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By Abhishek Kumar, T. G. Sitharam, Surender Singh

The height of tailings pond (TP) embankments is frequently raised to accommodate the ever-increasing volume of tailings released by the mining industries. Excess pore water pressure (EPWP) may develop during the height-raising operations, which can affect the overall stability of TP. This article presents a detailed stability analysis for the embankments of an existing TP, the height of which was increased twice utilizing downstream (D/S) and upstream (U/S) construction techniques. A rigorous two-dimensional transient fully coupled-stress-pore pressure analysis is performed in the finite element-based package RS2 to examine the build-up of EPWP during different stages of construction. Furthermore, an attempt is made to investigate the feasibility of future height raising, with due consideration given to the influence of embankment raising rates. Results from the analysis show a development of higher EPWP within the tailings deposit in comparison to the embankments of TP, indicating the development of an undrained-like condition. The study further reveals that the development of EPWP is highly affected by the rate at which embankments of TP are being raised. A higher rate of embankment-raising results in the development of greater EPWP in comparison to a lower embankment-raising rate, which may lead to the ultimate collapse of TP. Furthermore, based on the stability analysis, the height of existing TP can be further raised by 4 m (two lifts of 2 m height) utilizing the U/S construction technique. A thorough cost and benefit analyses are however required before implementing the results of the current analysis since the storage capacity of TP is reduced while raising by the U/S method.

May 16, 2023

By P. R. Sheorey, D. Barat, B. Singh

Presented is a stability analysis for a trial stope in a lead-zinc mine. The trial scope would have an excavation width of 20 m with an initial height of 3 m. Filling would commence when the scope was heightened to 6 m. A two-pronged approach to predict the stability of such an opening was used viz. the finite element method and the rock mass classification method. Corroboration is shown to exist between the two methods. Deep borehole extensometer observations during stope extraction have been compared with predicted displacements.

Jan 1, 1981

By M. Akram

Stability assessment of entry roofs is an essential precursor to all underground design. Both multi-seam interaction and longwall mining can subject entries to radical changes in the surrounding stress field. Such loading changes frequently produce instability and failure in the roof, floor and pillars. Roofs are shown to be vulnerable to stress-induced failures, particularly when the load is unsymmetrical. To predict the effects of changes in stress field, roof failure conditions under increasing loads were studied using finite element analysis and body loaded photoelastic models. A large range of geologic conditions were evaluated and incorporated into the model using Monte Carlo methods. Entry analysis using the model showed the roof to be particularly vulnerable to shear with the location of the failure site changing to meet loading and geologic conditions. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Based on this research a roof stability model SESAME was constructed for roof stability evaluation under specified loading conditions.

Jan 1, 1993

By Ebrahim Ghasemi, Mohammad Hossein Kadkhodaei, Mosareza Jalilian

Entry-type mining methods, such as cut and fill method, play a significant role in underground mining, and they are still suitable methods for extracting deposits with irregular shapes and with weak host rocks. In these mining methods, the stability of the open spans is important for improving worker safety and increasing ore recovery. This study focuses on the application of six data mining classification methods, namely multinomial logistic regression (MLR), classification and regression trees (CART), logistic model tree (LMT), decision tree (J48), multivariate adaptive regression spline (MARS), and gene expression programming (GEP), in order to develop predictive models for stability assessment of underground entry-type excavations. For this purpose, a database containing 399 case histories of entry-type excavations from seven Canada underground mines was used. These models predict the stability status of entry-type excavations based on two input parameters, dimensions of the span and rock mass rating (RMR). The performance of developed models was evaluated using six performance metrics namely accuracy (ACC), sensitivity (SE), precision (PR), Matthew’s correlation coefficient (MCC), area under the receiver operating characteristic (ROC) curve (AUC), and performance index (PI). The results showed that all developed models can be used to predict the excavation stability, but the comparison of models indicated that the J48 model provides the highest performance with ACC = 0.900, SE = 0.869, PR = 0.922, MCC = 0.835, AUC = 0.891, and PI = 4.417. Thus, the proposed J48 model can be applied to identify the susceptibility of span instability in the entry-type mining, and if instability has been predicted, the necessary measures, including the use of suitable support systems, can be considered to reduce the casualties resulting from span instability.

Feb 26, 2024

By Xiang Li, Xibing Li

It is paramount that the stability of rock slopes be correctly accounted for under diverse operating and environmental conditions. Owing to different sources of uncertainty entailed in such stability problems, conventional deterministic approach through the calculation of a factor of safety (FOS) cannot reflect quantified uncertainties explicitly and sufficiently. Thus it is highly desirable to invoke the reliability approach to consider uncertainties in a systematic manner. Nowadays, the current design standards have an increasing tendency to ensure rock slope stability by pre-defining a target reliability index (or target probability of failure), viz., the reliability level of a rock slope is pre-set as a target to be satisfied. In such a situation and considering the fact that the FOS used as an indicator of slope performance still has a very wide acceptance, we focus on proposing an inverse-reliability-based methodology which aims at developing a two-fold indicator strategy, i.e., using the FOS and reliability together to deal with slope stability problems. The basic idea behind it is to utilize a so-called inverse first-order reliability method (IFORM) to directly calibrate the FOS provided the target reliability index has been given. In this way, the calibration scheme relating the FOS can be rationally done by not only incorporating uncertainties, but also satisfying a desired level of the prescribed reliability. Based on this, to make the IFORM computationally feasible and also reduce its computational cost, we introduce the response surface method (RSM) to generate a surrogate for the FOS-based limit state function (LSF), considering the lengthy and complicated form of the FOS in some recognized methods (e.g., within the framework of limit equilibrium). Distinguished from the existing RSMs that potential inadequacies may arise, we present an RSM based on a hybrid approach combining support vector machine (SVM; used as a regression technique) and uniform design (UD; pertaining to experimental design). Using a representative example of rock slope stability problem, we demonstrate the feasibility and validity of the developed methodology, during which the associated sensitivity study and further discussion are also performed. By dint of such a methodology, we can establish a link between the conventional deterministic approach and the reliability approach, where a logical and realistic framework is provided, for cases achieving the specified reliability, to assist in selecting the FOS which remains adequate for rock slope stability even in the face of uncertainty.

Jan 1, 2015

By I. Grigoriev, A. Yolkin, E. Freiberg, A. Fedchun, A. Kolichko

Abstract: The paper describes the engineering-geological conditions and the structural decisions of the underground machine hall of Rogun HPP under construction in Tadjikistan on Vaksh river as well as the results of physical model studies and long-term in-situ investigations of the variation of the stress-strain state of the surrounding rock mass and the supports of openings, and the assessment of the stability of openings during and after the construction. The analysis of the results of long-term in-situ observations and previous model studies permitted to make the assessment of the present-day state of the machine hall and give recommendations of its further use. Zusammenfassung: Im Vortrag werden die ingenieurgeologischen Bedingungen und konstruktiven Lösungen für die unterirdischen Maschinenhalle des in der Republik Tadshikistan am Fluss Wachsch im Bau stehenden Rogunskaja-Wasserkraftwerkes, die Ergebnisse von experimentellen Forschungen (in physikalischen Modellen) und Naturbeobachtungen der Spannungs-Verformungszustandsänderungen des umliegenden Felsmassivs und Ausbaues von Untertagebauten, sowie Ergebnisse der Bewertung der Standfestigkeit von Untertagebauten während des Bauvorganges und nach der Bauperiode beschrieben. Auf Grund der Analyse von Ergebnissen der dauernden Naturbeobachtungen und früher durchgeführten geomechanischen Modellversuche wird der heutige Zustand der Maschinenhalle des Wasserkraftwerkes bestimmt und werden die Empfehlungen für ihren weiteren Benutzung angeführt. Annotation: L’exposé décrit les conditions d’ingénieur et celles géologiques, et les solutions constructives de la salle des machines de la Centrale hydroélectrique (CHE) Rogounskaya sur le fleuve Vakhch, les résultats d’études expérimentales (sur des modèles physiques) et d’observations extérieures sur place concernant des changements de l’état de tension-déformation d’un massif environnant et du cuvelage des excavations, ainsi que les résultats d’évaluation de la stabilité de l’excavation au cours de la construction et à la période post-construction. A la base de l’analyse des résultats des observations de longue durée et des études préalables géomécaniques sur des modèles, l’évaluation de l’état actuel de la salle des machines de la CHE est effectueé, et les recommandations sur son utilisation ultérieure sont présentées.

Jan 1, 2003

By B. T. Wells

This work concerns the stress fields encountered around mining tunnels. A critical review is undertaken of the various analytical assessments of the support requirements for mining tunnels. Comments are made regarding degree and type of support together with method and timing of installation. The results have been used to indicate the type of support required in different mining and geological conditions.

Jan 1, 1981

By Gy. Deák

The Romanian mining industry, especially salt mining, is going through a restructuring phase taking into account the Environment Acquis of the European Union1. In order to preserve the centuries-old salt mines and to develop new ones, in the same salt rock deposit, the long term stability assessment of the saline complex is very important. This case study refers to the Praid salt mine, which includes old salt mines, with impressive sizes, located above the new mines, with activity in progress, in order to provide the means and solutions for efficient conservation and sustainable exploitation for the salt resources. The DKRControl method and FLAC 3D code were used in order to assess the confidence level for the computed prediction of the stability of the salt mine complex salt.

Jan 1, 2008

By J. M. Galera, M. D. Rodriguez, V. Pozo, S. Cooper

"Cobre Las Cruces mine extracts copper minerals from a VMS deposit located in the well-known Iberian Pyrite Belt (IPB). As an open pit, it is distinguished geologically from other IPB mines by the presence of around 150 m of Tertiary soft marls, known locally as the Guadalquivir Blue Marls, followed by a regionally important aquifer. Below the marls and aquifer the mineralization is hosted by rocks typical of the Palaeozoic within the IPB, comprising gossan, tuffs, slates, and sulphides.This combination of a substantially soft rock and more competent, older (but still occasionally problematic) Palaeozoic lithologies constitutes a unique geological framework and presents substantial challenges in maintenance of slope stability, and therefore operational safety, at the mine site. This paper describes the fundamental design, excavation, and monitoring measures implemented at the mine to maintain safe production, and the lessons learnt during the mine development. IntroductionAs a modern Spanish mine, Las Cruces is committed to the use of best available technology and practices with the aim of guaranteeing the production of ore in a safe environment. From a practical perspective, this implies the realization of a high quality pit design, ongoing geotechnical mapping of exposed slopes to ensure conformity with design, and use of leading geotechnical surveillance technology to complement visual observations. The focus of this article is to illustrate how, at a mine site with potentially problematic soil/rock conditions, multiple advanced techniques employed from design stage analysis through to final pit configuration and vigilance, were combined to achieve an overall control of the ground conditions. In Figure 1 the layout of the pit is shown, illustrating development at the beginning of 2015."

Jul 1, 2019

By V. Rajaram

The oil shales of the Green River Formation in the United States have been considered as a source of liquid hydrocarbons since 1908, with the first retort constructed in Colorado in 1917. However, it was not until 1944 that the mining characteristics of oil shale were investigated in a systematic manner. During the period 1944 through 1956, the Selective Mine and the Demonstration Mine (also referred to as the Anvil Points Mine) were operated by the U. S. Bureau of Mines (USBM) near Rifle, Colorado. Significant progress was made in developing a room and pillar mining method by which oil shale could be mined safely at a very low cost per ton. Mechanical properties of oil shale were determined, safe room spans and roof support techniques were established, and drilling and blasting methods for oil shale were developed. As a follow-on to this USBM effort, a consortium of six oil companies with Mobil Oil Company as project manager carried out a research program during the period 1964-68 at the Mobil mine, located in the vicinity of the Anvil Points mine. Rock mechanics investigations were conducted as a part of this research program, and consisted of laboratory studies, in-situ stress determinations, and roof and pillar instrumentation. This paper will discuss the findings at the Anvil Points mine and Mobil mine to illustrate the stability considerations in underground oil shale mining.

Jan 1, 1983

By Fraser CJ

Stability control plays a prominent part in the planning and execution of coal winning in the deep open cuts in the Latrobe Valley operated by the State Electricity Commission of Victoria (SECV). Different stability mechanisms affect the individual overburden and coal faces. These are the classical rotational slip in overburden and the three-dimensional tetra- hedral wedge or planar block slip in the coal faces. The stability of the overall batters is affected by the so-called "block sliding" mechanism, which is unique in Australian open cuts. The basal stability of the open cuts is affected by pressure from water in confined aquifers underlying the coal being excavated. This paper describes each of these mechanisms and the current monitoring and con- trol techniques practised by the SECV.

Jan 1, 1982

By Yanfa Gao

Clusters of underground openings were developed around the shaft bottom of Tangshan Mine. They were deep and located in soft rock strata. After development, those openings have been subjected to considerable deformation and damages. A combined supporting method including grouting and bolting, shotcrete lining and brickwork was used. This paper analyzing the theories on which this supporting method was based. A new theory called "Disturbed Creep" was developed for deformation prediction of openings surrounded by strata subjected to stresses close to limiting or failure strength. Keywords ground pressure, deep mine, soft rock, stability control

Jan 1, 2002

By S. S. Peng, V. Z. Sun

One of the major concerns of ground control in a coal mine is the prevention of roof, pillar and floor failures of the mine entry. To better design and evaluate the stability of a mine entry within a certain level of confidence, a reliability approach is introduced. The advantage of using the reliability approach, rather than the conventional safety-factor (SF) method, is that it not only takes variability of both rock/coal properties and stress into consideration but also assesses the stability of each component and the mine entry as a whole. Therefore, it is anticipated that by using this approach the current ground-control technology in a coal mine will convey a better sense of confidence. The results of a case study show that there is a significant difference in mine entry stability between the current design method and the reliability approach.

Jan 1, 1999

By V. Z. Sun

One of the major concerns of ground control in a coal mine is safety against failure of one of three components (i.e. roof, pillar, or floor) of the mine entry. In order to better design and evaluate stability of the mine entry with a certain confidence, a reliability approach is introduced rather than using the conventional safety factor (SF) method only. Advantages of using the reliability approach is that it not only takes variability of both rock/coal properties and stress distribution into consideration, but also assesses the stability of each component and mine entry as a whole system. Therefore, it is anticipated that, by using this approach, the current ground control technology in coal mine will convey a better sense of confidence. The results of a case example show a significant influence on the current design concept and stability evaluation of mine entry.

Jan 1, 1997

By D. Moses, J. A. Onyango

Carbonatites are generally competent rock masses with rock mass rating class II rating 60–74. In spite of their competency, they tend to be affected by weak features like manganese-iron veins and/or in situ rock damage due to brecciation associated with carbonatite complexes. Rock slope failure in such hard rocks is complex since such structures within the rock mass form weak links that could potentially control slope instability. In this contribution, a numerical simulation using phase2 v 7.0 was carried out to investigate the influence of in situ rock damage on the stability of mine pit walls. The outcome reveals that, the existence of breccia in the competent rock mass has the capability to reduce the slope stability performance particularly at gentle dipping angles of emplacement in close range to the slope toe. However, as the emplacement position of breccia moves away from the pit wall, the stability performance increases at gentle dipping angle <50º. On the contrary, at the dipping angle of 50° the performance of slope reduced, and at steeper angles >50° the impact becomes negligible. Thus, from a series of analyses, mine design in brecciated rock masses, the ratio of 1:5 between the breccia distance from slope toe and pit depth should be implemented to counter its impact, and if the breccia is within or close to the pit limit, a deliberate effort must be made to mine it out.

Sep 1, 2025

By J. C. Konopka, S. A. G. Poppen, E. K. Roesner

Many shafts have experienced stability problems during shaft sinking because the designer failed to fully appreciate the conditions he would encounter. Some shafts have failed during construction because the ground supports provided to compensate for the expected conditions were inadequate despite the most careful investigations and analyses. To design a ground support which is ultimately safe to achieve stability during shaft sinking would be too costly and impractical and, therefore, many shafts would simply not be constructed. The design of a ground support for shaft sinking based on an intimate understanding of the expected ground behaviour and stress development during excavation combines the art of mining with the science of geotechnical engineering. Where no historical design data is available, the designer of the ground support must: 1. classify the rocks and soils and assess their behavioural characteristics; 2. calculate the primary and secondary stresses; 3. design and/or select a ground support system which will ensure stability of the excavation during shaft sinking.

Jan 1, 1983

By Joseph G. Franzone, Alan K. Kuhn, Jerry J. Oliver

INTRODUCTION Tailings produced by many uranium milling operations consist of fine sands with some silt and slimes. When fine sandy materials are placed by hydraulic methods behind an impermeable dam, they are deposited in a loose state and some portion remains saturated. These saturated, loose fine sands are highly susceptible to liquefaction, the phenomenon in which a monotonic or cyclic disturbance causes excess pore water pressure and, concurrently, a total loss of strength in the sand. Once liquefied, the fine sand flows, causing collapse of supported structures. The potential for such a liquefaction failure was identified and successfully treated at Sohio Western Mining Company&apos;s L-Bar Uranium Operations near Seboyeta, New Mexico. The Sohio tailings dam is an earthfill starter dam with tailings raises constructed upstream of the starter dam crest. Beginning with the start of mill operations in 1976, tailings were deposited hydraulically in the impoundment behind the starter dam. As the tailings level approached the crest of the starter dam, beached tailings were excavated and placed in lifts by a dozer to form two raises above the crest of the starter dam. As the impoundment has gradually filled with tailings, the decant water pond level has risen. Correspondingly, the water level in the tailings dam, upstream of the chimney drain, has also risen. By August 1980, the phreatic surface was above the crest of the starter dam and stability analyses indicated that the tailings dam did not have the safety factor of 1.0, under static loading with liquefaction, implicit in the 1980 New Mexico State Engineer&apos;s requirements. The problem related directly to the high phreatic surface in the loose sandy tailings behind a dam structure that was not capable of resisting failure which might develop in liquefied tailings. Two methods of stability enhancement were considered for the Sohio dam. One method was reinforcement of the dam using a clay buttress placed against the downstream slope. The other method was installation of horizontal drains through the starter dam to drain decant water and lower the phreatic surface. Either method would increase the stability of the dam. However, the comparative analysis of the methods indicated that horizontal drainage offered significant advantages in cost and could provide a more direct remedy of the source of the problem, the saturated section of tailings. In addition, a drainage system would be more amenable to modification and more quickly installed than a buttress. On the other hand, a clay buttress could be more directly controlled, would involve routine earthwork, and has successful precedent. Therefore, the buttress approach would involve less risk. After weighing the advantages of both methods and the costs versus risks, the horizontal drainage approach was selected. Consequently, a horizontal pipe drain system was recommended and designed (D’Appolonia, 1981a). This paper describes the design and installation of the drainage system and its initial performance. PIPE DRAIN SYSTEM DESIGN Design Criteria and Parameters To increase the stability of the dam to acceptable levels, the drainage system had to lower the phreatic surface behind the dam to the level calculated to give a minimum safety factor of 1.0 under conditions of liquefaction. In addition, the system needed to be essentially self-operating, easy to maintain, and economical. To accomplish these objectives, the following design criteria were established: 1. The pipe drains must lower the phreatic surface at least 4.3 m (14 ft.) at the midpoint along the dam (the deepest section) and by proportionately smaller amounts toward the abutments to satisfy safety factor requirements.

Jan 1, 1982

By C. E. Brechtel

Bench cut-and-fill stopes with heights between 85 and 105 ft are being excavated in the lower levels of the B-NEATH Zone. Estimates of pillar strength and pillar loading indicated a high probability of pillar failure. Some changes in mining practice were made to minimize impacts of pillar failure and a rock mechanics instrumentation program was employed to monitor stability during mining of the first stopes. Limited pillar failure, in the form of destressing, was observed in the initial stopes; however, global stability during mining was good. Instrumentation data indicated that predictions of pillar strength and stress were quite close to field results.

Jan 1, 1989

By C. Steve

ABSTRACT: In this paper, the stability evaluation and bifurcation criteria are presented for the Jinping arch dam structure. The bifurcation models in failure status of the arch dam are derived from the uniqueness of the controlling equation of dam behaviours, and the relative phenomena between positive definition of dam structural tangent stiffness and bifurcation are given in the paper. Then the structural collapse criteria for arch dam are discussed based on the energy mode. A stability criterion of dam based on the connection of yield zones is proposed according to the implementation of elasto-plastic FEM (finite element method) numerical analysis. In accordance with this judging method, nonlinear FEM analysis is used for Jinping arch dam. The failure process of the Jinping dam was simulated and yield zones were found under the overloading condition. Keywords: Stability evaluation, bifurcation, failure process, Jinping arch dam ZUSAMMENFASSUNG: In der Verliegenden Arbeit wird ein integrater geomechanisch Modellversuch fuer Jinping Bogenstaumauer Vorgesstellt. Die Bogenstaumauer liegt aut der komplizerten felsformationen. Der Zerstoerungsmechanismus, die Stabilitaetsfaktoren und die Interaktion zwischen der Bogenstaumauer und den Seiltichen. In der Vorliegenden Arbeit wird eine dreidimensionale finite element analyse fuer die seitlichen. Gestein sauflager mittels dem Bruchmodell Vorgestellt, da fuer Jiniping Bogenstaumauer angewandet wird. Ein Bruch mechanismus model einschliesslich der statistischen parameter der Gesteinfes tigkeit wird entauckeit. RÉSUMÉ: Das ce documènt a été faite une analyse d’elemt limité de trois dimensions dn fondement de construction de roche faisant appel au modéle de l’endommagemnet à fracture, analyse appliquée an fondement du bar ragevoute de Jinping. Ce documènt décrit le test de modéle géomecanique intégral pour le barrage-voûte de Jinping L’ampleur du modéle en question constitute l’une de plus importantes en China. Ils correspondent par faitement anx calculs des résultats.

Jan 1, 2003

By Xianming Zhou

Mining economics is such that too conservative in safety will result in a considerable penalty in mining cost. However, initial planning and design of a mining project often must be done without complete information. The assurance of economical and safe mining is thus difficult. This study is focused on the improvement of the mine design associated with Zhaoyuan Gold Mine in P.R. China as more information becomes available. Attention is given to the selection of backfill structures. Based on a proposed practical finite element model, a design, which is believed to be not only reliable but also cost-effective, is recommended for further mining operations in this mine.

Jan 1, 1989