Thermomechanical behavior of Pravcicka Brana Rock Arch (Czech Republic)

The paper discusses the results of research devoted to the preservation of a natural heritage site carried out at Pravcicka Brana Rock Arch, the largest natural sandstone bridge in Europe, located in the Bohemian Switzerland National Park, Czech Republic. One of the objectives of the study was to explore natural diurnal and annual temperature oscillations at the shallowest part of the rock mass and to acquire an insight into the heat balance both at the surface and within the rock mass. In 2009, four thermocouples were embedded at two positions (eastern and western sides) in a longitudinal direction sequence: rock surface and three different depths 0.10, 0.40, and 0.90 m. Calculation of heat flux inside the rock mass was treated with Fourier’s series which analyzes periodic temperature variation into a set of harmonics of the dominant diurnal or annual waves. Based on the results of Fourier’s analysis, fundamental thermophysical parameters were determined. These were used as the input data to establish a numerical model of temperature distribution in the near surface depth and thermomechanical (kinematic) behavior of the rock arch. Apart from in situ temperature monitoring data, the displacement time series data for the period 1993–2012 recorded by portable crack gauges in 1-month intervals were available. Finally, the rate of displacements in the model simulations was analyzed and compared with those recorded by on site displacement monitoring. Model simulations detected the existence of thermally driven deformation comprising both quasi-cyclic (reversible) movements and irreversible (plastic) deformations which in fact affirm the idea that temperature oscillations are the most contributing factor to the total displacement rate observed at the Pravcicka Brana Rock Arch. Based on the results of model simulation, the authors address the key issue whether the actual deformation mechanism and dynamics will have any influence on the stability of the Pravcicka Brana Rock Arch.