固结度计算中通常将固结系数视为常数,实际上并非如此.通过研究软土固结系数在压缩过程中随应力水平变化的规律,推导出正常固结和超固结状态下固结系数与有效应力之间的表达式.在正常固结状态下,当应力水平小于在前期固结压力时,固结系数随应力水平的增加而增加;当超过前期固结压力后,固结系数随应力水平的增加而减小;在超固结状态下,固结系数随应力水平的增加而增加,在一定程度后趋于平稳.室内试验结果进一步说明了和验证固结系数这一特点.推导的固结系数与固结应力水平关系表达式是可行的,其计算值与试验结果的变化趋势一致,大小基本吻合,将其用于计算变形速率和固结度中,可提高准确性. 相似文献
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Rock Mass Rating (RMR) measurements from 65 sites within Huntly East underground coal mine are presented. All measurements are in coal, for which the dominant discontinuities are vertical cleat. Basic RMR values using two discontinuity spacings are presented: overall RMR based on the average spacing of all individual discontinuities; and cleat zone RMR based on the average spacing between zones of cleat. Cleat orientations are highly variable, but on average approximately parallel horizontal stress axes (face cleat follows maximum horizontal stress axis, butt cleat follows minimum horizontal stress axis).Contours of RMR variations throughout the mine are used to compare rock mass conditions with geological structure. It is apparent that: (1) RMR is least within downthrown fault blocks, and particularly immediately on the downthrown sides of faults, and greatest in upthrown fault blocks; and (2) RMR contours parallel horizontal stress axes within fault-bounded blocks, and bend to parallel faults at block boundaries. From similar contours for parameters contributing to RMR, the Rock Quality Designation (RQD), groundwater rating, and discontinuity condition rating create most of the observed variations in RMR. RQD is determined from the measured discontinuity frequency and hence is a measure of the degree of fracturing of the rock mass. This is interpreted as influencing the groundwater and condition parameters directly by allowing greater water ingress. Discontinuity frequency is greatest (least spacing) in the immediate vicinity of faults, and in downthrown fault blocks, generating low RMR values. Within fault blocks RQD varies little, so RMR contours align with cleat orientations.As RMR contours, faults, stress field and cleat orientation are clearly interrelated, there is unequivocally a connection between RMR and structural geology; this allows some predictive capacity in terms of ground conditions. If geological features can be accurately defined through either drilling programs or seismic surveys, then ground conditions may be predicted before panels are driven. 相似文献
195.
T. Masuda S. Nakayama N. Kimura K. Onodera A. Okamoto 《Journal of Structural Geology》2004,26(12):2203-2209
A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ1−σ2)/(σ1−σ3) was calculated to be 0.64, indicating that σ2 lies closer to the midpoint between σ1 and σ3 than to σ3. 相似文献
196.
We perform a global statistical investigation into the problem of Coulomb stress triggering of earthquakes by using the Harvard CMT catalogue of shallow earthquakes from 1976 to 2001. We consider ‘earthquake pairs’, i.e., pairs of successive earthquakes occurring near each other with similar focal mechanisms, and address the problem of whether or not the change of the Coulomb failure stress (CFS) produced by the first earthquake of the pair ‘encourages’ the occurrence of the second one. An interesting feature is that such a Coulomb stress-triggering phenomenon has an apparent focal mechanism dependence: for thrust earthquakes, a more evident triggering effect can be observed. 相似文献
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