Tektonicky a hydrogeologicky vliv na stabilitu stol ve krtinskem udoli

Four adits excavated in the Křtiny Valley at the beginning of 1950s were documented and monitored during last several years. Three of the adits (I to III) were excavated in limestones, namely Lower Givetian Lažánky Limestone of the Býčí skála cycle of the Macocha Formation. Adit IV started in biotitic granodiorites of the Brno massif, but after ca 200 meters Devonian rocks were encountered - Devonian basal clastics and then Lažánky Limestone. Stratigraphical succession is in normal order, but the contacts are tectonic. Devonian basal clastics are violet to greyish-green quartzitic sandstones with rare sericitized feldspars. Granodiorites and basal clastics also form tectonic slices (in one place boudinaged) along a major tectonic line documented in adits I and II. Both these rock types were additionally altered, suffered sericitisation and chloritisation, harder quartz grains were cataclased.
Walls and ceiling of the adits seem to be stable except for several shear zones documented in adit IV and I and II particularly. The shear zone in adits I and II has a massive, up to several meters thick gouge zone comprising highly strained granodiorite, Devonian basal clastics and limestones. A very well developed fault gouge can be observed which is in places extremely fine grained and form bands several centimeters thick of distinctive rusty brown, grey or ochre coloration. This shear zone is highly unstable accompanied by massive cave-ins. Configuration of faults bordering this shear zone suggest further cave-ins in the future.
Groundwater flows into adits chiefly from surrounding karst aquifers, which are recharged by water infiltrating on the Babická plošina plateau. Chemical composition of groundwater is characterized by high calcium and bicarbonate content, which causes together with suitable conditions in the adits precipitation of sinter crusts. Water-saturation of faults is strongly affected by climatic conditions and while during dry periods the water-saturation is minor, it may increase rapidly after heavy rainfall or snow melting. Strong water-saturation of the faults decreases significantly stability of fault gouges and adjacent areas.

References

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