Pillar System Research Articles

An improved method for long-term stability evaluation of strip mining and pillar design

Underground coal mining is characterized by the formation of extensive pillars. Coal pillars serve various purposes, and their instability failure characteristics play a vital role in safety mining. Considerable studies have been conducted over the last few decades on pillar instability and failure analyses. It was concluded that pillar failure for system instability is governed by both the strength of the pillars and the load acting on the pillars. There are several methodologies to evaluate pillar failure for instability; however, each method has its own applicable conditions, and none of them are applicable to all circumstances. This study focuses on methodologies (theoretical models, numerical simulations, and field measurements) for estimating pillar system loads and strengths. In the theoretical model, pillar failure criteria are significant factors for calculating coal pillar strength, and the primary factors for instability evaluation are noted. The general steps of the numerical simulation methods are summarized and analyzed. The finite element method is the most widely used method, whereas the discrete element method has become popular in recent years. Pillar stress, deformation, and fracture development are the main concerns when assessing pillar failure characteristics in field measurements. Finally, we list primary study interests (pillar failure analysis in abandoned and deep coal mines) on coal pillar failure analysis in future studies based on the development of underground coal mining.

Construction of reasonable pillar group for undersea mining in metal mine

Abstract In order to achieve the safe mining in Sanshandao Gold Mine, five schemes of secure pillar group are designed. Using the method of the renormalization group, the failure mechanism of the pillar group is explored, and the safety factor of the pillar system is also obtained. The displacement characteristics, stress–strain laws, distribution of plastic zone and damage range of different pillar group are analyzed using numerical calculation software FLAC3D. To determine a reasonable pillar group scheme, the pillar stability and roof deformation are utilized to evaluate the safety of the pillar group. In addition, the theory of fuzzy comprehensive evaluation is adopted to verify the optimal scheme. The pillar group with the lowest roof deformation value is chosen as the optimal plan, which renders a factor of safety of 2.06 for the pillar group. According to this scheme, pillars with the width of 10 m are set along the strike of undersea deposit with the interval of 50 m. Rib pillars of 15 m in width are set at the location of the exploration line of 127, 151 and 167. The analysis can be used to provide guidance for optimal design of pillar structures in undersea mining.

3D Numerical Analysis for Effect of Mechanical Properties on Failure Process of Serial and Parallel Rock Pillar System

3D Numerical Analysis for Effect of Mechanical Properties on Failure Process of Serial and Parallel Rock Pillar System

A comparative study of three pillars system and banking methods in accounting long-term purposes of retiree in Indonesian saving account

Human productivity is the main capital in economic activity. This main factor leads to the fact that the continuity of human resources in economic sector depends on the limited productivity age. In other word, once the economic agents has reach the limit of the productivity age. Hence they enter the pension state. In this case, the preparation of ‘old-age’ fund become crucial and should be initiated before the pension state to avoid the destitute condition of retiree. Two most simple and familiar methods in preparing the pension fund are The Three Pillars system and banking methods. Here we simulate the both of the methods for the synthetic data of investment program and analyse the result. The result gives the idea that the Three Pillar System has effective prospect in Long-term scheme. However, the banking method is likely adapted to the short-term plan.

Characterizing strata deformation over coal pillar system in longwall panels by using subsurface subsidence prediction model

The ground control stability problem due to underground large mine openings often associates with large movements and deformations of strata. The situation becomes more complicated when relative subsidence research involves zones above the coal pillar. Continues fractures in strata created by such subsidence progress may become the pathway of fresh air delivery or water migration in the strata aquifer which would cause the problems of underground coal combustion or water resource losing. Hence, knowing the subsurface strata movement characteristics over gob and coal pillar to make any subsidence predictions are desired for mining engineers to estimate any damages happened in the subsurface strata in advance. This paper proposes a prediction model for investigating subsurface strata movements over the pillar. Using the calculated subsidence results, the related strata fraction distributions are characterised. For validation reason, extensometer boreholes are used to identify the subsurface strata caving progress in a long-wall panel. The measurement results agree with the predications derived by the model shows the reliability of the model. Such research efforts can well help to understand the moving behaviour of all strata over the coal pillars and assist mining engineer to efficiently deal with the possible crack pathways over the coal pillar.

Justification of Spatially-Planned Solutions and Determination of the Dimension Block in the Working of the Medium Thick Inclined Coal Seams with the Room and Pillar System

Technological parameters for working out of the medium thick inclined coal seams with a diagonal arrangement of a line of a working face. An analysis of the constraints that apply the technology and the complexities of the mining and geological conditions of the Quang Ninh coal basin. The possibility and expediency of using the foreign experience of working out of the medium thick inclined coal seams in the mines of Vietnam and justification of spatially-planned solutions for working. The scheme of preparation and working out of the excavation area is given in view of the technological features in difficult mining and geological conditions, using the room and pillar system and determination of the rational length of the block along the strike.

Coal pillar design when considered a reinforcement problem rather than a suspension problem

Current coal pillar design is the epitome of suspension design. A defined weight of unstable overburden material is estimated, and the dimensions of the pillars left behind are based on holding up that material to a prescribed factor of safety. In principle, this is no different to early roadway roof support design. However, for the most part, roadway roof stabilisation has progressed to reinforcement, whereby the roof strata is assisted in supporting itself. This is now the mainstay of efficient and effective underground coal production. Suspension and reinforcement are fundamentally different in roadway roof stabilisation and lead to substantially different requirements in terms of support hardware characteristics and their application. In suspension, the primary focus is the total load-bearing capacity of the installed support and ensuring that it is securely anchored outside of the unstable roof mass. In contrast, reinforcement recognises that roof de-stabilisation is a gradational process with ever-increasing roof displacement magnitude leading to ever-reducing stability. Key roof support characteristics relate to such issues as system stiffness, the location and pattern of support elements and mobilising a defined thickness of the immediate roof to create (or build) a stabilising strata beam. The objective is to ensure that horizontal stress is maintained at a level that prevents mass roof collapse. This paper presents a prototype coal pillar and overburden system representation where reinforcement, rather than suspension, of the overburden is the stabilising mechanism via the action of in situ horizontal stresses. Established roadway roof reinforcement principles can potentially be applied to coal pillar design under this representation. The merit of this is evaluated according to failed pillar cases as found in a series of published databases. Based on the findings, a series of coal pillar system design considerations for bord and pillar type mine workings are provided. This potentially allows a more flexible approach to coal pillar sizing within workable mining layouts, as compared to common industry practice of a single design factor of safety (FoS) under defined overburden dead-loading to the exclusion of other relevant overburden stabilising influences.

Influence of the Roof Movement Control Method on the Stability of Remnant

In the underground mines, there are geological and mining situations that necessitate leaving behind remnants in the mining field. Remnants, in the form of small, irregular parcels, are usually separated in the case of: significant problems with maintaining roof stability, high rockburst hazard, the occurrence of complex geological conditions and for random reasons (ore remnants), as well as for economic reasons (undisturbed rock remnants). Remnants left in the mining field become sites of high stress values concentration and may affect the rock in their vicinity. The values of stress inside the remnant and its vicinity, as well as the stability of the remnant, largely depend on the roof movement control method used in the mining field. The article presents the results of the numerical analysis of the influence of roof movement control method on remnant stability and the geomechanical situation in the mining field. The numerical analysis was conducted for the geological and mining conditions characteristic of Polish underground copper mines owned by KGHM Polska Miedz S.A. Numerical simulations were performed in a plane strain state by means of Phase 2 v. 8.0 software, based on the finite element method. The behaviour of remnant and rock mass in its vicinity was simulated in the subsequent steps of the room and pillar mining system for three types of roof movement control method: roof deflection, dry backfill and hydraulic backfill. The parameters of the rock mass accepted for numerical modelling were calculated by means of RocLab software on the basis of the Hoek-Brown classification. The Mohr-Coulomb strength criterion was applied.

Release of Self-Healing Agents in a Material: What Happens Next?

A microfluidic chip-like setup consisting of a vascular system of microchannels alternatingly filled with either a resin monomer or a curing agent is used to study the intrinsic physical healing mechanism in self-healing materials. It is observed that, as a prenotched crack propagates across the chip, the resin and curing agent are released from the damaged channels. Subsequently, both the resin and the curing agent wet the surrounding polydimethylsiloxane (PDMS) matrix and spread over the crack banks until the two blobs come in contact, mix, and polymerize through an organometallic cross-linking reaction. Moreover, the polymerized domains form a system of pillars, which span the crack banks on the opposite side. This "stitching" phenomenon prevents further propagation of the crack.

Overview of the Portuguese Three Pillar Pension System

In order to cope with alleged future financial problems, several changes were made to the design of the Portuguese pension system since 2000. The aim was to achieve the diversification of retirement income sources across providers, both public and private, across the three pillars: public, industry-wide, and personal, and also across the financing forms of pay-as-you-go and funded. This paper describes these changes and analyses the results regarding, principally, the weight of each pillar and the investment performance of both public pension reserves and private pension funds. The main finding is that, in effect, there is one substantial longstanding pillar, and that is the public system.

Failure analysis of thin spray-on liner coated rock cores

Abstract Thin spray-on liners (TSLs) are surface support materials used in mining and civil engineering projects since 1990s with a wide ranging area of application from bolt/mesh support replacement to pillar reinforcement systems. This study presents the investigation of pillar reinforcement capacity of the TSL coated andesite rock core by compression test to mimic pillar reinforcement effect. The uniaxial compressive strength (UCS), modulus of elasticity (E), and energy absorbance capacity of uncoated and 5 mm coated cores having 25, 55, 75, and 100 mm diameters were compared. It was observed that there was no significant improvement in strength or stiffness for the homogenous rock cores coated with

Non-linear autoregressive neural network approach for inside air temperature prediction of a pillar cooler

ABSTRACTThe volcanic plate made pillar cooler system is designed for outdoor spaces as a heat exchanging medium and reduces the outcoming air temperature which flows through the exhaust port. This paper proposes the use of artificial neural networks (ANNs) to predict inside air temperature of a pillar cooler. For this purpose, at first, three statistically significant factors (outside temperature, airing and watering) influencing the inside air temperature of the pillar cooler are identified as input parameters for predicting the output (inside air temperature) and then an ANN was employed to predict the output. In addition, 70%, 15% and 15% data was chosen from a previously obtained data set during the field trial of the pillar cooler for training, testing and validation, respectively, and then an ANN was employed to predict inside air temperature. The training (0.99918), testing (0.99799) and validation errors (0.99432) obtained from the model indicate that the artificial neural network model (NARX) may be used to predict inside air temperature of pillar cooler. This study reveals that, an ANN approach can be used successfully for predicting the performance of pillar cooler.

Deformation of the rock pillar caused by bed operation using the room and pillar system

The copper ore deposit of the Legnica-Glogow Copper Mining District a one-deck bed formed from the contact of weak sandstone rocks, and solid, durable dolomite rocks, separated by a layer of copper slate. The bed operation is carried out using the room and pillar system. The course of deformation in such bed operation systems is determined by the mutual interaction of particular elements of the geo-mechanical system which include: the roof slab, the pillars and the excavation bed. Due to the possibility of human intervention, structural pillars – whose strength properties can be determined by the appropriate selection of their dimensions and shape – play a particular role in this system. The optimization of the properties of these pillars is mainly based on the results of laboratory tests of rock samples in the strength test machine and on the basis of visual observations of their behavior in situ. The article presents the experimental results carried out under pit conditions in order to determine the rock pillar reaction. Suitable observations were made using the so-called volumetric method. The obtained results were discussed in relation to the results of strength tests on rock samples, indicating the limited similarity to the deformation characteristics.

Incorporating changing duty cycles in CM-shuttle car matching using discrete event simulation: a case study

Ignoring changing duty cycles result in equipment mismatch which increases operating cost and misallocation of resources. The objective of this study is to investigate the effect of changing duty cycles on the optimal shuttle car fleet size used to mine a particular panel width. A room and pillar mining system is modelled using discrete event simulation and validated using data from a real mine. Experimental analysis is conducted to evaluate the effect of ignoring changing duty cycle in a 17-entry coal panel. Changing duty cycle is accounted for by determining the optimal fleet size in defined segments within the panel. The study shows that, for the 17-entry panel studied, a fleet of four shuttle cars is optimal for the entire panel when changing duty cycle is not accounted. However, by accounting for changing duty cycle, a fleet size of four is only optimal for 80% of the defined segments.

Reflections on narrow-reef platinum mining pillar design systems as applied to a large platinum exploration feasibility project

Reflections on narrow-reef platinum mining pillar design systems as applied to a large platinum exploration feasibility project

Incorporating changing duty cycles in CM-shuttle car matching using discrete event simulation: a case study

Ignoring changing duty cycles result in equipment mismatch which increases operating cost and misallocation of resources. The objective of this study is to investigate the effect of changing duty cycles on the optimal shuttle car fleet size used to mine a particular panel width. A room and pillar mining system is modelled using discrete event simulation and validated using data from a real mine. Experimental analysis is conducted to evaluate the effect of ignoring changing duty cycle in a 17-entry coal panel. Changing duty cycle is accounted for by determining the optimal fleet size in defined segments within the panel. The study shows that, for the 17-entry panel studied, a fleet of four shuttle cars is optimal for the entire panel when changing duty cycle is not accounted. However, by accounting for changing duty cycle, a fleet size of four is only optimal for 80% of the defined segments.

Financial planning for retirement in young adults: Interaction of professional experience, knowledge, and beliefs

IntroductionYoung people in Slovakia are facing a very high-consequence financial decision soon after entering their first job as they must decide whether to join the 2nd pension pillar. Since 2004 the 2nd pension pillar presents a new possibility of financial planning for retirement (hereafter FPR) in Slovakia. While in the 1st pension pillar employees can count on a defined level of retirement benefits based on a computation that reflects their salary and years of service (DB pension), in the 2nd pillar employees invest their contributions in pension funds at one of the private financial institutions. The 2nd pension pillar in Slovakia represents a type of defined contribution plan (DC pension), where retirement income is calculated on the basis of the worker's level of pre-retirement contributions. Unlike the 1st state pillar, participation in the private 2nd pillar is not mandatory for Slovak employees nowadays. At the same time, only people up to 35 years can enroll in the 2nd pillar.The decision of an individual employee whether to enter the 2nd pillar has far-reaching consequences because a process of undergoing finance reform comprises the massive shift from defined benefit (DB) to defined contribution (DC) retirement plans for young adults. The changes in the retirement income system are aimed at an increase in responsibility for one's retirement income that will no longer be determined by one's employer and the state, but instead will largely depend on the saving and investment decisions of an individual employee. Yet many legal and economic changes, which accompany the 2nd pension pillar system in Slovakia from its inception until now, make this decision-making environment rather unclear and difficult to understand.In addition to enrolling in the 2nd pillar, there are many other decisions young people need to make with regard to FPR, such as investment choices in the 2nd pillar or participation in the 3rd pillar. These high consequence choices find most young people quite unprepared. Indeed, despite the importance of the financial decisions that young adults need to make, financial retirement planning decisions remain an area within which individuals receive little formal and/ or informal education.Studies on financial preparation for retirement have focused mostly on demographic indicators associated with FPR among all people of working age or they focused on older individuals approaching retirement. In the present study we examine the psychological, cognitive and motivational forces that underlie planning and saving for retirement in young people. Factual financial knowledge, financial hands-on experience, and personal beliefs on FPR are explored as important psychological variables which can broaden our understanding of the psychological forces that drive young people to prepare financially for their retirement.Financial Knowledge and FPRFactual knowledge and understanding of financial matters are arguably one of the necessary prerequisites of the ability to make personal financial decisions efficiently (Croy, Gerrans, & Speelman, 2010; Hershey, Austin, & Gutierrez, 2015; Lusardi & Mitchell, 2011a, 2011b). There is a wealth of evidence that insufficient financial knowledge in adulthood results in a range of negative outcomes. For instance, a low level of financial literacy and numeracy have been identified as the root cause of poor retirement saving and investment decisions (Lusardi & Mitchell, 2011a, 2011b). Many studies show that engagement in planning for retirement and saving rates are deeply impacted by one's level of financial and investment knowledge (Croy et al., 2010; Van Rooij, Lusardi, & Alessie, 2011). According to recent research of retirement saving across eight European countries, financial literacy positively influences retirement savings, so that individuals with a higher level of financial knowledge show a greater tendency to save for retirement (Fernandez-Lopez, Otero, Vivel, & Rodeiro, 2010). …

An assessment of coal pillar system stability criteria based on a mechanistic evaluation of the interaction between coal pillars and the overburden

Coal pillar design has historically assigned a factor of safety (FoS) or stability factor (SF) according to their estimated strength and the assumed overburden load acting on them. Acceptable FoS values have been assigned based on past mining experience or a statistical link between FoS and probability of failure (PoF). Pillar width-to-height (w/h) ratio has long been established as having a material influence on both pillar strength and its potential failure mode. However, there has been significant disagreement on using both factor of safety (FoS) and w/h as part of pillar system stability criterion, as compared to using FoS in isolation. This paper will argue that there are valid technical reasons to bring w/h ratio into system stability criteria (other than its influence on pillar strength), as it is related to the post-failure stiffness of the pillar, as measured in situ, and its interaction with overburden stiffness. When overburden stiffness is also brought into pillar system stability considerations, two issues emerge. The first is the width-to-depth (W/D) ratio of the panel and whether it is sub-critical or super-critical from a surface subsidence perspective. The second relates to a re-evaluation of pillar FoS based on whether the pillar is in an elastic or non-elastic (i.e., post-yield) state in its as-designed condition, as this is relevant to maintaining overburden stiffness at the highest possible level. The significance of the model is the potential to maximise both reserve recovery and mining efficiencies without any discernible increase in geotechnical risk, particularly in thick seams and higher depth of cover mining situations. At a time when mining economics are, at best, marginal, removing potentially unnecessary design conservatism is of interest to all mine operators and is an important topic for discussion amongst the geotechnical community.

Unanticipated multiple seam stresses from pillar systems behaving as pseudo gob–case histories

Underground coal mining in the U.S. is conducted in numerous regions where previous workings exist above and/or below an actively mined seam. Miners know that overlying or underlying fully extracted coal areas, also known as gob regions, can result in abutment stresses that affect the active mining. If there was no full extraction, and the past mining consists entirely of intact pillars, the stresses on the active seam are usually minimal. However, experience has shown that in some situations there has been sufficient yielding in overlying or underlying pillar systems to cause stress transfer to the adjoining larger pillars or barriers, which in turn, transfer significant stresses onto the workings of the active seam. In other words, the overlying or underlying pillar system behaves as a “pseudo gob.” The presence of a pseudo gob is often unexpected, and the consequences can be severe. This paper presents several case histories, summarized briefly below, that illustrate pseudo gob phenomenon: (1) pillar rib degradation at a West Virginia mine at 335m depth that contributed to a rib roll fatality, (2) pillar rib deterioration at a Western Kentucky mine at 175m depth that required pillar size adjustment and installation of supplemental bolting, (3) roof deterioration at an eastern Kentucky mine at 400m depth that stopped mine advance and required redirecting the section development, (4) coal burst on development at an eastern Kentucky mine at 520m depth that had no nearby pillar recovery, and (5) coal burst on development at a West Virginia mine at the relatively shallow depth of 335m that also had no nearby pillar recovery. The paper provides guidance so that when an operation encounters a potential pseudo gob stress interaction the hazard can be mitigated based on an understanding of the mechanism encountered.

Experimental and Numerical Investigation on the Bearing and Failure Mechanism of Multiple Pillars Under Overburden

To reveal the mechanical response of a multi-pillar supporting system under external loads, compressive tests were carried out on single-pillar and double-pillar specimens. The digital speckle correlation method and acoustic emission technique were applied to record and analyse information of the deformation and failure processes. Numerical simulations with the software programme PFC2D were also conducted. In the compressive process of the double-pillar system, if both individual pillars have the same mechanical properties, each pillar deforms similarly and reaches the critical stable state almost simultaneously by sharing equal loads. If the two individual pillars have different mechanical properties, the pillar with higher elastic modulus or lower strength would be damaged and lose its bearing capacity firstly. The load would then be transferred to the other pillar under a load redistribution process. When the pillar with higher strength is strong enough, the load carried by the pillar system would increase again. However, the maximum bearing load of the double-pillar system is smaller than the sum of peak load of individual pillars. The study also indicates that the strength, elastic modulus, and load state of pillars all influence the supporting capacity of the pillar system. In underground space engineering, the appropriate choice of pillar dimensions and layout may play a great role in preventing the occurrence of cascading pillar failure.