Stability Analysis Of Pillars Research Articles

Research on Hard Rock Pillar Stability Prediction Based on SABO-LSSVM Model

The increase in mining depth necessitates higher strength requirements for hard rock pillars, making mine pillar stability analysis crucial for pillar design and underground safety operations. To enhance the accuracy of predicting the stability state of mine pillars, a prediction model based on the subtraction-average-based optimizer (SABO) for hyperparameter optimization of the least-squares support vector machine (LSSVM) is proposed. First, by analyzing the redundancy of features in the mine pillar dataset and conducting feature selection, five parameter combinations were constructed to examine their effects on the performance of different models. Second, the SABO-LSSVM prediction model was compared vertically with classic models and horizontally with other optimized models to ensure comprehensive and objective evaluation. Finally, two data sampling methods and a combined sampling method were used to correct the bias of the optimized model for different categories of mine pillars. The results demonstrated that the SABO-LSSVM model exhibited good accuracy and comprehensive performance, thereby providing valuable insights for mine pillar stability prediction.

Stability Analysis of Pillars in Underground Limestone Mine Using Three-Dimensional Scanning Techniques

Stability Analysis of Pillars in Underground Limestone Mine Using Three-Dimensional Scanning Techniques

Cave mine pillar stability analysis using machine learning

The large scale of cave mines leads to many challenges, including operational logistics and geomechanics design. In current practice, pillar stability assessment relies almost exclusively on stress analysis. However, stability is also affected by other factors including those related to operational aspects of the mining method, the effects of which are difficult to account for during the design stages. In this paper we present a case study of the application of a machine learning approach to evaluate the influence of these operational factors on pillar stability at the Chuquicamata underground cave mine in northern Chile. Due to the likely multi-factorial damage process leading to collapses and considering the different pillar conditions, a tree-based machine learning method was used and analysed to improve the understanding of the relative importance of the various contributing factors. Unlike stress analysis methods, it does not require any a priori knowledge of failure mechanisms, nor the calibration of associated controlling parameters. The proposed random forest model predicted pillar collapses with 80% accuracy despite limited samples to model from. The main contributing factors to collapses were found to be related to available pillar volume, cave front geometry, and time under abutment stress conditions. The effects and interactions of such factors were also studied, showing that careful and improved control over operational conditions can significantly reduce the likelihood of pillar collapses. These conclusions could not have been obtained from stress analysis alone, illustrating the complementary nature of conventional stress analysis and machine learning approaches.

Numerical Analysis of Pillar Stability in Longwall Mining of Two Adjacent Panels of an Inclined Coal Seam

Longwall mining is one of the most widespread methods globally. During the preliminary development of the working, the coal seam is sectioned into panels divided by protective pillars. The pillars are necessary for maintaining the service life of underground mines, a highly productive stope, and personnel safety. In this work, we apply the finite-difference continuum damage mechanics approach to modeling the stress–strain evolution of the rock mass during the extraction of two adjacent longwall panels of an inclined seam. A new modification of the damage accumulation kinetic equation is proposed. The numerical-modeling approach accounts for an explicit number of numerous factors affecting the rock mass behavior. These factors are gravity forces, lithology, tectonic stresses, natural discontinuities, geotechnical, and mining parameters. When the model parameters are calibrated against the in situ observations, the results of the numerical-modeling approach provide a reliable basis for a pillar stability assessment. We build a structural model of a rock mass containing an underground working based on a simplified stratigraphy of the Kondomsky deposit, Kuznetsk coal basin, Russia. Based on the results of the numerical modeling, the stability of a pillar is analyzed. A new numerical technique extending the classical approach to the stability analysis is proposed and verified against the field data.

Assessment of coal pillar stability using principal component analysis and stepwise selection and elimination

Prediction of pillar stability is one of the most critical tasks in underground mining industries. This pillar stability analysis requires many input parameters and some of them are difficult to be determined. Various statistical based analysis is presented in literature for assessing pillar stability successfully. In the present work, the data from three mines had been to determine the factor of safety. A total of 63 pillar cases had been collected from the mines. Principal component analysis (PCA) and Stepwise selection and elimination (SSE) models were developed by using multi variate linear regression (MLR) on 45 data sets and subsequently the proposed models were validated on 18 different data sets. The value of coefficient of determination (R2) is 0.86 and 0.84 for PCA and SSE respectively. The root mean square error for PCA and SSE are found to be 0.112 and 0.123 respectively. On validation of the proposed model developed by PCA and SSE, the PCA model provided a better validation results. Hence, PCA is recommended for modelling pillar stability.

Stability analysis of underground mine hard rock pillars via combination of finite difference methods, neural networks, and Monte Carlo simulation techniques

Pillar stability is always evaluated using the safety factor (SF), which is defined as the ratio of pillar strength to pillar stress. However, most researchers have estimated pillar stress using the pillar shape ratio (w/h), uniaxial compressive strength (UCS) of the intact rock mass, and pillar depth (H). In this study, the geological strength index (GSI) of hard rock pillars was considered as a new variable for predictive purposes. This index was developed by combining numerical simulation software (i.e., FLAC3D) and a backpropagation neural network (BPNN). A hard rock pillar stability analysis, based on three methods including deterministic method, sensitivity analysis, and Monte Carlo simulation (MCS), was performed. A new formula was proposed to estimate the SF values based on the predicted stress, considering the GSI variable in the deterministic method. The sensitivity analysis indicated that the variables impacting the SF from high to low are UCS, GSI, w/h, and H. In this study, pillar stability was analyzed mainly using the GSI and MCS techniques. The MCS results revealed that the GSI is also a major factor in pillar stability and has a greater effect on weak pillars than on strong ones. Furthermore, a pillar is more likely to be unstable when both the GSI and the UCS are decreased. This study provides several references and procedures for improving the design of stable pillars considering the GSI as an important factor.

STABILITY ANALYSIS OF SECURITY PILLARS WITH DI-MENSION 10 X 10 M FROMED BY ORE OF MINERAL BODY DURING THE EXPLOITATION OF THE "TREPÇA" MINE IN STANTËRG

Abstract: The Trepça mine in Stanterg consists from several mineral bodies, which if compared to the mineral bodies in the North and South part of mine can be found in different size. Their size in the hori-zontal plane ranges from 300-7000 m2 and as a matter of fact in the primary exploitation phase, only about two of thirds part of ore is used, while the remaining ore is used like pillars in the secondary stage with special methods. Since the beginning of exploitation at Trepça mine landfill, the security pillars are left in dimensions 10x10m, on the schedule of chess fields, at distances from 16 to 20m and all pillars at those distances are stable and over-dimensioned. In this paper we investigate the stability of the securing pillars with dimensions 10x10m, with surface S = a*b = 10*10 = 100m2 with a distance between them of 10 to 22m. Pillar stability analysis aims to increase the safety factor along with the increase of exploitation depth.

Performance of a coal pillar at deeper cover: Field and simulation studies

Exhaustion of coal reserve, extractable by conventional longwall method of working at Czech mines, provided an opportunity to try modified Room and Pillar (R&P) method to extract high grade coal locked-up in larger shaft protection pillar at around 900 m depth. The shaft pillar is divided into various R&P panels and the development process in a panel followed a constant gallery width of 5.2 m and 3.5 m height. This development in the shaft pillar by bolter miner resulted oblique and inclined pillars of 860–1225 m2 area. Stability of these pillars is realised to be vital for optimum recovery of high-grade coal from these panels. No empirical formulation is found suitable for the design of pillars at such a depth. Therefore, an attempt is made to select a better representing one through comparative study of the available formulation. CMRI formula is found to be an alternative solution for designing pillars at this depth as it contains depth of cover as a design parameter. This parameter in the formulation is included to take care of the in situ stress conditions and compactness of the material at higher depth of cover. Further, a number of geo-technical instruments are installed in two pillars of Panel V for an analysis of their stability during the development. An attempt is made to develop a strain-softening based numerical modelling approach, calibrated by field studies and CMRI empirical formulation, to assess pillar performance at deeper cover. This development is found to be helpful in pillar stability analysis, when the installed instruments ceased to work. Further, an apprehension of pillar failure by extrapolation of field results is not confirmed on simulated models. This paper briefly presents a discussion of difficulties involved in pillar design at higher depth followed by results of field and simulation conducted for the deep Czech mine.

Probability and reliability analysis of pillar stability in South Africa

A deterministic approach is frequently used in engineering design. In this quantitative design methodology, a safety factor, which is typically a strength-to-stress ratio, is derived as an index for the stability assessment of the engineering design. In underground coal mining applications such as pillar design, however, the inputs of pillar design are variables. This is widely overlooked in the deterministic approach. A probabilistic approach assessing the probability of failure or reliability of a system might be an alternative to the conventional quantitative methodology. This approach can incorporate the degree of uncertainty and deviations of variables and provide more versatile and reliable results. In this research, the reliability of case histories from stable and failed pillars of South Africa presented by Merwe and Mathey is examed. The updated Salamon and Munro strength formula (S-M formula) and Merwe and Mathey strength formula (M-M formula) are evaluated through a probabilistic approach. It is concluded that stable pillar cases have a reliability value greater than 0.83 while the reliability value of failed pillar cases are slightly larger than 0.50. There seems to be a positive relation between safety factor and reliability. The reliability of a pillar increases with pillar width but decreases with depth of cover, pillar height and entry width. The reliability analysis also confirms that M-M strength formula has a better distinction between the stable and failed pillar cases.

Proposal of 2D finite element model for square pillar stability analysis

It is suggested that 2D finite element method models are used for square pillar stability analysis. Equivalent width of strip pillar that is represented by FE models is determined from tributary area method by introducing equivalence of square and strip pillar loads in tributary area method analysis. With FE analysis it is shown that pillar loads are close to expected, but tributary area method is limited to pillars of small heights and with horizontal deposits. Proposed methodology provides opportunity to model much complex conditions and sequencing of excavation with respect of sequential stress redistribution.

Elimination of boundary effect for laminated overburden model in pillar stability analysis

The laminated overburden model (LaModel) has been widely used for pillar design and stability analysis. As a boundary element program, the LaModel program is sensitive to the boundary condition, which should be considered before creating the model. To eliminate the boundary effect in a LaModel pillar stability analysis, a suitable boundary buffer zone is needed around the model edge. The radius of influence (R) and the abutment load extent (D) are two major factors that affect the stresses and displacements calculated in LaModel. To determine the optimum buffer zone extent, a database of case histories was analyzed using the LaModel program. Values for R and D were varied until a buffer zone having negligible influence on the pillar stability factor (SF) of the active mining zone (AMZ) was determined.

Analysis of pillar stability of mined gas storage caverns in shale formations

The observed failure of mined storage caverns in shale formations indicates that one of the major causes of pillar failure is the effect of jointing, fracturing, and deterioration of the shale in the outer portions of the pillar due to a combination of stress slabbing and slaking. The effect of width/height ratio on pillar capacity is also apparent. After the collapse of the Lick Creek, Illinois, room and pillar cavern in 1973, a design approach has been developed for pillar size and loading that takes into account rock and geometric conditions that influence stability, including the conditions that led to the failure at Lick Creek. This paper presents a design criterion for evaluating the overall stability of the pillars in mined gas storage caverns in shale formations. The study includes the closed form pillar stability calculations as well as three-dimensional numerical analyses to verify the analysis method.

Thermal–mechanical–numerical analysis of stress distribution in the vicinity of underground coal gasification (UCG) panels

During underground coal gasification (UCG), whereby coal is converted to syngas in situ, a panel (cavity) is formed in the coal seam. Unlike other underground mining methods, the coal and country rocks in the vicinity of a UCG panel are subjected to high temperatures which may be in excess of 1000°C. UCG operation imposes significant geomechanical changes to the strata. In order to understand these changes, numerical modeling can provide a comprehensive and qualitative understanding of the UCG process. In this paper, a new approach, namely, Underground Coal Gasification-Pillar Stability Analysis (UCG-PSA) is presented to estimate the protection pillar width in UCG based on the Controlled Retraction Injection Point (CRIP) configuration. The UCG-PSA approach considers development load, side abutment load, front abutment load, thermal stress along with cavity syngas pressure as a lateral pressure to determine the protection pillar width. Furthermore, the role of the crushed zone around a pillar was considered in the estimation of the pillar strength. A new 3D Thermal–Mechanical (TM) model is developed for UCG based on the CRIP configuration to predict stress distribution in the vicinity of the UCG panel and to verify the UCG-PSA approach results using the FLAC3D software. In this model, a panel is subjected to high syngas pressure and high temperature. Moreover, after each step of gasification the modeling of caved material is performed. The results of the TM model compared with the Mechanical (M) model show that the stress distribution increased at the front of the face and pillar edge due to the thermal stress. In addition, the results show that the maximum side abutment stress at a depth of 600m is 63.1MPa and applied at a distance about 3.5m away from the pillar edge while in the M model it is 59.2MPa. The proposed methodology could provide a consistent and simple way for the stability analysis of pillars in UCG sites.

Analysis of Pillar Stability in Thermal Energy Storage Caverns Using Numerical Modeling

Underground Thermal Energy Storage (UTES) systems store thermal energy in aquifers, boreholes, or caverns with the purpose of avoiding the sporadic characteristics of renewable-energy resources or recovering industrial waste heat. Cavern TES (CTES) system may be more expensive in construction than the other two storage methods, but its advantages include high injection and extraction powers and the flexibility in selecting a heat storage medium. The first large-scale cavern for CTES system, which is toroidal shaped, was constructed for storing hot water of 40–90 C in Lyckebo, Sweden and 5,500 MWh of heat was stored between seasons (Nordell et al. 2007). Storage cavern in CTES system should be designed to ensure structural stability of storage space and provide good thermal storage performance as well. However, these two objectives conflict with each other, because increasing height-to-width ratio of the cavern improves the storage performance and simultaneously increase the structural instability due to its slender shape (Park et al. 2013). It can be thus suggested to divide a single large cavern into multiple smaller caverns with high aspect ratios (Park et al. 2014), and cavern spacing affecting the temperature and stress distribution of the pillar between caverns becomes one of the main factors taken into account when designing the multiple caverns. Generally, closely spaced caverns are preferred for efficient placement of surface and underground facilities and favorable to reduce the heat loss due to the temperature difference between surrounding rock mass and storage medium. This technical note seeks to determine a width of the pillar that is structurally stable between two rock caverns for thermal energy storage, based on numerical simulations using a thermal–mechanical coupled model. The influence of pillar width on the stability is compared with that of cavern depth and in situ stress condition, and the stress distributions of pillars with different widths are analyzed.

An analytic solution describing the visco-elastic deformation of coal pillars in room and pillar mine

Coal pillar deformation is typically nonlinear and time-dependent. The accurate prediction of this deformation has a vital importance for the successful implementation of mining techniques. These methods have proven very important as a way to excavate coal resources from under buildings, railways, or water bodies. Elastic and visco-elastic theory are employed with a Maxwell model to formulate an analytic solution for displacement of coal pillars in room and pillar mine. These results show that the visco-elastic solution adequately predicts the coal pillar deformation over time. We conclude that the visco-elastic solution can predict the coal pillar and roadway displacement from the measured geological parameters of the conditions in situ. Furthermore, this method would be useful for mine design, coal pillar support optimization, ground subsidence prediction, and coal pillar stability analysis.

Modeling Uncertainties in Mining Pillar Stability Analysis

Many countries are now facing problems related to their past mining activities. One of the greatest problems concerns the potential surface instability. In areas where a room-and-pillar extraction method was used, deterministic methodologies are generally used to assess the hazard of surface collapses. However, those methodologies suffer from not being able to take into account all the uncertainties inherent in any hazard analysis. Through the practical example of the assessment of a single pillar stability in a very simple mining layout, this article introduces a logical framework that can be used to incorporate the different kinds of uncertainties related to data and models, as well as to specific expert's choices in the hazard or risk analysis process. Practical recommendations and efficient tools are also provided to help engineers and experts in their daily work.

Analysis of pillar stability on steeply pitching seam using the finite element method : Kripakov, N P US Bureau of Mines report RI 8579, 1981, 33P

Analysis of pillar stability on steeply pitching seam using the finite element method : Kripakov, N P US Bureau of Mines report RI 8579, 1981, 33P