At present, the share of coal seams in the mines of the Soviet Union with hard-to-collapse roofs is quite high.
The combined (explosive-hydrodynamic) method of massif de-strengthening is developed by the employees of LMI with the participation of employees of the company Sakhalinugol and is used in the mining of formations with hard-to-collapse roofs ...
Employees of the Leningrad Mining Institute together with workers of the mine № 1/2 of the trust “Uglegorskugol” in 1967-1968 conducted at the mine observations of the manifestations of rock pressure at different methods of excavation and roof management. The purpose of the observations was to improve the technology of excavation of semi-decaying layer VI and to choose the most rational method of roof management. Formation VI is relatively sustained, the excavated thickness is 0.95-1.10 l, the dip angle is 8-15° The roof of the formation is represented by layered mudstones (0.4-0.6 m) and dense fine-grained sandstones (15-20 m). The stratum is underlain by argillites (0.1 m) and siltstones of medium strength, up to 8-10 m thick.
Joint efforts of the staff of the Leningrad Mining Institute and the Sakhalinugol combine in 1967-1968 conducted numerous mine and laboratory studies aimed at improving the development systems, mechanization of cleaning works and roof management of thick layers of hollow dip.
As it is known, the stability of pillars is significantly affected by the heterogeneity of rocks, presence of various layers, inclusions and ice. In order to clarify this influence in the Laboratory of Mining Pressure of LMI in 1963-1967 a set of studies was carried out, including the study of bearing capacity of pillars with weak interlayers of other rocks and ice inclusions for the conditions of Arkagalinskoye, Sangarskoye, Dzebariki-Khaya coal deposits and Baltic shale deposits...
In the mines of the Baltic oil shale basin, extensive industrial tests of different variants of the chamber mining system have been carried out for several years. In order to correctly determine the parameters of the system, the behavior of rock pressure was studied at the mine No. 3 of the Slantsy Combine, in particular, the stability of the pillars was investigated. The commercial oil shale bed with a total thickness of 2–3 m is almost horizontal at a depth of 30–100 m under the conditions of the basin and consists of four layers of oil shale and three rock partings. In the roof and floor of the seam, limestones are interbedded with clay and oil shale.
The combined chamber-lava system combines elements of the pillar and chamber systems. The system has the following characteristic features: the main roof is supported for a long time by specially left supporting pillars; to increase the bearing capacity of the immediate roof and to control the condition of the roof in the goaf, a light wooden support is installed, designed to support only the lower layer of the immediate roof with a thickness of no more than 4 m; the face of the chamber-lava, with a total length of up to 215 m, advances similarly to longwall extraction — in parallel cuts in one direction; the face area with a width of 3.4–3.8 m is not supported at all.
