Open-pit Mine Slope Research Articles

Energy Catastrophe of Jointed Rock Slope Considering Spatiotemporal Variability of Strength

The spatiotemporal variability of rock mass strength for jointed rock mass is crucial for the stability of open-pit mine slopes. The Dagushan Open-pit Iron Mine was taken as the background to systematically study the unloading damage and energy evolution of high slope jointed rock mass. Through a field survey of mixed rock slope and fuzzy C-means clustering optimization analysis, the random distribution parameters of two dominant joint sets of rock mass were determined, and a three-dimensional joint network of rock mass was reconstructed. Additionally, a numerical analysis method is proposed for the energy evolution of jointed rock mass considering the spatiotemporal variation of strength, and the variation trends of gravity potential energy, elastic strain energy, and dissipation energy of jointed rock slope were analyzed. Moreover, based on the cusp catastrophe theory, an energy criterion was established for jointed rock mass slope instability. Furthermore, the energy evolution mechanism of deformation and failure of jointed rock slope under mining was elucidated. The slope safety factor obtained from the energy cusp catastrophe dissipation energy cusp catastrophe is the same as that obtained from the limit equilibrium Janbu method.

Slope stability analysis using deterministic and probabilistic approaches for poorly defined stratigraphies

The stability of slopes directly affects human lives, the environment, and the economy. Inaccurate geological profiles within numerical slope stability models can lead to potentially catastrophic consequences when model conditions do not appropriately reflect real-life stratigraphy. In cases where localised deposits are prevalent, probabilistic methods are often necessary to accommodate for unknown or poorly defined stratigraphies. Currently, there are no commercial geotechnical software packages that simulate probabilistic constitutive behaviour of materials within finite element methods for large-scale stratigraphic analysis. Instead, commercially available probabilistic methods such as the random limit equilibrium method are incapable of incorporating non-linear constitutive soil behaviour. For this reason, advanced constitutive models are seldom coupled with probabilistically varying soil layers or spatially variable soil parameters. The objective of this research is the implementation of a simplified method for probabilistic stratigraphic analysis within a commercially available FE environment, providing a technique to assess the effects of stratigraphic uncertainty on slope stability. The proposed method is presented, highlighting the impact of localised thin layers of soft material as well as their frequency and location on the slope of an operational open-pit mine. The significance of these stratigraphic effects is presented through a case study of Australia’s second-largest open-pit mine, at which the stability of a collapsed coal slope is analysed. To improve the reliability of the finite element method for slope stability assessment, the Monte Carlo approach has been incorporated to consider varying shear strength distributions for models incorporating advanced constitutive behaviour. Thicker probabilistically generated deposits of silty material resulted in increased slope Factors of Safety. Similarly, greater proportions of silty deposits within a predominantly clayey interseam produced larger safety factors than slopes without localised thin silty layers. Stratigraphic analysis indicated that the Factor of Safety was most sensitive to localised silt layers at depths greater than 83 m below ground level.

Implications of DFN Model Selection in Open Pit Bench Stability Analyses

A coupled Discrete Fracture Network (DFN) – Limit Equilibrium Analysis (LEA) approach to the design of bench face slopes in open pit mines has significant advantages over conventional analyses. The reliability of this approach is directly related to the quality of the input data and the ability for the generated DFN to adequately capture the characteristics of the rock mass. Different DFN model generators have specific input requirements and inherent assumptions. This paper addresses the critical issue of selecting an appropriate DFN model. Through a worked example, it illustrates the implications of selecting a series of different DFN models and generators on the stability analyses, and interpretation of the results. This is shown to have significant impact on the design of open pit slopes.

Influence research of weak layer on slope sliding mode and stability

Weak layer is an important factor leading to slope instability, which cannot be ignored in slope stability analysis. In order to explore the influence of weak layers on the slope slip mode and stability of the slope, this paper selects typical open-pit mine slopes containing weak layers as the engineering background, and comprehensively uses geological survey, laboratory tests, theoretical analysis and other methods to verify the characteristics of slope geological structure and physical mechanical properties of soil, at the same time, uses simplified Bishop method to analyze the change law of slope stability under the change of weak layer dip angle, and finally clarifies the influence of weak layer on slope slip mode and stability. The results show that: the initial dip angle of the weak layer is 6°, the corresponding stability factor is 1.553 and the initial landslide mode is the combined failure of shear arc and weak layer. As the dip angle of the weak layer increases, the slope stability coefficient decreases. When the dip angle of the weak layer increases to 56°, the slope slip mode is transformed into the translational failure formed by the weak layer, and the stability factor is reduced to 1.055 at this time.

Optimal Design of Presplit Blasting Network of Deep Concave Open-Pit Mine Slope with Heterogeneous Complex Rock Mass

To ensure that the mining steps of deep concave open-pit coal mines with heterogeneous complex rock masses in arid areas are safely bounded by the design requirements and form a fixed side wall, to avoid the occurrence of instability and disaster caused by blasting vibration, based on non-homogeneous rock mass structure, lithology characteristics, fracture surface composition, morphology and joints, analysis of fissure development trend, and case studies of wedge-shaped landslide accident caused by blasting vibration, we proposed: (1) The pre-split instantaneous denotation charge is the dosage used for the segment unit charge of the primary blast hole and buffer hole, and it’s used for calculating . Based on this, the time intervals of segmented detonating cord and fuse are calculated and the actual detonating unit charge is decided. (2) Leave lateral free surface on the fixed side boundary and drill inclined blast holes along the slope of the steps, connect detonating cords to the blasting network, multi-point instantaneous detonate uncoupled segmented charge holes, use the pre-crack and fracture surface to reduce the damage caused by the explosion shock wave of the primary and buffer blasting holes. (3) The main blast hole and buffer hole are connected by non-conductive detonating cord and “four-way” blasting network, couple continuous concentrated charge using non-conductive detonating cord and fuse plus or detonator plus segmented ammonium dynamite initiator and expanded ammonium oil charge for millisecond interval detonation. Control the number of blasting holes and unit detonating charge over equal segments of fuse and detonating cord, reduce the impact of close-range blasting vibration of vertical deep holes on fixed side wall and step slope. Results of the blasting experiment show that using the technology of detonating cord in combination with non-conductive detonator’s pre-split hole millisecond differential blasting network plus reserved free face and segmented unit charge detonation, provide 1-2 blasting lateral free face or positive free face, making the blasting effect dispersed around the blasting hole. It has better solved the major safety problem of instability and disaster caused by the blasting effect on the fixed border-to-boundary steps of deep concave open-pit mine in arid region.

An Automatic Monitoring Method of Slope Deformation in Open-pit mine based on BP Neural Network and GIS Technology

At present, the research on BP neural network has achieved good results in many industries and fields, but there are few projects in the application research of mineral resources mining. Under the social background of the rapid development of electronic information technology, BP neural network and GIS technology are combined to carry out research and application, which will provide a new research path for slope deformation monitoring and disaster prevention in mining area. Therefore, in the paper, the key technology of open-pit mine slope deformation automatic monitoring based on BP neural network and GIS technology was put forward. Firstly, the advantages of BP neural network were analyzed and BP neural network was selected as the prediction model of slope deformation. The artificial fish swarm algorithm was used to improve the BP neural network to improve the performance of the model. Based on the analysis and construction of GIS technology, the combination application of BP neural network and GIS technology was discussed. Through practice, the application effect of the technology was verified, and it has good theoretical and practical value

Parameter inversion and location determination of evolutionary weak layer for open-pit mine slope

In light of the complex and dynamic mechanical properties of evolving weak strata in open-pit mines, and the consequent difficulty of determining their mechanical parameters, this study uses the ultimate balance theory, along with the back analysis method combined with monitoring data on field displacement, to carry out parameter inversion using the FLAC3D numerical simulation software. The edge slope of a working pit of the Weijiamao open-pit mine was used as research object to this end. As the results obtained by the constitutive model were consistent with the field monitoring data, the evolving weak strata in the slope and the position of the landslide in the mine could be obtained. The landslide was directed northeast. The mechanism of the edge slope of the working pit was identified as unloading shear failure, and the feasibility of the method of parameter inversion was verified. The internal friction angle ϕ and cohesion C of evolving weak strata in the slope of the open-pit mine were also obtained, where this compensated for the deficiency of laboratory tests and enabled the transformation from qualitative to quantitative analysis. This can provide a reliable basis for the safe operation of open-pit mines.

Physical model test study on shear strength characteristics of slope sliding surface in Nanfen open-pit mine

A physical model for the footwall slope of Nanfen open-pit mine, China was established using a self-developed deep geological engineering disaster model test system. A thermosensitive similar material, paraffin, was selected to simulate a weak structural plane in the slope to reproduce the landslide process. From an experimental perspective, the variation trend of shear strength parameters of weak structural plane and the mechanical support characteristics of NPR (negative Poisson’s ratio) anchor cable under the condition of a large landslide deformation and failure were examined. The results of this model test showed that slope failure has four distinct stages: (1) soil compaction stage, (2) crack generation stage, (3) crack propagation stage, and (4) sliding plane transfixion stage. According to the test results, the rock mechanics parameters of weak surface in the footwall slope of Nanfen open-pit mine were calculated. The cohesion is approximately 1.35 × 105 Pa, and the internal friction angle is approximately 6.33°. During slope failure, the NPR anchor cable experiences a large deformation but no damage occurs, indicating that the NPR anchor cable can be continuously monitored and reinforced during the deformation and failure of landslide. The stress characteristics of NPR anchor cables during the test are consistent with the monitoring results of Newtonian force at the landslide site, proving that NPR anchor cables are effective and reasonable in landslide monitoring and early warning.

Numerical Modeling on Anisotropy of Seepage and Stress Fields of Stratified Rock Slope

Stratified rock mass is a common rock mass structure and distributed widely on the earth’s crust. High-density distribution of stratified structural planes in the stratified rock mass has a great influence on the mechanics properties of the rock mass, such as anisotropy of stress and seepage. Therefore, anisotropy is the inherent characteristic that must be considered in the stratified rock mass as well as the stratified rock slope stability. According to the anisotropic characteristics of stratified rock mass, an anisotropic seepage-stress coupled model for the mechanical behavior of stratified rock slope is proposed based on the anisotropy elasticity theory. The model is validated by simulating seepage and stress fields of an idealized slope using the finite element method. The deformation and stress-dependent permeability of the slope are predicted and compared well with the previous study, thus confirming its capability in characterizing the response of rock slope that is dominantly affected by rock anisotropy. Finally, the model is used to simulate the anisotropic properties of a stratified rock slope of Fushun west open-pit mine, China. The simulation is in good agreement with the actual measurement, which means the proposed model is capable of simulating anisotropic properties of the stratified rock slope.

Geomechanical and Acoustic Properties of Intact Granite Subjected to Freeze–Thaw Cycles during Water-Ice Phase Transformation in Beizhan’s Open Pit Mine Slope, Xinjiang, China

The deterioration of rock geomechanical behaviors subjected to freeze–thaw (F–T) action is a determining factor for rock engineering and rock structures in cold regions. In this work, taking six groups of granite obtained from an open pit mine as the research object, F–T cycle treatment, in-situ AE (acoustic emission) monitoring and ultrasonic detection techniques were performed to experimentally reveal the effects of F–T fatigue damage on the mechanical and acoustic properties of granite. The results indicate that the F–T action impacts the rock’s mesoscopic structure, deformation, strength, P and S-wave velocities, AE pattern and energy release. The accumulated AE counts and accumulated AE energy show a decreasing trend as the F–T cycle increases. The frequency spectrum revealed that the width of the low frequency band decreases and the high frequency band increases with increasing F–T cycles, indicating that there is an increase in large-scale cracks for a sample with high F–T treatment. In addition, energy balance analysis further illustrates the energy dissipation and release mechanism. The energy proportion used to drive the crack propagation is relatively small with high F–T treatment, and the final released energy becomes the minimum. The energy evolution characteristics analyzed by the energy balance approach is in good agreement with AE results. It is suggested that the F–T fatigue damage influences the rock energy storage and release characteristics and the instability of rock in the cold regions.

Study on the Freeze-Thaw Damage of Granite Under Impact Loading

The freeze-thaw damage of granite was studied used SHPB tests and numerical simulation in the paper. All the granite samples were taken from high altitude localities in Tibet, China, which were made impact loading test after freeze-thaw cycles. The strain rate was unified in the use of SHPB tests combined with numerical simulation to analyze the relationship between dynamic strength and freeze-thaw cycles. The results shows, under different freeze-thaw cycles, the shapes of the reflected and transmitted waves before and after freeze-thaw are different, mainly reflected in the great difference of the curves before and after the peak. With the increase of the freeze-thaw cycles, the peak value of the strength curves decrease apparently and the peak stress decreases apparently after 10 cycles. Samples have different strain rates with the same incident wave under different freeze-thaw cycles. The dynamic strength of granite is associated with the strain rate and the freeze-thaw cycles. Study on the freeze-thaw damage of granite under impact loading is the basis of the granite dynamic constitutive relation and it is important to analyze the stability of open-pit mine slope in seasonal frozen regions.

Perspectives on the prediction of catastrophic slope failures from satellite InSAR

We demonstrate the potential of satellite Interferometric Synthetic Aperture Radar (InSAR) to identify precursors to catastrophic slope failures. To date, early-warning has mostly relied on the availability of detailed, high-frequency data from sensors installed in situ. The same purpose could not be chased through spaceborne monitoring applications, as these could not yield information acquired in sufficiently systematic fashion. Here we present three sets of Sentinel-1 constellation images processed by means of multi-interferometric analysis. We detect clear trends of accelerating displacement prior to the catastrophic failure of three large slopes of very different nature: an open-pit mine slope, a natural rock slope in alpine terrain, and a tailings dam embankment. We determine that these events could have been located several days or weeks in advance. The results highlight that satellite InSAR may now be used to support decision making and enhance predictive ability for this type of hazard.

Map of the potential geotechnical susceptibility for operational pit slopes

Abstract This article proposes a procedure to elaborate a map that presents the potential risk of failure occurrence in the operational slopes of open pit mines. First, it is necessary to collect the available geological-geotechnical data and perform a field mapping, in order to verify and validate the most representative parameters and to characterize the discontinuity families of the rock mass. Then, the mine should be sectorized, considering all the data collected, the geometry of the operational slopes and its development until the final pit. The next step will be to define and to evaluate which failure modes have greater or lesser potential to occur in the pit and to assign weights to them. In this study, the weathering, planar failure, and plane circular failure potentials were evaluated. As a result, it is possible to develop a map with the susceptibility level of the sectors. This map will help make technical and managerial decisions in order to reduce the risk level of the sectors and to promote an increase in the operational safety of the mine.

Prediction of Blast-Induced Ground Vibration in an Open-Pit Mine by a Novel Hybrid Model Based on Clustering and Artificial Neural Network

Ground vibration (PPV) is one of the hazard effects induced by blasting operations in open-pit mines, which can affect the surrounding structures, particularly the stability of benches and slopes in open-pit mines, and impact underground water, railway, highway, and puzzling for neighboring communities. Therefore, controlling, accurate prediction, and mitigating blast-induced PPV are necessary. This study contributed a new computational model in predicting blast-induced PPV for the science community and practical engineering with high accuracy level. In this study, a novel hybrid artificial intelligence model based on the hierarchical k-means clustering algorithm (HKM) and artificial neural network (ANN), namely a HKM–ANN model, was considered and proposed for predicting blast-caused PPV in open-pit mines. Accordingly, input data were first clustered by the HKM algorithm, and then, the ANN models were developed based on the obtained clusters. For this aim, 185 blasting events were collected and analyzed. A hybrid model based on fuzzy c-means clustering (FCM) and support vector regression (SVR), i.e., FCM–SVR model, which was proposed by previous authors was also applied for comparison of results with our proposed HKM–ANN model. In addition, an empirical method, several ANN and SVR models (without clustering), FCM–ANN, and HKM–SVR were developed for comparison purposes. For measuring the performance of the improved models, coefficient determination (R2), root-mean-square error, and variance account for were used as the performance indicators. The results show that the HKM algorithm played a significant role in improving the accuracy of the ANN models. The proposed HKM–ANN model was the most superior model in estimating PPV caused by blasting operations in this study.

Effect of wetting and drying cycles on microstructure of rock based on SEM

To study the effect of periodic water circulation on rock mass, chlorite–amphibolite rocks from the slope of Nanfen open-pit iron mine in Liaoning province were chosen as the engineering samples and were investigated using uniaxial compressive experiment and scanning electron microscopy. The effect of different wetting and drying cycles on the mechanical properties and microstructure of the rocks was investigated. The characteristics of pore parameters from the SEM images were obtained by Image Pro Plus image processing software. The results show that with the increase in number of wetting and drying cycles, the uniaxial compressive strength of the rock decreases and the porosity increases significantly. The weakening of macroscopic mechanical properties of rocks is closely related to the changes in microstructures of rocks. The water–rock interaction changes the size, shape and porosity of the rock pores and then affects its mechanical properties. Based on the combination of macro and micro, quantitative analysis of the weakening process of rocks subjected to wet and dry cycles can provide a better reference index for evaluating the stability of geotechnical engineering.

Research on Dynamic Evaluation Model of Slope Risk Based on Improved VW-UM

There are many accidents of slope failure due to rainfall at home and abroad, which have caused heavy casualties and property losses. Stability analysis and evaluation of slope have become a research hotspot. Aiming at the slope stability under different rainfall, this paper takes Yuebao Open-pit Mine slope as an example, has constructed a dynamic variable weight (VW) model of influencing factors on slope stability, and has analyzed the dynamic change and correlation of the slope indexes weights under different monthly maximum rainfall. On this basis, the dynamic evaluation model of slope stability has been established based on uncertainty measurement (UM), and the risk importance (RI) q which is proposed has quantitatively evaluated the risk degree of slope. The results show that under different monthly maximum rainfall the weight of each index is no longer a fixed value but a nonlinear and dynamic change law, and there is a strong correlation among the monthly maximum rainfall, internal friction angle, and cohesion. In addition, the q increases gradually with the increase of the monthly maximum rainfall, and the stability evaluation results are highly consistent with the HP1 slope, which have verified the reliability of the dynamic evaluation model. So, it can provide technical support for the safety production and management of open-pit slope and can also provide reference for related research.

Study Effect of Geological Parameters of the Slope Stability by Numerical Modelling, Case Limestone Career of Lafargem’sila, Algeria

The stability of slopes in open pit mines is an issue of great concern because of the significant detrimental consequences instabilities can have. The stability of open pit is controlled by several geotechnical and geological factors, the most important cracks in the rocks as well as various and homogeneous of layers. In the case of study presence of a tensile crack is the most critical case in the calculation of factor of safety because of the possibility of the presence of waters in this crack that influence negatively on the stability of the open pit with traction crack, Then the mechanical characteristics of the crack filling material are more degraded than those of the marl layer between the layer of limestone open pit LAFARGE. With the differences both methods possess, sensitivity analyses and comparisons of result were done using Slide, Flac and Plaxis software for the analysis of sliding and stability of open pit. These evaluations have been performed by the limit equilibrium method through the SLIDE software, the finite element, finite difference methods through PLAXIS and FLAC respectively.

Effects of the Loading and Unloading Conditions on Crack Propagation in High Composite Slope of Deep Open‐Pit Mine

In the process of open‐pit excavation and stacking of dump along the side wall, the rock mass inside the composite slope undergoes complicated loading and unloading effect, which are manifested as triaxial stress → horizontal unloading → axial loading. In this study, a corresponding mechanical model of crack propagation in composite slope under loading and unloading effects was established. The stress‐strain curves and deformation characteristics of rock under different stress paths were studied. A series of different tests under unloading pressure condition were carried out to study the behavior of the rock fracture under different confining pressure paths. The results showed that under the same initial stress conditions, the deviator stress required for rock unloading failure was less than that of the conventional triaxial compression. The axial deformation of rock samples was gradually increased with the increase of unloading, and the unloading easily led to rock failure. By analyzing the crack propagation mechanism under loading and unloading stress field, the analytic relation of the limit height of the composite slope with the crack morphology as the variation was determined when crack propagation occurred near the slope surface. This study provides a technical note on local damage and cracks propagation of a fractured rock mass under the loading‐unloading effects in high composite slope.

Stability analysis of the north-eastern slope of Daralou copper open pit mine against a secondary toppling failure

Secondary toppling failures have complicated mechanisms. In these instabilities, some natural or manmade external factors motivate and overturn a rock mass. One of the most common types of secondary toppling failures is slide-toe-toppling mode. When a blocky or layered rock mass is overlaid by a soil or weak rock mass, the combination of a toppling failure in the rock at the toe and a circular or non-circular sliding in the soil or weak rock in the top leads to this hybrid failure. In 2015, such failure occurred in north-eastern slope of Daralou copper open pit mine. During this instability, the slope consisted mainly of two 10-m benches and one 4-m semi-bench. Since it was supposed to excavate the slope to the depth of 54 m, experts were worried about the project facing a similar larger failure in the future. Hence, a widespread investigation was carried out on the failure. Firstly, the mechanism of this instability was clarified with geological and geotechnical surface and subsurface investigations. Next, existing analytical solution which had been presented for analysis of static slide-toe-toppling failure was modified and some new equations were obtained for analysis of the failure under dynamic condition. Then, a computer code was developed based on the new equations for evaluation of the instability. In the next step, the failed slope was analyzed using the code and finite element method, and outcomes of these analyses were compared with real conditions. The comparison showed that there was satisfactory agreement between the analytical, numerical and actual results. Therefore, these methods were used to predict the behavior of the final slope in static and dynamic conditions. These evaluations indicated that if displaced materials are completely excavated and removed from the mine and overall dip of the slope is reduced, the final slope will be stable against slide-toe-toppling failure. This paper summarizes the results and concludes that both the modified analytical approach and finite element method are able to analyze a slope against the secondary toppling mode. Furthermore, the research proves that re-sloping and unloading are two adequate methods which can be used for stabilization of the failure.

Influence of drain hole inclination on drainage effectiveness of coal open pit mine slope

Drain hole has an important role to reduce groundwater table on a slope of coalopen pit mine. Groundwater condition on acoal open pit mine slope with a homogeneous groundwater flow media is highly dependent on the type of lithology and the groundwater bearing-rocks. The drain hole on acoal open pit mine slope is very influential on the water discharge and the length of the drain hole. This paper presents a discussion on the effect of drain holeinstallation with an inclination angle of 65° and 90° on the discharge and drain hole length. The results show that the drain hole with an angle of 65° results in greater groundwater discharge than the 90° angle. In addition, the drain hole with inclination angle of 65° is shorter than that of the drain holeinstalled with an inclination angle of 90°, thus reducing the operating costs of the open pit mine slope drainages.