ABSTRACT:

The paper describes a stability analysis of an existing Austrian small-scale underground mining operation. The mine concerned is a gypsum mine where multi-level room and pillar mining is employed. For the assessment of the stability of the mine, a combination of subjective, empirical and numerical methods was used. On the basis of these investigations a rock mechanics design for future mining areas has been done.

INTRODUCTION

1.1 Purpose

The main purpose of this study was the evaluation of the stability of room and pillar workings in an old Austrian gypsum mine with the objective of revising future room and pillar workings.

1.2 General information

The mine is situated about 30 km south of the city of Salzburg. Gypsum production commenced at the beginning of the 20th century. The gypsum/anhydrite deposit has a strongly irregular contact-zone to the hanging wall. The hanging wall rock is a moraine consisting of marl intermixed with clay. This material has very poor mechanical properties. On the basis of geophysical profiles, the contact of gypsum body was localized at a depth below the surface of less than 14m. The mining method employed is multi-level room and pillar mining by means of drilling and blasting. At present three mining levels are in operation. Over time the size and orientation of the pillars was altered. Current mining dimensions are 7x7 m square pillars with at a height of 6 metres. The width of the rooms is about 8 metres. The thickness of the overburden varies from less then 20 m to 100 metres. Each of the levels is accessed from surface. The individual levels are connected through ventilation holes and ramps. The annual production is approximately 60.000 tons with a staff of 5 employees.

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