Pit Slope Angle Research Articles

Research on controlled mining of end slope fire-burned area in open-pit mine

To solve the problem of controlling mining in the open-pit mine end slope fire-burned area, applying multivariate function fitting to the roof and floor modeling of multi-coal seam open pit mines, introducing the factor of coal quality changes in the fire-burned area, determining coal quality information at each location through proximate analysis of coal, to establish the net profit model of the mining area, it is determined the net profit of each mining position by numerical integration, the final mining position was determined without failure by calculating the slope stability based on the numerical simulation of strength reduction. Taking the Dananhu No. 2 open-pit mine in Hami, Xinjiang, China as the engineering background, the fire-burned area III within the southern end slope boundary of the first mining area is 240 m. It was finally determined that the optimal mining position is when the advancement degree is 182 m, the ultimate pit slope angle is 25°, the three-dimensional slope stability is 1.305, the profit is 671.96 million yuan, The deep boundary of the southern end slope fire-burned area of the slope is reduced by 58 m. This paper solves the problem of end slope mining in Dananhu No. 2 mine, and maximizes its net profit under the condition of ensuring safe production.

A heuristic method for production scheduling of an open pit mining operation

ABSTRACT A mathematical model for production scheduling of open pit mines maximises the net present value and satisfies the reserves, pit slope angle, and production capacity constraints. A solution to this model aims to deliver an extraction sequence and the movement of materials across various stages within the operation over a defined planning horizon. However, given that the mineral reserves delineated into thousands of mining blocks form the geological input, the model falls in the category of large-scale optimisation problems, i.e. it is computationally intractable, and exact methods cannot solve realistic scenarios of the problem. Therefore, this paper contributes an alternative to the conventional mathematical model along with a corresponding heuristic method to solve this proposed model. An implementation of the proposed method at various realistic instances reveals better performance in terms of net present value, computation time and optimality gap as compared to the traditional methods.

Behaviour pattern of rock mass haulage energy intensity in deep pits

A significant portion of mineral deposits developed by open-pit mining is opened to the full depth by road transport ramps without the use of combined transport. In most cases, this is dictated by the high rate of a pit deepening and multi-stage development. In this study, the energy intensity of rock mass (RoM) haulage from the working zone of a pit to the surface is considered at several hierarchical levels. Mineframe software was used to study 3D-models of open pits with different slope angles in order to test the method of analytical calculation of a pit volume that allowed ensuring accuracy under a wide range of mining conditions. The findings of the research are as follows: with an increase in the pit bottom diameter, the zone of stabilization of rock mass lifting (haulage) height shifts to greater target depths. An increase in the pit slope angles entails shifting the weighted average height to deeper elevations. By increasing the pit target depth, combined modes of transport become more economical in comparison with dump trucks due to an increase in the total volume of rock mass. Depending on the comparison purpose, it was proposed to use different types of energy intensity. For a broad estimation of the rationality of the pair “scheme of opening – mode of transport” for open pits, the ratio of potential energy intensities of rock mass haulage of a considered option of a pit opening and its basic option without transport berms was used. The ratio of potential energy intensities as a function of a pit depth was determined. The values of total energy intensity of rock mass haulage from a pit to the surface were also established.

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.

Numerical simulation of the open pit stability based on probabilistic approach

Purpose. To identify development regularities related to a stress-strain state and stability of the open pit walls while mining the steeply inclined iron-ore body at various stages of mining considering deterministic and stochastic components of the rock mass structural heterogeneity. Methodology. Numerical 3D simulation of the rock stress-strain state; application of the strength reduction procedure to determine a safety factor, taking into account the rock mass heterogeneity based on a stochastic model. Findings. The distribution of maximum shear deformations and displacements within the rock mass, making up the pit wall, has been obtained. Potential slide surfaces and safety factors have been determined at various stages of the inclined ore body mining. The effect of the rock mass structure on the pit wall stability has been estimated. A comparison of calculations based on the 3D and 2D models has been carried out. The correction coefficient has been obtained, which allows using the 2D model for multivariate calculations. The relationship of safety factor versus the overall slope angle has been developed. Originality. It has been proved that pit walls retain their stability (the stability factor (SF) is not less than 1.27) while mining the steeply inclined ore body with the transverse panels from top to bottom within each newly cut layer, despite the increasing depth of mining. It is shown that modeling of the real geological structure of a three-dimensional rock mass area factors into the decrease in (by 7%) the safety factor in comparison with the results of the homogeneous model. A probabilistic-statistical approach has been proposed to consider the heterogeneity of the rock mass and avoid unreasonably optimistic forecasts of the pit wall stability. It is shown that 3D modeling gives SF, which differs by 8% from the values obtained in the 2D model. This allows substantiating the correction coefficient to improve the 2D modeling results. Practical value. The regularity of changes in the pit wall stability has been determined depending on the overall pit slope angle in terms of mining-geological and mining-technical conditions of the Kachar deposit, taking into account the real rock heterogeneity.

Design acceptance criteria for operating open-pit slopes: An update

ABSTRACT Open-pit slope engineering involves balancing economic imperatives and risk, where an optimum pit slope design seeks to safely steepen the pit slope angles to minimize the mining of waste, therefore maximizing ore recovery. Open-pit Design Acceptance Criteria (DAC) had been proposed and adopted by industry, and the Guidelines for Open Pit Slope Design, published in 2009, finally provided a consistent set of guidelines. Since the publication of these guidelines, it has been the industry experience that practical DAC requires consideration of multiple levels of design confidence, ranging from highly uncertain greenfield sites to mature operations; the unique nature of consequences associated with open pit wall failures as opposed to other civil and mining structures; and differences between operators’ risk appetite. This article presents the state of practice for inter-ramp and overall open-pit slope design in the mining industry and develops flexible DAC for operating pits that addresses the considerations outlined. The criteria are rooted in robust risk tolerance principles, previously adopted criteria, a database of open-pit designs, and mathematical validation for criteria in terms of both Factor of Safety (FoS) and Probability of Failure (PoF).

Investigation of Bishop’s and Janbu’s models Capabilities on Slope Stability Problems with Special Consideration to Open Pit Mining Operations

One of the most effective parameters in economics of open-pit mines is the pit slope angle, so that the slope angle more than the optimum value increases the probability of a large failure in the pit wall and the slope angle less than the optimum value leads to increasing stripping ratio and reducing net present value of mine. Therefore, in this paper, considering the limit equilibrium methods of modified Bishop and modified Janbu and numerical models of the slope stability analysis, the effect of overall slope angle on the Economics of open pit mines was investigated. In addition, it was shown that selecting the overall slope angle less than the optimum value leads to reducing the depth of open-pit mining (the ultimate pit depth) and consequently, reducing the net present value of mine. Finally, in homogenous and Isotropic media, the results of Bishop and Janbu and numerical modeling are close together.

Combined method of opencast and underground mining of valuable ore

The efficiency of the combined opencast and underground mining of deposits directly depends on the overburden amount within the open pit boundaries. The amount of overburden to be removed, in its turn, is determined by the angles of the open pit slopes. At the same time, the influence of the open pit slope angle on the amount of the rock mass within the open-pit contours increases in an arithmetic progression with the mining depth. This fact confirms the direct relationship between the open pit slope angle and the efficiency of the mining operations from both an economic and ecological points of view. The article considers the technology for mining steeply inclined deposits of valuable ores by means of underground chambers mined out in advance with consolidating stowing to support unworked sides of an open pit called “well”. The chambers which can be not only vertical but also inclined at an angle of 60-80° serve to create an artificial fence (a ring concrete support). The work of the fence supporting the open pit side is markedly different from that of retaining walls of any type since the consolidating stowing mixture used to create the fence provides an ideal contact of the concrete wall with the enclosing rocks, thus making it impossible for an artificial fence to overturn. The proposed combined mining technology is expected to reduce considerably the number of the overburden operations, to minimize the damage caused by mining operations to the environment, and to increase the intensity of mine workings.

Open Pit Geotechnics: Designing Slopes for a Very Deep Hole

For most hard rock surface mining operations, the development of an open pit is required to extract the ore resource. In designing an open pit, the challenge is to develop the most cost-effective pit slopes that can be mined safely. Pit slope designs can be fairly complex, particularly with many open pit depths exceeding 300 m and the deepest open pits exceeding 1,000 m. The process of developing a safe but optimized pit slope angle is the same regardless of the pit scale; however, the greater stress changes and increased highwall exposures associated with deeper pits tend to correlate with an increased risk of instability.

Assessment of Slope Stability for Deep Pits in Sedimentary Strata

With advances in technology increasing the economic depth limit of open-cut mines, including those in sedimentary strata, the design of stable slopes has become more critical. Increased use of geophysical logging to compliment more traditional geological and geotechnical logging provides an unprecedented detailed description of the rock mass from surface to sub-seam. Making full and best use of this data in a quantifiable, repeatable and transparent manner for the stability assessment of slopes requires a step beyond simplifying assumptions during limiting equilibrium and numerical stress analyses. By describing a repeatable deterministic model with parameterised input data we provide the basis for detailed probabilistic studies for the quantification of uncertainty. This paper considers the implication on slope stability, as measured by a Factor of Safety, of describing the strata at near geophysical log resolution. A comparison is made when representing the rock mass at increasing levels of detail with justifiable property estimates. We find that for deep pits in sedimentary rock masses a detailed description of the strata at near log resolution together with explicit representation of the near surface blast damaged zone becomes more critical as pit slope angle is optimised. This approach is demonstrated to capture the composite failure mode in sedimentary strata so that the predicted failure mode becomes a combination of low angle slip on weak units with high angle shear failure through stronger rock units as observed in the field. Compared to models with a simpler description of the rock mass, our model predicts that the mass of rock at failure becomes increasingly shallow and localised and is displaced near horizontally out of the pit slope, a failure mode observed in the field.

Finite element method (FEM) groundwater inflow modeling associated with an unconfined aquifer into the open-pit coalmine of the Phulbari area, NW Bangladesh

This paper uses a two-dimensional finite element method (FEM) numerical modeling to predict groundwater inflow from an unconfined aquifer into the open-pit coalmine in the Phulbari area of northwest Bangladesh. The rock mass of the unconfined aquifer in the Phulbari coal deposit is highly porous and permeable. Interconnected pores within rock mass are the main paths for groundwater flow. Model assumes groundwater inflow rate through the rock mass associated with interconnected pores. Eleven stages of computation associated with variable overall pit slope angle (OPSA) 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, and 35° are presented here. Model reveals that the probable inflow rate from unconfined aquifer in the open-pit coalmine would be about 377.68, 364.93, 354.38, 340.20, 331.29, 326.36, 316.86, 315.36, 308.03, 302.86, and 298.00 m3/h with relevant slope angles of 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, and 35°, respectively. It is reasonable to emphasize that the computed inflow rate (m3/h) in the present numerical model would be effective through unit width of rock strata up to the pit depth of about 320 m in the Phulbari coal deposit. From the simulation results, it is thought that the open-pit coalmine in the Phulbari area would be an environmentally challenging issue because of regional unconfined mega-aquifer.

A New Methodology for Open Pit Slope Design in Karst-Prone Ground Conditions Based on Integrated Stochastic-Limit Equilibrium Analysis

Using the Chengmenshan Copper Mine as a case study, a new methodology for open pit slope design in karst-prone ground conditions is presented based on integrated stochastic-limit equilibrium analysis. The numerical modeling and optimization design procedure contain a collection of drill core data, karst cave stochastic model generation, SLIDE simulation and bisection method optimization. Borehole investigations are performed, and the statistical result shows that the length of the karst cave fits a negative exponential distribution model, but the length of carbonatite does not exactly follow any standard distribution. The inverse transform method and acceptance–rejection method are used to reproduce the length of the karst cave and carbonatite, respectively. A code for karst cave stochastic model generation, named KCSMG, is developed. The stability of the rock slope with the karst cave stochastic model is analyzed by combining the KCSMG code and the SLIDE program. This approach is then applied to study the effect of the karst cave on the stability of the open pit slope, and a procedure to optimize the open pit slope angle is presented.

Rational Research of Deep Concave Open-Pit Slope Angle of Lower Part

With the rapid advance of industrialization,the consumption of mineral resources is increasing.For open pit mine,many of them went into deep mining.The current,widespread adoption of open pit slope angle makes deep concave mining has a huge stripping ratio.So many mines in trouble,on the premise of guarantee the deep sunken open pit slope stability increase slope toe can bring huge economic benefits,and a lot of research work has been done.This paper describes the factors affecting the stability of open-pit mine slope,the slope rock mass stress analysis,to calculate the lower steep slope economic benefits,puts forward reasonable suggestions the future research direction of the slope stability of open-pit mine.

Optimization of slope angle and its seismic stability: A case study for the proposed open pit coalmine in Phulbari, NW Bangladesh

The present study reflects upon the results of substantial program of two-dimensional Finite Element Method (FEM) numerical analyses of the open pit that links to slope angle optimization associated with the safety factor of the pit slope of a coal mine in Bangladesh. In the present analyses, two types of models have been presented. The first model estimates safety factor without seismic effect on the overall pit slope of the model; the second model incorporates safety factor with seismic stability of the model. The calculated optimum slope angle of the first model is 31° with a rational safety factor of 1.51, prior to the seismic effect. However, the value is reduced to 0.93, 0.82, and 0.72, after we applies the seismic effect in the second model with M6, M6.5, and M7, respectively. Finally, our modeling results emphasize that for the case of the proposed Phulbari coalmine, there is extremely high prospect for causing massive slope failure along the optimum pit slope angle with 31° if the mine area felt seismic shaking, like the Sikkim (in northern India) earthquake with M6.9 on September 18, 2011.

Stability Assessment of a Pit Slope Under Blast Loading: A Case Study of Pasir Coal Mine

In Pasir mine, coal seams and host rocks of varying thickness have been uniquely deposited with an average dip angle of 85°. The host rocks are weak and mainly composed of mudstone and sandstone comprising of 90–95% of the total pit volume. The thickness of coal seams and host rocks ranges from sub-metric to few tenths of meter. The overall safe pit slope angle was evaluated to be 27° for mining depth of 50–150 m. Several slopes failure incidents have occurred in the mine causing considerable disruption in production and monetary loss. It is envisaged that slope failures may be triggered due to blasting conducted in steeply dipping stratified deposit. In order to investigate the causes of slope failures, peak particle velocity (PPV) and accelerations at various locations from the blast site have been measured. In addition, finite element models of pit slope have been analyzed by applying static or gravity loading as well as blasting or dynamic loading. This paper elaborates the results of in situ measurements of ground vibration and numerical investigation and suggests possible causes of slope failures in Pasir mine.

Geological control on slope failure mechanisms in the open pit at the Venetia Mine

Research Article| September 01, 2003 Geological control on slope failure mechanisms in the open pit at the Venetia Mine Wayne Peter Barnett Wayne Peter Barnett De Beers Consolidated Mines Limited, Premier Mine, P.O. Box X1015, Cullinan 1000, South Africa, e-mail: wayne.barnett@debeersgroup.com Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2003) 106 (2-3): 149–164. https://doi.org/10.2113/106.2-3.149 Article history first online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wayne Peter Barnett; Geological control on slope failure mechanisms in the open pit at the Venetia Mine. South African Journal of Geology 2003;; 106 (2-3): 149–164. doi: https://doi.org/10.2113/106.2-3.149 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The Limpopo Belt is a complex accretionary terrane that has undergone numerous deformational events. Tectonically juxtaposed lithology, open to isoclinal folding, cross-cutting and re-activated shear zones, and closely interlayered metamorphic gneisses and schists make pit slope design and maintenance risky. Pit slope design effects the stripping ratio and the “bottom-line” profitability of a mine. The geological model is the basis on which a pit design starts. At Venetia Mine the model is a tight, northward verging syncline that plunges shallowly towards the east-northeast. The geology has been modeled three-dimensionally using GEMCOM software. The jointing patterns have been studied and hypothetically related to the geology. The synform fold model implies three major pit slope design sectors, the (a) southern limb, (b) fold hinge zone and (c) northern limb of the fold. The southern limb experiences predominantly planar failure, a problem that has resulted in a reduction in the pit slope angle from 51° to 37° and 44° in two of the southern domains respectively. The northern limb undergoes bench-scale toppling and wedge failure. The hinge zone suffers only from local wedge failure. Bench-scale folding and brittle faulting have created more local problems. Some faults create large slope-scale wedge failures. These geological variations and the relative orientation/position of the excavation necessitated the definition of a total of 11 geotechnical domains, each with an individual pit slope design. The improved understanding of the geology and its impact on the rockmass behaviour will lead to improved blasting practices and steeper slope angles. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Incorporation of slope design into optimal pit design algorithms

The design of an optimum open-pit requires an estimate of a set of average and safe slope angles. Pit slope angles may vary throughout a deposit to accommodate varying rock characteristics and ore/waste ratios. If insufficient geotechnical information is available, the pit slopes may be found from other mines of similar size and geological conditions. If the mine is in operation, predefined or existing pit slopes can be used in the design of the optimum pit. Two approaches are described and associated computer programs for the estimation of a set of safe average pit slopes for use in an optimal pit design program are presented. The first approach determines the steepest safe angle by kinematic analysis; the second includes methods for the design of slopes by limit equilibrium analysis in terms of the safety factor or the probability of failure determined by application of the Monte Carlo simulation technique.

Mine water risk in open pit slope stability

Water pressure due to groundwater presence has a great influence on the open pit slope stability and for that reason the risk of slope instability is dependent on water level in the slope. Factor of safety could be reduced from 1,3 to 1.0 if the water level increases. In all cases in open pit mining practice more than 40% of slope instability risks depend on groundwater conditions in the slope, To prevent slope failure, effective drainage system can be installed, and other factors can remain unchanged. The importance of controlling water surface in open pit slope is emphasized. In general, increasing the open pit slope angle and decreasing the failure risks, is directly proportional to effective drainage system.

Examples of open pit mining instability

Abstract Geotechnical technology for surface mining has become increasingly sophisticated as lower grade ore deposits are being developed. With larger and deeper open pits, more detailed and accurate investigation has become necessary during the past decade. Many variables influence successful open pit operations. These include ore grade, metal price, development costs, construction costs, mine design, stability and operating costs. With the great increase in the size of open pits to depths over 600 ∼ 800 meters, the determination of pit slope angle and control of wall stability has a major influence on project economics. This paper briefly discusses preliminary considerations for pit slopes from a geotechnical standpoint to optimize economics and safety, describes recent developments in stability engineering and to illustrate a wide range of stability problems, typical examples are briefly reviewed.

Strength and Durability Properties of Core Lithologies from Coal-Bearing Tyonek Formation, Cook Inlet Region, Alaska: ABSTRACT

The Tyonek Formation (late Oligocene to middle Miocene) is a nonmarine unit of sandstone, siltstone, and claystone that contains large quantities of strippable subbituminous coal and lignite. The geotechnical properties, determined by field and laboratory tests on core from the Capps and Chuitna coalfields, dictate the equipment needs for excavation, determination of pit slope angle for mine planning, and durability of excavated spoil to weathering degradation. Point-load strength index tests are rapid and inexpensive field tests approximating the tensile and unconfined compressive strength of rock types. These tests, combined with laboratory uniaxial compression tests, were used to rank the formation lithologies in order of decreasing strength: coal (2,670 psi), carbonaceous claystone (825 psi), siltstone (435 psi), claystone (375 psi), and sandstone (145 psi). Except for coal, the lithologies range in hardness from soft soil to soft rock. Laboratory slake durability index tests, which measure the deterioration potential of rock masses as a result of cyclic wetting and drying, were used to rank lithologies in order of decreasing durability: claystone (49%), carbonaceous claystone (46%), siltstone (40%), and sandstone (20%). The cored Tyonek lithologies are noncarbonate, and their strength and durability increase with decreasing grain size and increasing clay-particle content. Compressional wave velocity, combined with point-load data, indicates that most of the rocks could be removed by bulldozers with ripping blades or by scrapers and shovels. However, coal (with rare exceptions, the strongest lithology tested) would require blasting before removal. End_of_Article - Last_Page 674------------