The practice of designing the support of underground workings is based on the recommendations of regulations. The rock mass displacement towards the mined-out area are is the determining parameter. For its estimation the package of nomograms and correction factors is suggested, the choice of which is rather subjective, which reduces the reliability of the calculations. In the present work, on the grounds of theoretical and experimental investigations, the methods of estimating the coefficient of rock massif structural weakening is introduced and stress concentration at the outline of the underground working, which is based on the fractal investigations of the working geometry. Calculation formulae are adapted to various types of jointed structure of rock massifs: with parallel and chaotic systems of fissures, which form the blocky structure of the massif. The methods suggested don’t contradict the recommendations of regulations and significantly extend the calculation base of designing the loading on the underground workings support.
Stability of jointed rock mass outcroppings is determined, as a rule, by a process of rock shift along the surface of weakness (fissure). Shift parameters depend on the strength characteristics of enclosing rock and fissure geometry. The present article considers the procedure of analysis of rock mass stability by the example of the real conditions of an open pit at the deposit Udachnoye. The methods of division and quantitative estimation of roughness parameters and tortuosity of fissures are introduced on the basis of their trajectory fractal analysis. The procedure of building up the certificate of strength at the rock shift along the fissure is described. The real trajectory length is determined and the surface area of fissures with the account of their tortuosity and fractal dimension estimation. The analysis of stability of outcroppings is introduced under various value of the angle of fissure incidence. The results of the analysis make it possible to determine the coefficient of stability of the outcroppings, together with the allowable load on the benches of an open pit. The discussed methods of analysis can by applied for various conditions of opencast and underground development of jointed rock mass.
In the process of tunneling the mine workings with the help of drilling and blasting operations, the quality of delineation possesses great significance, i.e. obtaining the section which is maximum designated to the designed outline of the working. The quantitative measure of the degree of the outline curvedness of the working is its fractal size. Particularly, it determines the size of the working section perimeter in mining. In this connection in order to quantitatively estimate the outline deviation from the designed one, the outline blasting quality criterion in the shape of the fractal coefficient of the working shape is suggested. It represents the relation of the working conform representation section area to its perimeter: under the constant working section area, the worth the quality of the delineation is, i.e. the bigger the perimeter is, the smaller the fractal coefficient of the shape is. The surface heterogeneity of the working leads to the increase in the concentration of stresses in its outline. Consequently, fractal coefficient of the shape can serve as the estimation of the coefficient of the stresses concentration. In order to study the given problem, the measurements of the sections of 32 workings in Severouralsk bauxite mines have been fulfilled. The correlation analysis of the results has shown the reliable relation of the fractal coefficient of the shape of workings with the coefficient of the stresses concentration in its outline. The results acquired make it possible to estimate the quality of drilling and blasting operations and the stability of rocks in the working.
The article raises the question of the interrelation between the processes of mineral production. Production cycles are considered in the relationship with their energy characteristics with regard to excavation in the face in time. The article analyzes previously published materials on the establishment of the relationship between the processes of drilling and explosive rock mass destruction. The article considers energy characteristics of excavation in conjunction with explosive destruction; the approach is proposed to the determination of relation of excavation and loading of rock mass in the vehicles; promising direction of exploring technological ties is identified. The results of the analysis of modeled operation of some rope crawler excavators of different capacity of the bucket when working in one cut are introduced. It is shown that the energy content of explosive destruction and the energy content of excavation are characteristically connected with the face displacement velocity. At that the total energy content of explosive destruction and excavation decreases with the increase of the face displacement velocity. The latter indicates the fact that increase in the intensity of excavation in the quarry leads to the reduction of energy consumption for the processes.
The work suggests the functions of yield surface and plastic potential on the basis of the author’s earlier investigations. The limiting surface for the given functions is the surface of solid bodies (rocks) destruction, which is described by the law of Coulomb. In fact, the suggested function represents the law of plastic deformation of solid bodies. It is analytically proved that in the process of plastic deformation there occurs the turn of structural elements of the solid body. On the basis of the given investigations some discrepancies are explained, which are observed in the process of rock strength tests. Energetic variational principle of breaking (destruction) of solid bodies is obtained. On the basis of this principle the appearance of ring structures in the premises of some mine workings is explained - the phenomenon of zone disintegration of rocks. The dependence is suggested to calculate the scale factor of the given phenomenon. Geometric vicinity of sliding surface shape in slopes to the arc of circle is justified.
In the processes of ore dressing the problem of high energy consumption in the technologies of mineral and technogenic disintegration is still up-to-date. Investigations, made at the variety of ores, confirmed that the work of internal forces under disintegration just marginally transforms into a new surface, i.e. into mineral release properly. Wave techniques are potentially innovative directions of disintegration energy cost reduction; they use the effect similar to “rheological blast”. The work examines the results of the investigation of surface-active substances (SAS, which serve as the surface energy reducer) influence on destruction processes of dimensionally deformed samples of various ores. As compared to the “rheological blast”, where destruction initiators are shear deformations of volume-stressed body, the work introduces the confirmation about the fact that SAS can cause the generation of new surfaces due to internal elastic energy collected under volume deformation. Investigations made with the samples of titanomagnetite , ferruginous quartzite, and chromite and rare metal ores with various SAS, confirmed the presence of the effect of spontaneous fissuring at the moment of SAS introduction into volume deformed material. Microfractographic analysis of alternation products has showed mainly intercrystalline rupture with minimum number of aggregates and primary revelation of ore minerals in natural size are determined in all examined samples of ores under dimensional deformation.
Rock breaking in a mine working in the presence of developed fissure system happens, as a rule, due to the shift along the surface of weakness. Experimental investigation of the given process is complicated by a high labor intensity of full-scale experiments and impossibility of multiple shears along one and the same fissure. In this conditions imitational modeling of the process with the method of Monte-Carlo is an efficient means of investigation. For its realization the establishment of quantitative relations is required, which define the character of rock deformation before and after the achievement of ultimate shearing stress at the shear. On the basis of experimental investigations the present work determines the equations of ascending and descending branches of stress-strain curve. The equation of shear rigidity of fissures on the basis of the fractal dimension of its trajectory is obtained. Estimation procedure of remaining strength at rock shear along the fissure is substantiated. Model validity check by way of comparing the results of its realization with experimental data has shown their statistically reliable correspondence within the accuracy of observations. The application of the developed model allows investigating regularities of shear along the fissure process for various rocks and conditions. Averaging of multiple realizations of a model increases the reliability of received date.
Rock massifs are usually in ultimate stress state, and maximum values of stresses are limited by strength characteristics of rock massifs. Ultimate rock equilibrium is maintained by stresses uploading with the development of brittle deformation within the massifs. Mass fissures of pre-deformation develop in near-surface zone of brittle deformation. The power of this zone in rock massifs reaches 300–500 m. The network of interrelated open fissures of pre-deformation forms harmful complex of near-surface rock jointing close to earth surface. Geomechanical rules of brittle deformation processes development predetermine the forming of vertical fissure zoning. Quantitative rules of vertical fissure zoning development allow determining basic geomechanical characteristics of rock massifs.
Condition and properties of rocks are significantly dependent on blocky structure and fissure structure of rock mass. Due to the complexity and low repeatability of real experiments, a more effective and informative means of investigation is statistic modeling of fissures on the basis of Monte Carlo method. The work argues the methods of modeling the trajectory of fissures on the basis f their characteristics as fractal objects. Mathematical frameworks for models are given on the basis of fractal brownian movement, approximation of fissures sinuosity by sectionally linear functions and their modeling with a method of middle shifts. Managing parameter of the model is fractal dimension of a fissure trajectory (Hölder condition). The means of generating open fissures edges coordinates are examined. Three model implementations are provided: mirror reflection tension joints edges; shift fissures edges modeling according to common algorithm and fissures midline determination under their edges shifts within established scale. Computer programs worked out allow modeling fissure structure of rocks, as well as the processes of fissures origination and development under various influences upon the massif in the course of its exploitation.
Dilatancy plays the most important role in the generation of strength and stress-strain state of rock massifs. It is determined by the tension crack of a fissure edges at shifting. The work examines the mechanism of dilatancy at tension crack of a fissure edges along the line of sinuosity and roughness. The results of experiments on the shift of rocks along the fissure are introduced. Linear and non-linear character of longitudinal and transversal deformations at the shift of rocks along the fissure is described. Dependence of dilatancy parameter on the coefficient of roughness and sinuosity is determined. The procedure of building up the certificate of rock strength at rock shift is revealed with the use of initially set value of dilatancy parameter with the help of fissures geometry characteristics. The possibility of direct use of fissure geometry characteristics is pointed out for the construction of two-stage shift of rocks at non-linear representation of the certificate of rock strength. The results of the investigations can be used for the forecast of strength and stability of fissured rock massifs.