Pit Slope Research Articles

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.

Reliability Assessment of an Open Pit Slope on Bong Iron Ore Mine

Slope stability on Bong mine is crucial for securing a balance in the gross national product of Liberia. The mine is being operated using conventional open pit methods with slope angles optimally designed to maximize ore stripping quantity. However, a working slope has displayed signs of uncertainty. The overall inclination of the slope is 56°, and the proposed maximal excavation is 315.42 m, but current depth in ore is approximately 50%. Based on the study of slope geological characteristics, the physical and mechanical parameters of rock mass and the geometrical calculation of stoping, the study is tailored on the mechanism of inspecting stress-strain behavior in response to seasonal variation of rock moisturization as a more suitable means of stope slope stability analysis in this case. This study took full account of local rainfall and other meteorological conditions. Slope stability is investigated via stereographic projections and stability assessment using the Shear Strength Reduction (SSR) method based on FLAC (Fast Lagrangian Analysis of Continua) numerical modeling technique in three dimensions to predict the stress-strain behavior of the open-pit slope and evaluate its stability state. Global stability has been analyzed under natural and saturated conditions and it is found that the slope is critically stable and needs proper attention.

Study on the variation characteristics of the anchor cable prestress based on field monitoring in a foundation pit

Field monitoring was conducted on the variation of the tension in prestressed anchor cables used in a foundation pit engineering. Based on quite a few data obtained from in-site monitoring and other literature, the variation features of anchor tension were summarized concerning the install positions on a single anchor pile, anchoring strata, and locations on the plane of the foundation pit. The tension in selected anchor cables was monitored during the whole construction process from their locking to the completion of the whole construction. The results show that the anchor tension of anchor cables shows a three-stage variation. Anchor tension in cables decreases dramatically in a short period after the locking stage. Afterward, it fluctuates during the partial construction of the foundation pit which could mainly be attributed to the excavation of the subsoil close to the cables as well as the locking of the cables underneath. Finally, it tends to be stable after the completion of the whole construction. The strata condition of the cable anchored in and the position of the cable on the plane of the foundation pit would significantly affect the final anchor tension as the cables stabilized. The better the geological conditions of the anchoring strata and the closer the anchor cable is to the middle of the foundation pit slope, the greater the final anchor tension.

Analysis Method of Landslide Early Warning and Prediction Supported by Ground-Based SAR Technology

Objectives Landslide early warning and prediction is the key and difficult problem in landslide dynamic disaster research. The timeliness and accuracy of early warning are two key indicators to evaluate the effect of landslide early warning and prediction. Methods Remote sensing monitoring is an important technology for landslide disaster prevention and control. Ground-based SAR(synthetic aperture radar)provides an advanced technology for remote sensing monitoring of landslides in short distance, and provides a wealth of data sources for accurate positioning of landslides, delineating the scale of landslides, analysing and judging the risk of landslides and predicting the time of landslides. Based on the classic three-stage theory of slope deformation evolution, we adopt the monitoring data of ground-based SAR, which has the characteristics of near real-time, coverage monitoring area and surface deformation information. Combined with the characteristics of the short period, high density and surface coverage of slope monitoring data, a dual index landslide early warning method based on deformation speed and deformation area is proposed. According to the negative correlation between deformation velocity time series curve and slope stability, we put forward the processing methods of velocity inversion, de-limit and unequal period smooth processing, and establish the landslide prediction model with fast convergence of stability. Results The landslide early warning method with double indexes of deformation velocity and deformation area can effectively improve the accuracy rate of landslide warning, and then the accuracy of landslide prediction can be effectively improved by taking the reciprocal of velocity, removing the limit value and unequal period smoothing treatment. Different periods of data processing methods have their own applicability, short processing cycle processing data curve, the prediction of landslide occurrence time is more accurate, the prediction of landslide occurrence time is late, long processing cycle is opposite. Conclusions Through the field practice and application of the open pit slope, it shows that the early warning and prediction method has strong practicality and accurate prediction results.

The analysis of computer aided methods applied for pit wall stability rating

A comparative analysis of the results of the pit slope stability rating carried out under normative technique and Scad Office Slope application is presented. The possibility of combination of normative technique and computerized calculations to gain integrity and computation operability is suggested.

Evaluation of geometrical parameters affecting on the optimal slope design of Shadan Gold-Copper Open Pit Mine

The main objective of this research is to present a stable and optimal design of the ultimate slope of the eastern wall of Shadan Gold-Copper open pit mine based on the calculation of minimum factor of safety (1.20) by numerical modeling method under different conditions of slope geometry. Numerical modeling was performed using finite difference method (FDM) and FLAC3D software which is capable of calculating the factor of safety (FOS) by shear strength reduction method. Therefore, a set of 3D numerical models in different scenarios were investigated by varying the geometrical properties of the pit slope (width, height and face angle of bench, pit depth and overall slope angle). Based on the analysis carried out during the different scenarios, finally the fifth scenario with minimum safety factor of 1.20 was introduced as the proposed pattern. According to the initial design (first scenario) with a safety factor of 1.39, in the fifth scenario by decreasing the benches width from 6.8 m to 5 m and increasing their height from 10 m to 12 m which increases the slope angle of the bench face (from 70 degrees to 73 degrees) and overall slope angle (from 43 degrees to 52 degrees), safety factor of the ultimate slope was reduced to a minimum of 1.20. The maximum impact of the change in the safety factor is related to shear strain and horizontal displacement in the model such that the maximum shear strain (1.12 e-2 m) and the maximum horizontal displacement (-25.75 cm) are related to the fifth scenario with minimum safety factor (1.20). Whereas, the maximum vertical displacement (29.63 cm) is related to the first scenario model (FOS = 1.39) with the maximum slope height (pit height) of about 219 m, which shows the least influence on the value of the safety factor.

Effect of Blast-induced Ground Vibration on Factor of Safety of Pit Wall Stability

The regulated maximum peak particle velocity (PPV) from blasting operations of an open-pit coal mine is less than 2 mm/s to prevent mainly any public disturbance such as ground vibration and air blast. However, the blast-induce ground vibration can also decrease the stability of pit slope, which has not been intensively studied. A claystone pit wall, which is geotechnically investigated as having a plane failure type and the natural condition factor of safety (FS), has been selected for this study. The FS is selected to measure the effect of blast-induced ground vibration on the slope stability. The limit equilibrium, pseudo-static 1 (), and pseudo-static 2 () methods are used to determine the FS. The vibration results of blasting monitored at three slope positions: crest, middle, and toe, from two areas at the same pit wall, are recorded by blasting seismographs. Maximum charge weight per delay and the distance from blast areas to seismographs are collected to construct the scaled distance. The percentage change of FS of three methods from both areas compared to natural condition FS are all less than 4 percent considered that the slope stability is safe from blasting vibration (less than 15 percent). The relationship between the FS and maximum PPV from the limit equilibrium, pseudo-static 1 (), and pseudo-static 2 () methods indicate that the adverse maximum PPVs given the unity FS are 16.60 and 4.58, and 4.74 mm/s, respectively. The regulated PPV less than 2 mm/s at the mine is reasonable to prevent any possible plane failure. However, many impact parameters have not been included in this study, and their effects may disturb the pit wall stability.

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).

Application research on slope deformation monitoring and earthwork calculation of foundation pits based on UAV oblique photography

The stability of foundation pit slopes is a key concern during the construction of foundation pits. The deformation and instability of slopes will pose a major threat to the safety of foundation pits construction. Based on the foundation pit project of Shenzhen Dapeng People’s Hospital, this study uses DJI phantom 4 RTK drone to collect oblique photography data of the foundation pit in different periods, reconstructs high-precision 3D virtual models through the Bentley ContextCapture software and generates the Digital Surface Model (DSM) data. The model quality report shows that the accuracy of the three-dimensional model is better than 5 cm, up to about 1 cm. Spatial analysis of DSM data in different periods using ArcGIS can obtain the deformation of the foundation pit slopes. This method can also be used for the calculation of earthwork excavation of the foundation pit, which can effectively reduce the field workload of traditional earthwork surveys.

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.

Slope stability analysis of man-made soil body surrounding the abandoned hydraulic dump

Introduction. Pit slope sections directly adjoining hydraulic dumps are characterized by the higher risk of landslide, especially in case of storing dry overburden rock over the hydraulically filled overburden. It is contributed to by the combination of the following factors: increase of the total height of the slope, development within the slope of a waterlogged zone of weakness with complex footprint map and depth configuration; excessive pore pressure within this zone which grows by means of adding dry dump to hydraulically filled rock. To reduce risks connected with man-made soil body slope stability violation, slope stability analysis is carried out based on the results of geological survey, hydrogeological observations and geophysical sounding. Research aims to analyze the stability of the Krasnobrodsky coal pit man-made mass adjoining the Bakhtykhtinsky hydraulic dump based on the 3D geological-geophysical model. Methodology. The authors of the article offered and realized the algorithm of analyzing the stability of slopes based on 3D geological and geophysical models formed by integrating geological, hydrogeological and geophysical data. Results. Based on geological survey data analysis, hydrogeological survey and electric sounding, 3D geological-geophysical model of a man-made soil body adjoining Bakhtykhtinsky hydraulic dump has been built. Slope stability analysis of an actual state of the man-made soil body has been carried out. ISSN 0536-1028 «Известия вузов. Горный журнал», № 5, 2020 55 Summary. In order to develop a 3D geological-geophysical model, in addition to slope geometry, it is necessary to set the boundaries of waterlogged rock in a footprint map and in depth, and monitor pore pressure within this zone. To determine slope section with minimum safety factor it is necessary to carry out cyclic calculation with gradual reduction of approach and design section rotation increment.

METHODOLOGY OF INSTRUMENTAL CONTROL OF STABILITY OF QUARRY SLOPES USING GNSS TECHNOLOGIES

The article describes the methodology of instrumental monitoring of the stability of Karatemir open pit slopes using GNSS technologies. An iron ore deposit was selected to carry out the study. The exploitation of subsurface use facilities developed in an open way requires regular monitoring of the stability state of the instrument array. This is the main task for the safe and efficient operation of the entire field. The favorable conditions for conducting observations and the accuracy of satellite observations are also described. The analysis of the stability status of career slopes.

Determination of the main technical reasons for the fall of pile driving machine near the slope of the foundation pit

The study was conducted to determine the main technical reasons for the fall of the pile-driving machine that occurred when driving-in of piles in the immediate vicinity of the slope.As a result, slope stability of the soil in the process of driving-in of reinforced concrete piles near the slope crest of the underlying pit was determined. The calculations were performed using the following four well-known methods: methods of Fellenius, Krey, Terzaghi, Chugayev. The loss of stability of the soil was caused by the imbalance of external and internal forces (the presence of construction equipment and stored materials near the slope and its dead load). The calculations were performed for six loadcases of the earth wall. The article presents in detail the case in which the slope collapsed.The importance of the results for the construction industry lies in the need for a comprehensive study of safety issues at all stages of the life cycle of construction projects, starting with the preparation of a design assignment, surveys, design, construction, operation, repair, reconstruction, etc.

Study on plants and their ecological characteristics in the sand pit regions of Moscow

Industrial activity of human being, with each passing year, leaves an ever-growing danger on the environment worldwide. The extraction of mineral soil and non-metallic materials from sand pits has caused serious damage to the environment. Damage was embodied by soil cover destruction which occur at mining sites followed by processing of minerals and the most effective way of reclaiming disturbed land is by biological reclamation. To implement biological reclamation, a comprehensive study of sand pits ecological plants’ characteristics was studied on the Northern and Southern exposure slopes of sand pits in Moscow Region. Geobotanical descriptions on experimental sites of 5 × 5 m2;, made according to standard methods. About 127 species of higher vascular plants from 29 plant families were found on the surveyed sand pits, three of which have the most representation (Compositae, Gramineae and Fabaceae). Among the plants in the spectrum of life forms, the overwhelming majority are hemicryptophytes. In the spectrum of life forms, perennial herbaceous polycarpic were dominant. Ecological analysis of sand pits plants showed that the plants, mainly, belong to the meadow ecological-cenotic group, notwithstanding the proportion of forest species.

Acoustic emission and CT investigation on fracture evolution of granite containing two flaws subjected to freeze–thaw and cyclic uniaxial increasing-amplitude loading conditions

The deterioration mechanism and fatigue fracturing evolution of granite with two pre-existing flaws experiencing freeze–thaw (F-T) treatment are investigated in this work. The flaws in the rock sample were prepared as a combination of a horizontal flaw with an upper inclined flaw above the horizontal flaw according to the joint characteristics in an open pit slope. In-situ acoustic emission monitoring combined with the post-test 3D computed tomography (CT) technique was employed to reveal the fracture evolution behaviors of rock treated with 0, 50, and 80 freeze–thaw cycles. Results show that the freeze–thaw damage impacts the frost heaving force, cyclic deformation, AE activates, crack coalescence pattern and fatigue life of the granite samples. The accumulative AE count/energy decreases with increasing number of freeze–thaw cycles, and the accumulated AE count/energy in a loading stage gradually grows faster. In addition, AE spectral frequency analysis reveals the impact of previous freeze–thaw damage on the formation of the crack scale, the sample is prone to producing large scale cracks under high freeze–thaw treatment. Moreover, 3D reconstructed CT images present an internal crack network pattern, and the most striking finding is that a simple crack network forms for a sample experiencing high F-T fatigue damage. It is suggested that deterioration of the rock bridge structure is strongly impacted by the accumulative freeze–thaw damage. The testing results are helpful to understand the influence of freeze–thaw and fatigue loading on the fracture evolution characteristics of rock in cold regions.

Design of open pit slopes for caving

Design of open pit slopes for caving

Rapid and robust slope failure appraisal using aerial photogrammetry and 3D slope stability models

Slope failures are an inevitable aspect of economic pit slope designs in the mining industry. Large open pit guidelines and industry standards accept up to 30% of benches in open pits to collapse provided that they are controlled and that no personnel are at risk. Rigorous ground control measures including real time monitoring systems at TARP (trigger-action-response-plan) protocols are widely utilized to prevent personnel from being exposed to slope failure risks. Technology and computing capability are rapidly evolving. Aerial photogrammetry techniques using UAV (unmanned aerial vehicle) enable geotechnical engineers and engineering geologists to work faster and more safely by removing themselves from potential line-of-fire near unstable slopes. Slope stability modelling software using limit equilibrium (LE) and finite element (FE) methods in three dimensions (3D) is also becoming more accessible, user-friendly and faster to operate. These key components enable geotechnical engineers to undertake site investigations, develop geotechnical models and assess slope stability faster and in more detail with less exposure to fall of ground hazards in the field. This paper describes the rapid and robust process utilized at BHP Limited for appraising a slope failure at an iron ore mine site in the Pilbara region of Western Australia using a combination of UAV photogrammetry and 3D slope stability models in less than a shift (i.e. less than 12 h).

Step-by-step investigation of engineering and geological conditions of mineral deposits for safe mining

Introduction. Engineering and geological processes as a result of process operation at deposits often develop at an exponential rate. This problem is specific due to complex and multifactorial nature of the processes which arise when rock mass interacts with mine workings. For this reason engineering and geological information should be obtained step by step beginning with the stage of prospecting and evaluation and proceeding at the stages of construction and operation of mine workings. Research aim is to consider methodological basis to form the databases of geological engineering information about mining facilities at various stages of their life cycle. Research methodology. The types of operations have been described on acquisition and interpretation of engineering-geological information required to detail models of the engineering-geological conditions at every stage. An important factor in creating a reliable and functioning geomechanical model of mineral deposits is survey operations follow-up and gradual transition from regional and provincial engineeringgeological conditions and tectonic structure to engineering-geological conditions of a specific deposits or occurrence. Research results. By the example of chrome field located in the Polar Urals within the Rai-Iz massif, all detail stages of mineral deposits engineering-geological conditions model have been established taking into account the conditioning selected components and factors; possible problems have been described and the results of step-by-step predictive estimates of mine workings stability have been presented. Summary. The research present an example of engineering-geological data detailing by the results of the gamma ray log and caliper logging at the stages of pit slope stability forecast model construction. Obtained in the course of long-term data collecting and processing, the model of Tsentralnoe field has proved its efficiency in the course of mining.

The effect of blasting on a high-pressure gas pipeline located within the borders of a mine take

Introduction. This article shows the results of investigating the allowable dynamic load on the II category high-pressure gas pipeline installation site located within the borders of a mine take, which is connected with blasting at SLK Cement open pit. Research aim. The research is aimed at increasing the level of secure operation of a gas pipeline and establishing restrictions in the seismic impact of mining (blasting) towards the gas pipeline installation site. Methodology. The methods of IM UB RAS has been applied concerning the determination of allowable distances from a blast in the open pit to the secure facility (gas pipeline) depending on the mass of the explosive at the timing stage, soil condition coefficient, and the allowable speed of seismic vibrations. Results. It has been determined that taking into account the depth of blast in the open pit and corresponding geological conditions, by means of changing mass at the timing stage, it is possible to totally eliminate the negative impact of a blast on a gas pipeline installation site. A design scheme has been proposed to determine secure distances to the high-pressure gas pipeline depending on the angle of open pit slope and the depth of blasting in the open pit. Summary. A dynamic design analysis has been carried out of blasting force action on soil and highpressure gas pipeline. It has been recommended to establish some restrictions in explosive mass at the level of minimum hazardous values. And for the future blasts it is also recommended to design a charge initiation scheme with explosive mass of less than one ton at the timing stage.

Angren coal pit Centralny landslide slope stability analysis based on a three-dimensional geological-geophysical model

Introduction. In the course of mining mineral deposits by opencast, natural stress state of adjacent rock mass changes giving rise to geomechanical processes which lead to pit slopes deformation. It can be prevented by mean of detecting landslide-hazardous zone by using three-dimensional geological-geophysical models based on the data bases from prospecting surveys and geophysical sounding of the adjacent rock. Research aim is to develop and evaluate basic provisions of the methods of forecasting slope stability based on three-dimensional geological-geophysical models which include the following information: the results of geophysical sounding (waterlogged zones boundaries); databases of exploration wells (physicalmechanical properties of soils in the zones of water saturation and natural moisture content, and the relief of the natural surfaces of weakness); design and actual position of mine workings. Methodology. In order to find the most hazardous section in the adjacent rock mass an algorithm of forecasting has been proposed and adjacent rock mass stability has been analyzed based on threedimensional geological-geophysical models. Results. A three-dimensional geological-geophysical model of Centralny landslide has been constructed as a result of analyzing geological survey databases, surveying instrumental observations over the deformations, and electrical sounding of the adjacent rock mass. Values of the friction angle and cohesion were found with using the inverse calculation method. Centralny landslide stability forecast has been analyzed as of the year of 2018 and after the final completion of the first stage of loading-out the front section in 2025. Summary. Developed an algorithm of slope stability analysis makes it possible to solve the task of finding the most hazardous section or landslide area by means of computer-based realization.