Spoil Piles Research Articles

Mine Drainage and Oil Sand Water.

Mine drainage from the mining of mineral resources (coal, metals, oil sand, or industrial minerals) remains as a persistent environmental problem. This review summarizes the scientific literature published in 2014 on the technical issues related to mine drainage or mine water in active and abandoned coal/hard rock mining sites or waste spoil piles. Also included in this review is the water from oil sand operations. This review is divided into the four sections: 1) mine drainage characterization, 2) prediction and environmental impact, 3) treatment technologies, 4) oil sand water. Many papers presented in this review address more than one aspect and different sections should not be regarded as being mutuallyexclusive or all-inclusive.

Contribution to the knowledge of Cordaites species from the Kladno-Rakovník Basin, Middle Pennsylvanian (Bolsovian), Czech Republic

Abstract Newcollections from the spoil piles of the Theodor mine in Pchery and Schoellermine in Libusin (Kladno-Rakovnik Basin, Czech Republic) yielded a new Cordaitesspecies and improved knowledge of the extent of the cuticular variabilityof the species Cordaites wartmannii Simůnek.Based on cuticles, it has been proven that the species Cordaites polynervus Simůnek is conspecific with Cordaiteskladnoensis Simůnek. The newspecies, Cordaites theodorii Simůnek& Haldovský sp. nov.,established on strongly papillate cuticles, is characterized by the presence ofsmall teeth on the leaf margin. This feature is new for the genus Cordaites.The palaeoecological significance of papillae on Cordaites cuticles isdiscussed. It is probably an adaptation to living on a peat substrate. Comparison of the species Cordaites wartmannii Simůnek and Cordaites barthelii Simůnek is made. Adaxial cuticles of Cordaiteskladnoensis and Cordaites wartmannii are so similar that it isdifficult to distinguish these species by means of the adaxial cuticle alone.

Catchment reconstruction — erosional stability at millennial time scales using landscape evolution models

An important part of planning for the rehabilitation of a mine site is the design of stable final landforms for waste rock dumps or spoil piles. Whilst able to be assessed over the short-term (years to decades), the longer term behaviour (centuries to millennia) of such landscapes is not within any meaningful human time frame of observation. Predictive numerical models, therefore, form an important tool with which current landscape behaviour and longer term trajectory can be assessed. However, an important issue associated with the use of models is the ability to assess the reliability and accuracy of the model. Here the SIBERIA and CAESAR-Lisflood Landscape Evolution Models (LEMs) are used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the Ranger uranium mine in the Northern Territory, Australia, for a simulated period of up to 1000years. Utilising both models in this study enabled an independent assessment of likely landscape processes and evolution as well as each model. Results show that SIBERIA and CAESAR-Lisflood produce erosion rates and patterns that are broadly similar. At millennial time scales, short-term processes such as gullying appear to be the dominant erosion features in the proposed landforms and may produce substantial erosion in terms of size and amount of hillslope material eroded and transported downslope. Vegetation was found to have a major effect on the erosion potential of the landform surface. Overall both models produce very similar results.

Mine Drainage: Characterization, Treatment, Modeling, and Environmental Aspect

Globally, mine drainage is a persistent environmental problem facing the mining industry. This review covers the literature published in 2013 on topics relating to acid mine drainage (AMD) or acid rock drainage (ARD) due to the presence of sulfide bearing minerals in active and abandoned coal/hard rock mining sites or waste spoil piles. This review is divided into the four sections: 1) mine drainage characterization, 2) mine drainage treatment 3) modeling and simulation, and 4) environmental aspect. Many papers presented in this review address more than one important topic and different sections presented in this review should not be regarded as being mutually‐exclusive or all‐inclusive.

Using LiDAR data to locate a Middle Woodland enclosure and associated mounds, Louisa County, Iowa

LiDAR data is used to locate an enclosure reported at the McKinney site (13LA1) as well as destroyed mounds associated with the Toolesboro mound group National Historic Landmark (13LA29). Using various geo-visualization and interpolation techniques, one of us (Riley) located the earthwork enclosure, eight mounds, and possibly a ninth or an excavation spoil pile. An anomaly north of 13LA1 and within the detected enclosure area were also identified. There is no modern survey relating to these two anomalies. Our results support historic accounts regarding the location and shape of the McKinney enclosure and its relationship to the Toolesboro mound group. All features found by LiDAR will be ground truthed in the future.

Minerals and Mine Drainage

A review of the literature published in 2012 on topics relating to acid mine drainage (AMD) or acid rock drainage (ARD) due to the presence of sulfide bearing minerals in active and abandoned coal/hard rock mining sites or waste spoil piles is presented. This review is divided into the following sections: 1) Characterization and Assessment, 2) Protection, Prevention and Restoration, 3) Toxicity Assessment, 4) Fate and Transport, 5) Biological Characterization, and 6) Treatment Technologies. Due to the complexity of the minerals and mine drainage, many papers presented in this review address more than one important topic, indicating that they can be categorized into more than one section. Therefore, the different sections presented in this review should not be regarded as being mutually‐exclusive or all‐inclusive.

A comparison of three methods for the quantification of greenhouse gas emissions from spontaneous combustion in open-cut coal mines

Greenhouse gas emissions from spontaneous combustion in coal mines are currently excluded from national inventories by the United Nations Framework Convention on Climate Change because there are no robust methods available to quantify the emissions. This article reports on investigations of three approaches being pursued with the aim of developing methods which are sufficiently robust to enable these emissions to be included in inventories. The first method was based on the use of airborne thermal infrared photography coupled with chamber measurements of emissions from hot mine spoil pile surfaces. In the second method, crosswind traverses of the plume using an instrumented vehicle were used to estimate the emission fluxes. The third method was based on inverse atmospheric modelling using stationary CO2 monitors. All three methods showed considerable scatter in their estimates but also showed appreciable overlap. While the three methods used in this study have shown convergence, there is still considerabl...

Assessment of Heavy Metal Contamination in Soils around Coal Mine Spoil Piles in Shiguai District of Baotou, Inner Mongolia, Northern China

The concentration of heavy metals (Cr, Cu, Ni, Zn, Mn and Fe) were studied around coal mine spoil piles in Shiguai district of Baotou located in Inner Mongolia grassland and desert transition zone. Aim of the study is to control soil heavy metal pollution of coal mining area and provide the basic data information. The results indicated that concentrations of Cu, Cr, Ni and Zn in the soil along the roadsides were higher than other sampling areas. The pollution characteristic and the elements of heavy metal contamination were corresponding with the concentrations of the different types of coal mine spoils. According to the single factor pollution index, soils from different regions were contaminated by Cr, Cu, Ni, Zn, Mn and Fe in varying degree. The pollution degree was in order: Cu > Cr > Fe > Zn > Ni > Mn. Nemerow’s synthetical pollution index indicated that soils from the roadsides had the most serious heavy metal contamination, the index was 3.11. The order of pollution level in different regions was: roadsides > flood land > farmland > woodland. The health and stabilization of environmental quality are being threatened by soil heavy metals.

Marine Archeological Survey of the Proposed Bolivar Ferry Dredge Spoil Pile Expansion Area, Galveston County, Texas

Archeologists from AmaTerra Environmental, Inc. (AmaTerra) and Southeastern Archaeological Research, Inc. (SEARCH; collectively the Team) conducted intensive underwater archeological remote sensing survey on behalf of the Texas Department of Transportation (TxDOT) on a proposed dredge spoil expansion area south of the Bolivar Peninsula at the mouth of Galveston Bay, Galveston County, Texas. The survey was required for compliance with the National Historic Preservation Act of 1966, as amended, due to dredge permits to be issued by the US Fish and Wildlife Service, and the Antiquities Code of Texas, due to its location on lands owned by a political subdivision of the State of Texas (the Texas General Land Office). Completed under Antiquities Permit 6272, the survey area includes the 51-acre dredge spoil expansion footprint and the original 16-acre dredge spoil pile (67 acres total). The archeologists utilized towed marine magnetometer and side-scan sonar survey along 12 parallel, 20-meter-interval transects to assess the full archeological Area of Potential Effects. The survey area was found to be littered with isolated modern metallic debris. Side-scan sonar imagery revealed a submerged surface that was generally flat with no indications of shipwrecks and a large oyster reef along the southwestern quarter. One large metallic feature located within the survey area (Anomaly M1) was identified as a fallen modern navigational sighting marker tower. None of the archeological survey data, sensor readings, or imagery from the proposed expansion area is consistent with expected signatures of historic-age shipwrecks. Archeologists did re-identify the previously-documented magnetic anomaly M44 that was recommended for avoidance or testing within the original dredge pile area. If the avoidance zone continues to be observed, it will not be impacted by the current undertaking. As such, the project is recommended to proceed with no Historic Properties, State Archeological Landmarks, or archeological sites impacted in accordance with guidelines outlined in 36 CFR 800 and 13 TAC 26. No sites were identified and no artifacts were collected during the course of the survey. Accordingly, all project-generated notes, forms, and other materials will be permanently curated at AmaTerra’s office in Austin, Texas and SEARCH’s office in Pensacola, Florida.

Description of a New Genus and Species of Scallop (Mollusca: Bivalvia: Pectinidae) from the Upper Cenozoic of North Carolina

A new genus and species, Patriciapecten iona, are described in the subfamily Chlamydinae (Mollusca: Bivalvia: Pectinidae). Patriciapecten is characterized by a shell with commarginal ledges giving an undulating surface, strong radial ribs, and no intermediate hinge teeth. The type locality is the Lee Creek Mine operated by the Potash Corporation of Saskatchewan (formerly Texasgulf, Inc.) near Aurora, Beaufort County, North Carolina, where the specimen was collected in a spoil pile. This site, which is primarily upper Cenozoic, ranges from the Miocene Period through the Holocene Epoch.

A new general empirical approach for the prediction of rock mass strengths of soft to hard rock masses

It is almost impossible to prepare representative cores of rock masses including discontinuities patterns for laboratory studies. To overcome these difficulties, researchers have focused on developing empirical equations for estimating of the stress–strain behavior of a rock mass, including measurements of the discontinuity patterns. As can be seen in the literature, the uniaxial compressive strength value of rock mass ( UCS RM ) can be estimated by reducing the uniaxial compressive strength of intact rock material ( UCS i ) based on the quality of a rock mass, represented by variables such as Rock Mass Rating ( RMR), Geological Strength Index ( GSI) and Q value. For this reason, a unique reducing curve form empirical equation has limited application and generally, cannot be applied to all kind of rock masses from particularly soft to hard rock masses. In this study, a new general empirical approach is constructed to estimate the strength of rock masses of varying hardness. The new empirical equations have been calibrated using data from five slope failures and four sets of uniaxial compressive strength data of rock masses. In the new empirical equations, the UCS i is considered not only to be a scale parameter used in the strength reduction but also used to adjust the degree of strength reduction in conjunction with elastic modulus of the rock material ( E i ). The disturbance factor on the rock mass is taken into consideration by two separate reduction factors applied to the Structure Rating ( SR) to capture increasing joint density, and to the s and m b parameters of the Hoek–Brown criterion, to decrease the degree of interlocking. Hence, non-interlocked (cohesionless under zero normal stress) rock masses such as spoil piles can also be modeled in the new empirical approach.

Experimental study for the particle size distribution of mine spoil pile cross section

The aim of the experiment is to analyze and view the distribution of gangue with different particle sizes in mine spoil pile cross section. According to the Dimensional method, ‘Pi’ theorem was employed first to abbreviate ten physical and mechanical parameters to three dimensionless groups, and then the similarity criterion and coefficient of the experiment were determined and calculated based on particle size distribution curve. The similarity model was designed and constructed to represent the process of the mine spoil pile. The profile of the final model shows that the small sized particles mainly compose the upper zone of the mine spoil pile, while the bottom of the pile is dominated by bigger sized particles, and the intermediate section presents a zigzag stripe cross-bedding structure which is composed by small-medium scale particles and medium-large scale particles. Each stripe has two critical angles: one is the angle in which gangue particles can maintain their stability condition, with approximate range from 24° to 26°; and the other is the angle in which particles can stop gliding downwards, approximately varying from 34° to 36°.

Element residence and transport during subduction-zone metasomatism: evidence from a jadeitite-serpentinite contact, Guatemala

Jadeitite is a rare constituent of serpentinite-matrix mélange bodies from certain subduction complexes. Most jadeitite crystallizes from Na-, Al-, and Si-bearing fluids that are apparently derived from multiple subduction-zone sources. Even though jadeitite is near-end-member NaAlSi2O6 in major element composition and is volumetrically minor in subduction complexes, its trace elements and stable isotopes appear to record fluid compositions not directly seen in other subduction zone metasomatic systems. Prior to our work, how jadeitite-forming fluids interact with serpentinite host rocks and serpentinizing fluids were largely unknown, because serpentinite-to-jadeitite contacts are generally not exposed. In the Sierra de las Minas, Guatemala, we have studied a 3 m-wide pit transecting the contact between a mined-out jadeitite body and its host serpentinite. An apparent transition zone between the former jadeitite and nearby serpentinite exposed in the mine pit contains four texturally distinct rock types of differing outcrop colours, composed of albitites and meta-ultramafic rocks. (The jadeitite body is now represented only by a large spoil pile.) Seven samples from the contact zone, jadeitite from the spoil pile, a serpentinite outcrop approximately 1 m outside the pit, and a jadeitite nodule within the contact zone albitite were analysed for major, minor, and trace elements. Abundances of Al2O3, Na2O, MgO, FeO, Cr, Ni, and Sc track the contact between sheared albitite and foliated meta-ultramafic rocks. These elements change from values typical of Guatemalan jadeitites in the jadeitite block and albitites in the contact zone to values for Guatemalan meta-ultramafic rocks and serpentinites across the contact zone. In addition, the abundances of SiO2, CaO, Fe2O3, K2O, Rb, Cs, and Y show important features. Of greatest interest, perhaps, approximately 15 cm from the contact with meta-ultramafic rock, Zr, U, Hf, Pb, Ba, Sr, Y, and Cs in albitite are greatly enriched compared to elsewhere in the contact zone. Element enrichments spatially coincide with the appearance, increase in modal abundance, and/or increase in grain sizes of zircon, rare earth element (REE) rich epidote, titantite, and celsian within albitite. All of these ‘trace-element-rich’ accessory minerals show poikiloblastic inclusions of albite, which suggests that they grew concomitantly in the metasomatic zone. Graphical and computational methods of evaluating mass changes of metasomatites relative to likely protoliths show that, near the contact, fewer minor and trace elements in albitite show 1:1 coordination with presumed protoliths. Most metasomatitites are enriched in large-ion lithophile elements (LILE) and heat-producing elements (HPE) relative to likely protoliths. Albitite near the contact with meta-ultramafic rocks also shows ultramafic components. Except for a Ca-rich actinolite schist zone, the meta-ultramafic rocks are depleted in LILE and HPE relative to serpentinite; host serpentinite is itself under-abundant in these elements relative to average upper mantle or chondrite. In summary, the metasomatic zone shows more evidence for the introduction of components to albitite and actinolitic meta-ultramafic rock than it does for exchange of protolith components between jadeitite and serpentinite. The fluid that presumably formed the metasomatites was sufficiently rich in LILE and high-field-strength elements (HFSE) to both saturate and grow minerals in which Zr, Ba, and Ti are essential structural constituents and/or HFSE, LILE, and HPE minor to moderate substituents. These geochemically diverse element groups were fixed in albitite via the crystallization and growth of new accessory minerals within these rocks during albititization. The amount of LILE and HPE-depleted meta-ultramafic rock appears to be too small to call upon a local source for the LILE and HPE-enrichment seen in albitites. Therefore, LILE and HPE must be of exotic origin, carried and deposited by fluids within the albitites at the jadeitite-serpentinite contact. This contact clearly testifies to an alteration style that involved crystallization of ‘trace-element’-rich minerals during fluid flow; this process appears to be essential to mass transfer within subduction zones.

Greenhouse gas emissions from low-temperature oxidation and spontaneous combustion at open-cut coal mines in Australia

Abstract Spontaneous combustion and low-temperature oxidation of waste coal in open-cut coal mines represents a potentially large source of greenhouse gas emissions. In this paper, emission fluxes of CO2 and CH4 from spoil piles and waste coal dumps measured at 11 mines in the Hunter Valley and Bowen Basin in Australia are presented. The data displayed considerable scatter, which is consistent with the inhomogeneous nature of spoil pile material and permeability of surfaces. Despite the scatter, emissions were able to be classified into three broad categories according to the intensity of the spontaneous combustion present in the material. Average emissions ranged from about 12 kg CO2-e yr− 1 m− 2 to 8200 kg CO2-e yr− 1 m− 2, depending on the intensity of the spontaneous combustion. There was also, within the scatter of the data, an approximately linear trend of increasing emission flux with increasing surface temperature. A key finding of the research is that the emission rates of greenhouse gases from spoil piles where there is no spontaneous combustion, but only low-temperature oxidation of coal and coal waste, are similar to the emission rates due to biological activity from vegetated surfaces. However, further research is required to quantify the degree to which spoil piles that have no spontaneous combustion contribute to the anthropogenic atmospheric CO2 burden.

The impact of pyrite variability, dispersive transport and precipitation of secondary phases on the sulphate release due to pyrite weathering

The objective of this study was to investigate the impact of flow, transport and geochemical parameters in the unsaturated and saturated zones on the release of SO4 from overburden lignite spoil piles into the adjacent lake. A vertical one-dimensional model was set up using the reactive transport simulator SULFIDOX in order to account for the unsaturated zone. The SULFIDOX model was calibrated for effective diffusion using measured O2 in the gas phase and SO4 concentrations in the liquid phase from the unsaturated zone of the heap. The results show high sensitivity to O2 supply and initially present gypsum, but the inclusion of secondary mineral precipitation in equilibrium is of minor importance for the results. To account for the transport of released SO4 from the saturated zone into the surface water, scenarios were performed by using SULFIDOX results as input concentration for a two-dimensional vertical model set up with PROCESSING MODFLOW and MT3D. These scenarios indicate a rising discharge of SO4 into the adjacent lake due to continued pyrite weathering for 80 a. Results are highly sensitive to dispersivity, whereas the spatial variability of pyrite distribution did not show any influence on the results. The consideration of initially present gypsum shows a major effect on the modelled SO4 release.

Spontaneous Vegetation on Overburden Piles in the Coal Basin of Santa Catarina, Brazil

Abstract The objective of this work was to select indigenous vegetal species for restoration programs aiming at the regeneration of ombrophilous dense forest. Thirty‐five spoil piles located in the county of Sideropolis, Santa Catarina, that received overburden disposal for 39 years (1950–1989) were selected for study because they exhibited remarkable spontaneous regrowth of trees compared to surrounding spoil piles. Floristic inventory covered the whole area of the 35 piles, whereas survey on phytosociology and natural regeneration studies were conducted in 70 plots distributed along the 35 piles. Floristic inventory recorded 83 species from 28 botanical families. Herbaceous terricolous plants constituted the predominant species (47.0%), followed by shrubs (26.5%), trees (19.3%), and vines (7.2%). Results from surveys on phytosociology and natural regeneration, focused on shrubs and trees, recorded incipient ecological succession. In addition, the most adapted species recorded on the overburden piles, as ranked by index of natural regeneration (RNT) plus importance value index (IVI), were as follows: Clethra scabra (RNT = 23.93%; IVI = 17.28%), Myrsine coriacea (RNT = 20.93%, IVI = 11.26%), Eupatorium intermedium (RNT = 7.56%, IVI = 0.40%), Miconia ligustroides (RNT = 5.84%, IVI = 2.37%), Ossaea amygdaloides (RNT = 3.84%, IVI = 1.30%), Tibouchina sellowiana (RNT = 3.29%, IVI = 1.94%), Eup. inulaefolium (RNT = 2.65%, IVI = 0.80%), and Baccharis dracunculifolia (RNT = 2.28%; IVI = 0.56%). High values of IVI and RNT exhibited by the exotic species Eucalyptus saligna (IVI = 21.73%, RNT = 51.41%) indicated strong competition between exotic and indigenous species. Severe chemical (acidic pH and lack of nutrients) and physical (coarse substrate and slope angle of 40–50°) characteristics displayed by the overburden piles constituted limitations to floristic diversity and size of indigenous trees, indicating the need for substrate reclamation prior to forest restoration.

Life Beneath the Surfaces of Active Jurassic Dunes: Burrows from the Entrada Sandstone of South-Central Utah

Within the Middle Jurassic Entrada Sandstone of south-central Utah, cylindrical burrows, 15–95 mm diameter, are abundant in large-scale, eolian cross-strata. Burrows are oriented at a high angle to stratification and commonly extend more than 30 cm below their surface termini. They are rarely inclined more steeply than 22°. Many are sinuous, and they sometimes branch (∼120°) at bends. Burrows terminate upward against flat-topped cones of structureless sandstone that are up to 15 cm deep and present at numerous, closely spaced stratigraphic horizons. Entrada eolian dune deposits also host abundant burrows likely produced by small insects. Both large and small burrows are most numerous in the uppermost parts of very thick (up to 35 m) compound sets of cross-strata generated by superimposed dunes migrating along the lee slopes of giant dune ridges. The size and morphology of the large burrows and the nature of their fills suggest that they were excavated by vertebrates, possibly insectivores, but the possibility that scorpions or spiders dug the burrows cannot be ruled out. In modern dunes, the top 20 cm of rain-moistened sand dries quickly, but underlying sediment can remain moist for long periods. Conical pits formed on the dry surface of Jurassic dunes at the tops of burrows that were primarily excavated in underlying moist sand. Cones composed of structureless sandstone are active fills produced when burrowers pushed moist sand to the surface, forming spoil piles. Most cylindrical portions of the burrows were also actively backfilled; remaining parts were passively filled when burrow walls collapsed. Cones at burrow tops now delineate thin (∼5–10-cm-thick) packages of cross-strata that record slow (seasonal?) dune migration. Rainfall on dune surfaces allowed scattered plants, insects, and insectivorous vertebrates to inhabit the Entrada sand sea. Burrows provided animals with refuge from the hot, desiccating surface conditions.

Preparative isolation and characterization of heavy metal complexes from acid mine drainage and surface wastewater

AbstractA preparative method was developed to sample dissolved organic carbon (DOC) and heavy metals (Ni, Mn) from polluted surface waters. Main focus was set on the preparative production of freeze‐dried samples mainly composed of organic ligands from heavy metal complexes. First characterizations were done in the aqueous phase. Finally, freeze‐dried samples provide stable organic matter for multiple characterizations. Acid mine drainage of the former mining area of Ronneburg (Germany) hold elevated concentrations of heavy metals and low concentrations of DOC. Municipal wastewater, passing the spoil pile, held elevated concentrations of DOC and low concentrations of heavy metals. Dissolved components smaller than 0.45 μm and larger than 1 nm were concentrated by nanofiltration. Organic heavy metal complexes were isolated from this solution by size‐exclusion chromatography (SEC). Different size classes of molecules were collected from the column effluent, depending on their elution time, and were characterized by UV spectroscopy, ICP‐OES, and DOC measurements. All samples held organic heavy metal compounds with different retention times. The organic heavy metal complexes in acid mine drainage had higher retention times than complexes from municipal wastewater. Most interestingly, we found different affinities of heavy metals to different size classes of DOC. This affinity of the heavy metals differs with size and origin of the DOC.

Stability of Spoil Piles at Two Coal Mines in Turkey: Geotechnical Characterization and Design Considerations

One of the major problems in surface mining of coal is the stability of disposed overburden materials. Geotechnical considerations are thus very important in rational planning for disposal, reclamation, treatment, and utilization of mine waste material. The subject of this study is the stability of spoil piles at open pit coal mines located in the Central Anatolia, Turkey. The coal is produced from two adjacent open pits. While a large portion of the spoil piles dumped at the Central Pit has experienced slope failure, no spoil pile instability has been experienced at the South Pit. This article outlines the results of field and laboratory investigations to describe the mechanism of the spoil pile failure in the Central Pit and the geotechnical design considerations for the spoil piles at the South Pit based on the experience gained from the previous spoil failures. Limit equilibrium analysis carried out for the large-scale spoil failure indicated that deep-seated sliding along the interface between underclay and dragline spoil piles and rotational slip through the overburden spoil material may be all occurring simultaneously as water migrates through these areas. Sensitivity analyses revealed that spoil pile instability is not expected at the South Pit when the currentmore » spoil placement method is used as long as the generation of high water pressures in the spoil piles is not permitted. Comparisons between the results of finite element analysis and long-term monitoring data also confirmed the results of sensitivity analyses and indicated a vertical deformation associated with compaction of the spoil material.« less

Spoil pile instabilities with reference to a strip coal mine in Turkey: mechanisms and assessment of deformations

With the increasing adoption of the surface mining of coal, problems associated with spoil pile instability, which affects resource recovery, mining cost, and safety and presents environmental hazards, have become a matter of prime concern to mine planners and operators. The study of geotechnical aspects is thus very important in the rational planning for the disposal, reclamation, treatment and utilization of spoil material. A strip coal mine, one of the largest open pit mines in Turkey, is located in Central Anatolia and provides coal to a thermal power station. Coal production is carried out in two adjacent open pits, the Central Pit and South Pit. A large-scale spoil pile instability over an area of 0.3 km2 occurred within the dumping area of the Central pit. In addition, small-scale movement occurred in the outside dumping area. This paper outlines the results of field and laboratory investigations to describe the mechanisms of the spoil pile instabilities and to assess deformations monitored over a long period following the failure. Shear test results indicate that the interface between the floor and spoil material dumped by dragline has a negligible cohesion and is the most critical plane of weakness for spoil pile instability. Back analyses based on the method of limit equilibrium and the numerical modelling technique, and observations in the pit revealed that failure occurred along a combined sliding surface consisting of a circular surface through the spoil material itself and a planar surface passing along the interface between the spoil piles and floor. The analyses also indicated that pore water pressure ratios of about 0.25 satisfy limiting equilibrium condition and that rainfall about one month before the failure may be a contributing factor to the instability. Movement monitoring data obtained following the failure over a 1.5-year period suggested that the ongoing deformations were mainly due to compaction of the spoil material. Based on the monitoring data and the results of the analyses, the failure mode of the local instability occurring at the outside dumping area was considerably similar to that of the large instability.