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The article presents two case studies of investigat ion carried out on plots of land, intended for multi-family residential development, lying on a former lignite mining area in Zielona Gora. It was underground mining, op erating in the years 18401948. Lignite deposits were extracted with the room and pillar method, i.e. with an overlayer collapse, causing deformations on the sur face of the ground. In the first case study, there was no detailed mining data. In o rder to identify the geological structure under the planned seven-floor multi-famil y building, seismic surveys were performed with the technique of multichannel a nalysis of surface waves (MASW). Three seismic profiles were performed. They r vealed the presence of several zones where S-waves had smaller velocity va lues. In order to verify whether the zones with the smaller values of velocity co rrespond to e.g. lower soil density resulting from collapsed exploitation room, some drillings were undertaken to the depth indicated in geophysical investigation. A dditionally, the CPT and dynamic probing were also performed. The data obtaine d allowed to determine the soil parameters necessary for the safe design and f oundation of the building. In the second case study, a historical mining map with the marked location of the shaft and the main galleries was used. Formerly, geologic al and engineering documentation for construction works had been prepared, base d on 30-meter drillings and soundings with a heavy probe. The mining maps and t he contemporary maps were mapped one on another carefully and accurately, cal ibrated with historic buildings. Thus, the accuracy of 5 m was obtained. Additionall y, investigation with the MASW technique was performed. Ten seismic profiles w re performed, and then verified by drillings. Also, dynamic probing in the vicinity of the expected location of the shaft was performed. Neither the MASW invest igation nor the dynamic probing did not reveal any alterations in the soil c ndition, which would suggest the presence of the properly liquidated shaft. Thus , ba ed exclusively on the cartographic material, the area comprising the liquidate and backfilled shaft was established. The area was excluded from the plans for th e intended building erection.

GEOLOGICAL AND SEISMIC INVESTIGATION OF FORMER LIGNITE MINING AREA IN ZIELONA GÓRA – TWO CASE STUDIES