Determination of mechanical properties of a rock mass in in situ conditions is a complicated and still unsolved problem. Therefore, when solving practical problems, indices of ultimate strength in uniaxial compression and tension, obtained by testing samples of these rocks taken from the most characteristic locations of the mass, are used as a characteristic of rock strength. However, this raises the question of the validity of extrapolating the results of laboratory tests from samples to rock masses.

Observations of the behavior of the side rocks and fastenings of preparatory workings in the conditions of Novovolynskoe coal deposit were carried out by a permanent group of DonUGI with the participation of the author and with the help of engineering and technical workers of mines and trust Novovolynskugol. In the coal-bearing strata of Novovolynskoe deposit there are four coal seams. Two of them, occurring at a depth of 350-375 meters, are working - Volynsky 1 (n7) with a thickness of 0.1-1.2 meters and Volynsky 2 (n3) with a thickness of 0.1-2.1 meters. Bedding of strata is almost horizontal, dip angle is 4-5°. The presence of a number of tectonic disturbances in the form of discharges with displacement amplitudes ranging from a few centimeters to 20 m was detected. Sandy and sandy-clay deposits are significantly developed in the rocks containing coal seams.