R&D National Institute for Metals and Radioactive Resources, Bucharest, Romania
Keywords: dry salt mining, stability computation, DKRControl method
ABSTRACT: The stability assessment of the complex salt cavities, placed inside the salt rock mass, represents areal scientific and technical challenge for any researcher focused on the geomechanics field. The purpose of this paper is 3D stability modelling for the Praid salt mines, Romania, taking into account the salt cavities mining dynamics and also the intrinsic parameters’ effect over the salt rock mass behaviour (e.g. insoluble and water soluble residuum contents). FLAC 3D code (Itasca, 2007) was used for numerical computation, in connection with Kubrix and 3D Shop software, for the geometry and meshing preparation. The proper computation was performed using DKRControl method principles. The authors developed the preliminary computation, taking into consideration the exploitation dynamics of the salt mines, the properties of the rock salt determined in the laboratory, and calibrating the model in accordance with one major effect of the instability phenomenon, well known and localized in space, such as the roof collapse of the Jozsef Salt mine. The results of this numerical model exploitation could represent a good start for a detailed analysis of the stability assessment of the Praid salt cavities complex, at global and especially at local level.
Introduction
Salt has, perhaps, played the pre-eminent part in the development of European culture and industry. From earliest times, man and his animals have needed salt in their diet and civilisations have been built and wars fought over the availability and supply of salt. Salt mines several hundreds years old exist, and even a millennialong "saline" culture within the border of the Romanian area, in the same time with nowadays active mining sites. Long before modern mining methods were developed, huge salt underground cavities were created, of enormous and impressive sizes (more than 90 m in height and 20 m in width). These mines are under threat of collapsing as long-term geotechnical and hydro-geological conditions are changing and indeed many have already collapsed. Praid salt mine is one of these sites. The aim of the Praid saline complex global stability computation is to diagnose problematic areas for salt mine museums as cultural heritages and to determine the long term influence over such of the mining activity in progress at the Mina Noua and Telegdy salt mines, in order to provide the means and solutions for efficient conservation and sustainable exploitation for both, man-made and natural salt resources.
General presentation of the Praid salt mine
The Hill of the Salt (the highest point – 576 m), covers the biggest salt body from the country, with 2.7 ÷ 3.0 km development in depth. In horizontal section, the salt diapir has an elliptic form, with diameters of 1.2 ÷ 14.0 km and in vertical section it has a huge mushroom shape. This irregular form is a characteristic feature of the salt bodies from Transylvania, Romania (Horváth, 2005). The salt from Praid is very old (Badenian inferior age ÷ the middle Miocene age), sometimes 20 - 22 million years ago. This salt settlement is one of the biggest from Europe. Its reserve could provide the salt need for Europe for hundreds of years in future, for which reason it is nicknamed Europe’s salt cellar. The beginning of the salt mining history lasts ever since the Roman period. In written documents there are remembered four surface excavations ("amphitheatre" type) and some bricks with the inscription: LVM (Legio V. Macedonica). The systematic underground exploitation began in 1762, when the József mine was opened in the South-West side of the Salt Hill. This mine had a bell-shape, Figure 1, and it was one of the first undergroundmines in Praid.
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