Influence of the microstructure and roughness of weakness planes on the strength anisotropy of a foliated clay-rich fault gouge

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