THE APPLICATION OF NON-DESTRUCTIVE METHODS TO ASSESS THE STABILITY OF THE NATIONAL NATURE MONUMENT OF THE PRAVČICKÁ BRÁNA ROCK ARCH, CZECH REPUBLIC
The study contains the results of non-destructive research of the Pravčická Brána Rock Arch which focuses on the structure and natural dynamics of this rock formation and its current level of stability. The main results include a description of the block fabric of the rock body and the nature of the contact zone between the arch beam and the southern pillar, discovery of relatively fresh secondary fissures and identification of zones with weakened strength within the sandstone massif. Also the local hydrodynamic regime was determined by a combination of geophysical methods. Long-term monitoring has demonstrated slow and irreversible body movements and reversible quasicyclical movements associated with changes in temperature on a scale of days up to years. The collected information was used to develop a structural deformation model of the arch body, including a description of the nature of the disintegration. The work was designed to fully respect the protective conditions of the site, to facilitate future follow-up activities and to monitor any possible negative changes in the rock massif.