Topographic stress and rock fracture: a two-dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations: TOPOGRAPHIC STRESS AND ROCK FRACTURE
Topographic stress and rock fracture: a two-dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations: TOPOGRAPHIC STRESS AND ROCK FRACTURE
复制标题
地形应力和岩石破裂：任意地形的二维数值模型以及与钻孔观测的初步比较：地形应力和岩石破裂
DOI：
10.1002/esp.3646
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发表时间：
2015
影响因子：
3.3
通讯作者：
Singha, Kamini
中科院分区：
文献类型：
--
作者：
Slim, Mirna;Perron, J. Taylor;Martel, Stephen J.;Singha, Kamini
理论计算表明，地表地形引起的弹性应力在某些景观中可能大到足以使岩石破裂，这反过来又会影响边坡稳定性、侵蚀速率和基岩水文特性。这些计算通常涉及理想化的地形剖面，很少直接比较预测的地形应力和在特定现场观察到的裂缝。我们使用一个数值模型来计算所测量的地形剖面引起的应力，并将计算的应力场与在浅钻孔中观察到的裂缝进行比较。该模型采用边界元法计算在环境构造应力存在下任意地形剖面下的应力分布。当应用到地形剖面在宾夕法尼亚州中部的萨斯奎汉纳页岩山临界区天文台，该模型预测剪切断裂将发生基于莫尔-库仑准则，有相当大的差异，在剖面的应力与深度下的山脊和谷底。我们计算了防止剪切破坏所需的最小内聚力，Cmin，作为现有裂缝压裂或再活化潜力的代表。我们比较了Cmin的深度剖面与位于谷底的四个钻孔的成像测井结构分析，发现在基岩的最高15 m处，裂缝丰度随深度急剧下降，与Cmin的模拟剖面一致。与此相反，Cmin增加与深度在可比的深度低于山脊，这表明山脊断裂丰度模式可能会有所不同，如果地形应力确实很重要。因此，目前的结果是一致的假设，地形可以影响地下岩石断裂模式，并提供了进一步的观测试验的基础。版权所有© 2014约翰威利父子有限公司.
Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr–Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure,Cmin, as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles ofCminwith structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile ofCmin. In contrast,Cminincreases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests. Copyright © 2014 John Wiley & Sons, Ltd.