Pillar Extraction Research Articles

Coal Pillar Extraction Under Weak Roof

This article offers an examination of a retreat mining method conducted at the Pinoura Mine in India from 2010 to 2017. The method is atypical for coal mines of India’s coalfields. The method executes depillaring in a single pass and does not require the formation of galleries and support installation in splits, thus, reducing the cycle time. A variety of observations are discussed throughout this work and emphasis is placed on field measurements and depillaring under weak roof (RMR = 40–45). This paper discusses design techniques, specifically the estimation of the snook (remnant pillar) size, and important practical observations after the fact. The execution of this method was eventually conducted in eleven panels.

Extraction of ore reserves from pillars in room-and-pillar mining

The geotechnical situation in mines using the open stoping methods is governed by complex geomechanical behavior of rock mass around rib and level pillars. The impact of rock pressure on underground excavations grows in this case, and dynamic events due rock pressure happen more often. The latter became the reason for implementing this research. In terms of steeply dipping ore bodies, safe mining of earlier left pillars is feasible. The best scenario for pillar extraction, considering their parameters, is caving to open and partly filled with overlying rocks stopes. The geomechanical calculations during justification of mining parameters during extraction of ore reserves from pillars have determined regular patterns in the stress–strain behavior of rocks mass, which contributes to qualitative and quantitative prediction of safe and feasible mining conditions. The zones of instability in structural elements of the geotechnology, including pillars, are detected. The author proposes the order and sequence of pillar caving to open and partly filled stopes at the admissible completeness and quality of extraction.

LamNI - an instrument for X-ray scanning microscopy in laminography geometry.

Across all branches of science, medicine and engineering, high-resolution microscopy is required to understand functionality. Although optical methods have been developed to `defeat' the diffraction limit and produce 3D images, and electrons have proven ever more useful in creating pictures of small objects or thin sections, so far there is no substitute for X-ray microscopy in providing multiscale 3D images of objects with a single instrument and minimal labeling and preparation. A powerful technique proven to continuously access length scales from 10 nm to 10 µm is ptychographic X-ray computed tomography, which, on account of the orthogonality of the tomographic rotation axis to the illuminating beam, still has the limitation of necessitating pillar-shaped samples of small (ca 10 µm) diameter. Large-area planar samples are common in science and engineering, and it is therefore highly desirable to create an X-ray microscope that can examine such samples without the extraction of pillars. Computed laminography, where the axis of rotation is not perpendicular to the illumination direction, solves this problem. This entailed the development of a new instrument, LamNI, dedicated to high-resolution 3D scanning X-ray microscopy via hard X-ray ptychographic laminography. Scanning precision is achieved by a dedicated interferometry scheme and the instrument covers a scan range of 12 mm × 12 mm with a position stability of 2 nm and positioning errors below 5 nm. A new feature of LamNI is a pair of counter-rotating stages carrying the sample and interferometric mirrors, respectively.

Geomechanical and geotechnical features of rib pillar extraction in the Korobkovo iron ore deposit

Geomechanical and geotechnical features of rib pillar extraction in the Korobkovo iron ore deposit

SoCalGas and Electrochaea commission new biomethanation reactor in US

Field studies have found that, generally, a roof fall takes place after certain amount of roof strata sagging. Recent applications of auto warning tell-tale (AWTT) instrument as an early warning system at different depillaring panels found it to be simple, economical and efficient during the coal pillar extraction (called depillaring). AWTT is able to watch the set value of roof sagging continuously in time. However, the application of AWTT experienced two practical issues: (i) fixing roof sagging warning value before the fall of overlying strata and (ii) deciding horizon above which its anchorage point of AWTT needs to be installed. Different field experiences noticed that an anchorage horizon at 10 m depth from the ceiling of a gallery works satisfactorily for goaf edge. But fixation of the roof sagging warning value, before the fall of overlying strata, is found to be complex. Generally, the warning value for a given site conditions is determined by extensive field monitoring and correlation of the roof sagging value at the goaf edge with corresponding roof falls. Field studies found that modulus of elasticity and thicknesses of immediate roof are important parameters in deciding the warning value of the roof sagging. These studies also indicated that the variation in size of the left-out ribs and goaf span influence the warning value. These observed facts about the warning value for an AWTT are studied in laboratory using a numerical modelling approach in FLAC3D. The results obtained through developed simulated models are found to be in close agreement with those of the field studies. Attempts are also made to quantify the influence of above-mentioned parameters over the warning value through collated results of different studied models. The obtained results of field and laboratory investigations are presented and discussed in this paper for strata control in a depillaring panel.

Influence of preparation method on extraction of rib and floor pillars in mining thin ore bodies

Influence of preparation method on extraction of rib and floor pillars in mining thin ore bodies

Roof sagging limit in an early warning system for safe coal pillar extraction

Field studies have found that, generally, a roof fall takes place after certain amount of roof strata sagging. Recent applications of auto warning tell-tale (AWTT) instrument as an early warning system at different depillaring panels found it to be simple, economical and efficient during the coal pillar extraction (called depillaring). AWTT is able to watch the set value of roof sagging continuously in time. However, the application of AWTT experienced two practical issues: (i) fixing roof sagging warning value before the fall of overlying strata and (ii) deciding horizon above which its anchorage point of AWTT needs to be installed. Different field experiences noticed that an anchorage horizon at 10 m depth from the ceiling of a gallery works satisfactorily for goaf edge. But fixation of the roof sagging warning value, before the fall of overlying strata, is found to be complex. Generally, the warning value for a given site conditions is determined by extensive field monitoring and correlation of the roof sagging value at the goaf edge with corresponding roof falls. Field studies found that modulus of elasticity and thicknesses of immediate roof are important parameters in deciding the warning value of the roof sagging. These studies also indicated that the variation in size of the left-out ribs and goaf span influence the warning value. These observed facts about the warning value for an AWTT are studied in laboratory using a numerical modelling approach in FLAC3D. The results obtained through developed simulated models are found to be in close agreement with those of the field studies. Attempts are also made to quantify the influence of above-mentioned parameters over the warning value through collated results of different studied models. The obtained results of field and laboratory investigations are presented and discussed in this paper for strata control in a depillaring panel.

Optimisation of binder alternative for cemented paste fill in underground metal mines

To maximise ore recovery safely and economically, a proper backfill design of required strength is imperative to facilitate extraction of adjacent stopes. Ordinary Portland cement (OPC) has a direct impact on the strength gained by the paste fill mix and is also a major contributor to the backfilling cost. This has prompted the users to go for partial replacement of OPC with readily available industrial wastes such as fly ash and jarosite to obtain a paste mix of desired strength. This paper highlights the use of a mathematical model to predict the strength requirement (unconfined compressive strength and cohesion) of self-supporting paste fill for secondary pillar extraction of stopes in metal mines. This paper also highlights extensive laboratory investigation carried out for partial replacement of OPC with fly ash and jarosite to map the changes in the strength of paste mix with time. Initially, the percentage of OPC required to achieve the designed strength was evaluated and subsequently, the percentage of OPC in the mix was replaced gradually with fly ash and jarosite. Laboratory results indicated that the strength of the paste mix increases with curing period (7, 14, 28 and 56 days) and the chemical composition of the ingredients also played a major role in strength development. The results were then compared with the required strength predicted from the model to obtain proper paste mix for existing mine’s stope dimension.

Risk Evaluation, Design, Implementation, Instrumentation, and Verification for Crown Pillar Extraction at Pinos Altos Mine

The Santo Nino ore body at Pinos Altos Mine has been in production since 2009 using both open pit and underground mining methods. Between 2015 and 2017, an extensive study evaluated extraction strategy of the Santo Nino crown pillar. The Agnico Eagle project team evaluated geomechanical, operational, safety and economical risks before developing a comprehensive plan to extract the Santo Nino crown pillar by underground stoping. The geomechanical aspects of that study focused on interpreting in situ rock mass conditions and understanding the mechanical and hydrological/hydrogeological mechanisms influencing ground reaction during open pit and underground mine operations to make meaningful forward predictions for crown pillar extraction. Numerical modeling played a significant role in making forward predictions. To minimize uncertainty in those predictions, the model parameters were calibrated using measured pit slope deformations, back analysis of historical slope instabilities and underground observations of rock mass conditions. Ultimately, it was decided that long-hole stoping would be utilized for crown pillar extraction. The pit floor would be used as a drilling horizon, and the upper most level of the underground operations served as the mucking horizon. Various safety and operational risk mitigation strategies were developed and implemented; this included geomechanical monitoring using the in-pit radar system and numerous borehole extensometers installed underground to monitor ground deformations. The calibrated numerical model results provided valuable input for the design of the instrumentation program, and once the crown pillar came into production in late 2017, the instrumentation provided valuable data for model verification and stope design adjustments.

Development of a model to estimate strata behavior during bord and pillar extraction in underground coal mining

Instrumentation and monitoring is undertaken aiming at evaluation of changing values of rock mechanic parameters, namely, dilation, load, convergence, and stress, during mining for a safe strata control. It enables the mining practitioners to anticipate roof fall–related dangers in advance and taking subsequent preventive measures while depillaring. The coal measure formations consist of relatively weaker stratified rock masses. Bed separation occurs in the overlying strata due to induced mining stresses, which cause the rock mass in its surrounding to displace. These occurrences can be monitored by installing geotechnical instruments at judicious locations to avoid occurrence of any dangerous condition due to roof fall. Improper anticipation of strata movement during extraction in coal mining is one of the principal causes of accidents due to roof and side collapses. Also, the installed instruments can help in prediction of any apprehensive condition during depillaring. Preventive measure can be taken if the strata movement is monitored and roof fall is predicted in advance. The study is aimed to develop a conceptual model roof fall warning index, based on critical strata movement during underground coal extractions. Numbers of mining aspects, such as analysis of instruments’ reading, geo-mining parameters, physico-mechanical properties roof formations, and induced stress, are taken into considerations for development of the model. This study is mainly focused to predict a critical strata movement value for safety of the bord and pillar method of mining, perticularly depillaring.

Megalith quarries for Stonehenge's bluestones

Abstract

ОТРАБОТКА ПРЕДОХРАНИТЕЛЬНОГО ПОДКАРЬЕРНОГО ЦЕЛИКА В УСЛОВИЯХ ЕГО ПОДРАБОТКИ ПОДЗЕМНЫМИ РАБОТАМИ

One of the problems taking place during development of ore deposits is untimely preparation of reserves to extraction. Hence, entire effectiveness of the development is reduced. Therefore, for the reserve replacement previously left different ore pillars are developed more often. That’s why issues related to safe extraction of pillars are currently important in modern conditions of deposits. In the context of one of gold ore deposit with strongly marked geological structural indetermination of solid the method of extraction of previously left underworked underquarry protective pillar is proposed and justified for keeping of productive capacity and provision of the deposit stable functioning. In the work geo-mechanical model of the deposit represented with general technological scheme of mining during extraction of previously left underquarry pillar with saving of actual mine technical infrastructure conditioned with open and underground development of the deposit is developed. Numerical finite element simulation has been adopted as main instrument for the study. It is established by calculations that underground extraction of underworked underquarry protective pillar of steep ore deposit is limited with extension of wide zones of possible solid destruction with way out into daylight surface due to significant broken condition of the deposit.

Aseismic Mining Subsidence in an Abandoned Mine: Influence Factors and Consequences for Post-Mining Risk Management

In the Lorraine area of eastern France, decades of iron-ore mining from 1850 to 1997 have left vast underground cavities beneath or in the vicinity of urban areas. Several major collapses occurred in the southern part of this iron-ore basin in the 1990s, after the mine closure and the flooding of underground mine workings. Following these large-scale collapses, the French government initiated a strategy of post-mining risk management to prevent and control risks associated with these ground failures. The high-risk zones are secured either by reducing the vulnerability while the moderate risk zones are monitored for public safety purposes by using in situ monitoring. This monitoring relies mainly on real-time microseismic systems, to detect precursors to a rapid large-scale collapse. After the progressive closing and then flooding of the northern iron basin ending in 2008, subsidence was observed in a town of the Lorraine basin in autumn of 2009. However, this local subsidence, with a low velocity of few centimeters per month, was not clearly detected by the borehole microseismic monitoring station located nearby. Only some microseismic events were recorded, which could not be unambiguously related to the beginning of the subsidence event. To better understand this lack of microseismic precursor a geophysical investigation was launched. A calibration blast experiment was carried out from a remaining old underground access in order to answer to the following questions: (1) what is the seismic wave attenuation field?; (2) what is the minimum source power that can be detected by the sensors?; (3) what is the impact of the geology, the faults corridor and the integral pillar extraction zone on the wave propagation field? The results of this study show strong anelastic attenuation of the seismic waves though the monitored overburden most likely related to the extensive fault system intersecting the study site. Strong attenuation might explain the lack of detected microseismicity during the subsidence event. In order to clarify this issue, a mobile GPS monitoring system was designed and tested to address this type of situation in future.

Using LaModel to analyze coal bumps

Coal bumps have long been a safety hazard in coal mines, and even after decades of research, the exact mechanics that cause coal bumps are still not well understood. Therefore, coal bumps are still difficult to predict and control. The LaModel program has a long history of being used to effectively analyze displacements and stresses in coal mines, and with the recent addition of energy release and local mine stiffness calculations, the LaModel program now has greatly increased capabilities for evaluating coal bump potential. This paper presents three recent case histories where coal stress, pillar safety factor, energy release rate and local mine stiffness calculations in LaModel were used to evaluate the pillar plan and cut sequencing that were associated with a number of bumps. The first case history is a longwall mine where a simple stress analysis was used to help determine the limiting depth for safely mining in bump-prone ground. The second case history is a room-and-pillar retreat mine where the LaModel analysis is used to help optimize the pillar extraction sequencing in order to minimize the frequent pillar line bumps. The third case history is the Crandall Canyon mine where an initial bump and then a massive pillar collapse/bump which killed 6 miners is extensively back-analyzed. In these case histories, the calculation tools in LaModel are ultimately shown to be very effective for analyzing various aspects of the bump problem, and in the conclusions, a number of critical insights into the practical calculation of mine failure and stability developed as a result of this research are presented.

Some rock engineering aspects of multi-reef pillar extraction on the Ventersdorp Contact Reef

Some rock engineering aspects of multi-reef pillar extraction on the Ventersdorp Contact Reef

Effect of Shaft Pillar Extraction on Stability of Main Shaft: A Case Study at Xincheng Gold Mine, China

Mining of ore body in the vicinity of a shaft has a significant influence on its stability. The in situ monitoring and numerical simulation are employed to analyze the effect of shaft pillar extraction at Xincheng Gold Mine. The XI# ore body is recently found around and beneath the shaft, and mining in this area may be detrimental to the shaft. Firstly, on the base of geological survey and in situ displacement monitoring, mechanical parameters of rock mass are obtained and the displacement around the shaft is measured. Secondly, the sensitivities of five main factors that may affect the shaft displacement are analyzed by means of orthogonal experiment according to the numerical simulation with FLAC3D. Finally, a numerical model is established according to the in situ condition; in order to forecast the shaft displacement induced by mining activities of XI# orebody, the Mining Priority Index (MPI) is put forward and used to select the optimal mining sequence. Based on the comparison between the numerical results with the monitoring data, it is determined that the ore within 100 m from the shaft is not suggested to be extracted until the last period of the shaft life.

Design of Snook in Depillaring Panel Using Continuous Miner

Different patterns of extraction of pillars during depillaring operation with continuous miner are adopted depending upon the geo-mining condition. Various sizes of snook are left during final extraction of coal in mechanized depillaring operation. The size of the snook plays a significant role in providing safe mining condition. Stability of the snook left during final extraction with continuous miner was analyzed using numerical modelling. A case study has been chosen for the simulation of the depillaring process with three scenarios of varying width of snook, i.e., 3.5, 4.5, and 5.5 m. The mine panel consists of 4 × 8 array of pillars having the width of 41 m center to center. Double split and fender method of mining is used with the straight line of extraction. Field investigation shows that the failure of immediate roof occurs after extraction of two or three fenders (i.e., about 40 m). The thickness of immediate roof was 2 m. A numerical model of a depillaring panel was simulated with three different sizes of snook, i.e., 3.5, 4.5, and 5.5 m in the study. An immediate roof of 2 m thickness was considered in the model. An interface has been introduced in between immediate and main roof. The immediate roof behaves as a cantilever during depillaring. It is concluded from the simulation of different size of snooks that snook width of 5.5 m shows reasonable residual strength to hold the immediate roof. Higher tensile stress was developed at the top of the immediate roof above the edge of the snook which leads the possible roof failure towards the goaf side. Vertical stress profile and yield profile in the panel at different stages of mechanized depillaring have also been plotted.

Rib stability: A way forward for safe coal extraction in India

Ensuring rib stability during pillar extraction is of prime importance in bord and pillar (B&P) method of underground coal mining with caving. Rib stability has been assessed here by way of assessing factor of safety (FOS), a ratio of the strength of rib to stress on it. Earlier formulations for rib stability when applied to case studies gave very low FOS value suggesting significant ground control problems, which were contrary to the field observations. This has necessitated the need to revisit the concept of rib stability. The stress coming on the rib is estimated with the use of numerical modeling technique using the FLAC3D software. The methodology of assessing rib-stability with the help of suggested rib-strength formulation has been validated at eight Indian coal mines. The outcome of this study finds relevance and importance in ensuring underground coal liquidation with improved safety and conservation.

Extraction of locked-up coal by strengthening of rib pillars with FRP – A comparative study through numerical modelling

In some of the coalfields in India, coal seams are only developed but no extraction of pillars is possible due to the presence of surface or sub-surface structures and also non-availability of stowing materials which leads to huge amounts of coal being locked-up underground. Spontaneous heating and fire, accumulation of poisonous gases, severe stability issues leading to unsafe workings and environmental hazards are the major problems associated with the developed coal pillars. So, there is a pressing need for a technology for the mining industry to extract the huge amount of coal locked-up under different constraints. In this study, the locked-up coal is proposed to be extracted by artificially strengthening the rib pillars. The detailed comparative study is carried out to know the increase of extraction percentage of locked-up coal by strengthening the rib pillars with FRP. Extraction methodology is designed and studied through numerical modelling for its stability analysis to evaluate its suitability of application in underground.

Analysis of Geomechanical Factors Affecting Rock Bursts in Sedimentary Rock Formations

Rock bursts are defined as sudden, violent failures of rock mass that are of such a magnitude that they expel large amounts of coal and rock into the face area during longwall or pillar extraction in sedimentary rocks. In an attempt to develop tools for assessing stress bump potential, the first author initiated a comprehensive study using site specific information from 25 case studies undertaken in U.S. mines. This effort builds on an initial study while expanding the data base and including additional variables and analyses. Multiple linear regression and numerical modeling analyses of geological and mining conditions were used to identify the most significant factors contributing to stress bumps in coal mines. Twenty-five factors were considered initially (mechanical properties of strata, stress fields, face and pillar factors of safety, joint spacings, mining methods, and stress gradients, among others). Allowances were made for favorable local yielding characteristics of mine roof and floor in reducing damage severity. Pillar and face factors of safety were calculated using displacement-discontinuity methods for specific geometries in case studies having experienced both violent and nonviolent failures. This work identified the most important variables contributing to coal bumps and violent failure of near seam strata. These are [1] mechanical properties of strata, including local yield characteristics of a mine roof and floor, [2] gateroad geometry and/or gate pillar factors of safety, [3] stress gradients associated with the approach of mining to areas of higher stress concentrations such as abutment stresses from multiple seam mining, and [4] roof beam thickness, joint spacing, and stiffness characteristics, which influence cave conditions and dynamic loading. The latter variables, combined together to form a new variable called “strata rigidity-cavability”, reflect some of the most important aspects of violent failure, i.e. having massive and stiff near-seam stratigraphic units capable of absorbing high strain energy, forming high stress on mine structures and poor cave conditions, and thus the potential for dynamic loads.