Open-pit Mine Slope Research Articles

Quantitative hazard assessment system (Has-Q) for open pit mine slopes

Rock slope hazard assessment is an important part of risk analysis for open pit mines. The main parameters that can lead to rock slope failures are the parameters traditionally used in geomechanical classifications, the slope geometrical parameters and external factors like rainfall and blasting. This paper presents a methodology for a hazard assessment system for open pit mine slopes based on 88 cases collated around the world using principal components analysis, discriminant analysis and confidence ellipses. The historical cases used in this study included copper, gold, iron, diamond, lead and zinc, platinum and claystone mines. The variables used in the assessment methodology are uniaxial compressive strength of intact rock; spacing, persistence, opening, roughness, infilling and orientation of the main discontinuity set; weathering of the rock mass; groundwater; blasting method; and height and inclination of the pit. While principal component analysis was used to quantify the data, the discriminant analysis was used to establish a rule to classify new slopes about its stability condition. To provide a practical hazard assessment system, confidence ellipses were used to propose a hazard graph and generate the HAS-Q. The discriminant rule developed in this research has a high discrimination capacity with an error rate of 11.36%.

Integrating Rock Engineering Systems device and Artificial Neural Networks to predict stability conditions in an open pit

Stability performance of newly open pit slopes are is affected by many factors, namely, overall complex geological environment, water flow, in situ and induced rock stresses, continuous blasting effects and construction methods. It is therefore important to identify the critical parameters affecting slope stability, as well as their interactions, in order to reduce the associated uncertainty and risk. In this paper, we extend a worldwide open pit slope stability database further and build on the use of an open pit mine slope stability index to predict the stability conditions, coupling Rock Engineering Systems (RES) and artificial neural networks, namely, Back Propagation and Self Organising Maps. The Open Pit Mine Slope Stability Index (OPMSSI) can be computed as a simple weighted sum of ratings for all parameters involved in the RES. The basic device used in the Rock Engineering Systems approach is the Generic Interaction Matrix (GIM). By coding the GIM cause-effect coordinates, relevant cause-effect plots are generated indicating interaction intensity and dominance. We propose the coding of the GIM using scatter plots produced by an unsupervised, trained, self-organising map and a comparison with GIM coding through connection weights resulting from a trained back propagation neural network. Depending on the resulting OPMSSI, the approach informs on low, medium and high susceptibility levels associated with stable status, failure at set of benches or overall slope failure, respectively. Verification of results suggests that OPMSSI, resulting from self-organising maps, appears to be superior to a back propagation algorithm in prediction capacity and that the SOM proves to be an informative knowledge extraction tool.

Development of drain hole design optimisation: a conceptual model for open pit mine slope drainage system with fractured media using a multi-stage genetic algorithm

High rainfall in equatorial regions leads to high groundwater levels or pore pressures and a high risk of landslides on the slopes of open pit mines, hindering mining operations. To lower the groundwater level surrounding a slope, a drainage system is needed. A drain hole is a part of a drainage system which utilises gravity to drain groundwater. Drain hole installation in fractured media requires the determination of the number, location, length and other parameters of the drain holes. Drain holes are frequently installed in uniform configurations or in layouts with uniform spacing, which are often ineffective and uneconomical, as some holes are not in the right positions or directions within the fractured media. This paper attempts to develop a conceptual model of an optimised configuration of drain holes by setting the drain hole parameters, or decision variables, such as number, location and length, in such a way that it produces the most effective and efficient outcome by maximising groundwater lowering and minimising cost. The optimisation is supported by the multi-stage genetic algorithm method in combination with a groundwater simulator, hereafter called the multi-stage GWSim-GA SO method. The procedure of the conceptual model will be further developed and used as a framework in the groundwater management of fractured media of an open pit mine slope.

Slope monitoring and stability analysis of open pit mine based on fiber Bragg grating sensing technology

With the further development of resources, it is urgent to carry out on-line safety monitoring and early warning for high and steep slopes. Fiber Bragg grating technology used in the slide force monitoring can achieve the slope stability evaluation and the landslide pre-warning. The design and development of the fiber Bragg grating cable force sensor was carried out and achieved the automatic temperature compensation of fiber Bragg grating cable force measurement sensor in this paper, the center wavelength and the stress, temperature has a good linear relationship, the practice showed that the fiber Bragg grating anchor cable force sensor could meet the needs of open pit mine slope stability monitoring.

Study on Stability Analysis and Monitoring Technology of Deep Concave Open-Pit Mine Slope

In this paper, using the FLAC3D software to establish the numerical model of the rock slope in the south of Washan stope and to compare and verify with the monitoring result, reference is made to the original engineering and hydrogeological data of Washan stope. The results show that the stability of the South slope is mainly affected by the dominant structural plane, and the potential slip surface and the dominant structure surface are the same. During the recovery period of -120m platform residual mine, the disturbance stress is increasing but the overall amplitude is small and the slope is relatively stable.

Stability Analysis of a Large Gold Mine Open-Pit Slope Using Advanced Probabilistic Method

A large gold reserve was recently discovered at Haveri district of Karnataka state of India where open-pit mining was planned to extract these deposits. Stability analysis for open-pit mine slope at this site is presented in the article. Extensive geological investigations and laboratory testing suggested high variability in geological features of discontinuities, rock mass quality and intact rock properties. Hence, it was decided to perform stability analysis of the rock slope using probabilistic approach along with deterministic approach. Deterministic analysis was carried out with average properties of rock, and reliability analysis of the rock slope was carried out using both traditional and advanced probabilistic methods. In traditional probabilistic method, rock mass strength properties were treated as random variables without considering spatial variation of rock properties and reliability index was evaluated by Monte Carlo (MC) simulation on augmented radial basis function-based response surface. In advanced probabilistic analysis, spatial variability of rock mass strength properties was considered by generating anisotropic random field using Fourier series method with spatial averaging over finite difference zones. Reliability index was then estimated by performing MC simulation using random finite difference method. A comparison was provided between the results of stability analysis of slope from all these approaches. Rock slope was found to be stable in both deterministic and probabilistic approaches; however, the degree of stability predicted was different for both methods. Deterministic approach was found to be inappropriate to analyse the stability of slope having rock mass with variable properties. Further, reliability index and expected performance level of slope were highly underestimated by traditional probabilistic method as compared to advanced probabilistic method.

Combined methodology for three-dimensional slope stability analysis coupled with time effect: a case study in Germany

High-steep slopes in open pit mines are much more likely to collapse due to mining operations. Challenges such as data acquisition, precise numerical models and adaptable methodologies have impeded more reliable results of slope stability analysis based on the current methods. Within this context, this paper proposes a combined methodology using light detection and ranging technology to capture high-resolution slope geometry, three-dimensional geological and geotechnical modeling technologies for creating high-quality numerical simulation models and finite-element slope stability analyses combined with a new automatic strength reduction technique to analyze complex geotechnical problems. At the end, the methodology introduces a time series analysis to improve the reliability of the calculated factor of safety. A case study in the deepest open pit mine in Hambach, Germany, was conducted to test and demonstrate the effectiveness and applicability of the proposed methodology.

Cooperative monitoring and numerical investigation on the stability of the south slope of the Fushun west open-pit mine

The south slope of the Fushun west open-pit mine in China is geologically complex and is a high-steep rock slope. In recent years, a larger deformation has appeared in the south slope, with the gradual formation of a potential landsliding block that is estimated to be over 300 m3. The east and south boundaries of the block have been identified using different monitoring techniques. However the west boundary has not yet been clearly delineated, a situation which undermines safety assessments and the slope management of the mine. The focus of this was on how the microseismic technology, DInSAR technique and the numerical method are used to determine the shape and formation of the west boundary of the potential sliding block. We found that the upper part of west boundary as determined by numerical simulation is concordant with that determined by microseismic monitoring. The surface deformation area coincides with the DInSAR monitoring results and damage area based on in situ observations. Numerical simulation provides supplementary information on the distribution of stress and the formation process of the west boundary that cannot be observed directly on-site. The microseismic monitoring system was able to capture the progressive rupture of the west boundary during the deformation of the block. The cooperative monitoring strategy together with the numerical simulation can delineate the sliding surface and provide a method for a comprehensive assessment of the slope stability of other similar open-pit mines.

Investigating the effect of earthquakes on open pit mine slopes

This paper develops a database for studying the circumstances under which dynamic loading of earthquake can cause slope failure in deep open pit mines with a long lifetime. The database includes 177 open pit mines hit by earthquake and 95 natural slopes and 37 tailing dams which have been failed by earthquakes. Both earthquake parameters and geomechanical characteristics involved in each case-study are investigated. From this information, the elements playing role in the earthquake-triggered failures in natural slopes and tailing dams are identified and used to indicate conditions that may result in earthquake-induced failures in open pit mines. The result shows that even though the valley shape geometry and absence of the top weathered layer make open pit mines less prone to earthquake-induced failures, excessive pore pressure in pit slopes still carries the risk of earthquake-triggered failures in open pit slopes. Only limited numbers of open pit mines have been so far exposed to earthquakes with the same parameters as those causing failure in natural slopes and tailing dams. That is, the response of open pit mines to higher magnitude, shallower, and closer earthquakes is still unknown. Studying the earthquakes that have caused failure in other slopes, it is concluded that open pit mines may still experience reportable failures if struck by earthquakes with local depth of less than 40km, epicentral distance of less than 100km, and magnitude of greater than 6.0. The necessity of accounting for seismic loading in slope stability analyses and active dewatering for open pit mines located in seismically active areas are also discussed.

Role of Geometry and Stiffness Contrast on Stability of Open Pit Mines Struck by Earthquakes

We develop a database containing 95 historical natural slope and 37 tailing dam failures triggered by earthquake. The database analyses show that earthquake-triggered failures in natural slopes are mostly initiated in the narrow ridges. We also collect published data on 177 open pit mines struck by earthquakes of which 85 mines are located in the seismically active areas. The database indicates no reportable failures triggered by earthquakes in the affected mines. We employ a finite element code to investigate the geometrical and stiffness contrast effects distinguishing the behavior of natural slopes and tailing dams from open pit slopes experiencing earthquake dynamic loading. It is concluded that narrow ridge and the top soil layer in natural slopes and the hill-shaped geometry and unconsolidated top later of tailing dams amplifies the horizontal peak ground velocity by factor of 8 compared to open pit mine slopes. Our numerical modeling of the rock slopes suggests that the typical pit geometry and the competent material in open pit mines boost the slope stability through decreasing the topographical amplification effects.

Investigation into the effect of fault properties on wave transmission

SummaryThe estimation of wave transmission across the fractured rock masses is of great importance for rock engineers to assess the stability of rock slopes in open pit mines. Presence of fault, as a major discontinuity, in the jointed rock mass can significantly impact on the peak particle velocity and transmission of blast waves, particularly where a fault contains a thick infilling with weak mechanical properties. This paper aims to study the effect of fault properties on transmission of blasting waves using the distinct element method. First, a validation study was carried out on the wave transmission across a single joint and different rock mediums through undertaking a comparative study against analytical models. Then, the transmission of blast wave across a fault with thick infilling in the Golgohar iron mine, Iran, was numerically studied, and the results were compared with the field measurements. The blast wave was numerically simulated using a hybrid finite element and finite difference code which then the outcome was used as the input for the distinct element method analysis. The measured uplift of hanging wall, as a result of wave transmission across the fault, in the numerical model agrees well with the recorded field measurement. Finally, the validated numerical model was used to study the effect of fault properties on wave transmission. It was found that the fault inclination angle is the most effective parameter on the peak particle velocity and uplift. Copyright © 2017 John Wiley & Sons, Ltd.

Estimation and Engineering Application of Jointed Rock Mass Strength

It is an important significance that reasonable value of strength parameters of jointed rock mass for slope design and stability evaluation. On the basis of the deformation and strength of the rock block and survey of rock mass structure, strength of jointed rock masses is estimated by Hoek-Brown strength criterion. It is used to analysis excavation process of an open pit mine slope. The result show that strength parameters of slope rock mass determined by the Hoek-Brown empirical criterion takes rock structure, rock fragment strength, stress state into consideration, what reflects the nonlinear characteristics of the rock mass destruction effectively, and accord with jointed rock slope deformation and failure characteristics. It has important reference value to the actual project.

Pull Experiment to Validate Photogrammetrically Predicted Friction Angle of Rock Discontinuities

The estimation of the mechanical properties of rock joints is crucial in terms of safety when it comes to design of slopes in open pit mines or caverns used for the storage of hazardous materials, for instance – nuclear waste. Photogrammetry provides a simple, objective method for joints roughness assessment, without the need for expensive and time consuming laboratory tests or subjective empirical methods. In this study, a new photogrammetric method was used to estimate the roughness, shear strength and friction angle of a discontinuity of 2 m by 1 m fresh rock joint. The estimation was done by analyzing the profiles of digital models of joint surface. Surface Length and Slope Measurement methods were used to calculate the values of Joint Roughness Coefficient (JRC) of analyzed surfaces. Next, the shear strength and friction angle of the rock discontinuity were obtained experimentally with multistage pull testing. The results obtained with both methods were analyzed and compared. JRC values from photogrammetrically created digital models of the joint surface were overestimated due to the low density of the models, which resulted in high noise to signal ratio. Shear strength obtained with photogrammetrically created models were overestimates in relation to the results of the pull test by approximately 45%. The errors made during this research are analyzed in the article and recommendations on how to improve reliability of the results are made. Main error in photogrammetric prediction was low density of the point clouds and in laboratory test too low stiffness of the test arrangement. The alternative methodology for photogrammetric studies used in previous stage of the research project was tested during this study and was proven to give significantly higher accuracy of generated digital models. The stiffness of the testing machine and proper positioning of the sample halves on top of each other were identified as the most sensitive aspects of methodology of big scale pull test when it comes to the reliability of results.

Analysis on Slope Stability of Open Pit Coal Mine Based on Grey Support Vector Machine

Shenhua BaoRi XiLe open-pit coal mine slope is located in the seismic belt of hulunbuir prairie in Inner Mongolia, which belongs to the high frequency and intensity earthquake zone, with rainfall concentrated, poor geological distribution, under the influence of complex environmental factors, extremely easy to cause landslide. This paper uses grey model and support vector machine (SVM) to establish slope model, and carries out stress and strain characteristics under the condition of natural, rainfall, earthquake and calculation and analysis of stability. Through the experiment, it analyzes the stability coefficient of downhill under rainfall condition, and obtains the different strength reduction of safety factor list. At the same time, give full consideration to the uncertainty of the earthquake, assume a variety of working conditions of the earthquake, it conducts dynamic analysis of the slope in detail, and gets the dynamic characteristics curves of the monitoring points. Results show that, relative complex terrain conditions, climate conditions and at a high intensity earthquakes area, are the main factors to induce landslides in this region. Therefore, this paper provides a reliable basis for further study of the effects of rainfall and earthquake on slope and disaster prevention and mitigation.

A new prediction model for rock slope failure time: a case study in West Open-Pit mine, Fushun, China

Establishing an accurate method for predicting the failure times of rock slopes subject to creep deformation is challenging, but at the same time crucial for preventing damage to properties and loss of life. In this paper, the Medium–short Term Prediction of Landslide by Polynomial (MsTPLP) model is proposed based on the Levenberg–Marquardt (LM) algorithm. The West Open-Pit mine in Fushun, NE China is currently the largest open-pit coal mine in Asia. The landslide on the southern slope of the West Open-Pit mine was selected as the study case. Global Positioning System (GPS) monitoring is employed in landslide displacement monitoring. Based on the analysis process of the MsTPLP model, the displacement time series derived from GPS monitoring points is selected as the input. The model parameters of the MsTPLP model are obtained using the Levenberg–Marquardt (LM) algorithm. The predicted failure time of a landslide, which is the output, can be determined according to the prediction criteria of the model. The prediction results show that the MsTPLP model can provide accurate landslide displacement predictions (correlation coefficient R 2 > 0.98 and average relative error ARE < 17 %). The forecasting results of the landslide show that the estimated failure time is Mar 5, 2014. Based on field investigation and displacement analysis, the landslide on the southern slope of the West Open-Pit mine occurred on Mar 9, 2014. The predicted and actual failure times are significantly close, demonstrating the potential of the new method in landslide prediction.

Assessment of rock slope stability at Cham-Shir Dam Power Plant pit using the limit equilibrium method and numerical modeling

There is global concern about the stability of rock slopes in open pit mines while the limit equilibrium technique used for modeling complex geometries and forces fails to provide a complete understanding of the behavior of rock slopes due to its inherent shortcomings. However, numerical approaches to modeling complex rock structures have improved the general understanding of these slope structures. In this study, geological and geotechnical data were obtained from both exploration drill holes and laboratory tests using face mapping and scanline surveys to reveal three major joint sets related to the regional tectonic history at the Cham-Shir dam power plant pit in Iran. The joints play an important role in the slope stability of the open pit, notably in terms of planar and wedge failures. Moreover, both the limit equilibrium technique and the discrete element method were employed to analyze the stability of the Cham-Shir dam power plant pit in an attempt to evaluate its behavior under both supported and unsupported conditions in the three modes of continuous rock mass, rock mass with two joint sets, and rock mass with three joint sets. Results show that the rock mass is stable in the continuous mode. The possible failure must, therefore, be due to the structure type and the joint sets at the site. To address the requirements and to resolve the problem, a simulation study was conducted. Based on the findings, stage by stage excavations are recommended for the study site.

Coupled Time Domain Integration Algorithm for Numerical Manifold Method

AbstractA temporal coupled explicit–implicit time integration algorithm is proposed to improve the computational efficiency of the numerical manifold method (NMM) for seismic stability analysis of rock slope. It includes a coupled time integration scheme, a phase transfer criterion, and an associated contact algorithm. To calibrate the proposed algorithm, a block sliding along a slope under seismic excitation and a block rocking under half-sine pulse shaking are simulated. The traditional limit equilibrium method (LEM) for slope stability analysis determines the factor of safety (FoS) without considering the time-dependent effect. The developed algorithm is able to simulate jointed rock slope seismic stability taking advantage of the NMM for continuous and discontinuous deformation analysis. An open-pit mine slope excited by the El Centro earthquake wave is studied. The simulated results are in good agreement with the results based on the traditional NMM, whereas the computational efficiency is improved s...

Image processing for erosion control of open-pit mines

Soil erosion is one of the most severe land degradation problems afflicting many parts of the world where topography of the land is relatively steep. Owing to inaccessibility to this steep terrain, such as slopes in open-pit mines and forested mountains, advanced data processing techniques are required to identify and predict high risk erosion zones. Unlike existing methods that require human observations, which can be expensive and error-prone, the proposed approach uses a fully automated algorithm to indicate when an area is at risk of erosion; this is accomplished by processing Landsat and aerial images. In this paper, an image processing algorithm is presented to identify the scene of an image by classifying it in one of six categories: open-pit mine, mountain, forest, degraded forest, cropland, and grassland or orchard. This paper focuses on automatic scene detection using global features with local representations to show the gradient structure of an image. The output of this work counts as a contextual cueing and can be used in erosion detection, and for erosion control in a variety of applications; particularly, predicting erosion risks in open-pit mines. We also discuss the environmental implications of deferred erosion control in open-pit mines.

An improved fractal prediction model for forecasting mine slope deformation using GM (1, 1)

The forecasting slope deformation potential is required to evaluate slope safety during open-pit mining, allowing us to formulate and promote effective emergency strategies in advance to prevent slope failure disasters. Although fractal models have been used to predict slope deformation, such limitations as low prediction accuracy, poor stability and the requirement for large amounts of data must be overcome. This article proposes an improved fractal model to forecast mine slope deformation using the grey system theory. The GM (1, 1) model is used in the improved fractal model to optimize the fitting function of the fractal dimension because of its high computational efficiency and strong fitting ability. Data sequences spanning 13 days from 11 global positioning system monitoring stations in the Jinduicheng open-pit mine in Shaanxi Province, China, were applied to forecast the slope deformation. The results from both the traditional fractal model and the improved fractal model can accurately forecast the slope deformation value fairly close to the actual field monitoring value, but the latter can make a more accurate prediction than the former. There is a significant relationship between the prediction accuracy and the data sequence dispersion. Further analysis revealed that our improved fractal model is more capable of resisting the volatility existing in the data sequences than the traditional fractal model. These findings assist in understanding the applicability of prediction models and the deformation trends of open-pit mine slopes.

Development of an early-warning time-of-failure analysis methodology for open-pit mine slopes utilizing ground-based slope stability radar monitoring data

The recent introduction of ground-based slope stability radar in open-pit mines to complement conventional geodetic monitoring programs provides near real-time deformation measurements over a broad coverage area; this allows geotechnical engineers to observe the spatial distribution of pit wall movements and their progression over time. This paper presents a newly proposed early warning time-of-failure (TOF) analysis procedure for use in real-time with ground-based radar measurements designed to be integrated in an open-pit mine’s trigger action response plan (TARP). The inverse-velocity and slope gradient (SLO) TOF analysis methods are applied to radar displacement measurements using a new systematic multi-pixel selection technique termed the “percent deformation method.” The utilization of the percent deformation method in the proposed real-time TOF analysis methodology gives more-reliable results than current practice by providing recommendations for pixel selections, data filtering, where and how to undertake TOF analyses, and presenting TOF results in real time. The addition of a more rigorous, methodical treatment of radar monitoring data when faced with critical slope instability will reduce uncertainty and increase confidence in any trigger action response decisions, helping to ensure a safer work environment.