State Of Rock Mass Research Articles

Strength anisotropy of jointed rock slope considering mining damage: a numerical analysis method

A combination of Hoek–Brown strength criterion and geological strength index (GSI) rock mass classification is a common method to determine rock mass strength. However, the conventional method involving the determination of disturbance coefficient (D) cannot reflect the anisotropic characteristics of strength of jointed rock mass when considering mining damage. A numerical analysis method is proposed to determine the value of D using jointed rock damage tensor and mining damage evolution simulation. The anisotropy of rock mass strength at different mining depths for a high jointed rock slope in Dagushan open-pit mine was analyzed by mining damage simulation. Additionally, the Rosenblueth moment point estimation principle was combined with Monte-Carlo method to obtain the random strength of a jointed rock mass considering the effects of mining probability damage. The results show that the influence of the unloading due to excavation to stress state of rock mass is relatively obvious within 100 m away from the slope surface, however, the area of drastic change of damage is limited to a range of ∼50 m. Moreover, the reliability of local slope, analyzed using limit equilibrium method (Janbu), shows that consideration of spatiotemporal anisotropy of rock mass with mining damage is closer to reality.

Ensuring Wall Stability in the Course of Blasting at Open Pits of Kyzyl Kum Region

Involvement of deep deposits in mining predetermined the trend of development of open pit mining towards increasing the depth of open pits. The main limitation imposed on drilling and blasting in the near-contour zone of an open pit is the need to protect the pit walls and engineering structures on the walls from seismic effects of huge blasts. As practice shows, the most effective and proven method of protecting pit walls is the use of blasting by presplitting method, creation of a shielding gap and a shielding layer of blasted rock mass, i.e. pre-splitting of the pit walls, preceding the huge blast. Therefore, the study of stress-strain state of the near-contour rock mass, determination of the parameters of blastholes for edge pre-splitting (preliminary shielding gap formation) in open pits is an urgent task. The analysis of the pit wall design and stress-strain state of rock mass at Kokpatas deposit exploited by Navoi Mining and Metallurgical Combine allowed to determine the model, as well as the method for calculating stress-strain state of the rock mass. When assessing stability of the pit walls, an approach known as the displacement method was used. Applying the boundary integral equations method allowed to develop an algorithm for calculating stresses in the rock mass for the conditions of Kokpatas deposit. A technique has been developed for experimental studies of blasting contour blasthole charges (blasting by pre-splitting method) using models, allowing to study fracturing on volumetric models and wave interaction by the method of high-speed video recording of the blasting process in transparent models, as well as to determine the parameters of stress waves during blasting in samples of real rocks. A method for formation of stable pit wall slopes, an excavator method for bench pre-splitting on ultimate envelope (contour) of a pit, and a method for initiating blasthole charges in the near contour zone of a pit have been developed and implemented in the industry.

Brazilian disc test study on tensile strength-weakening effect of high pre-loaded red sandstone under dynamic disturbance

Tensile failure (spalling or slabbing) often occurs on the sidewall of deep tunnel, which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance. To reveal the mechanism of rock tensile failure caused by this coupled stress mode, the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic disturbance. Based on the pure static tensile fracture load of red sandstone specimen, two static load levels (80% and 90% of the pure static tensile fracture load) were selected as the initial high pre-static loading state, and then the dynamic disturbance load was applied until the rock specimen was destroyed. The dynamic disturbance loading mode adopted a sinusoidal wave (sine-wave) load, and the loading wave amplitude was 20% and 10% of the pure static tensile fracture load, respectively. The dynamic disturbance frequencies were set to 1, 10, 20, 30, 40, and 50 Hz. The results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load, and both parameters decrease significantly with the increase of dynamic disturbance frequency. With the increase of dynamic disturbance frequency, the decrease range of tensile strength of red sandstone increased from 3.3% to 9.4% when the pre-static load level is 80%. While when the pre-static load level is 90%, the decrease range will increase from 7.4% to 11.6%. This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic disturbance. In this tensile failure mechanism of the deep surrounding rock, the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure, the pre-static load level dominates the tensile failure strength of surrounding rock, and dynamic disturbance promotes the strength-weakening effect and affects the weakening range.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ УСТОЙЧИВОСТИ БОРТОВ УГОЛЬНЫХ РАЗРЕЗОВ ПОД ДЕЙСТВИЕМ РАСПРЕДЕЛЕННЫХ НАГРУЗОК

The open method of solid minerals winning occupies a significant place in the total opening of the mining complex deposits of the Republic of Kazakhstan. In the energy band, a prominent role belongs to the Ekibastuz coal basin, where a number of large coal strip mine operates. The level of subsurface, equal parts of spoil bank of the external and internal stripping after a while lead to complex problems of ensuring the stability and safety of mining operations. The location of large external rock dumps on the bead surface has a negative effect on the stability of the latter. The purpose of the work was to establish the degree of the external rock dump influence located on the bead surface on the stability of adjacent rock mass of the coalmine depending on the distance of the dump to the upper edge of the side. There was numerical simulation of stress-strain state of adjacent rock mass under action of distributed load from rock dump carried out. It has been shown that studies of any point stability of the array from this type of load should be carried out on the basis of elasticity and the use of the finite element method theory implemented in packages of programs oriented specifically to scientific and engineering applications. There are the methodology and results of numerical modeling of quantitative assessments of various sections stability of the side loaded with an external rock dump with a height of 160m presented on the example of «Ekibastuz» coal mine. Based on a certain theory of rock strength and the criteria for their discontinuity, limit estimates of the critical distance of the external rock dump from the upper edge of the side were obtained, at which the latter may lose stability.

The Principle of Invariant Stress of the Surrounding Rock of the Hole under the Condition of Equal Pressure in the Deep Rock Mass

Based on the hydrostatic pressure theory of initial stress state of rock mass, combined with Saint-Venant’s principle central idea, the principle of invariant stress of surrounding rock mass of the hole under the condition of equal pressure in deep rock mass is put forward. Numerical simulation is used to study the properties of surrounding rock and section shape of different holes, the depth of the plastic zone, the range of stress influence, and the relationship between them. The study results showed the following. (1) In the current mining depth range, it is difficult to reach the limit of 5 times the hole radius under the condition of invariant pressure of deep rock mass, and it has a significant impact on the near field and relatively small impact on the far field, reflecting the localization effect of the stress influence range. (2) The increase of stress influence range mainly moves outward with the increase of plastic zone range, and its growth slope is low and tends to be horizontal, and the increase amount is negligible. (3) When the failure range of the plastic zone of the hole is small, the influence range of the stress does not change itself, which reflects the stress invariability of the small-scale failure of the surrounding rock of the hole. The research results verify the principle of stress invariability of the surrounding rock of the hole under the condition of equal pressure of the deep rock mass, which is consistent with Saint-Venant’s central idea.

CALCULATION OF THE GEOMECHANICAL STATE OF MINE WORKING SUPPORT AND SURROUNDING ROCK MASS IN CONDITIONS OF MINING ORE DEPOSITS IN EAST KAZAKHSTAN

The statement of the problem of determining the stress-strain state of support and rock mass around the mine working in unstable rocks, in case of voids filling with phenol resins is proposed. The initial parameters used in the calculations correspond to the conditions of mining ore deposits in East Kazakhstan. The distribution character of stress fields in the support and their change depending on geometric sizes of the area filled with phenol resins is determined. It is shown that using phenol resins causes formation of a uniform pressure of surrounding rocks on the arch part of the support and facilitates an increase in its stability.

Information technologies of geomechanical events integrated simulation

Introduction. Neither national nor foreign practice can guarantee high-quality assessment of enclosing rock mass state and reliable substantiation of rational geomechanical solutions. It is confirmed by actual accident and breakdown rates including catastrophic force majeure. So, current methods of geomechanical analysis need principal improvement. Research aim is to develop information technologies of integrated deterministic stochastic modeling within the system of assessing and ensuring the quality of geomechanical solutions, which is the set of interconnected estimates and indicators, such as efficient, available, reliable and adequate information on enclosing rock mass properties and state, compliance with the requirements of normative documents, geomechanical risks rates by the factors of breakdown, accident and environmental hazard factors, potential damage from risk aftermath, financial receipts and expenses which include dominant functions of potential damage and monitoring effectiveness. Methodology. Research has been carried out based on the simulation builder, basic software aimed at design, checkout and probation of new integrated deterministically stochastic models of geomechanical events. The models fulfill research, training and demonstration functions, reserve modeling process and output, simulation errors and drawbacks elimination by Monte Carlo method. The main feature of the builder is the availability of interconnected components, determination and simulation. Such complex provides the researcher with important complementary information: deterministic method fulfills safety functions and determines analysis results non-contradiction to the requirements of normative documentation; probabilistic method ensures objective evaluation of geomechanical risks or safe features with the possibility to obtain clear effectiveness by the factors of economic and social security, eliminates or significantly reduces the probability of unnecessary expenses. The universality of the approach to creating information technologies of geomechanical solutions simulation which implement the deterministic simulation complex based on the methods of nonparametric statistics is confirmed by the instances of simulation in multivariate statement. The scope of the investigation includes mine engineering structures of construction, open, integrated technologies of mining enterprises and specific underground development targets in various sectors of national economy. Summary. Information technologies of geomechanical events simulation based on the complex of deterministic and simulation methods and the procedures of nonparametric microstatistics make decisive contribution in the system of assessment and ensuring the quality of geomechanical solutions. The universality of IT development is noted together with their availability for a wide range of users, their simplicity and implementation efficiency

Two cases of post-limit deformation of rock mass surrounding underground opening

The authors analyze stress state of rock mass around an underground opening in two cases of post-limit plane-strain deformation: when the modulus of compression is much higher than the modulus of post-limit deformation and when the modulus of post-limit deformation is much higher than the modulus of compression. In the first case, the damage zone sizes are obtained depending ultimate elastic strains and strength of rocks. In the second case, the solution in the rock damage zone differs from the traditional elastoplastic solutions by the increase in the maximum shear strength with distance from the boundary of underground opening.

Stress state of underground opening support considering its interaction with rock mass

This study addresses stress state of support systems in underground mine openings when the boundary of an opening is incompletely relaxed from forces commensurable with the initial stress state of rock mass. The calculation algorithm is based on the stiffness matrix composed of mechanical characteristics of intact rock mass. The features of the stress state of underground mining opening support in various modes of deformation of the opening boundary are determined.

Newest Tectonics and Modern Geodynamics of Mining Industrial Areas of Central Kazakhstan

The rapidly developing mining industry in the territory of Central Kazakhstan leads to emergence of near the areas of active mining of tangible earthquakes of technogenic genesis, which creates difficulties in their operation. Displays of irreversible changes in the state of rock mass with the development of new structures, active faults. The features of the formation of potentially dangerous areas of the occurrence of seismicity. We have considered one of the major factors the features of modern tectonics and modern geodynamics of ore-industrial facilities in Central Kazakhstan.The shield of the young platform is a wide area protrusion of the basement of the epigercina platform, adjoining mountain-building area in the southeast, and in all other directions sinking under Mesozoic-Cenozoic deposits. Geomorphologically it is a vault, complicated by increases of a higher order with contrastingly expressed tectonic layers. The seismic events were concentrated on the boundaries of the active of passive blocks of the earth’s crust of Neogene-Quaternary tectonic activity of the Kazakh shield.The active impact on the geological environment of industrial explosions will change the geodynamical activity and as consequence occurring technogenic earthquakes in the fields of central Kazakhstan.

Assessment of stability of the enclosing rocks of Kupol Deposit based on the analysis of their fundamental physical and mechanical properties (Chukotka Autonomous Okrug, Anadyr District)

The object of this research is the examination of stability of volcanogenic-sedimentary and effusive rocks in the mine workings of Kupol Deposit. The subject of this research is the analysis and assessment of the physical and mechanical properties of these rocks in the solid, considering the intensity of fracturing and the degree of their water content, using the indicators developed by Professor N. S. Bulychev and Professor G. L. Fisenko. The data acquired in real assessment of the state of rock mass prove the choice of applied ground support at Kupol mine. Research methodology is based on the analysis of structural-tectonic peculiarities of Kupol deposit, which defines the high degree of disintegration of complex set of rocks and dictates the need for development of staging approach towards characterization rock stability in mines – from the samples to the full array. The scientific novelty lies in the fact that this work is first to implement phasic approach towards evaluation of stability of the rocks in Kupol mine for transition from the results of laboratory studies of rock samples to assessment of their actual behavior during the exploration of the deposit in severe mining, geological and hydrogeological conditions. It is noted that the Deposit is associated with the volcano-tectonic depression of the Okhotsk-Chukotka volcanic belt, complicated by younger volcanogenic tectonic activity, and is located in the zone of the Middle Kayemraveemsky fault of 1st level of latitudinal outstretch. Analysis is conducted on the implemented system of field development in complex mining and geological conditions.

Research methods for seismoacoustic monitoring of large underground facilities

Large underground mine workings of hydropower facilities created in complex engineering-geological and seismic conditions significantly differ from industrial underground facilities designed for different purpose in their construction, operation and operating conditions. This makes it extremely urgent to organize seismic-acoustic monitoring in order to ensure their safe and reliable operation and prediction of the status of the underground circuit. The solution of this problem requires the improvement of methods and techniques for field observations of the operation of underground structures during construction and operation. In this paper, we formulate the basic principles of the organization of seismic-acoustic monitoring of the rock mass state that contain mine workings. We propose system of seismic-acoustic monitoring of a complex of underground structures, for example, the underground circuit of the Rogun HPP, which is under construction. The paper presents the field observation technique using seismoacoustic methods: seismic transmission and profiling, seismic well logging, acoustic emission method for concrete and boreholes, dynamic response method for assessing the quality of concrete-rock contact, ultrasonic well logging, ultrasonic studies of rock samples and concrete structures. Effective qualitative and quantitative parameters have been determined, which make it possible to assess the degree of change in physical parameters in the internal parts of rock massifs that occurs under the influence of natural and technogenic factors. This is done in order to assess ultimate strain levels and to find indicators of the critical state of the geological environment in problem areas.

Classification Method for Surrounding Rock of Highway Tunnel Based on Quantization of Tunnel Face Structure

By studying tunnel face images collected during a highway tunnel excavation,we establish the classification system of photolithography by MATLAB programming. According to the rock mass index (rock block size index or RBI) concept,19 virtual lines are arranged in turn to the tunnel contour line,and the difference of the brazier rock mass structure is evaluated synthetically by 19 RBs of the radial direction of the face. Based on the structure,the distribution of comprehensive index of the rock mass structure (Z-RBI) is obtained through a comprehensive evaluation of the rock surface,and the corresponding relationship between the Z-RBI and rock structure type is determined. Considering the hardening degree of rock mass,the Z-RBI,groundwater condition,and initial geostress state,we propose the BP classification method for tunnel rocks,and we evaluated the BT method by using the analytic hierarchy process standard in an actual project. The comparison of the BT classification method and traditional BQ method reveals that the result of the former is more in accordance with the actual level of the excavated rock face than that of the latter method.

Оценка удароопасности при освоении глубоких горизонтов Николаевского месторождения

The paper presents results of conducted research using regional and local methods of forecast and control over geomechanical state of the rock mass at burst-hazardous Nikolayevskoye field, located in a geodynamically active region. The study subject is the ore mass of Nikolayevskoye field, characterized by man-induced and tectonic disturbances and high geodynamic activity. The aim of research was practical implementation of methods and instruments of forecast and control over geomechanical state of the burst-hazardous rock mass and safety improvement of mining operations. Exploitation practice of burst-hazardous fields demonstrates that forecast accuracy of hazardous rock pressure demands cutting-edge multi-level systems, where local methods and tools complement regional ones. A regional forecast of rock-burst hazard at Nikolayevskoye field was performed by means of seismoacoustic method using automated control system for rock pressure (ACSRP) «Prognoz-АDS». Local forecast was carried out using «Prognoz-L» device, geophysical (sample disking) method and visual observations of dynamic pressure manifestations in the mining tunnels. Quality assessment of stress-strain and burst state of the rock mass was performed using specialized software «PRESS 3D URAL». Integration of engineering and geomechanical data in the process of conducting research guarantees a relevant assessment of rock-burst hazard in various areas of the field at various stages of its development. Practical verification of the system, where local methods and tools complement regional ones, demonstrated satisfactory results at Nikolayevskoye mining plant, which makes it recommendable for other mining facilities extracting ore at great depths under similar conditions of active geodynamic processes.

Evaluation of stress state in rock mass surrounding underground structures of waterworks

Using the data of the numerical modeling of stress state in rock mass surrounding deep-level structures of waterworks, the author finds regular patterns and specific features of stress distribution under stage-wise underground construction. It is shown in the paper that as cross-section of an underground structure is enlarged, inelastic strain zones arise nearby the structures, and parameters of these zones are determined.

Stress state of rock mass during stoping under pit bottom in the presence of slide rocks on the pit bottom

The article studies influence of slide rocks on the bottom of Internatsionalny open pit mine on stress state of rock mass during stoping under the pit bottom. The stress distribution during extraction of ore reserves from the initial layer under the pit bottom is determined. The post-limiting deformation zones in ore body during formation of a crown pillar are delineated using the Mohr–Coulomb criterion. The authors give a predictive estimate of alteration in stress state of the crown pillar with the advance of stoping.

FEM simulation of deformation of self-stress rock mass with disjunction nearby a tunnel

In the work the constitutive equations which allow to describe the structurally inhomogeneous rock mass taking into account the property of rocks to accumulate and release elastic energy, are applied. The finite element algorithm and programs for solving plane boundary-value problems are developed. The authors solve a problem on deformation of rock mass with a disjunction surrounding a tunnel. It is shown that driving of horizontal tunnel nearby the disjunction can provoke the accumulated elastic energy release, which affects stress-strain state of rock mass around the tunnel

A step-by-step analytical procedure to estimate the in-situ stress state from borehole data

Knowledge of the in situ stress state of rock mass is fundamental for engineering, geological and geophysical applications. In situ stress state determination requires in principle the evaluation of the three principal stresses and the related principal directions, but it is widely recognized in the literature that the maximum horizontal stress is the most difficult component to accurately estimate. In the context of borehole methods, this paper proposes a step-by-step analytical procedure to estimate some bounds to the maximum horizontal stress, starting from a geomechanical description of the rock and relying on information generally available in the engineering practice. The procedure is divided in substeps, each one requiring additional information about the mechanical properties of the rock and on the geometrical properties of the failed portion of rock: more information available implies a lower uncertainty on in situ stress estimate. Furthermore, since the proposed procedure is analytical, it allows a complete and very easy implementation in a spreadsheet. The aim of the work is thus to provide a rigourous but simple analytical tool that can be used in engineering practicte to estimate some bounds to the maximum horizontal in situ stress state. The approach is finally validated by means of both numerical simulations, performed with a sophisticated numerical tool, and experimental field data coming from the literature.

Influence Zone Division and Risk Assessment of Underwater Tunnel Adjacent Constructions

Compared with ordinary tunnels, the influence analysis of underwater tunnel adjacent constructions is more complicated. At present, the empirical method used to divide the influence zone of the tunnel adjacent constructions has great uncertainty. So it is of great significance for actual construction and design to determine the influence zone accurately according to theoretical calculations. In this paper, based on the Hoek–Brown nonlinear failure criterion of rock mass and taking seepage factor into account, the stress state of rock mass around the underwater tunnel adjacent constructions can be deduced by elastoplastic theory. Then combined with the concept of “loose zone-bearing zone”, the influence zone division method of underwater tunnel adjacent constructions is proposed, and it is applied to the analysis of engineering examples. Through the deduced theoretical formulas, the influence zone of underwater tunnel adjacent construction can be divided into extensively strong, strong, relatively strong, weak, and noninfluence zones. Corresponding the influence zones with the risk levels in the code, different control measures are adopted for different risk levels, which can provide certain guidance for the design and construction of tunnel in practical engineering.

Experimental Study on Comprehensive Real‐Time Methods to Determine Geological Condition of Rock Mass along the Boreholes while Drilling in Underground Coal Mines

The geological condition is essential for mining design and disaster control in underground coal mines. The present research focuses on the real‐time assessment method on rock mass condition during drilling boreholes. In situ comprehensive experiments were carried out using three methods, which are measurement while drilling (MWD) system, vibration measurement while drilling (VMWD) system, and borehole camera detecting system. In the MWD system, the operating parameters of the drilling machine were recorded, and a dimensionless index Id based on the collected parameters was adopted to assess the geological condition along the borehole. The results show that the state of rock mass can be well classified using the MWD system for both the cross‐layer and in‐seam boreholes. In the VMWD system, the vibration of the drilling bit was monitored, and the signal was analyzed in both time domain and frequency domain. The results indicate that the rock mass condition can be quantitatively evaluated using the mean square value of the signal and qualitatively estimated using the energy of the spectrum. In the borehole camera system, the photos of the rock mass along the borehole could be well captured, and the identified rock mass condition was used to verify the results of the MWD and VMWD systems. Comprehensive compassion between the results from the three systems shows that all the methods can give valuable information for the geological condition, and the outcomes of the different methods are generally comparable. For practical purposes, the advantages of the involved three detecting systems are discussed.