Geological Institute Strashimir Dimitrov

The application of graphite in a number of traditional and new technologies and products leads to: 1) increasing demand for high-quality graphite raw materials. The greatest attention is paid to dimensions, chemical purity, structural order, thermal resistance, electrical conductivity, semiconductor properties, density, resistance to the effects of acids, bases and other aggressive substances, etc.; 2) a sustainable increase in raw material prices over time, especially for coarse-grained graphite; 3) a search for graphite substitutes in some industries; 4) recycling of end-of-life graphite products (USA, China, EU); 5) increasing graphite production in the world. China is the leader in the production and export of graphite raw materials, followed by India, Brazil, etc.

The problems related to rock slope stability of excavations realized in differing in genesis rock complexes are the object of the present paper. The stability of these slopes depends on the natural fracture system in the massif, the additional fracture systems occurring in the rock masses during the excavation works as well as on the resistance against weathering of the rock massif. The investigation of the above problems was carried out in the excavations of the Sofia-Mezdra railway line, which crosses the Stara Planina Mountain chain. The mountain ridges are built of rock complexes with various composition and genesis. The railway construction was started in the middle of the 19th century. The commissioning of the line was on November 8, 1899. Rock slopes with different height and inclination were formed during the railway construction. In the course of a period exceeding 110 years the rock slopes have been subjected to weathering processes that have inevitably exerted effect on their stability too. The modern safety requirements for the railway line operation impose the performance of different stabilization activities. The design of the safety measures is connected with the assessment of the rock slope stability as of the present moment. The diverse geotechnical characteristics and geological conditions of rock massifs, built of sedimentary rocks (argillites and sandstones), metamorphic rocks (gneisses and quartzites) and volcanic rocks (various diabase types), have been considered.