Experimental investigations of the last two decades have made it possible to confirm the presence of the tectonic component of rock stresses or the tectonic component of rock pressure. Tectonic stresses have boas determined by in situ measurements in underground workings and test wells present in mines (60% of igneous deposits and 20% of sedimentary ones mainly) which are situated on the territory of Europe, Asia, America and Australia. In a number Of regions the values of tectonic stresses are 10–20 fold the level of possible gravitational stresses (Markov 1977).
The analysis of in situ measurements has established that the level of tectonic stresses (T) in the exceed massif may be approximately calculated according to the formula:
where 6s - is the compressive strength of rock at the axial compression. In most cases the orientation of tectonic stresses is horizontal or weak-inclined.
Construction of all kinds of underground workings, large hydrotechaical foundation pits, dam caverns and other structures causes the concentration of stresses in the adjucent area. When the horizontal force exist in the massif the con-centration of stresses in the roof and foot of underground workings as well as in the bottom of excavations during underground construction can several times exceed the stresses existed in the massif before the construction of these structures (Markov,1977, Turcnaninov, Markov et al. 1978).
Thus during the construction of workings in the tectonically-stressed massifs the stresses can appear around the outline of a working and can be equal tp or even considerably exceed the ultimate strength of rock masses. In such high-stressed massifs a process of rock destruction takes place in the outline of a working during the construction of the structures. This process can manifest itself in forms of rock bursts, or natural development of rock spellings.
(Figure in full paper)
Fig. 1. Rock destruction in the roof of a working under the influence of high horizontal tectonic stresses;
destruction in the roof of a working (cross-cut, level +252 m of the Kirovsk apatite mines);
a scheme of destruction development in the roof of a working under the influence of tectonic stresses (1 - zone of dynamic destruction, 2 - zone of active fracturing, 3 - zone of equilibrium permanent state;
destruction of well's walls.
destruction of a horizontal working as a result of the influence of high tectonic stresses in one of the Kola peninsula's mines. In situ mine observations testify that the development of the destruction of workings is of different nature and depends on the level of stresses, directions of workings and strength characters of rock.
If a form of a rock section and its disposition in regard to the main stresses are chosen suchthat they don't cause any concentrations of tectonic stresses then the outline of the working preserves stable state. The stability is written down as the following criterion ratio:
where 61_ is the longitudinal stress near the outline that is parallel to the longitudinal axis of the pit;
