At present, the development of minerals is carried out and designed at great depths. Practice shows that at depths of about 800 m the stability of mine workings significantly deteriorates. To predict their stability, it is necessary to comprehensively investigate the physical and mechanical properties of rocks, especially rheological properties, such as stress relaxation.

To fully characterize rocks, it is necessary to take into account their rheological properties, one manifestation of which is creep. Creep testing of rocks under uniaxial compression requires the use of rather heavy equipment-special spring presses. The strain is measured between the ends of the rock specimen, while a homogeneous stress state is observed only in the middle part along its height. In the study of rock creep by bending test of the specimen, simpler setups are used and at a certain ratio of the span of the specimen to its height, the stress state can be considered close to homogeneous.

The geological section of the roof of the Leningrad deposit is rather complex and is characterized by a great variety of lithological types (from weak clay shales to very strong limestones), their variability in terms of distance from the tundish roof and thickness. The most dangerous in terms of the possibility of collapse is a 90-centimeter layer of rocks, counting from the roof of the promplast, the section of which is the most complex and can be generalized in the following form.