At the mines of the Severouralsk bauxite basin deposits are developed at a depth of 900-1000 m and it is planned to design and develop new horizons at a depth of 1500-2000 m. At greater depths, mining and geological conditions of deposit development become sharply more complicated, and dynamic forms of manifestations of rock pressure intensify. Mining strikes occur under a certain combination of mining-geological and mining-technical conditions. These combinations are extremely diverse and are associated with the influence of many factors, which determine not only the occurrence of rock bumps, but also their strength and the nature of the impact on mine workings. A survey of mine workings of mines in the Severouralsk bauxite basin was carried out in order to determine the compliance of the types and parameters of fastenings used with mining-geological and mining-technical conditions.
On the basis of the laws of changing the parameters of the dynamic stress field during the interaction of seismic waves with the mine workings the requirements to the seismic resistant armoring of mine workings in the zones of rock bumps and mass explosions are formulated. The operability of traditional types of anchors under dynamic loads is evaluated. The optimum design of fortification of excavations in the shock-hazardous areas is a combined support from steel-polymer or reinforced concrete anchors with a solid filling of the boreholes with a fortifying composition enhanced by piles of long (up to 3.5 m) reinforced concrete anchors in the place of wave exit on the contour of the excavation. The length of the anchors is chosen according to the tensile stress zone overlap.
The parameters of dynamical phenomena influencing the seismic resistance of underground structures are determined. It is shown that the main input data for determination of the vibration velocity in the massif are the maximum energy of the expected dynamic phenomenon and the distance from the excavation contour to its source. The distance from the excavation contour to the center of disturbance depends on the excavation location relatively to the zone of high seismic activity. In the zones which are really dangerous according to dynamic manifestations of rock pressure, the distance to the center of fault zone is taken with consideration of the sizes of zone of unconsolidated rocks with lowered stresses and the sizes of increased stress zone (support pressure) around the excavation. The laws of distribution of dynamic stresses around the excavation were established depending on the distance to the center of the underground drift and the energy of the rock shock. By means of the computer program TABLE CURVE 2D the hyperbolic dependence is revealed which is used for the calculation of the dynamic stresses when estimating the stability of mine workings and choosing parameters of earthquake-proof roofing for capital and preparatory mine workings of mines of the Severouralsk bauxite basin.
The analysis of the stability of mine workings is carried out, the features of disturbances of rocks stability in the contour zone of the massif depending on the type and energy of the dynamic phenomena, the nature of the distribution of dynamic stresses are determined. Energy classification of dynamic phenomena, showing the nature of the impact of dynamic phenomena on mine workings is compiled. Analysis of dynamic manifestations of rock pressure showed that during the dynamic phenomena of both types, the zone of rock mass disturbance significantly exceeds the size of the focal zone. Disintegration zones may occur around mine workings of deep mines. Formation of these zones around excavations in the ultimate massifs occurs as a result of static circumferential tangential stresses near the excavation contour and dynamic effects from rock bumps and mass explosions by brittle fracture and delamination of the contour massif.
The development of the mining industry is associated with the development of deposits at great depths in difficult mining and geological conditions. A number of large Russian mining companies have already reached deposit development depths of 1000-1500 m, the depth of the projected Severouralsk mines is 1500-2500 m. For deep mines, an important problem is the choice of the optimal option for the penetration and transportation of minerals to the surface. In work three variants of opening of deep horizons of mine "Red Riding Hood" of JSC "Sevuralboksitruda" are considered: opening of deep horizons with deepening of existing vertical shafts, the stage scheme of opening by slopes with a base horizon -860 m, the stage scheme of opening by blind vertical shafts with base horizon -860 m and a device of underground head frames. Technical and economic evaluation of the most rational options was carried out. Analysis of results showed that the volume of capital mining works on a variant with opening by blind gradients is more on 17120 m 3 at cost of excavation on a surface of 1 m 3 rock, including general expenses of a mine, 2350 rubles. The second variant in the approximate cost expression will exceed the third in the sum 40232000 rubles. The received sum is approximately one third of annual financing of mining-capital works for "Sevuralboksitruda". Consequently, according to technical and economic indicators it is expedient to open deep horizons according to the step-by-step scheme by blind vertical shafts with the base horizon -860 m and the device of underground headframes.
Field observations of the displacement of rocks around the preparatory and cleaning workings (operations) of SUBR mines (shafts) establish the effect of stratification of the roof of workings (operations) and cleaning chambers under the action of seismic waves. The shifts are traced to a depth of up to 4 m, and almost instantaneously, at the moment of the rock impact. When modeling the process of interaction of a flat straight wave with workings (production) of rectangular, vaulted and shapes of cross-section, it is shown that the probability of reaching the limit state of the host rocks due to the maximum difference in the main pressure (stress) is higher in workings (production) of rectangular and more shapes. Based on the revealed dynamics (changes) of seismic pressure (stress) and regularities of deformation of the host rocks, the design of reinforcement (strengthening) of the roof of chambers and joints of excavations (workings) with deep reinforced concrete anchors was developed.
Blast wave influence on rock stability in mine openings is given an account of. Results of mathematical modelling of a dynamic stress field created in the massif due to wave interaction with the mine opening have been analysed. A stress field influenced by short wave blasts has been studied. Equations of dynamic balance for theoretically elastic environment, supplemented with boundary and initial conditions for the corresponding components of stress tensor, serve as the basis of a mathematical model developed by V.V. Karpenko and G.A. KoIton. The set of 5 equations was solved using S.K. Godunov numerical technique. Input data are assumed on the basis of the mining conditions at the Severniy (Northern) mine (blast hole diameter - 76 mm; blast type - granulite AC-8). A particular case of blast influence at 10 m range between the charge and the gallery roof (r =370) has been studied. Distribution diagram parameters of the forward-moving elastic wave compression phase have been determined using analytical dependence for a cylinder-shaped charge blast (amplitude σ o = 9.6 MPa, period of time t - 1.2 ms, speed C 1 - 4500 m/s). It has been demonstrated, that form the direction of the forward-moving wave, refracted and diffracted waves create in the massif an extensive zone of radial tension stress, peaking at 1.6 at the distance of 0.8-1.0 R from the contour. In lateral areas, the blast wave produces concentration of tangential compression stresses up to 1.6 σ o . An estimation of mine destruction caused by the energy of dynamic development has been given. Besides dynamic compression and tension stresses, repeated blasts and impulse stress load and relief on the massif also influence stability of the mine openings. An estimation of rock stability criteria at the entry contour during joint action of static and dynamic stresses has also been given.
