Acta Geodyn. Geomater., Vol. 9, No. 3 (167), 401–407, 2012 GABRIELA LOCALITY: STARTING GEODETIC OBSERVATIONS TO DETECT THE SURFACE MANIFESTATIONS FROM UNDERMINING Vlastimil KAJZAR *, Hana DOLEŽALOVÁ, Kamil SOUČEK and Lubomír STAŠ Institute of Geonics, Academy of Sciences of the Czech Republic, v.v.i., Studentská str. 1768, 70800 Ostrava-Poruba, Czech Republic, Phone +420 596 979 111, Fax +420 596 919 452 *Corresponding author‘s e-mail: kajzar@ugn.cas.cz (Received March 2012, accepted June 2012) ABSTRACT A new observation network has been built to observe the surface manifestations of undermining at Gabriela locality. This locality lies in the Czech part of the Upper Silesian Coal Basin and the history of the hard coal underground exploitation is more than 150 years long here. Recently, the last coal mining panel was started to be exploited here. Its location and mining parameters are very suitable for the analysis of the actual and future surface changes caused by undermining. The fixed points of the observation network are surveyed by geodetic GNSS method. This method enables the evaluation of both vertical subsidence and horizontal displacements. Such complex evaluation of processes on the surface of the undermined territory makes it possible to understand the progress of the subsidence depression and to capture the final phase of the surface undermining changes, i.e. the phase of the subsidence decline. KEYWORDS: GNSS, underground mining, mining subsidence, horizontal displacements seam was discovered here at the depth of 104 m and two years later, the Gabriela mine was founded. Even though several disasters happened here, the mine’s production was growing in the next decades. Later, the mine was renamed but it was productive until 2004. Church of St. Peter of Alcantara, a surviving witness of the mining decades in the region, can be found approx. 400 m far from the Gabriela mine in the north-west direction (see Fig. 1). The church was built in 1736 and today it is the most leaning church in the Czech Republic. The building leans 6.8 degrees off the vertical as a result from undermining. From 1854, a total of 27 coal seams were exploited from under the church, with the total combined thickness of 46.8 m. As a result, the ground under the church subsided 37 meters. To survive the ground deformations from undermining, the building’s foundations were reinforced as a part of a general reconstruction. Neighbouring buildings were demolished due to undermining. The local environment can be characterized as a mining landscape with no permanent buildings. A vegetation begins to flourish on the former mine spoils deposits. The effects of undermining may cause significant changes mainly on the local roads and rail tracks, infrastructure projects, or on the stability of the sewage storage basin dams. The rock mass consists of typical for the Upper Silesian Coal Basin upper carboniferous molasse INTRODUCTION The Ostrava and Karviná region in the Upper Silesian Coal Basin has been affected by hard coal mining for more than 200 years. While in Ostrava part of this region the exploitation was ended in the 90s, in Karviná part of the region, the underground exploitation of the hard coal deposits is still active. Thus, some areas suffered from multiple undermining through the decades. Gabriela locality is one of them. The history of the hard coal underground exploitation is more than 150 years long here. The surface effects of mining of mineral deposits are generally given a great attention (Briggs, 1929; Whittaker et al., 1989). Their research in the Upper Silesian Coal Basin has been going on for decades (Knothe, 1953; Neset, 1984; Martinec, 2003). Further development in this field is today due to the use of new geoinformation technologies. Possibilities of using these modern surveying methods in the real conditions of the Upper Silesian Coal Basin were verified by e.g. (Perski, 2000; Kadlečík et al., 2010; Lazecký et al., 2010; Kajzar et al., 2011, etc.). GABRIELA LOCALITY The Gabriela locality is situated in the Darkov mining area in the Upper Silesian Coal Basin near the town Karviná in the north-eastern part of the Czech Republic (see Fig. 3). The locality occupies an area of approx. 3 km 2 . The mining history goes back to the 19 th century in this locality. In 1852 the first hard coal