Assessment of stress status in pillars based on laboratory trials

摘要

Being in the possession of several salt deposits (Ocna Mures, Praid, Cacica, Tg. Ocna, Ocnele Mari, etc.), Romania can be considered from this point of view as a fortunate country. The extraction rhythm is constantly increasing with the output growing from 368.000 tones in 1938 to 3.000.000 to tones in 1970 and 5.000.000 tones in 1985. The first underground method of exploitations have employed conical and bell/shape rooms diameters of 60 m, and heights up to 100 m - Tg. Ocna, Slanic Prahova, Praid. Presently, since the extraction of salt is by dry-methods, two specific methods are generally in use: 1. Rectangular room - and - pillars method, with small room sizes. 2. Small rooms and square pillars method. The first one can be applied for depths up to 200 meters, the second method being used for depths reaching 1000 meters. The first method is presently in use, at the Praid saline only, the small rooms and square pillars technique being generalized at Ocna Dej, Slanic Prahova, Fetele Targului, Tg. Ocna, etc. The height of rooms is about 8 m, their width being of (14 - 16) m and the length of pillars ranging between 14m and 17 m. When several levels are already excavated (Slanic Prahova. Tg. Ocna, etc.) between the levels is left a 8 m thick floor. For example, at Fetele Targului, Tg. Ocna, the IXth excavation level corresponds to the depth of 250 m.