The Realmonte Salt Mine near Agrigento (Italy) is being developed by the room and pillar method, according to a multilevel layout. At the end of 1985, with the working development at lower levels, intense slabbing problems became particularly evident in the pillars located in the Yorkshop Area, at a depth of 100 m approximately. This prompted a Rock Mechanics Programme to be undertaken including: laboratory studies, geophysical surveys by seismic refraction methods, numerical modelling, and in situ monitoring. In order to bring the failure mechanism under control, stabilization measures were applied by lashing the pillars with hoist cables. The present paper describes the results obtained during various investigations carried out, with major emphasis placed on the numerical modelling studies, measurements and observations of the stabilization system performance, over a time period of four years.
The present paper is written with reference to the Realmonte Salt Mine (near the city of Agrigento, Italy), where a salt deposit is being excavated by the room and pillar method, according to a multilevel layout. Workings within the mine are extensive, with openings between approximately 0 and -142 metres below datum. The most systematic workings have been carried out on the -30 and -45 levels. The purpose of the paper is to describe the pillar stability problems that occurred at the mine during development at lower levels, and the stabilization measures that were applied. Following a brief description of the geological conditions and the mining method used, the slabbing and overstressing occurrIng in a few pillars located in the Workshop Area at the -30 level will be illustrated.
With the thinking that the mine design may be inadequate, mostly in relation to the workings to be deepened, a Rock Mechanics Programme was undertaken. The results obtained during the various investigations carried out as a part of this programme will be described. The purpose has been to understand the overstressing phenomena Occurring in the Workshop Area, where instability was such as to impair the working conditions. However, an important objective has been to provide the basic data needed in order to assess the stability conditions of the underground structures, with consideration given to the future mine development.
The Realmonte Salt Mine is located in Sicily, in the South-Vestern part of the Agrigento Province. The mining horizons are part of an evaporitic sequence bounded on the upper side by marl ("Trubi Formation"), limestone, gypsum, anhydrite, and polyhalite, interspersed with beds of kainite. Tripoli and clay layers are at the lower side. Two kainitic beds, with 14.5% and 13% of K20 respectively, form the fifth and sixth layers, separated by an inter-layer of halite, with a low NaCl content.
Schematically, the geological structure is an anticlinal fold, with East-Vest axis, and the top located approximately near to the town of Realmonte. Tectonic movements in a South-North direction, related to the African plate, deformed intensively this fold, thus creating a nearly vertical salt deposit in the Southern limb
