Rock Fracture Process Research Articles

Study on the influence of natural cracks on the mechanical properties and fracture mode for shale at the microscale: An example from the Lower Cambrian Niutitang Formation in northern Guizhou

A large number of natural cracks exist in shale reservoirs, and the presence of natural cracks weakens the integrity of shale, which is an important factor governing the effectiveness of shale gas extraction. In this paper, shales from the Lower Cambrian Niutitang Formation in northern Guizhou were scanned by electron microscopy, their microstructures were selected for digital image processing, and uniaxial compression numerical tests were conducted on shale models containing different natural crack dips using the rock fracture process system RFPA2D-DIP to study the effects of natural cracks on the mechanical properties and fracture patterns of shales at the microscopic scale. The study shows that the peak strength and elastic modulus of shale increase with increasing natural crack inclination angle. The fracture modes of shale at the microscopic scale can be roughly divided into four categories: similar to I-type fractures (0°), oblique I-type fractures (15°, 45°, 60°, 75°), folded line fractures (30°), and V-type fractures (90°). Natural cracks within shale are found to have a significant effect on the distribution of stress. Acoustic emission can reflect the stress change and rupture process for shales containing natural cracks with different dip angles at the microscopic scale. The presence of natural cracks has a significant effect on the AE energy and fractal dimension. The magnitude of the AE energy increases with increasing stress level and reaches a maximum value at 90°, while the value of the fractal dimension is found to zigzag upwards because the value of the fractal dimension is jointly influenced by both newborn cracks and native natural cracks.

Rock dynamic fracture by destress blasting and application in controlling rockbursts in deep underground

Destress blasting is regarded as an active mitigation measure for preventing rockbursts in deep underground works, whose mechanism and effectiveness, however, have still been in debate. A self-developed combined finite-discrete element method software is implemented in this study to first model the rock fracture process induced by a single-hole destress blasting based on a practical blast in a deep gold mine with high in-situ stresses. The effects of accelerometer holes and bedding planes are discussed. Then, a two-round tunnel face excavation in deep underground with high in-situ stresses is modelled, which reproduces the occurrence of the excavation-induced rockbursts. Finally, destress blast-holes are introduced into the same model prior to the two-round tunnel face excavation to investigate the effect of the destress blasting on the excavation-induced rockbursts. It is found that the fractures induced by the destress blasting shift the high abutment pressure induced by the excavation away from the tunnel face and then protect the tunnel wall from fracturing. The numerical modellings reveal that the success of the destress blasting in controlling excavation-induced rockbursts depends on not only the site condition but also the design of the destress blasting such as the arrangement of the blast-holes and the explosive charges.

Modelling of progressive failure mechanism of mine pillars

Rock fracturing process around underground openings is mainly a process of progressive slabbing with the generation of surface-parallel fractures in the initial stage, and shear failure is likely to occur in the final process. The difficulty of capturing this behaviour through conventional continuum modelling has led to the development of advanced constitutive laws for use in continuum models. Recently, an enhanced continuum constitutive approach to simulate strain-softening based on the Hoek-Brown failure criterion has been presented. This advanced Hoek-Brown model with Softening introduces a hyperbolic decay of the material properties affecting the post-peak response and the nonlinear dilation, thus enabling to investigate failure modes in the form of dilatant shear bands. Moreover, to restore the objectivity of the numerical solution during the development of strain localization phenomena, a viscous regularization technique has been implemented within the model. The performance of this constitutive model has been proved and, in this paper, further numerical computations are reported concerning the brittle failure process occurring in mine pillars, thus confirming the capability to capture failure mechanisms during excavation within a strain localization regime.

On the mechanism of rock fracture with tools made of hard alloys and polycrystalline superhard materials

When studying the process of rock fracture with tools equipped with polycrystalline superhard materials (PSHM) and hard alloys, the main regularities of the fracture mechanism, despite the significant differences in physical and mechanical properties of the used tool materials, are assumed to be identical. This approach not only reduces the efficiency of using the created rock-destroying tools, but also limits the scope of application of polycrystalline superhard materials. Experimental studies using various methods of obtaining information shown significant differences in the mechanism of rock fracture by hard alloys and polycrystalline superhard materials. The study of the zone of the pre-destroyed surface showed that when cutting rocks with PSTM, the process of destruction is carried out not only by the entire polycrystalline plate, but also by ridged diamond formed on the cutting edge and rear surface of the tool. At the same time ridged diamonds, when embedded in the rock, create high contact stresses and an additional network of microcracks interacting with microcracks formed due to the embedding of the entire cutting edge of the plate. The impact of two independent indenters simultaneously increases the zone of the pre-destruction layer in the rock mass, which leads to a more significant decrease in its strength and, as a consequence, to the intensification of the process of rock destruction by the PSTM tool. In case of wrong choice of PSTM application area and operation modes, errors in tool design and insufficient cooling, ridges are not formed on the cutting edge and back surface of the polycrystal. As a result, the polycrystalline insert works as a carbide insert and the efficiency of the PSHM tool is sharply reduced. The use of knowledge obtained as a result of the conducted research makes it possible to create tools equipped with diamond-hard-alloyed inserts, the wear resistance of which is dozens of times higher than that of similar tools made of hard alloy. For example, effective tools equipped with diamond-hard-alloyed inserts have been created and widely introduced into practice for rotary drilling of boreholes, degassing wells, anchoring of mine workings, saw stone cutting, drilling of abrasive permafrost soils and others. Keywords: polycrystalline diamonds cutters (PDC), hard alloys, pre-destruction zone, rock breaking tools, rock destruction.

A testing system to understand rock fracturing processes induced by different dynamic disturbances under true triaxial compression

In this context, a testing system to understand rock fracturing processes induced by different dynamic disturbances under true triaxial compression was developed. The system is mainly composed of a static loading subsystem, a dynamic loading subsystem, a specimen box subsystem, and a data measurement subsystem. The static loading subsystem uses low stiffness loss frame structure technology, which greatly improves the frame stiffness in the three principal stress directions (up to 20 GN/m) and ensures the demand of the disturbance experiment in both the prepeak and postpeak stages. The disturbance loads with frequency of 0–20 Hz and stress level of 0–30 MPa were applied using large flow parallel oil source technology characterized with high heat dissipation efficiency. For the disturbance loads with frequency of 100–500 Hz and stress level of 0–30 MPa, they were realized by using high-frequency and centimeter-per-second-scale low-speed disturbance rod technology. Three rigid self-stabilizing specimen boxes were utilized to provide support for the specimen and deformation sensors, ensuring the stability and accuracy of the data obtained. To verify the performance of the true triaxial test system, disturbance experiments were conducted on granite specimens. The results show that the experimental device satisfies the requirements of original design, with an excellent repeatability and reliable testing results.

RESEARCH ON NONLINEAR VARIATION OF ELASTIC WAVE VELOCITY DISPERSION CHARACTERISTIC IN LIMESTONE DYNAMIC FRACTURE PROCESS

The elastic wave propagating in rock has velocity dispersion characteristic that holds an imperative significance in rock engineering. This paper aims at study elastic wave velocity dispersion characteristic in limestone dynamic fracture process. For this purpose, the experiment of elastic wave propagates in the limestone when cyclic loading and unloading process is conducted, and elastic wave velocity dispersion characteristic is analyzed. Based on multifractal theory and Raiga model, the influence of fracture degree on velocity dispersion characteristic is discussed qualitatively and quantitatively with evolution characteristic of the AE event. The research results indicate that there is velocity dispersion characteristic when elastic wave propagates in the limestone sample, which presents positive correlation between velocity and frequency. The variation of wave velocity dispersion characteristic is consistent with that of AE activities and both of them show a nonlinear increase trend with an increase of loading. The reason for velocity dispersion characteristic is that the retarding effect of microcracks on elastic wave velocity with different frequencies is different, and the effect is enhanced with the microcrack scale increasing. According to the variation of multifractal parameter [Formula: see text] of the AE event energy series, the limestone sample under loading experiences a transformation process from small-scale microcrack to large-scale microcrack and small-scale microcrack dominance to multi-scale microcrack coexistence, and this complex transformation process results in nonlinear variation of velocity dispersion characteristic. Further, the multifractal parameter [Formula: see text] is introduced into Raiga model to establish the velocity dispersion quantitative model. The model can describe well elastic wave velocity dispersion characteristic, and indicates quantitatively that there is an obvious nonlinear positive correlation between the dispersion characteristic and the fracture degree. The research results have important theoretical and practical significance for understanding elastic wave velocity dispersion characteristic in limestone dynamic fracture process. It can provide important support for characterizing rock fracture process using elastic wave velocity dispersion characteristic.

An adaptive damage smear method for modelling the meso-fracturing process of rock

Numerical methods based on continuum mesoscopic representative volume elements (RVEs) are popular in simulating the rock fracturing process because they can characterize trans-scale crack propagation. However, two key prerequisites must be satisfied to achieve good performance from RVE-based smear methods: the minimum representation element must be a square, and the RVE size used to represent cracks must be close to the meso-scale. Thus, overcoming the serious computational burden caused by rock meso-fracturing modeling has become a long-term bottleneck issue. This study aimed to develop an adaptive downscaling modeling scheme for the scale restriction of rock meso-fracturing systems based on a local hierarchical refinement strategy and novel combined estimator advancements. Subsequently, based on the statistical meso-damage smear method, we simulated the adaptive meso-fracturing process of the rock. The results of several examples show that the adaptive damage smear method ensures the stability and continuity of the stress field in the stress concentration area of the model as well as enhances the computational accuracy. Additionally, the local downscaling refinement meshes used to cover the crack propagation path approach the expected mesoscopic scale required to characterize the failure morphology at a high resolution. Consequently, an optimal trade-off between the accuracy and computational effort can be realized. Compared to the global uniform fine model with the same resolution, the proposed adaptive strategies can significantly mitigate the computational burden.

Structural control within flawed rock specimens under external loading as visualized through repeating nucleation on multiple sites by acoustic emission (AE)

SUMMARYThe behaviour of discontinuities in rock mass have been experimentally investigated extensively for decades by a type of laboratory analogue of flawed rock specimens, taking the artificially prepared flaw(s) as the analogue of rock mass discontinuity(ies). The role of macroscale flaw(s) as controlling structure has been generally neglected. Here, we conduct detailed characterizations of the acoustic emission (AE) from the rock fracture process on the pre-flawed specimens under loading. Though the same phenomena from the literature can be reproduced within our tests, detailed spatial-temporal investigation on the AE events at the nucleation point suggests a different physical interpretation. Artificial flaw(s) play a non-negligible role as a controlling structure for the following rock fracture process including a series of nucleation points alteration via stress transfer. The interlocking parallelogram (IP) control and single-large-structural (SLS) control are two fundamental mechanisms initiated by the artificial flaws. Each of these two mechanisms are observed under a wide range of flaw settings and can potentially coexist within the across length scales. The scale-invariance feature is observed to be fundamentally different within the scale of specimens under SLS and/or IP control, suggesting the incompleteness at the specimen-scale for IP control. Therefore, no ‘fracture coalescence’ zone can be separately investigated without considering its external rock fracture evolution and confirming scale-invariance. Therefore, structural controlling mechanisms must be considered due to the pattern and AE characterization results.

Coupled CEL-FDEM modeling of rock failure induced by high-pressure water jet

The coupled Euler-Lagrange (CEL) method and finite-discrete element method (FDEM) are adopted to simulate the rock fracture process induced by high-pressure water jet and to solve the problems of highly nonlinear, fluid-solid coupling and large deformation. The water is characterized by the CEL model, and water can flow freely in the Euler mesh, which can better simulate the actual shape of water jets. The rock is integrated into the FEDM model, which is produced by embedding zero-thickness cohesive elements. The traction-separation criterion of the cohesive element is used to simulate the rock damage. In the simulation process of rock fracture by the water jet, infinite elements are used to realize the non-reflection boundary conditions, simulate real working conditions, and improve the calculation reliability. Furthermore, the VUSDFLD user subroutine is used to delete the elements outside the box and reduce the impact of the fallen rock debris on simulation speed, thus improving calculation efficiency. The formation process of rock impact pits and slits, as well as the velocity and distribution of water jets, are studied by comparing the simulation and experiments of water jet fixed-point impact and moving cutting. Subsequently, the fracture mechanism of rock under the water jet is revealed, presenting new possibilities for studies into rock fractures by high-pressure water jet.

Observation of fracture process zone and produced fracture surface roughness in granite under Brazilian splitting tests

In many rock engineering structures, the fracture network's complexity and the generated fractures' roughness are immensely important for understanding the hydraulic conductivity of the rock mass. Despite significant progress, the mechanisms governing nucleation and growth of fracture process zone (FPZ) are still debated. The present work investigates the characteristics of the FPZ and the surface roughness of the produced fracture in granite under tensile loading at two different loading rates. Acoustic emission (AE) and digital image correlation (DIC) techniques were simultaneously employed to monitor the development of the FPZ in disc specimens of granite subjected to Brazilian splitting tests. In addition, several roughness parameters of the produced fractures were measured, and it was tried to link the locations and the magnitudes of the AE events with the height distribution of the fracture surface. Our results indicated that the loading rate significantly influences the extent of the FPZ. The tensile strength of specimens also increased with the loading rate. The FPZ estimated from the AE and DIC data were in good agreement; however, AE provided a slightly wider process zone for all specimens, regardless of the loading rate. It was observed that reducing the loading rate led to a larger FPZ and generated macroscopic fractures with higher roughness characteristics. Moment tensor inversion of the AE signals revealed that in all tested specimens, macroscopic fractures, which are conventionally considered tensile fractures, are composed of three main cracking mechanisms at the microscale, including tensile, shear, and compressive sources. Focal mechanisms distribution showed that the cracks might initiate under tensile, shear, or a combination of both mechanisms. This study’s findings can help in better understanding the rock fracturing processes under tensile loading in granitic rocks for field applications.

Intermittency of Rock Fractured Surfaces: A Power Law

Roughness of rock fractured surfaces is one of the most important factors controlling fluid flow in rock masses. Roughness quantification is of prime importance for modelling the flow of ground waters as well as reservoir fluid mechanics. In this study, with the aid of high-resolution 3D X-ray CT scanning and image processing techniques, the roughness of four different rock types is reconstructed with a resolution of 16.5 microns. Moreover, the correlation and structure functions are used to analyse height fluctuations as well as statistical intermittency of the studied rock fractured surfaces. It is observed that at length scales smaller than a critical length scale, fractures surfaces are correlated and show multifractality. Monofractals are neither intermittent nor correlated; hence, a meaningful link between statistical intermittency and the correlation function of multifractals is expected. However, a model that considers this relationship and predicts multifractal spectra of disordered systems is still missing. A simple power law that can exactly forecast the multiscaling spectrum of rock fracture process zone is being introduced. It is explained how the exponent of this power function λi is related to the crossover length of correlation function ξ, and how this critical length scale can be objectively identified.

Identification of crack initiation and damage thresholds in sandstone using 3D digital image correlation

In this study, a non-contact image correlation measurement technique, Three-Dimensional Digital Image Correlation (3D-DIC), is employed to identify and quantify the evolution of rock crack initiation and propagation. With the aim of carefully investigating the cracking progress, a uniaxial compression test was conducted on sandstone specimens with a single pre-existing flaw. The surface and internal micro-fracture characteristics of the sandstone specimen were detected by combining 3D-DIC and acoustic emission techniques from both optical and acoustic perspectives. On the basis of the full-field deformation data derived by 3D-DIC, a method for determining the principal strain of cracks was defined, which aids in identifying the spatial propagation characteristics of rock cracks. Additionally, the crack principal strain method (CPSM) was proposed for determining the characteristic stress threshold of rocks based on the crack principal strain. Then, the results obtained from CPSM are compared to the conventional acoustic emission method (AEM) and axial stiffness method (ASM) tests. The research results suggest that AEM is suitable for identifying crack closure stress and crack initiation stress, whereas ASM and CPSM are superior for identifying damage stress. This work provides a novel method and concept for the measurement of non-contact characteristic stress thresholds, as well as has an insight into the detection and evaluation of the evolutionary process of rock damage and fracture.

The variation of micro-current in rock under loads and its microcosmic influence mechanism

Electromagnetic signal is a key means to monitor rock dynamic disasters. Its essential reason is the free movement of charges. At present, the variation law of microcurrents and the influence mechanism are still not clear in the loading process of rocks with different lithologies. Therefore, an electrical and mechanics experimental system of rock was established to explore the change rules of microcurrents generated in the loading process of rocks and the microscopic influence mechanisms. The research results showed that the microcurrent curves of different rocks had different change laws under low and high loading rates. At a low loading rate, the microcurrent was small and then increased exponentially. While the microcurrents went through three stages at high loading rates: rapid growth phase, gentle phase and mutation phase. The overall microcurrent level of marble was lower than granite and sandstone due to the lack of quartz. Quartz in the rock played a key role in current generation rate of loaded rock, but it was not a decisive factor. With a higher quartz content, the average current generation rate increased with the increase of grain size of the quartz crystal. Under the uniaxial compression of the rock, the piezoelectric effect and fracture power generation currents played the major role at different stages, and the piezoelectric-fracture synergy power generation mechanism was put forward. The research results could provide a theoretical basis for the mechanical influence mechanism of current generation during rock fracture process.

Fundamental physics distinguishes the initial stage acoustic emission (AE) behavior between compressive and fracture toughness tests in rock

We resolve a misunderstanding on the general observation of AE releases from mode-I and mixed-mode fracture toughness tests, and from compression tests on rock core or prismatic blocks. The fracture toughness tests expect few early AE while the compression test expects many. We investigate the detailed AE energy release organization from two novel approaches. From a system’s perspective, the former (mode-I and mixed-mode) undergoes a process of continuous entropy increase from the well-organized global condition regardless of having continuous energy input; the latter (rock core compression) displays a process of continuous entropy decrease until macroscale rock fracture formation. From perspective of elementary-damage-accumulation, the dynamic building process of the AE topology network from the mode-I or mixed-mode test displays a significantly stronger triggering effect compared to the rock core compression—especially in the early stages of these tests. Observations from both aspects consistently suggest the two types of rock fracture processes are of different physical processes. The analogue of the mode-I and mixed-mode fracture toughness tests is the pervasive process, while that of the rock core or prismatic block compression is the site percolation process. The pervasive source of the mode-I and mixed-mode tests provides a significantly lower energy barrier for the rock fracture formation than the rock core or prismatic block compression. Consequently, its early-stage AE releases will be suppressed or eliminated. Investigating the scaling features of the AE releases suggests the observational features for a notch-induced rock fracture process are universal across scale.

Pseudo-coupled hydraulic fracturing analysis with displacement discontinuity and finite element methods

Hydraulic fracturing is a widely employed technique in geoengineering. It is the most common stimulation technique to enhance reservoir permeability. Mathematical modeling of hydraulic fracturing must include several coupled processes, leading to complex and computationally expensive solutions, especially in 3D models. This complexity has led researchers to develop computational tools aiming at accuracy and acceptable computational costs. Several coupled and pseudo-coupled hydromechanical schemes have been proposed in association with the Finite Element (FEM) and Boundary Element Methods (BEM). On the other hand, semi-analytical methods apply to specific simple cases and provide approximations to more complex situations. This work proposes using the Displacement Discontinuity Method (DDM) associated with the Finite Element Method to model the hydraulic fracturing process. An explicit two-way pseudo-coupled scheme is developed where the DDM method solves the rock fracturing process. The FEM simulates fluid migration inside the fracture and the porous media. The results of the KGD problem considering impermeable and permeable conditions show good agreement with the proposed methodology. Finally, the accuracy of 2-D analyses while reducing the computational time suggests extending the FEM-DDM method to three-dimensional problems as a promising alternative to more complex fracture analyses.

Experimental investigation on the spatio-temporal-energy evolution pattern of limestone fracture using acoustic emission monitoring

The spatio-temporal-energy evolution characteristics of strong acoustic emission (AE) events on the crack surface were investigated during the process of a complete limestone rupture, in order to demonstrate the generation, expansion, and interpenetration of microcracks in rock samples. The results show that the process of internal deformation and rock fracture could be well represented using the spatial distribution of strong AE events. The spatial distribution of strong AE events was consistent with the fracture surface, with a good linear relationship between spatial fractal dimension and stress. The formation of the fracture surface occurred mainly in stable and rapid development stages. It shows that the evolution model of strong AE events cumulative energy on the fracture surface matched with the distribution of the Gaussian Amp function. The proposed cumulative energy formula for AE events can quantitatively describe the process of rock crack development, which could be used to describe the spatio-temporal-energy evolution pattern of AE for rock fracture.

Investigation of the Dynamic Pure-Mode-II Fracture Initiation and Propagation of Rock during Four-Point Bending Test Using Hybrid Finite–Discrete Element Method

A hybrid finite–discrete element method (FDEM) is proposed to investigate dynamic pure-mode-II fracture behaviors. The transition of continuum to discontinuum was applied to the FDEM through the use of three fracture modes, so that the whole fracture process could be modeled naturally. The FDEM was then employed to model the dynamic pure-mode-II fracture behavior of rock during a four-point bending test with a prefabricated notch. The results showed that the fracture initiated from the tip of the prefabricated notch under a relatively lower loading rate, i.e., 1 m/s and 5 m/s. However, when the loading rate reached higher levels, i.e., 10 m/s and 50 m/s, the prefabricated notch played a small role in the fracture patterns. Under these conditions, the fracture initiated from the center of the beam bottom or the stress concentration vicinity, instead of the tip of the prefabricated notch. Regardless of the loading rate, the obtained force-loading displacement curves showed a typical brittle material failure process. Additionally, by incorporating the empirical correlation between the static and dynamic strengths obtained from the dynamic rock fracture tests, the hybrid finite–discrete element method could effectively reflect the impact of the loading rate on the strength of the rock. To conclude, the hybrid finite–discrete element method is an effective instrument to investigate the fracture initiation and propagation of rock, since it can both naturally simulate the process of rock fracture and capture the effect of the loading rate on the rock behaviors.

Numerical Study of Rock Damage Mechanism Induced by Blasting Excavation Using Finite Discrete Element Method

In this paper, the mechanism of rock damage induced by blasting excavation is numerically studied by using an FDEM-based multiphysics fracture analysis software, MultiFracS. Based on the drainage channel project of Guanggu 1st Road to Gaoxin 4th Road, a numerical model considering the near-field fracture process is established to study the influence of a millisecond delay and construction technology on the blasting excavation. Firstly, the double side drift method model is established to analyze the influence of different millisecond delays on the peak blasting vibration velocity. Then, the rock fracture process of the surrounding rock around the blast holes under the blasting excavation construction technology of the double side drift method, the reserved core soil method, and the CRD method is studied, respectively. The numerical simulation results show that the mainshock phases of the blasting vibration velocity waveform generated by different bores overlap when the millisecond delay is small. With the increase in the millisecond delay, the mainshock phase is gradually separated, and the superposition effect of the blasting vibration is weakened. When the millisecond delay is greater than 40 ms, the peak blasting vibration velocity is not affected by the millisecond delay. In the three kinds of blasting excavation construction technologies, the double side drift method has a better effect on the deformation and the fracture control of the surrounding rock. The optimal millisecond delay and the rock fracture evolution process of the surrounding rock around blast holes with different blasting excavation construction technologies are obtained.

Study on Freezing-Thawing Failure Process of Natural Damage Sandstone Based on Cellular Automata

Natural damage such as internal cracks, pores, and discontinuous surfaces of rocks induces the formation, expansion, and interaction of mesofractures until macroscopic failure under the action of freeze-thaw and load. The failure process is the evolution of self-organization and has localization characteristics. The CT scanning test of sandstone with different freezing and thawing cycles was carried out. According to the theory of cellular automata analysis, combined with CT image processing technology, the numerical model of the mesostructure of the sandstone constructed with natural damage, and the numerical simulation test of the Brazilian splitting failure of natural damage sandstone was completed under freezing and thawing. The results show that the combination of CT image processing technology and CASRock numerical simulation software can dynamically describe the whole process of initial damage propagation, new crack generation, and penetration of rock containing natural damage under tension in a freeze-thaw environment. Due to random and disordered natural damage inside the rock, gradually changing to an orderly state under freezing and load, the rock shows discontinuous deformation after the plastic deformation reaches a certain degree and gathers at the initial damage expansion. The fracture process of natural damaged rock under freezing and load has continuous-discontinuous deformation characteristics. The existence of initial rock damage causes the rock’s localized deformation and failure characteristics. The form and size of the initial damage determine the direction of development of the surface of the sandstone fracture and the coalescence of the crack. The initial damage area of sandstone is expanded due to the freeze-thaw cycle. After loading, the local deformation and failure characteristics caused by initial damage have delay characteristics for penetration of the main cracks in the sandstone, which determines the formation and development direction of secondary cracks in the rock failure process.

Энергетические критерии квазихрупкого разрушения горных пород в технологических процессах их добычи и первичной переработки

This study aims to develop a methodology to calculate energy criteria based on the concept of quasi-brittle fracture of rocks in technological processes of mining and primary processing. The research has shown that the Griffiths-Irwin energy criteria that are derived from solution of the equilibrium problem for a plate with an internal fracture stretched by a uniformly distributed load, refer to a special case which meets the condition of the ultimate energy efficiency of fracturing a plate with defined geometrical dimensions (length, width). Having a theoretical value, these criteria do not meet practical applications, where it is necessary to consider the energy efficiency of the rock fracture process by normal rupture cracks for each specific mining technology. It makes no sense to calculate the irreversibly expended work within the quasi-static concept of rock fracture for its practical application without taking into account the energy efficiency, this being the main conclusion of the research performed. It is suggested to estimate the energy spent on forming two new unit surfaces, which corresponds to one fracture plane and characterizes the fracture resistance of the rock material, with the criterion that includes the ultimate specific energy intensity of the fracture deformation with account of the new complex textural and structural material constants and the energy efficiency of the fracture process.