Optimization of Chain Pillars Design in Longwall Mining Method

Chain coal pillars are parts of the structure of longwall mining system that play a significant role in the stability of the entries. With mechanization and developments in the various aspects of the method, higher efficiency in optimization of the design of chain coal pillars seems appropriate. In this paper, the three main methods of chain pillar design, namely the empirical, analytical and numerical methods are compared. Real data from the Tabas-Iran coal mines have been used in order to make the comparison process reliable. It is concluded that the most apparent advantage of the empirical method is the reliability of the results whilst the use of numerical methods enjoys the advantage of flexibility. On the other hand, the analytical methods are complex unless simplifying assumptions are made that can substantially decrease the accuracy of result which is thought to be the main advantage of the design method. A new method is therefore introduced here that combines all of the three presently used methods and by doing so, the new method has all the advantages of the three while minimizing complexities and inaccuracies associated with the use of the individual methods

Seismic analysis of horseshoe tunnels under dynamic loads due to earthquakes

Due to seismic events, such as earthquakes, the elastic waves propagate through a medium. The impact of these waves on underground structures is to provide dynamic forces and moments that may affect the stability of underground structures. The aim of this paper is to analyse the effects of seismic loads on the stability of horseshoe tunnels. As a case study, the stability state of the main access entry to C1 coal seam of Tabas collieries in Iran are analyzed using Phase2 software in static and dynamic states. It is often assumed that the effect of earthquakes on underground structures such as tunnels is negligible but the results of this study show that the stress caused by seismic loads can be harmful to the tunnel stability. It is concluded that the stress and displacement balance of forces around the tunnel are adversely affected and due to redistribution of these forces that create undue concentration in some areas, instability occurs in the tunnel. The paper also concludes that increasing the stiffness of the support system can increase the effect of the seismic loads. The analysis provided in this paper together with the conclusions obtained can serve as useful tools for the tunnel design engineers, especially in areas susceptible to seismic phenomena

Magnetic nanoparticles supported oxime palladacycle as a highly efficient and separable catalyst for room temperature Suzuki–Miyaura coupling reaction in aqueous media

A novel magnetic nanoparticle-supported oxime palladacycle catalyst was successfully prepared and characterized. The magnetically recoverable catalyst was evaluated in the room temperature Suzuki–Miyaura cross-coupling reaction of aryl iodides and bromides in aqueous media. The catalyst was shown to be highly active under phosphine-free and low Pd loading (0.3 mol%) conditions. The catalyst could be easily separated from the reaction mixture using an external magnet and reused for six consecutive runs without significant loss of activity.The authors are grateful to Institute for Advanced Studies in Basic Sciences (IASBS) Research Council and Iran National Science Foundation (INSF-Grant number of 93020713) for support of this work

3D strain softening modelling of coal pillars in a deep longwall mine

In longwall coal mines, the entries on both sides of the panel play a significant role in production rate and safety of operation. With increasing production amount, the rate of conveying material through such entries increases. Therefore, it is required to design wider entries. Support of these entries, particularly in deep mines is difficult. In this paper, by using FLAC3D program code a deep longwall coal mine is modeled. The coal seam has a strain softening property, and the analysis index of stress and deformation of ribsides and coal pillars at different loading levels are determined. Strain softening parameters is studied separately for each modeled coal pillar, and based on conventional formula the pillar strength are calculated. In a modeled longwall mine, the caving material at goaf zone are fully compact. The results shows that based on Mohr-Coulomb model, the strain softening occurs at maximum cohesion and friction, and at region of decreasing the strength of pillar in stress-strain curve. Because of 3D nature of analyses, the effect of front and side abutment load on stability of pillar are studied simultaneously. Therefore, the results of this study could be suitable criteria for appraisal of pillar design method at deep longwall coal mines

Estimation of Coal Pillar Strength by Finite Difference Model

Longwall mining is now predominately used in coal mines where somewhat difficult conditions exist. As in the case of all other underground mining methods, pillars are integral parts of the mining design. The choice of shape and dimensions of the pillars has significant impact on the recovery and hence on overall productivity of the mine. The process of pillar design in longwall mining entails the selection of a safety factor, which is done by estimating the magnitude of the load applied on the pillar and the load bearing capacity of such pillars. In this paper, finite difference modeling principles have been applied to a typical coal pillar. The pillar strength is then estimated with various width/height ratios. These results have been compared with the results obtained from the conventional methods of pillar design. The effect of roof and floor quality on the strength of the typical pillar has also been evaluated in the same manner. It is concluded that although the finite difference method is not always the perfect method for such estimation, but the results clearly demonstrate that it produces more acceptable design than the conventional method, especially under undesirable conditions regarding the interface between pillars, roof and floor. An additional advantage of such method is shown to be its capability of being applied in situations where complex parameters prevail

Selection of Tunnel Support System by Using Multi Criteria Decision-Making Tools

Selection of the optimum support system for underground openings such as tunnels is a complex process. In this paper, a new approach, based on a combination of the Analytical Hierarchy Process (AHP), the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and the Preference Ranking Organization METHod for Enrichment Evaluations (PROMETHEE) is introduced. For this purpose, the selection process is assumed to be a multi criteria decision-making problem. First, different support systems by using FLAC3D numerical code, based on technical, safety and stability parameters of the tunnel are specified. Then, taking economic and performance parameters as the decision criteria, by using the combination of AHP, TOPSIS, and PROMETHEE, the optimum support system is selected. As a real mine case study, this approach is used in the main access entry to C1 coal seam of Tabas collieries. Results clearly demonstrate that the proposed support system selection method is advantageous to other alternatives

A New Approach for Determination of Tunnel Supporting System Using Analytical Hierarchy Process (AHP)

In underground mining, the selection of support system for mine tunnel development plays a significant role in safety and economics of operations. Traditionally, such selection is on the basis of the experience of the design engineer. Nevertheless, the validity of such selection is questionable. A new approach for selecting the optimum tunnel support system based on Analytical Hierarchy Process (AHP) is proposed. In this new approach, the selection of the tunnel support system is considered as a multi criteria decision-making problem. Firstly, by using the numerical Finite Difference Method (FDM), based on technical and stability parameters of the tunnel, different support systems are specified. Then, by considering the economics and performance indices of each support system, a decision tree based on AHP model is generated and the optimum support system is selected. As a field study, the method is applied to Tabas collieries in Iran. It is concluded that the proposed support system determination is advantageous compared to other alternatives. Therefore, the proposed approach can assist the engineer in selection of optimum tunnel support system in different underground mining situations

Analyzing the effect of gradation on specific gravity and viscosity of barite powder used in excavation mud

Barite is an important additive material to increase the weight of excavation mud. It has been used extensively in the excavation mud industry. The barite particle sizes used in excavation mud is very important. There is a direct relationship between the amount on the sift of 200 and 325 mesh. By reducing particle sizes of the 200 and 325 mesh, the specific gravity of the barite power increased slightly. It could be concluded that increasing the size of the barite powder particle can reduce density, but this should be considered as a laboratorial error. Thus, granulation has a great influence on the viscosity of barite powder. According to previous studies dimensions below 325 mesh are very influential on viscosity. It can be said excavating companies consume more barite powder when the specific gravity of excavation mud is diminished because barite powder can enhance specific gravity but the viscosity goes up. There will be more problems in the excavation mud if viscosity increases

Risk criteria classification and the evaluation of blasting operations in open pit mines by using the FDANP method

Purpose. Mineral projects are heavily influenced by risk factors. By providing evidence-based information and analysis to make informed decisions about how to choose between options, a risk assessment can be made. Methods. In this study, the relationships of 46 criteria and 10 dimensions affecting the risk of blasting operations were investigated in order to determine the significance, effectiveness, relative weight of the criteria and dimensions as well as to prioritize the risk criteria of blasting operations. For this purpose, the combination of the FDEMATEL method and FANP method are used as FDANP. Findings. The most important criterion is the lack of specialized knowledge (C1). The damage to manpower criterion (C46) will receive the greatest impact from other criteria. The criterion for implementing the explosion plan, without respecting the design principles (C12) has most interactions with other criteria and the failure to determine the amount of production capacity (low or high) criterion (C45) has the least interactions with other criteria. According to the FDANP method, the number of explosions in one stage (C14) is the first criterion of the blasting operations risk. Originality. By controlling this criterion, the effects and destructive consequences of blasting operations can be prevented. Controlling this criterion reduces the risk of blasting operations and also reduces the damage by C46 criterion. From comparison, human resources dimension (D1) is the most effective and natural hazards dimension (D10) has the greatest interactions with other dimensions and is most affected among the other dimensions. The production and extraction consideration dimension (D9) has the least interaction with other dimensions and is less important. Practical implications. By reducing the destructive effects of blasting operations, two favorable results will be achieved: the reduction of damage caused by undesirable consequences and the assignment of a greater share of blast energy to the desired outcomes.Мета. Розробка класифікації критеріїв оцінки ризиків на кар’єрах із використанням методу аналітичної мережі нечітких процесів прийняття рішень на основі фактичної інформації та її комплексного аналізу. Методика. В даному дослідженні були вивчені взаємозв’язки 46 критеріїв і 10 параметрів, що впливають на ризик вибухових робіт, з метою визначення значущості, ефективності, відносної ваги критеріїв та параметрів, а також визначення пріоритетності критеріїв ризику вибухових операцій. Для цього був використаний метод FDANP, який являє собою комбінацію методу FDEMATEL (Fuzzy Decision Making Trial and Evaluation Laboratory) і методу FANP. Результати. Встановлено, що в оцінці ризиків відсутність спеціалізованих знань (С1) є найбільш важливим критерієм. Відзначається, що критерій завданих збитків робочій силі (C46) відчуває найбільший вплив з боку інших критеріїв. Критерій виконання плану вибуху без урахування проектних принципів (C12) найбільше взаємодіє з іншими критеріями, а критерій нездатності визначення обсягу виробничої потужності (низький або високий) (C45) взаємодіє з іншими критеріями найменше. Згідно з методом FDANP, кількість вибухів на одній стадії (C14) є першим критерієм ризику вибухових робіт. При порівнянні параметрів виявлено, що людські ресурси (D1) є найбільш ефективним параметром, а стихійні лиха (D10) найсильніше взаємодіють з іншими параметрами та найбільш схильні до їх впливу. Визначено, що параметр впливу виробництва та видобутку (D9) менше всього взаємодіє з іншими параметрами і менш важливий. Наукова новизна. Науково обґрунтовані математичні взаємозв’язки між величинами ризику підривних робіт. Встановлено, що, контролюючи критерій (C14), можна запобігти руйнівним наслідкам вибухових робіт, а управління даним критерієм знижує ризики вибухових робіт, а також зменшує шкоду за критерієм C46. Практична значимість. Зменшення руйнівного впливу вибухових робіт може призвести до двох сприятливих результатів: скорочення збитку, викликаного небажаними наслідками вибуху, і спрямованому використанню більшої частки енергії вибухових робіт для отримання бажаних результатівЦель. Разработка классификации критериев оценки рисков на карьерах с использованием метода аналитической сети нечетких процессов принятия решений на основе фактической информации и ее комплексного анализа. Методика. В данном исследовании были изучены взаимосвязи 46 критериев и 10 параметров, влияющих на риск взрывных работ, с целью определения значимости, эффективности, относительного веса критериев и параметров, а также определения приоритетности критериев риска взрывных операций. Для этого был использован метод FDANP, который представляет собой комбинацию метода FDEMATEL (Fuzzy Decision Making Trial and Evaluation Laboratory) и метода FANP. Результаты. Установлено, что в оценке рисков отсутствие специализированных знаний (С1) является наиболее важным критерием. Отмечается, что критерий нанесенного ущерба рабочей силе (C46) испытывает наибольшее влияние со стороны других критериев. Критерий выполнения плана взрыва без учета проектных принципов (C12) больше всего взаимодействует с другими критериями, а критерий неспособности определения объема производственной мощности (низкий или высокий) (C45) взаимодействует с другими критериями меньше всего. Согласно методу FDANP, количество взрывов на одной стадии (C14) является первым критерием риска взрывных работ. При сравнении параметров выявлено, что человеческие ресурсы (D1) являются наиболее эффективным параметром, а стихийные бедствия (D10) сильнее всего взаимодействуют с другими параметрами и наиболее подвержены их влиянию. Определено, что параметр учета производства и добычи (D9) меньше всего взаимодействует с другими параметрами и менее важен. Научная новизна. Научно обоснованы математические взаимосвязи между величинами риска взрывных работ. Установлено, что, контролируя критерий (C14), можно предотвратить разрушительные последствия взрывных работ, а управление данным критерием снижает риски взрывных работ, а также уменьшает ущерб по критерию C46. Практическая значимость. Уменьшение разрушительного воздействия взрывных работ может привести к двум благоприятным результатам: сокращению ущерба, вызванного нежелательными последствиями взрыва, и направленному использованию большей доли энергии взрывных работ для получения желаемых результатов.The authors would like to thank Mining Engineering Department, Islamic Azad University (South Tehran Branch) for supporting this research