Joints significantly reduce rock cohesion compared to unfractured rock, but the question is what effect the possible anisotropy of the shear strength of different types of rupture has on possible subsequent failure. Both natural samples of granodiorite with natural joints and fault surfaces and gypsum models have been tested on the Matest A129 Rock shear box apparatus. The shear strength of preexisting ruptures was measured under a fixed normal stress component. The anisotropy of the shear strength of the joints and fault surfaces reached more than 60 % of maximum strength, which is a very important value for solving structural loads. The shear strength was analyzed with polar plots. The pattern of the real joints typically showed a teardrop shape with one peak of strength in a certain direction and a minimum in the opposite direction. On the contrary, striated fault surfaces are characterized by two axial directions of minimal shear strength, i.e., longitudinal and transverse, and by two axial oblique directions with maximal shear strength, so the strength distribution in the polar graph has a four-cornered shape. The study showed that the anisotropy of the shear strength of various types of ruptures is their important feature.
This paper combines morphostructural analysis and geophysical methods in order to link the faults monitored inside Strašín Cave with faults and lineaments in the vicinity of the cave. The studied site is situated in SW Bohemia, at the foothills of the Bohemian Forest Mts. Main goal is to combine the morphostructural, morphometrical and geophysical methods in order to identify the fault system, monitored inside the cave. This will allow relevant interpretation of the observed movements in the frame of the local tectonic environment. The results show that the monitored faults are observable in the geophysical profiles and, using our knowledge of the structural setting, we have been able to link them with mapped tectonic structures in the vicinity of the cave. Thus, it has been demonstrated that even where outcrops are absent, the faults can be traced and that the monitored faults are significant enough to yield relevant data on tectonic movements. In addition, the combined resistivity and gravimetry profiles reveal a possible new, presently unknown, cave located 20 m below the surface about 200 m northnortheast of Strašín Cave., Filip Hartvich and Jan Valenta., and Obsahuje bibliografii