Abstract
Extraction of natural stone is usually carried out in surface quarries. Underground excavation is not a frequently used method. Due to the restrictive environmental legislature and limited stores of natural stone, underground extraction has become quite an interesting alternative. Dimensions of underground openings are determined with stability analyses. Prior to starting a numerical analysis of a large underground opening it is very important to determine the mechanism of failure and set up a proper numerical model. The continuum method is usually used in rock mechanics. A disadvantage of this calculation is that it cannot be applied to a large number of joints. Other methods are preferred, such as the numerical discrete method, which allows joint systems to be involved into calculations. The most probable failure of rock with several joint systems is block sliding. In the example of the marble of Hotavlje both methods were used. It was established that the continuum method is convenient for the global stability prediction of the underground opening. Further discrete method enable the block stability calculation. The analytical block analysis is still accurate for the a stability calculation of single block. The prerequisite for a good numerical analysis is sufficient quality data on geomechanical properties of rock. In-situ tests, laboratory tests and geotechnical measurements on the site are therefore necessary. Optimum dimensions of underground chambers in the Quarry of Hotavlje were calculated by using several numerical models, and the maximum chamber width of 12 m was obtained.
Highlights
Extraction of natural stone in underground chambers is quite rare in Slovenia and in other countries of the world
The results indicated that the majority of large underground openings was stable, provided the widthto-depth ratio was 2
Based on practical experiences gained by underground excavation in the Quarry of Hotavlje, the following conclusions can be drawn:
Summary
Extraction of natural stone in underground chambers is quite rare in Slovenia and in other countries of the world. Underground excavation becomes more and more interesting because of limited stores of natural stone and rigorous environmental regulations. The decision for such technology shall be based on geotechnical investigations of a rock massive. Maximum dimensions of chambers and galleries shall be estimated using a preliminary analysis. In this paper the term gallery is used for an underground excavation of a height of 4m and the term chamber for a higher one. In the stage a research gallery shall be excavated and various geotechnical equipment installed in it. Geotechnical measurements in a gallery can supply a very important information on the deformation and stress field and provide input data for the stability analysis
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