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Influence of the microstructure and roughness of weakness planes on the strength anisotropy of a foliated clay-rich fault gouge
Engineering Geology ( IF 7.4 ) Pub Date : 2021-05-11 , DOI: 10.1016/j.enggeo.2021.106186
J.M. Insua-Arévalo , M. Tsige , J.L. Sánchez-Roldán , E. Rodríguez-Escudero , J.J. Martínez-Díaz

Cataclastic rocks, as clay-rich fault gouges, are commonly present in brittle rock masses when fault zones appear during geological engineering projects. Highly deformed rocks that are of poor mechanical quality can lead to technical, safety, and economic problems in rock engineering. The aim of this study is to characterise the resistant behaviour of a highly deformed clay-rich gouge >40 m wide with a marked tectonic fabric that indicates strength anisotropy. We present the results of consolidated-undrained (CU) triaxial tests that were performed at low confining pressures (50, 150, and 300 kPa) on several sets of foliated gouge specimens with four different orientations in the tectonic fabric. Specimens were collected from the encapsulated rock cores of two research boreholes drilled through the Alhama de Murcia Fault (AMF), a main regional fault located in SE Spain. The strain–stress relationships and failure modes were established, indicating that the gouge behaves as hard soil or very soft rock. The test results were adjusted at each orientation using the non-linear Hoek and Brown criteria by considering the fault gouge as an intact material or as a tectonised rockmass. Here, we use the Geological Strength Index (GSI) as an indicator of the rockmass strength that depends on the direction of the tectonic fabric. However, the results from specimens with tectonic fabric that is oriented most favourably for failure were not the weakest in terms of rock strength. Such an anomalous result could be the result of asymmetry in the roughness of the weakness planes that is related to the original gouge microstructure characterised by the strong reorientation of clays in an S-C′ like tectonic fabric.

Our results will be useful for practical applications that are related to the stability of slopes and/or shallow underground excavations in brittle fault zones, and provide an inexpensive and easy way to preliminarily evaluate the anisotropic behaviour of this type of brittle fault zones for future engineering projects.



中文翻译:

薄弱面的微观结构和粗糙度对富含粘土的叶状断层泥的强度各向异性的影响

当在地质工程项目中出现断层带时,脆性岩体中通常会出现裂变岩石,即富含粘土的断层沟。机械质量差的高变形岩石会在岩石工程中导致技术,安全和经济问题。这项研究的目的是表征高度变形的富含粘土的凿子的抗性,该凿子宽度大于40 m,带有明显的构造织物,表明强度各向异性。我们介绍了在低围压(50、150和300 kPa)下对构造织物中具有四个不同方向的几套叶状凿样品进行的固结排水(CU)三轴试验的结果。样品是从两个通过Alhama de Murcia断层(AMF)钻出的研究井的包裹岩心中采集的,西班牙东南部的主要区域性断层。建立了应变-应力关系和破坏模式,表明该凿子表现为坚硬的土壤或非常软的岩石。使用非线性Hoek和Brown准则在每个方向上调整测试结果,方法是将断层泥视为完整的材料或作为构造岩体。在这里,我们使用地质强度指数(GSI)作为岩体强度的指标,而岩体强度取决于构造织物的方向。然而,从构造强度最有利于破坏的构造织物中得出的结果在岩石强度方面并不是最弱的。这种异常结果可能是由于薄弱面的粗糙度不对称而导致的,这种不平整与原始的凿孔微观结构有关,其特征是在SC'样构造织物中粘土强烈地重新取向。

我们的结果对于与脆性断裂带中的斜坡和/或浅层地下开挖的稳定性有关的实际应用将是有用的,并为初步评估此类脆性断裂带的各向异性行为提供了一种廉价而简便的方法,以供将来工程使用项目。

更新日期:2021-05-13
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