In the room and pilar method of rock salt exploatation it is necessary to investigate the rheological behaviour of massif on the frame of a room. We must make the measurements on the different profiles in a very large room. It must be done because the different deformations on different places alog the longest axis of the room occur. Measurements, which are presented here, point out the high complexity of the measurements, and the measurements interpretation problems. The basic idea of this work is a presentation of the methods of measurement, characeteristic reasult obtained, and its presentation. We must to present a new view in the rheologycal rock mass investigation in the large underground oppenings.

The measurement system

At the bebining along the longest axis of each room permanent plugs are fixid in the floor. The distance between the each plug is 2o m. Permanent plugs are 1.5 m lomg anchors, fixed with contrite along the l.3o m. On the top of each plug there is a special mark for measurement. In the midle, tetween each two plugs, there are profile point on the frame, fig. 1.a. There are 8 points on the cross cut measurement profile, fig. 1.b. Each anchor permanent profile plug is fixed o.5 m deep in the rock mass.

Underground surveys depend upon the exploatation condition, so that we can get sufficently accurate displacement of each point with the minimum time consuming measurement. horizontal and vertical angles measurements of the main points in the floor between the profiles are performed by theodolite Theo 010 Carl Zeis Jena. The distances are measured by staves Bala 2M. We also made a precise geometric level measurement by the Zeis Ni 00/ level instrument and by invar underground level staves. Profile point diplacement measurements are made by theodolite Theo o2o Carl Zeis Jena. Time distance between the two series of measurements was about 6 months. In the first stepen the space co-ordinates of each poligone points were determined. In the second phase by "ahead cutting" we find the space co-ordinates of each point on the each profile. The distance between the profile and poligonic fixed points is planed in such a way that we have got the ideal conditions for measurements and calculations.

The co-ordinate differences of the measurement between two points is space displacement of each point in each profile.

System of exploitation

Room and pilar method of rock salt exploatation is applied in Tushanj salt mine. Rooms and pillars are of the same width and practicly of infinite length relative to the width. Two horizonts are in operation now, on 44o m and 5oo m depth from the ground surface.

General consideration

In the case of a symmetrical, room cross cut in the homogen rock mass the displacement vectors of 8 points in profile should have a symetrical position, with the orientations toward the centar of the profile. In Tushanj rock salt mine, owing to the different influenting factors, there is no symetry in profile points displacements.

(Figure in full paper)

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