Stability Of Underground Openings Research Articles

Mechanical properties and risk characterization of surrounding rocks containing various blocks of arch-shaped holes under biaxial compression

In most rock engineering, the rock mass was cut into different blocks by natural structural planes, and the stability of underground openings was affected by the type, number, position and mechanical properties of rock blocks. In this study, the biaxial compression tests were conducted using rock-like material specimens with prefabricated arch-shaped holes and different types of blocks, and the failure and crack propagation properties of surrounding rocks were studied. Firstly, the location and danger degree of blocks in rock mass were classified, and the rock block danger analysis (BDA) method was proposed. Secondly, the support effect on the stability of surrounding rocks with different blocks was studied. Then, the deformation, strength, crack area ratio, and debris distribution characteristics of specimens were analyzed. Finally, the reasonable support schemes were proposed for surrounding rocks with different types and sizes of blocks. The test results showed that the σ-ε curve of holed rocks was similar to that of intact rocks, and the micro-cracks evolved into macro-cracks at crack destabilization expansion stage, followed by large deformation of whole specimens and spalling. Under support condition, as the block size increased, the crack area ratio decreased and the stability of holed specimens improved. Furthermore, the biaxial compressive strength of the surrounding rock and the stability of the holed specimens decreased as the block danger coefficients increased.

Experimental and Numerical Studies on Interaction Mechanism between Joints and a Hole in Rock-like Materials under Uniaxial Compression

To investigate the influence of joints on the stability of underground opening, uniaxial compression tests and FE analyses based on a microplane damage model for rocks has been conducted for rock-like models with a circular hole and a set of non-persistent joints. It was found that the peak strength and Young’s modulus decrease with the increase in joint continuity factor k, and variation of them with joint inclination angle β are W or V-shaped curves with the minima and maxima at β = 30° and 90°, respectively. The failure modes of the specimens and the collapse modes of the hole can be related to crack coalescence between the hole and the joints or matrix. Numerical simulation can reproduce the main features of macroscopic mechanical behavior and explain the anisotropic damage mechanism. The strong interaction between the hole and the nearest joint was revealed. During the elastic stage, stress concentration around the hole will be altered by the presence of the joints, and the effect may be strengthened with the increase in k. At the peak strength, the current stress concentration areas will be transferred from the hole surface to the interior due to stress loosening in damage localization bands/zones, and a higher hoop stress concentration factor may lead to lower strength.

Predicting the stability of open stopes using Machine Learning

The Mathews stability graph method was presented for the first time in 1980. This method was developed to assess the stability of open stopes in different underground conditions, and it has an impact on evaluating the safety of underground excavations. With the development of technology and growing experience in applying computer sciences in various research disciplines, mining engineering could significantly benefit by using Machine Learning. Applying those ML algorithms to predict the stability of open stopes in underground excavations is a new approach that could replace the original graph method and should be investigated. In this research, a Potvin database that consisted of 176 historical case studies was passed to the two most popular Machine Learning algorithms: Logistic Regression and Random Forest, to compare their predicting capabilities. The results obtained showed that those algorithms can indicate the stability of underground openings, especially Random Forest, which, in examined data, performed slightly better than Logistic Regression.

Justification of stability strategy for underground mine openings under higher effective anisotropic stresses

Stability of underground openings is one of the critical challenges in the mining industry. A mine support system design and installation depends on the conditions of mining. This is especially pronounced in the regions of active tectonics with horizontal stresses higher than vertical stresses up to 2–5 times. The tectonic stress-induced activity accompanies even comparatively shallow mining operations. Dense fracturing, spalling and bursting are observed in mines in Gornaya Shoria, or in Apatit JSC mines, at the depths of 150 to 400 m in Russia, at the depth of 260–400 m in uranium mines in Canada, 250 m in Tirol in Austria, or 100–200 m in Norway. As a result of the accomplished studies, the mechanism of fracture zones in adjacent rock mass during heading and mining in high-stress rock mass is defined. The parameters of these zones are determined subject to the rock mass quality, structure and stress–strain behavior. This allows developing the heading technology and mine support system design for the conditions of higher tectonic stresses. The main transient factors capable to affect underground openings are identified, and it is shown that the technology of heading and mine support under dynamic events caused by rock pressure depends on such determinants as: the quality of fragmentation by blasting, blasting sequence, temporary and permanent support designs and lag of the mine support behind the face advance. The proposed approach to the underground mine stability under higher effective anisotropic stresses ensures safe mining at optimal rates of heading.

Analytical studying the axial performance of fully encapsulated rock bolts

Fully encapsulated rock bolts are widely used in keeping the stability of underground openings and slopes. However, bonding failure at the bolt/grout (B/G) interface still occurs. Thus, a theoretical solution was proposed to investigate the rock bolting performance. The coupling and decoupling behaviour of the B/G interface is simulated with a bonding-slipping formula. The feasibility of this bonding-slipping formula was confirmed with physical experiments on rock bolts. Then, the rock bolt loading procedures were analysed. The advantage of this theoretical model is that all input parameters can be directly acquired from the experimental pullout scenario. Three physical pullout experiments, including laboratory and field tests, were used to validate this theoretical modelling. After validation, the deduced theoretical model can calculate the rock bolting performance. Then, this model was adopted to perform the parameter analysis. The results reveal that the loading phases of the B/G interface are independent of the encapsulated length. With the increasing encapsulated length, the B/G interface encounters the elastic, elastic-debonding and debonding phases in order. Moreover, with the increasing grouting material modulus, the rock bolt shows more brittle performance.

Evaluation of Stope Stability in Underground Mine; Hermyingyi (Sn-W Deposit) Mine in Myanmar

The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC3D 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines; Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of K = 0.5 than that of K = 1.0 and K = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.

Stress–strain analysis of rock mass during mining of protective pillar of vertical shaft

The implemented studies aim at the geomechanical assessment of safe mining, including safety pillars, within the limits of the protective pillar of shaft RESH in the Irtysh Mine, with estimation of influence exerted by stresses and strains on the rock mass, permanent excavations and ground surface. Slacked replenishment of the raw material resources makes re-extraction of ore reserves from pillars highly topical. It is found that ore loss in mining of the protective pillars reach 30% and above of total reserves at some deposits. Based on the analytical solutions and 3D FEM modeling in terms of the Irtysh Mine, the authors validate feasibility of safe partial extraction of ore reserves from the protective pillar of shaft RESH without aggravating effect on the shaft operation and on the ground surface. The feature of this study is using both specification documents and mathematical modeling, with regard to geology, structure and lithology of a deposit and rock mass, physical and mechanical properties and geometrical complexity of mine objects, which essentially improves studies into stability of underground openings and ground surface. It is found that the basic measure of safety I mining of the protective pillar of shaft RESH is establishing safety pillars.

Stability of Deep Underground Openings through Large Fault Zones in Argillaceous Rock

The stability of underground openings is pivotal to sustainable safe mining in underground coal mines. To determine the stability and tunneling safety issues in 800-m-deep underground openings through large fault zones in argillaceous rocks in the Guqiao Coal Mine in East China, the pilot industrial test, laboratory experimentation, and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of underground openings, and to study the stability control countermeasures. The main factors influencing the stability and tunneling safety include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass, groundwater inrush and gas outburst. According to the field study, the anchor-ability of cables and the groutability of cement-matrix materials in the argillaceous rock in the large fault zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the pilot excavation, including roof collapse, groundwater inrush, and debris flow. Control techniques are proposed and should be adopted to ensure tunneling safety and to control the stability of deep underground openings through large fault zones, including regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, floor grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the coal mine.

An Investigation on the Fabric Type Dependency of the Crack Damage Thresholds in Brittle Rocks

Fabric-guided micro-fracturing phenomenon in brittle rocks and its effect on crack damage thresholds remains subject to continuing research. The available fabric in rocks can act as a motivator for nucleation and/or extension and interaction of micro-fractures in a preferred orientation, or as a suppressor for growth of micro-cracks in a given direction by different mechanisms such as compliance (stiffness contrast) or preferred orientation of minerals and their boundaries. While anisotropy of brittle rocks in terms of their mechanical strengths can play a significant role in the stability of underground openings, the understanding of the dependency of crack initiation (CI) and crack propagation (CD) thresholds on the available fabric in rocks can improve predictions of the extension and density of micro-fracturing in different directions in the walls of underground openings. To better understand the fabric-guided micro-fracturing phenomenon, and also to study the effect of fabric types available in brittle rocks on their anisotropic behaviour, four types of brittle rocks with different types of fabric are investigated in terms of crack damage anisotropy in this paper. The rocks that are chosen for this study are limestone from the Cobourg Formation, Queenston shale, Olkiluoto mica gneiss and Lac du Bonnet granite. For each rock type, CI and CD thresholds are identified from the unconfined compressive strength testing data. The mechanical behaviour of the four rock types are investigated at each damage stress level and the contributing factors to the isotropic or anisotropic behaviour of the rocks at different crack damage thresholds are discussed.

Study on the Influence of Pit Excavation on the Stability of Underground Openings Using Different Models

Simplified plane strain model and 3-D model were used to research the influence of pit excavation on the stability of underground openings using the finite element method (FEM). Conclusion from the 3-D FEM study is that the central region of the pit will have a large springback deformation and the openings will also float up at the same time because of large ranges of pit excavation. When using the simplified two-dimensional plane strain model for the analysis of this problem, the size of the excavation region leads directly to two completely inconsistent results. If the excavation region was wider than the openings the springback deformation would be obtained, while the settlement would be obtained if the opening was wider than the excavation region. Therefore the two-dimensional plane strain model is not proper for the analysis of the stability of the openings under this condition.

Numerical simulation on rockburst of underground opening triggered by dynamic disturbance

The dynamic disturbance, which is termed as the time-dependent loading such as explosion, vibration, stress impact from neighboring rockbursts, earthquakes, may trigger the rockbursts around the underground opening at depth. A numerical model capable of studying the dynamic failure process of rock under coupled static geo-stress and dynamic disturbance is proposed, and it is implemented into the Rock Failure Process Analysis (RFPA), a general finite element package to analyze the damage and failure process of engineering materials such as rock and concrete. Based on the consideration of the static geo-stress, the RFPA-Dynamics is used to simulate the rockburst that is deemed to be triggered by dynamic disturbance around the deep underground opening. The effect of lateral pressure coefficient and dynamic disturbance waveform on the development of failure zone around the underground opening is numerically simulated. The numerical results indicate that the dynamic disturbance is one of the most important mechanisms that trigger the rockbursts around underground opening. Therefore, it is of theoretical and practical significance to investigate the effect of dynamic disturbance on the rockbursts of underground opening, especially for the underground excavation at depth where the surrounding rockmass is highly stressed. The numerical results also reveal that the contribution of the dynamic disturbances is closely pertinent to both the static geo-stress condition and the waveforms of the dynamic disturbance. In general, dynamic disturbance brings about the greater influences on the stability of underground opening with its increasing magnitude and prolonged duration. However, with regard to the specific static geo-stress condition and characteristics of dynamic disturbance, the contribution of dynamic disturbance to trigger the rockbursts must be examined based on numerical analysis according to the specific geo-stress conditions and characteristics of the dynamic disturbance.

Stability assessment in wide underground mine openings by Mathews’ stability graph method

Stability of underground openings is a major concern for the safety and productivity of mining operations. Rock mass classifications methods form the basis of many empirical design methods as well as form a basis for numerical analysis. Of the many factors which influence the stability of openings, span of the opening for a given rock mass condition forms a single parameter of design. In this paper, the critical span curves proposed by Lang, the Mathews' stability graph method, and the modified critical span curve obtained by the authors have been assessed. The modified critical span curve proposed by the author has been successfully used to assess the stability of wide underground openings in several limestone mines. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.

Modeling of Fracture and Damage in Rock by the Bonded-Particle Model

ABSTRACT Since potential disturbance of a near-field host rock could adversely affect the stability of underground openings and could possibly change the properties of rock mass, it is very important to evaluate deformation and fracturing characteristics of rock. In this study, PFC2D modeling as well as laboratory experiments were carried out to study characteristics of deformation and fracturing of rocks under uniaxial and triaxial compressive conditions. Laboratory experiments include stress-strain measurements and acoustic emission measurements to carry out the moving point regression analysis. Damage thresholds showed linear relationships with confining pressures. In addition, the feasibility of the application of the bonded-particle model to reproduce mechanical behaviors of rocks was explored by comparing model behaviors to results from experiments at different confining pressures. The model could exhibit macroscopic behaviors such as strain softening, dilation and fracture that arise from extensive microcracking throughout a bonded assembly. However, axial stress increments with increasing confining pressures were much smaller than those from experiments.

World Stress Map of the Earth: a key to tectonic processes and technological applications

Modern civilisation explores and penetrates the interior of the Earth's crust, recovers from it and stores into it solids, fluids and gases to a hitherto unprecedented degree. Management of underground structures such as boreholes or reservoirs take into account the existing stress either to take advantage of it or at least to minimise the effects of man-made stress. This paper presents the World Map of Tectonic Stresses (in short: World Stress Map or WSM) as a fundamental geophysical data-base. The impact of the WSM is pointed out: in the context of global tectonics, in seismic hazard quantification and in a wide range of technological problems in industrial applications such as oil reservoir management and stability of underground openings (tunnels, boreholes and waste disposal sites).

Damage and Fracture Characteristics of Kimachi Sandstone in Uniaxial Compression

ABSTRACT Some of the key concerns regarding the design of underground openings include the implication in potential ground disturbance caused by the excavation method and the redistribution of in situ stress. Both of these factors are related to the extent of brittle fracture damage which could adversely affect the stability of excavation boundary and could possibly change the properties of the near-field host rock. Therefore, the evaluation of deformation characteristics of a damaged rock is very important in analyzing the stability of underground openings. The development of stress-induced micro-cracking in rock samples under uniaxial compression was investigated by using stress-strain data, the moving point regression technique and AE measurements. In addition, damage thresholds and deformation parameters were identified. Finally, empirically modeled deformation behaviors were compared with experimental data. It was shown that crack initiation and crack damage for Kimachi sandstone occurred at 0.578σUCS and 0.822σUCS, respectively. However, it was difficult to find the crack closure threshold due to intrinsic properties of Kimachi sandstone related to its high porosity. The appropriate interval for moving point regression technique should be at least 5% of total data set. Approximately 16% of the total axial strain occurred during crack closure and nearly 40% occurred before crack initiation. In contrast, only 5.6% of the total lateral strains were recorded during the crack closure interval. The largest proportion of total lateral strain was seen to be attributable to the coalescence and unstable crack propagation. Modelled behaviors of Kimachi sandstone coincided well with test data.

A new approach to numerical method of modelling geological processes and rock engineering problems — continuum to discontinuum and linearity to nonlinearity

Numerical modelling as an efficient method is widely employed in various fields of science and engineering. In rock mechanics and geomechanics, considerable progress has been made in numerical simulation on nonlinear and discontinuum problems. However, there is a tendency in this field that the theoretical framework for nonlinear and discontinuum problems becomes more and more complicated and sometimes becomes less practicable. This paper gives a brief introduction to a newly developed numerical code, RFPA 2D (rock failure process analysis), which is mathematically a linear and continuum mechanics method for numerically processing nonlinear and discontinuum mechanics problems in rock failure. Although it is simple comparing with other numerical methods for nonlinear and discontinuum problems. It allows one to model the observed evolution of the progressive failure leading to collapse in brittle rocks. An important conclusion from the simulation results is that the microscale heterogeneity is the source of macroscale nonlinearity. Examples showing the potential applications are given in this paper. It can be seen that the RFPA 2D has a unique ability to reveal the evolutionary nature of the fracture phenomenon from microfracture scale to global failure, and the great potential exists in modelling mining induced rockbursts and stability of underground openings in greath depth. The capabilities to handle dilation, self-induced faults or even block movement and rotation should also attract applications in the fields of geomechanics as well as rock mechanics.

Assessment of rock mass strength for underground excavations

Abstract When the stability of underground openings is assessed, one must concern with local and global failure modes. Local failures may take place as long as rock blocks are kinematically movable into openings while global failure modes are associated with the stress state and the strength of rock mass surrounding openings. This fact is always confused in underground rock engineering. First, the authors briefly describe several approaches how to assess the strength of rock masses together with some new proposals for underground excavations. Then, the estimations by these methods are compared with each other as well as with experimental data. Finally, the validity of these methods are discussed and some recommendations are made for practical applications.

A hierarchical analysis for rock engineering using artificial neural networks

Rock behavior, such as the stability of underground openings, is controlled by many different factors which have varying levels of influence. It is very difficult to identify the relative effect of each factor with traditional methods, such as structural analysis and statistical approaches. This paper introduces a hierarchical analytical method based on the application of neural networks which reveals the different degrees of importance of these factors so as to recognize the key factors. This makes it possible to focus on the key factors and do rock engineering more efficiently. An example is given applying this approach to an underground opening.

Stability of underground openings in the storage of low and high temperature materials : Y. Inada, in: Comprehensive rock engineering. Vol. 2, ed J.A. Hudson, (Pergamon), 1993, pp 439–464

Stability of underground openings in the storage of low and high temperature materials : Y. Inada, in: Comprehensive rock engineering. Vol. 2, ed J.A. Hudson, (Pergamon), 1993, pp 439–464

Stability of underground openings: an old challenge, new problems (In French) : Maury, V Industrie MineraleV73, Nov 1991, P53–56

Stability of underground openings: an old challenge, new problems (In French) : Maury, V Industrie MineraleV73, Nov 1991, P53–56