Model Of Rock Mass Research Articles

Justification of optimal mining system parameters for Irokinda gold deposit

The engineering design development for Irokinda gold mining project required selection and justification of mining system parameters for Serebryakovskaya vein. Irokinda gold ore deposit occurs in the north of Buryatia. The local high-mountain terrain is dominated by the Alpine-type hillsides with slope inclinations up to 30–40°; the actual elevations of watersheds are more than 2000 m; the relative altitudes over the valley bottoms is up to 1000 m. Based on the studies into the physical and mechanical properties of the vein and enclosing rock mass, the roof rock stability diagram is plotted, which enables selecting the geometrical parameters of a stoping area by the preset height of the stoping level, and the design procedure is developed for the intermediate pillars. The inspection results of the parameters of stoping areas after the 3D stress–strain modeling of rock mass in Map3D show that the analytically obtained parameters of stoping areas ensure safe gold mining in reef drifting; in fringe drifting it is possible that critical stresses arise in pillars and promote their fracture, and sizes of the pillars should be increased by 20% as against their theoretical values. The use of the reasonable mining system parameters can reduce ore extraction time, enhance mining safety and lower ore dilution.The authors appreciate participation of Dr. Eng., Prof. V. A. Eremenko, Director of the Research Center for Applied Geomechanics and Convergent Technologies in Mining and NUST MISIS College of Mining, the Project Engineers of the Center and Post-Graduate Students Ch. V. Khazhyylay, A. R. Umarov, A. M. Yanbekov and M. A. Kosyreva, and NITS IGD CEO A. S. Pozolotin in this study.

Precise grading of surrounding rock based on numerical calculation of jointed rock mass

In this study, grading of surrounding rock was based on rock mass basic quality (BQ) according to Chinese specifications. A numerical approach was used to construct a synthetic rock mass model (SRMM) to represent the jointed rock mass and then obtain the strength of the rock mass. To construct a discrete fracture network, intact rock was represented by the bonded particle model and joint behaviour was represented by a smooth joint model. In a case study (Hongtuzhang tunnel), the micro properties of granite cores with different degrees of weathering were determined and the representative elementary volume of the surrounding rock was set as 15 × 15 m. Five slightly weathered, three slightly to moderately weathered and two moderately weathered granite surrounding rock mass models were established based on the probability distribution of joint sets in each borehole, and the conversion BQ value was acquired according to the calculated strength of the SRMM. The surrounding rock grades obtained using geological surveys were found to be higher than those predicted by the numerical method. The numerical calculation was consistent with actual excavation of rock mass at a borehole.

Calculation of blast hole charge amount based on three-dimensional solid model of blasting rock mass

The development and use of intelligent drilling rigs make it available to obtain accurate lithology data of blast drilling. In order to make full use of drilling data to improve blasting efficiency, the following research was carried out. First, a database is established to manage and store the blast hole data recognized by the intelligent drill. Secondly, the blast hole lithology data is taken as a sample, and the inverse distance square method is used to interpolate the blasting range's solid elements to generate a three-dimensional solid model of the blasting rock mass. Afterward, the blasting range polygon and stope triangle grid are used successively in the solid model to obtain the cut 3D solid model of the blasting rock mass; finally, the blast hole charge is calculated based on the cut 3D solid model of the blasting rock. The C++ programming language is used to realize all the blast hole charge amount processes based on the three-dimensional solid model of the blasting rock mass. With the application example of No. 918 bench blasting of Shengli Open-pit Coal Mine in Xilinhot, Inner Mongolia, the blast hole charge amount in the blasting area is calculated and compared with the results of single hole rock property calculation, the results show that the blast hole charge calculated by three-dimensional rock mass model can be effectively reduced.

Numerical Modeling of Frozen Rockmass and Its Stress State in Sinking

Numerical Modeling of Frozen Rockmass and Its Stress State in Sinking

Numerical study of the effect of rock anisotropy on stresses around an opening located in the fractured rock mass

The fractured rock mass is a discontinuous, heterogeneous, anisotropic medium in nature, including single, multiple or a network of joints with regular or irregular patterns located between the intact rocks. Anisotropy, as an inherent feature of rock mass, is a factor that causes the mechanical properties of rock to be various in different directions, so it is very important and necessary to be considered in the design of rock engineering structures. This study aims to investigate the effect of rock anisotropy on induced stresses around an opening like a borehole located in the fractured rock mass. For this purpose, the combination of discrete fracture network (DFN) method to construct a geometric model of rock mass, with distinct element method (DEM) to the numerical analysis of stress, was used. All coupled DEM-DFN models were developed based on the field data of the rock and joint system of the Sellafield site in the UK. The discrete fracture network models with different degrees of anisotropy, including a circular opening with two different cross-section areas placed at the center of model, were used for stress analysis. In each type of model, by applying different boundary conditions, the magnitude of induced stresses at selected points around opening is calculated, and then the obtained results are compared with the Kirsch method as a popular closed-form solution. The numerical results of this study showed that the presence of irregular joints with different orientations in the model caused anisotropy in the magnitude of induced stresses obtained around the opening. This is an important issue that the Kirsch method is not able to consider in the calculations. • Fractured rock mass is a discontinuous, heterogeneous and anisotropic medium including network of joints with the stochastic pattern located between intact rocks. • Anisotropy is a factor that causes the mechanical properties of rock to be various in different directions. • Coupled DEM-DFN models are developed to numerical analysis of stress around a borehole. • Presence of irregular joints with different orientations caused anisotropy in the amount of induced stresses around the borehole.

Quantifying strength and permeability of fractured rock mass using 3D bonded block numerical model

In this research, a 3D bonded block model (BBM) is applied to numerically quantify the strength and permeability of fractured rock mass. The reliability of the BBM is initially verified through comparisons between conceptual models and theoretical and laboratory results. A series of rock mass models incorporating complex fracture networks is then constructed, and the strengths are quantified accordingly. The rock mass is weakened when low fracture stiffness and friction angle are assigned, and steep fractures are simulated. In both cases the low strength is attributed to the decreasing frictional resistance of the initial fractures. The rock mass is further weakened when more persistent fractures are simulated, in which the weakening effects of the fractures are amplified. The numerical models are compared with the widely used Hoek-Brown strength criterion. The strengths resulting from the two methods converge only when steep and less persistent fractures are simulated. Numerical simulations also suggest that in general, the permeability is positively related to the strength for rock masses that are impermeable in the pre-peak loading stage. In such cases additional flow paths are formed and attributed to failed rock bridges. The research works provide new options to quantify the strength and permeability of fractured rock mass, and offer opportunities to examine relations between these parameters.

Investigation of Deep Shaft-Surrounding Rock Support Technology Based on a Post-Peak Strain-Softening Model of Rock Mass

To control the large deformation that occurs in deep shaft-surrounding rock, the post-peak strain-softening characteristics of deep jointed rock mass are discussed in detail. An equivalent post-peak strain-softening model of jointed rock mass is established based on continuum theory and the geological strength index surrounding rock grading system, and numerical simulations are performed using FLAC3D software. The convergence-constraint method is used to analyze the rock support structure interaction mechanism. A composiste support technique is proposed in combination with actual field breakage conditions. During the initial support stage, high-strength anchors are used to release the rock stress, and high-stiffness secondary support is provided by well rings and poured concrete. This support technology is applied in the accessory well of a coal mine in Niaoshan, Heilongjiang, China. The stability of the surrounding rock support structure is calculated and analyzed by comparing the ideal elastic-plastic model and equivalent jointed rock mass strain-softening model. The results show that a support structure designed based on the ideal elastic-plastic model cannot meet the stability requirements of the surrounding rock and that radial deformation of the surrounding rock reaches 300 mm. The support structure designed based on the equivalent joint strain-softening model has a convergence rate of surrounding rock deformation of less than 1 mm/d after 35 days of application. The surrounding rock deformation is finally controlled at 140 mm, indicating successful application of the support technology.

Characterization and Modeling Study on Softening and Seepage Behavior of Weakly Cemented Sandy Mudstone after Water Injection

Water injection-induced rock softening and the associated water seepage characteristics are the common and basic problems in underground reservoir construction and the prevention of mine water disaster. In this paper, a series of experimental studies was carried out to investigate these characteristics with the weakly cemented sandy mudstone collected from Shendong Buertai coal mine, China. The characteristics of water softening and the stress-seepage interactions in water-saturated weakly cemented sandy mudstone were directly obtained. Then, a modification method of the constitutive model for rock mass considering the softening effect and a stress-damage-driven model for permeability evolution were established. Research results show that water saturation reduces the tensile strength, compressive strength, and cohesion by 56% and reduces the elastic modulus by 28%. The hydraulic effects on Poisson’s ratio and internal friction angle are negligible. The relationship between the permeability of weakly cemented sandy mudstone with complete compaction deformation is to be divided into three stages of seepage shielding, seepage surge, and seepage recovery. Rock permeability in each stage has a negative exponential relationship with the effective stress. This research provides a theoretical basis for the researches of hydromechanical couplings on weakly cemented sandy mudstone, which is insightful for rock engineering practice.

Variable Weight Matter–Element Extension Model for the Stability Classification of Slope Rock Mass

The slope stability in an open-pit mine is closely related to the production safety and economic benefit of the mine. As a result of the increase in the number and scale of mine slopes, slope instability is frequently encountered in mines. Therefore, it is of scientific and social significance to strengthen the study of the stability of the slope rock mass. To accurately classify the stability of the slope rock mass in an open-pit mine, a new stability evaluation model of the slope rock mass was established based on variable weight and matter–element extension theory. First, based on the main evaluation indexes of geology, the environment, and engineering, the stability evaluation index system of the slope rock mass was constructed using the corresponding classification criteria of the evaluation index. Second, the constant weight of the evaluation index value was calculated using extremum entropy theory, and variable weight theory was used to optimize the constant weight to obtain the variable weight of the evaluation index value. Based on matter–element extension theory, the comprehensive correlation between the upper and lower limit indexes in the classification criteria and each classification was calculated, in addition to the comprehensive correlation between the rock mass indexes and the stability grade of each slope. Finally, the grade variable method was used to calculate the grade variable interval corresponding to the classification criteria of the evaluation index and the grade variable value of each slope rock mass, so as to determine the stability grade of the slope rock. The comparison results showed that the classification results of the proposed model are in line with engineering practice, and more accurate than those of the hierarchical-extension model and the multi-level unascertained measure-set pair analysis model.

Sampling and Distribution Parameter Analysis for Estimating Three-dimensional Fracture Orientation Distributions from a Circular Sampling Window

Precise evaluation of three-dimensional (3D) fracture orientation distributions is vital to a reliable discrete fracture network (DFN) model for rock mass. This study analyzed the accuracy and dispersion of the evaluated orientation distributions of fracture sets with different fracture geometric parameters. The geometric probability method by two-dimensional (2D) trace data is introduced and compared with the three methods of the Terzaghi family by one-dimensional (1D) orientation data. The Monte Carlo method generated many groups of 3D fracture networks to analyze the influence of uniform orientation distribution, average fracture diameter, and volume density on the evaluated orientation distributions. The results indicated that the piecewise distribution increases the computational complexity of the geometric probability method. This method can be used to effectively evaluate the orientation distributions of fracture sets with an average diameter greater than 0.25 m and volume density greater than 0.2 m−3.

Block cutting and searching method of fractured rock mass based on topological matrix

Aiming at the problem of block cutting and searching in fractured rock mass, a method of block cutting and searching in fractured rock mass based on topological matrix is proposed. According to the structural characteristics of fractured rock mass, the data structure of the model is established, which only contains node coordinates (vectors) and a numbering system; the line segments are divided into line segment units, which only intersect at the boundary by the algorithm of line segment intersection and discretization. The number matrix describing the topological relationship of points and lines system is constructed with the intersection and line segment as the core. According to the number matrix and geometric characteristics of spatial line segments, the number matrix for block search is obtained by cutting a non-closed polygon; without any geometric operation, only the index of the number in the matrix is used to search the blocks and form a seamless rock mass model; according to the spatial relationship between the clipped line segment and the block, the block reflecting the internal fracture is generated to form the final fractured rock mass model. Results indicate that this method can identify the distribution of complex blocks and their internal joints and fissures. It also has a great application prospect in the analysis of fractured rock mass.

Study on evolution process of water inrush disaster of tunnel based on the distinct element method

On the basis of the analysis of the geological characteristics of the construction adit of a water diversion project, in conjunction with the phenomena of water gushing, mud bursting and collapse encountered in the construction process of the tunnel, the fracture network model of the typical rock mass in the project area is established. Based on the seepage stress coupling mechanism of the fractured rock mass, the UDEC discrete element method is used to analyze the gradual development process of the surrounding rock fractures in the excavation process of the tunnel. The dynamic evolution law of tunnel water inrush is revealed, which could provide a good reference for the safe construction of underground engineering in water rich area and the design and control of surrounding rock stability.

Micromechanical thermo-hydro-mechanical coupled model for fractured rocks considering multi-scale structures and its engineering application

Most existing studies on the coupled thermal-hydro-mechanical models for fractured rock mass are formulated using the macroscopic phenomenology method. As a result, the micromechanical behaviors of discontinuities, which essentially control the macroscopic response of the material, are not well considered in modeling the thermal-hydro-mechanical coupling processes for disturbed rock mass. In this study, the fractured rock mass is characterized by an anisotropic medium containing arbitrarily distributed penny-shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of large scales. This is an anisotropic coupled thermal-hydro-mechanical model for deformed saturated rock masses, which is capable of considering the alteration of macro-meso discontinuities. A multiscale damage constitutive model for fractured rock mass with the thermal-hydro-mechanical coupling is presented based on the Mori-Tanaka homogenization method and the thermodynamics theory. The influences of anisotropic damage growth, sliding dilatancy and normal compression of small-scale microcracks, and shear sliding and mobilized degradation of large-scale fractures are commendably accounted for. To reflect the anisotropic strength, the interaction between large-scale fractures and small-scale microcracks is also considered by practically relating the microcracks damage resistance to the orientation of fractures. By capturing the deformation of fractures and the opening and connectivity variations of microcracks with the constitutive model, the multi-scale structural change-induced permeability variation is modeled by the volumetric averaging method. The constitutive model and permeability tensor formulation have been implemented in a FEM code, which is then coupled with the well-established non-isothermal fluid flow simulator TOUGHREACT by an interlaced algorithm to establish a coupled thermal-hydro-mechanical numerical simulation platform. A numerical example is finally performed to investigate the effects of multi-scale structures and thermal-hydro-mechanical couplings on the water injection-induced temperature, pressure, and deformation responses of a deeply buried geothermal reservoir. The research may provide a useful reference for deepening the study of the thermal-hydro-mechanical couplings in deep rocks.

Multiscale damage constitutive model of jointed rock masses based on the influence of crack initiation

A rock mass has a large number of macroscopic and microscopic defects, such as joint cracks and microcracks, which greatly affect its physical and mechanical properties. In this study, a multiscale elastoplastic damage model was proposed to describe the influence of the existence and evolution of two types of cracks on rocks. The macroscopic damage variable expressed by the stress intensity factor was derived on the basis of damage mechanics and fracture mechanics and regarded as a piecewise function with initiation stress as the dividing point. The rock was divided into two parts based on micromechanics: matrix and microcracks. The macroscopic damage was considered the deterioration of the mechanical properties of the rock matrix. Under the framework of thermodynamics, a constitutive model that could reflect the growth of macrocracks and the friction–damage coupling of microcracks was constructed. This model could reflect the physical mechanism of macroscopic and microscopic damage of jointed rock masses, so the physical parameters of the model had clear meanings. Lastly, the rationality of the model was verified via uniaxial compression tests of rock-like materials with a single flaw of different inclination angles.

A discrete element modeling of rock and soil material based on the machine learning

The discrete element modeling of rock and soil mass usually relies on tedious parameter adjustment and mechanical property testing operations to obtain appropriate mechanical parameters of the element. In this paper, based on the linear elastic contact theory, a discrete element model of rock samples was established based on discrete element software MatDEM with high-performance numerical analysis, and the actual mechanical properties of the model samples were predicted using a machine learning method, XGBoost algorithm. A certain amount of sample data sets was generated, and through numerical experiments, training, validation and test operation of the rock mechanical properties (compressive strength, Young’s modulus, Poisson’s ratio and tensile strength), the numerical model quantitative relationship between the actual and input mechanical properties was explored, showing the following results: (1) Based on the characteristics of the model 12000 rock samples and correlation analysis, the tag data shows that the input mechanical properties are positively correlated with the actual mechanical properties;(2) With the increase of the number of samples in the sample training data set, the training average error becomes smaller and smaller, and the error distribution becomes more and more stable.(3) The training results converge to the set threshold, and the prediction errors of mechanical parameters are all less than 4%, and the error distribution is stable, which proves that the machine learning method can quickly and accurately establish the rock model with specific mechanical properties.

Extraction of the discontinuity orientation from a digital surface model

The traditional field contact measurement for obtaining parameters of the rock mass discontinuity is of low efficiency and big workload, and the accuracy of the results are affected by human factors. In this paper a method is presented to automatically recognize the discontinuity based on the 3D digital surface model of rock mass obtained with the digital photogrammetry and SFM algorithm. The steps of rock mass DSM reconstruction include collecting rock mass images, matching image features based on the SIFT algorithm, reconstructing sparse point cloud, encrypting point cloud, and reconstructing the rock mass surface model. The main flow of the discontinuity recognition method include smoothing the DSM of rock mass, changing the searching radius and the angle threshold to split model plane, searching the discontinuity based on the regional growth principle, and fitting the discontinuity based on random sampling consistency to get the orientation. The method is applied to the underground experimental roadway in the Beishan area of Gansu, and the reconstruction of 3D digital surface model of roadway and the orientation acquisition of discontinuities are realized. The discontinuities are also mapped on the roadway model by groups. A comparison the results with those of the manual field measurement method and the existing discontinuity recognition software shows that the method proposed in this paper is of good accuracy and can provide a certain reference for engineering applications.

Development of Equivalent Stress- and Strain- Dependent Model for Jointed Rock Mass and Its Application to Underground Structure

Current design methods for underground structures surrounded by jointed rock masses fail to account for the deformational characteristics of these surrounding rock masses, employing only input parameters that are defined prior to construction. Thus, there is the need to investigate the effects on underground structures that result from the deformational characteristics of jointed rocks that undergo stress relaxation during their excavation. Comprehensive research is conducted in this study. First, we propose an equivalent stress- and strain-dependent model incorporating equivalent stiffness at small strains into a hyperbolic model from intermediate to large strains. Then, experimental tests are conducted to characterize the deformational characteristics of jointed rock masses and extract requisite model parameters such as joint properties and nonlinearity. Finally, two numerical simulations are conducted using the proposed model to determine its field applicability to an unlined circular tunnel. The nonlinear simulation results are compared with the conventional analysis method that uses a constant stiffness value. Our results show that the proposed equivalent jointed rock mass model, which considers stress-and strain-dependency, can be utilized for deformational analysis of underground structures involving excavations in jointed rocks.

2D- and 3D-FEM modeling of rock masses at the Şilenkar viaduct site (NE Turkey) with regard to bearing capacity

2D- and 3D-FEM modeling of rock masses at the Şilenkar viaduct site (NE Turkey) with regard to bearing capacity

The numerical modeling of heterogeneities by the finite element method in 3D setting

The paper proposes a variant of the algorithm for 3D numerical simulation of the rock mass stress-strain state in the vicinity of structural heterogeneities by the finite element method. Modeling of the stress-strain state is used, among other things, when analyzing the fractures in the rock mass, which can occur as a breakage or a shear along the weakening planes. The rock massif has a block structure, where the boundaries of various-scale blocks are structural disturbances of different orders. The surface planes of structural heterogeneities usually have complex geometry and spatial orientation, so the most adequate results can be obtained by 3D modeling of the disturbed rock mass. Besides, it is important to take into account the type of the stress-strain state, which can be not only gravitational, but also gravitational-tectonic, including horizontal loading of the rock mass. Accounting these features allows obtaining the most adequate geomechanical model of the studied object. For this purpose, the authors have studied and analyzed the existing approaches to modeling heterogeneities in the rock mass, including using the Goodman contact element, and developed its 3D modification. A mining engineer needs to have a handy tool that allows creating and editing a geomechanical model, taking into account mining plans and related sections. The model navigation, edition of its individual blocks to specify geology and creation of local sub-models make it necessary to use structured meshes of finite elements. Modification of the model with the introduction of contact elements entails the creation of an unstructured mesh, which complicates further manipulations with it. To solve this problem, a special zero element was developed, which allows saving a structured mesh format when implementing a contact element. This zero element, like the contact element, has zero thickness, and its nodes have averaged strength characteristics of adjacent blocks of the undisturbed rock mass. The result of these studies is a tool that allows creating 3D models of the rock mass stress-strain state, taking into account its structural heterogeneities and preserving the regular structure of the finite element mesh.

The role of numerical analysis in the study of the behaviour of hard-rock pillars

Rock pillars can be defined as the in-situ rock between two or more underground openings. However, one aspect that is seldom considered in analysis of hard rock pillars, and indirectly in synthetic rock mass models to determine rock mass strength, is the actual stress level and stress path imposed on the pillar due to the excavation sequence and the location of the pillars within the mine lay out. In this paper we propose to use numerical stress analysis to determine how stresses vary across the excavated pillars in a typical room-and-pillar mine lay out, and thus generate a spatially variable determination of pillar stability. Because of the computational difficulty associated with hybrid modelling of realistic discrete fracture networks, synthetic rock mass modelling is commonly carried out using a 2D approach. By comparing 3D and 2D results for selected cross-sections across, we believe the results of the analysis will provide the opportunity to better constrain the stability implications of a 2D approach to pillar design and synthetic rock mass modelling.