Classification of precise levelling instruments referring to the measurements of historic city centres

Abstract

The inventory of the complexes of historic buildings requires, among others, surveying, based on which changes in time would be monitored, including the value of subsidence, inclination of walls, cracks, etc. The necessity of monitoring of dislocations and subsidence of the ground occurs in different centuries old cities in Poland. In Jarosław, the city in the Podkarpacie voivodeship, such necessity mainly occurs in the main square, because the location of the city centre on the scarp of the San River, which has the influence on the thickness and the kind of cultural layer, where the objects are placed. A significant reason for monitoring is also the presence of the underground historical cultural monuments occurring within the main square. The carried out measurements of the subsidence of historical objects in the region of the old town, one should carry out with the use of proper sets for precise levelling. The equipment applied in this type of measurements should provide a proper accuracy, its class should, however, be justified economically. In the Geodetic Metrology Laboratory of the Faculty of Mining Surveying and Environmental Engineering of the AGH University of Science and Technology in Krakow, the studies were carried out for two groups of levellers, precise and technical, as well as two types of levelling rods: invar and fibreglass rods. Precise levellers require different approach to the studies and classification other than technical levellers. The applied studies were carried out according to the standards BN-78/8770-07, ISO 12857-1 and ISO 17123-2. Based on the obtained results and table contained in standard BN-78/8770-07, the levellers were given proper classes. After the analysis of the results of the carried out measurements the optimal sets for this type of surveying were presented.