Improvements in the supervision of mining areas and seismoactive regions by measurements of antiparallel tilts

Abstract

Two arrangements where antiparallel tilts are used for survey problems were checked. Arrangement 1 measure the loading variations of the pillars in salt mines. Here the tilt meters were installed at both sides of the pillars in the same direction, approximately perpendicular to the walls. For the calibration (at a neighbouring pillar), parallel records from a commercial pressure sensor were used. The measuring threshold reached by arrangement 1 was 10 1 Pa. This is 10 4 times smaller than those of the commercial pressure sensors, for instance the pressure cushion sensor of Kessels, Flentge and Kolditz (Patent DD 228 348/1985). Arrangement 2 was installed to control horizontal strain variations measured in the usual way in order to identify and eliminate instrumental effects. The reliability of the strain meter records is of special interest in seismoactive regions. Here the tilt meters measure at both sides of a man-made vertical slot 10 m long and 1 m deep. The tilt meters and the strain meter had the same measuring direction. The tilt effects of such a slot, which were measured with arrangement 2, were of the same order of magnitude as the tidal tilt effects recorded before the drilling of the slot. The measuring threshold of this arrangement for strain effects is 10 −10. Compared with known survey methods, the use of antiparallel tilts improves the sensitivity (arrangement 1) and the SNR (both arrangements) and enlarges the reliability of the measuring results by mutual controls (arrangement 2).