Geo-mining Conditions Research Articles

Constrained Maximization of the Economic Production Model of Lithium Ore Exploration in Nasarawa

Over 20,000 years ago, mining was discovered as one of the oldest production industries generating over US$700 billions’ of revenue in the world by a few mining companies. For some time, mining work has resulted in a very demanding affair as a result of greater depth, low-grade, limited resources, and complex geo-mining conditions. Therefore, optimization of the mining system plays a vital role in profit maximization with the satisfaction of many constraints. However, today’s mining industry uses complex and sophisticated systems whose reliability has become a critical issue. This work adopted the financial market theory of development to propose a maximized constrained optimization economic production model for lithium ore exploration in Nasarawa, Nigeria using three methods such as: the break-even principle method of cut-off grade between revenue earned and cost incurred; the mortimer’s method principle to determine ore based in two cut-off criteria (original and average good) and the lane method for net profit value thereby maximizing processing capacity. Data obtained from the field and the Ministry of Mines and Solid Minerals were analyzed using energy dispersive x-ray fluorescence (EDXRF) showing the presence of lithium. The froth flotation technique used showed the beneficiation thereby achieving improved lithium concentrates and the inductively coupled atomic emission revealed a high presence of lithium of over 1859 parts per million (ppm) and other minerals.

Numerical modelling approach for estimation of a yield zone in the face of a deep longwall panel

In the Longwall mining method, the coal face is being supported with two-legged or four-legged shield supports which improve better roof control between the face and canopy tip. The development of load on the face increases with the face retreating rate or the increase of the overhung length behind the shield support and as a result, the coal face tends to yield/fail. The yield/failure zone in the face extends depending on intensity of developed load due to the depth of mining, panel size, height of excavation and geometry of the overhung. The broken coal from the yielded face may fall on the shearer, armoured flexible conveyor (AFC), shield supports or may hit the deployed manpower in the face and causes the face stoppage which in turn results in to the loss of the project. It is therefore, a study is conducted to understand the face yield/failure behaviour considering various geo-mining conditions based on input parameters such as main roof thickness, overhung length, and material type and setting load. This paper develops a unique statistical model to predict the yield/failure zone in the longwall face. For this purpose, a total of fifty-four (54) three-dimensional finite element models in ANSYS software are developed and analyzed considering Drucker-Prager failure criterion.

Numerical analysis for assessing the effects of crown pillar thickness on ore dilution around the sub-level open stopes

Sub-level open stopes with delayed backfill are being used to extract massive, tabular, and steeply dipping ore bodies for increased productivity. Crown pillars in the orebody divide mining zones to increase productivity by enabling simultaneous production in two or more zones. Despite their effectiveness, these mining techniques may be accompanied by substantial amounts of overbreak, resulting in considerable ore dilution. This study investigates the effects of crown pillar thickness under various geo-mining conditions on hanging wall overbreak. Under plane strain conditions, 240 non-linear finite element models with the Mohr-Coulomb elastoplastic failure criteria were used for numerical analysis. The outcomes are analyzed in terms of Equivalent Linear Relaxation Depth (ELRD) and Equivalent Linear Overbreak Sloughage (ELOS). The results show that by increasing the crown pillar thickness from 5 m to 8 m, the ELRD and ELOS are reduced by roughly 45 % and 74 %, respectively, for a given material property.

Development of design norms for rib/snook during mechanised depillaring by continuous miner

This paper presents the efforts made to design irregular-shaped-heightened-rib/snook based on factor of safety (FOS) during mechanised extraction of already developed coal pillars by continuous miner. In situ monitoring of performance of different sizes of rib/snook with variation in their area, effective-width, width-to-height ratio and height under varying geo-mining conditions are studied comprehensively at 39 panels of 7 different mines and found a number of influencing factors affecting its design as per the field studies. Based on this study, a number of conceptual models are developed to understand the need of rib/snook and its interaction with different nature of roof at varying depth of cover. Further, a parametric study is carried out on calibrated numerical models by varying the area and height of rib/snook with nature of roof, depth of cover and panel width for the estimation of strength and stress over it. Empirical formulations are developed for estimation of a competent area, effective width and width-to-height ratio in a given geo-mining condition corresponding to a limiting value of FOS of 0.30–0.35. Further, the results of developed empirical formulations are validated with the field studies.

Numerical study of stability of coal pillars under the influence of line of extraction

In underground coal mining, strata instability is one of the most catastrophic hazards, which involves sudden and violent dynamic failure of the pillars and overlying strata. Despite decades of research, the contributing factors and mechanisms of failure of underground structures are still not completely understood. Hence, it remains challenging to forecast strata failures and quantify their likelihood of occurrence. This paper deals with the scope of application of different line of extraction in problematic conditions, such as when the pillars are surrounded by goaf areas or are overstressed or there are other transportation/coal evacuation issues. In this paper, the effect of line of extraction on pillar stability has been studied in the context of an Indian underground coal mine by way of a comparative analysis through numerical simulation. The stress on the coal pillars during depillaring have been found to be similar for steep-diagonal line and straight line of extraction. However, stress on the pillars in case of steep-diagonal line follows a better trend than straight line of extraction. Overall, the results of this study establish the scope of application of different line of extraction in geo-mining conditions which do not allow implementing straight line of extraction in mechanised depillaring.

Numerical Study on the Surface Movement Regularity of Deep Mining Underlying the Super-Thick and Weak Cementation Overburden: A Case Study in Western China

While surface movement regularities have been sufficiently understood in the mining practices of eastern China, the case seems to be very different in western China where the super-thick and weak cementation (STWC) overburden exists. To better understand such knowledge, we compared geomining conditions and surface subsidence data for 16 coal mines and developed a carefully calibrated numerical model, with primary concern the relationship between subsidence rate and mining scale. We find that mining under the STWC overburden is characterized by the extremely small subsidence rate compared to the deep mining cases in eastern China, and the unusual subsidence phenomenon should be regional rather than an isolated case. We also find that the critical subsidence basin can be formed only when the goaf length and width both reach about 3.3 h (h is the average mining depth), which is far beyond the conventional understanding. We suggest that the large-scale mining under the STWC overburden carries enormous risks, which require great attention. The reported data, findings, and suggestions in this paper should be quite useful for coal mines with similar geomining conditions, and are also important for ecological protection and sustainable development of western China.

Importance of Fracturing Hard and Massive Overlying Strata for Complete Extraction of Thick Coal Seam – Case Studies

Abstract Engineering efforts need to be organized as per the rock mechanic conditions of the site for efficient underground extraction of a thick coal seam. Geo-mining conditions of Indian coalfields have favoured development of thick coal seams on Bord and Pillar (B&P) method, where single lift depillaring of total thickness (SLDTT) is vital for their final extraction. Competency of heightened pillar is an important factor for uncontrolled roof-pillar interaction during caving of the hard and massive overlying strata. An increase in extraction height by underwinning of roof coal band of the thick coal seam during retreat, developed along its floor horizon, is found to be the main reason for the strength deterioration. Conducted field studies also showed that the presence of competent overlying strata caused caving after a large overhang inside the goaf varying from 6000 m2 to 12500 m2. An attempt was made to control the roof caving by a proportional increase in width of the heightened pillars and it worked well but caused the issue of resource conservation. However, another field study with SLDTT working below laminated and weak overlying strata experienced a smooth strata control condition. This fortifies the idea of strength reduction of the competent overlying strata by fracturing for a controlled strata behaviour. This paper presents the result of the field investigations to demonstrate the role of strength reduction of overlying strata for underground extraction of total thickness of a thick coal seam in single lift.

Status and prospects of underground coal mining technology in Vietnam

Underground coal mining in Vietnam plays an important role tonot only the sustainable coal industry but also the energy and social securityin this country. Although the Vietnam coal industry has produced 35–45million tonnes of raw coal per annum in past ten years, a great volume ofcoal resources remains distributed in complex geo-mining conditions andmostly unmined. This paper presents a brief review of the current andpotential technologies for cutting coal and controlling roof in Vietnamunderground coal mines. From the review, it is concluded that there is anurgent demand on improvement of current technologies as well as oninvestigation for effective application of more advanced mining methodsinto the industry, especially for deep mining at Red River Delta—the largestcoal basin in Vietnam.

Development of Support Plan and Operation Scheme for Semimechanized Longwall Face of Coal Seam 10T, Nam Khe Tam Mine – 86 Company, Dong Bac Corporation

Support plans and operation schemes of mine faces are critical technical documents inunderground coal mining management. The development and selection of a reasonable support plan andoperation scheme of the face are complicated because they involve many factors. In specific miningconditions, developing and selecting an appropriate support plan and operation scheme will improve theworking efficiency of equipment, increase labor productivity, and ensure workers' safety. This articleresearched a mining technology for the thin seams, focusing on coal seam 10T in Nam Khe Tam coalmine, 86 Coal Company. From the analysis of geo-mining conditions, the article developed and selecteda reasonable support plan and operation scheme for the face in coal seam 10T. After being used in thefield, the support plan and operation scheme have brought the face efficiency and safety.

Techno-Economic Feasibility of the Longwall Top Coal Caving Method Based on the FTCD Index: A Parametric Case Study in India

An extraction method for deep-seated thick seam deposits by underground mining with high resource recovery has remained a great challenge for Indian mining engineers, whereas the longwall top coal caving (LTCC) method has evolved as an effective method for various geo mining conditions in China and other counties. The percentage of top coal recovery (TCR) plays a predominant role in determining the feasibility of LTCC, which relies on the First Top Coal Caving Distance (FTCD). In this paper, the critical geotechnical parameters are identified, numerically simulated, and statistically analyzed, and the FTCD for Indian geo-mining conditions is developed and validated. A financial assessment is conducted, considering 70% top coal recovery at 85% performance level, cost of production escalated by 20% and fall in coal grade by two grades. The internal rate of return (IRR) for LTCC is 30.24% as per the sensitivity analysis where it is only 18% in single pass longwall method. This study contributes to evaluating both the technical and economic feasibility of introducing LTCC in Indian geo-mining conditions.

Quantitative Assessment of BIGV and Structural Response Based on Velocity and Frequency Around an Opencast Mine

Blast-induced ground vibration (BIGV) velocities and frequencies are of major concern due to their adverse effects and damage to structures. Therefore, it becomes essential to assess the velocities and frequencies induced by blasting in terms of quantitative and qualitative assessment to overcome the problems. There is a need for scientific studies using devices like triaxial geophone associated with a seismograph to measure the peak particle velocity (PPV) and dominant frequency which cause damage to domestic or residential structures near an opencast mine. Each mine has specific geo-mining conditions, and scientific studies provide appropriate results. In total, 32 number of blasting data sets were recorded at every 50 m from the blast site to the last observation point near the village. Ground vibration associated damage criteria is defined in terms of the PPV at different frequency levels and the strength of the structures under study. The permissible limits of BIGV has been provided by the Directorate General of Mines Safety, Dhanbad, India. The permissible PPV values of the BIGV in India is 2, 5, 10 for the historical and sensitive structures, 5, 10, 15 for domestic houses and 10, 20, 25 for industrial buildings at 25 Hz dominant excitation frequencies respectively. The recorded dataset has been proposed through standard models. The velocity amplitude versus frequency gives a reliable relationship about damage criteria of structures. The structures were analysed vis-a-vis PPV and dominant frequency to correlate the damage possibility. The present study carried out in a mega opencast project provides the basic knowledge to assess the safe distance from blasting site for specific charge of explosive, waves which are responsible for more damage to nearby structures and to determine the correlation coefficient between measured and predicted PPV values.

Analysis of the Geomechanical Phenomena That Led to the Appearance of Sinkholes at the Lupeni Mine, Romania, in the Conditions of Thick Coal Seams Mining with Longwall Top Coal Caving

Thick coal seam no. 3, block V, Lupeni mine was mined by longwall top coal caving (LTCC). After the coal mining, the ground surface underwent continuous subsidence, but since 2008, three sinkholes have appeared on the surface with important dimensions, atypical for the geo-mining conditions in this coal basin. This article is a synthesis of the study meant to decipher the geo-mechanical phenomenon that led to the emergence of these sinkholes and highlighting the main factors that contributed to the development of this phenomenon. For this purpose, measurements were made on the terrain deformations using photogrammetric methods and aerial laser scanning, when modeling with 3D finite elements, in elasto-plasticity and with the help of the Knothe–Budrik influence function. The factors that contributed to the occurrence of discontinuous subsidence phenomena are shallow mining depth, the LTCC mining method, and the presence of faults in the vicinity of the mining panels. Additionally, the geo-mechanical phenomena of subsidence terrace development and sinkholes in the mining subsidence troughs at the Lupeni mine were described.

A probability-based risk assessment of roof strata weighting in longwall panels

Weighting of the roof strata in a longwall panel poses serious stability concerns at the working face. Therefore, it is essential to estimate weighting in terms of its interval. Furthermore, difficulty arises during the prediction of roof weighting as rock mass contains inherent uncertainties. In order to cater to this need, probabilistic analysis has been employed. The article aims to decipher the suitability of Monte Carlo simulation technique for the assessment of caving of roof strata. In the current study, firstly, regression models have been developed to estimate periodic weighting interval and first significant main roof weighting interval using data from thirty (30) longwall panels in India. The regression models were then used as deterministic mathematical models for Monte Carlo simulation. It has been observed that the Monte Carlo simulation technique is an acceptable means to evaluate the uncertainties arising from varying geo-mining conditions. In addition to it, sensitivity analysis results exhibited that the tensile strength and unit weight of the main roof is the key factor that governs the interval and severity of the periodic weighting and the first significant main roof weighting.

Parametric study to design competent irregular-shaped remnants in mechanised depillaring

Mechanised depillaring (MD) has been proved to be a panacea for faster extraction of the developed pillars which is blocking access to deeper deposits and locking more than 3200 Mt of coal, developed by Bord and Pillar mining method in Indian coalfields. Depillaring of these square/rectangular-shaped developed pillars by continuous miner creates irregular-shaped ribs/snooks. Stability assessment of such ribs/snooks becomes a challenging task due to various issues faced in estimation of load acting upon it and their strength. Area-based approach for the design of rib/snook is found to be the most suitable criteria during MD. Field investigations supported for parametric investigation for a competent size of rib/snook with varying nature of roof and depth of cover. Taking help from previous studies to design such ribs/snooks on numerical models using FLAC3D, a parametric study is carried out using 3DEC. Strength of such ribs/snooks and load acting upon them is calculated with the help of calibrated numerical models in order to estimate their factor of safety. This paper presents a review of the previous researches and a novel numerical simulation technique for estimation of a competent size of rib/snook in a given geo-mining condition.

Stability analysis of a deep highwall slope using numerical modelling and statistical approach—a case study

For opencast working or pit design, understanding the stability of slope is a prime concern for design engineers prior to or during excavation of mineral. The factor of safety is one such index, which has been extensively used for determining the stability of slopes, underground pillars, tunnel structures etc. The numerical simulation of a deep highwall slope of Ramagundam Opencast-II Extension Project (RG OC-II Extn) has been done using finite difference-based software FLAC/SLOPE. Parametric analysis has been conducted by changing one parameter at a time (OPT) and keeping all other parameters fixed in order to understand the influence of various parameters, namely, density, angle of internal friction, cohesion, overall pit slope angle and depth on the stability of the highwall slope. It has been observed that all the parameters undertaken in this study have a strong and well-defined influence on the stability of the same. Kinematic analysis is also performed to illustrate the potential for various modes of highwall slope failures, namely, planar, wedge and toppling failures that may occur due to the presence of unfavourably oriented discontinuities. The analysis revealed that the highwall slope is not susceptible to structurally controlled failure. Subsequently, statistical analysis for building an empirical model for the prediction of factor of safety has been done considering the abovenamed parameters utilizing non-linear regression technique. The developed empirical formula can be used as a guiding tool for estimation of highwall slope stability at any mine in India possessing similar geo-mining conditions.

Height of interconnected fracture zone based on the impact of rock fragmentation and bulking

The Jurassic coal fields in western China are characterized by thick coal seams and weak overburden. The height of an interconnected fracture zone (HIFZ) is often abnormally high for fracture zones produced by coal seam mining. In this paper, HIFZ is discussed through theoretical analysis, in-situ investigation, and data fitting with regression analysis. A comparison of two calculation methods in this study indicates the applicability of calculating HIFZ by the first method, based on the mechanical relationships among fractured rock strata, i.e., (i) the flexural and breaking limit conditions of roof rock mass, (ii) influence of rock fragmentation and bulking, and (iii) thickness of excavated coal seam. In the second method, an analytical formula of HIFZ is obtained by a fitting regression analysis on the measured data of coal mines under similar geo-mining conditions. For the HIFZ in working face 103 of the Zhuanlongwan coal mine, the two calculation methods yield values of 109.74 m and 92.91 ∼ 114.57 m, respectively. The measured value is 107.67 m, obtained using the method of drilling double-end sealing and water leakage measurement. The results of both theoretical calculations are mostly consistent with the measured value, which verifies the effectiveness of the two prediction methods.

Finite element modeling of the stability of rooms and resistance structures from the Cantacuzino Mine

The Cantacuzino Mine was mined with small rooms and square pillars, on seven levels, over a period of 27 years, extracting over 2.3 million m3 of rock salt. Due to the specific geo-mining conditions, the support structures suffered different degrees of deformation, especially the cracking of the ceilings between the first 5 levels. This article presents a 3D finite element analysis, in elasto-plasticity, of the state of stress and strain that generated the deformation of the pillars and ceilings between levels.

A numerical modeling approach for evaluation of spalling associated face instability in longwall workings under massive sandstone roof

The majority of the longwall panels in India have been worked underneath massive sandstone main roof with soft coal/shale immediate roof. As the mining goes deeper, ensuring stability and consistent production from such workings is a great challenge for their safety and sustainable performance. In this scenario, understanding the face instability mechanism and its rock mechanics precursors have evolved as a significant design challenge for obtaining an optimal longwall geometry in complex geo-mining conditions. Research to date mostly focused on the failure mechanism and, in some part, displacement characteristics of the coal wall. In contrast, minimal work has been performed to address the critical research gap from the face failure to spalling with the associated rock mechanics parameters and its three-dimensional quantification. This paper considered the longwall panel of 250 m face length and 3.5 m working height in the Godavari Valley Coalfield, which was worked underneath 23.5 m massive sandstone roof at a cover depth of 323 m. The finite difference software FLAC3D was employed to investigate stress redistribution, failure characteristics, strain dynamics, and horizontal displacement of the coal wall until the occurrence of the main weighting. Accordingly, a set of criteria, namely, Percentage of Critically Strained Zone (PCSZ) and Percentage of Spalling Zones (PSZ), were proposed based on the critical limits of the lateral strain and the horizontal displacement of the face. The formation of these critical zones around the face was further correlated with the failure and caving characteristics of the massive sandstone roof.The study revealed that within 0–3 m distance ahead in the central region of the face, the extent of PCSZ in the Peak stress period was 46, which further enhanced and contributed in PSZ of 78 as noted during the weighting period. It is indicated that the impact of spalling dominated in the middle and the middle to the top portions of the face, covering 53% of total face length within 0–3 m regions ahead of the face. The relative influence of the failure and caving characteristics of the key roof positively correlated with the PCSZ and PSZ at the face. The critical limits of lateral strain (0.58%) and horizontal displacement (−15.40 mm), as projected in this study for evaluation of face instability, provided closer agreement with field observed extent of face spalling. The findings of the study supplements the existing knowledge about the mechanism of face spalling and its quantification in the Indian geo-mining conditions. The approach developed in this paper can be employed to analyze the extent of face instability during weighting periods.

Plane-Strain Modeling of Progressive Goaf Compaction in a Depillaring Working

The knowledge of the compaction behavior of goaf is critical for the stability and rational design of depillaring workings in a given geomining condition, particularly in conditions where part of the overburden is distressed in the presence of softcover comprising of dump material. In this study, a Bord and Pillar working from Jharia coalfield has been considered for the study of progressive caving behavior and goaf compaction under a similar geomining condition. An algorithm was developed and implemented with the help of FISH subroutines for plane-strain simulation of progressive caving of strata, filling of goaf and its compaction in a depillaring working using finite difference software—FLAC. The compaction and stress recovery of different goaf filled zones have also been evaluated with the progressive depillaring till the extent of working becomes extensive enough to offset the effect of cover depth. The findings show that the magnitude of the stress accommodated at the bottom of the goaf material is governed by the span of fractured strata and the distance between the face and the point of maximum stress in the goaf. The caved goaf material recovers almost 15% of the in situ stress after the main fall, whereas 89% of the stress recovery is observed at 200 m of face advance, which is almost twice the depth of cover. The goaf material spanning up to 40 m from the goaf edge achieves 50% of the maximum stress recovery at this stage. The modeling approach developed in this paper with the help of various subroutines amply explains the mechanism of compaction and settlement of the goaf material filled cyclically following progressive caving of roof in the depillaring working.

Application of CMRI-ISM RMR for Stability Analysis of Development Workings for Ballarpur Underground Coal Mine - An Empirical and Numerical Approach

Abstract Roof bolt failures in the mine generally occur due to the poor identification of the weak rock layers and considered as a major concern for underground coal mines in terms of its productivity and safety. The triggering factor responsible for underground roof failure is the presence of weak bedding planes and various geological discontinuities. Geological disruptions present in the mine roof seriously affect the continuity of the rock layers resulting in block failure. However, numerous improved methods have been suggested by a number of researchers but still, the upholding of the accidents due to roof fall is considered as a major challenge for underground mine workings. Thus, it is necessary to give proper emphasis on characterization of the roof fall so that stability of the mine workings could be increased and movement of the weak and layered strata can be arrested by applying an adequate roof bolting system. This mechanism of roof support gives the composite binding between the rock layers by restricting the roof fall. The stability of mine workings can be also increased by proper application of rock mass classifications system and adequate design of support system and finally, by extensive simulation methods and statistical methods like FLAC 3D numerical and statistical modelling to ascertain the stability of the workings. CMRI-ISM RMR (Central Mining Research Institute – Indian School of Mines Rock Mass Rating System) classification system is the most popular and practiced method for roof support design in Indian coal mines which is being successfully used from last several years for roof support design in Indian geo-mining conditions. This forms the basis to estimate the rock load and support design. In this paper attempt has been made to assess the stability of workings and pillars below the railway track by using empirical and numerical approach. After both the studies it can be said that, the galleries and pillars underlying the railways track are stable, as factor of safety in each case is more than 2. Later on, the study was also extended to see the effects of subsidence on the surface which reveals that, there shall be no such effect on the surface due to underground workings as the value of NEW (non-effective width) is less than 0.4 for both the cases.