Open-pit Limestone Mine Research Articles

Three-dimensional finite element simulation and reconstruction of jointed rock masses for bench blasting

During the numerical simulation of blasting in jointed rock masses, the accuracy of joint geometric parameters is one of the key factors affecting the numerical results. To facilitate the numerical simulation, most of the previous studies on blasting in jointed rock masses were conducted on regular jointed rocks, which is not conducive to fully revealing the dynamic responses and blast-induced damage characteristics of jointed rock mass. In this study, scanline sampling and borehole sampling were employed to obtain the surface and internal joint structures of the rock bench. To represent the joint geometry, a reconstruction technique for three-dimensional (3D) jointed rock masses in LS-DYNA was proposed utilizing MATLAB code. In the process, the elements on joint surfaces were identified and assigned mechanical parameters of joints to construct the 3D jointed rock model, where the geometrical properties of generated joints obey the statistical distribution obtained from the scanline survey. Taking an open-pit limestone mine as an example, a statistical analysis of the 3D distribution of joints was carried out and used to construct a 3D jointed rock numerical model for bench blasting. Comparisons between the bench slope extracted from the numerical model and the actual joint trace mapping from a rock exposure are performed, and the similarity between the two contour plots of joint orientations reaches 91.6 %. For comparison tests, the bench blasting was simulated by an intact rock model and the jointed rock model. The results indicate that the dynamic responses and blast-induced damage characteristics of jointed rocks are significantly affected by the geometry of joints. Compared with the intact rock model, the presence of joints causes stress concentration and local strengthening of rock damage between adjacent joints, which results in a 30.5 % increase in the damage volume. Furthermore, a field blasting test was conducted to analyze the accuracy of the jointed rock model. The results show that the fragment size distributions obtained from the jointed rock numerical model and the filed test are generally consistent, and the error between them in the proportion of rock fragments with a size of 0 ∼ 100 mm is only 12.8 %. These findings indicate that the proposed reconstruction method of the jointed rock model is considerably robust for characterizing the joint geometry of in situ rock masses and simulating the bench blasting in jointed rock masses.

ANALYSIS OF LIMESTONE QUARRY SLOPE STABILITY, NIMBOKRANG DISTRICT, JAYAPURA REGENCY, PAPUA, INDONESIA

Slope stability analysis generally uses the concept of factor of safety (FoS) value using several whole rock parameters. The slope stability analysis method that will be used in this research is the slope stability analysis method in open pit mines based on rock mass classification with the Rock Mass Rating (RMR) system and the Geological Strength Index (GSI) system and analyses the potential for landslides that can occur on slopes at that location with kinematics and limit equilibrium methods so that the type of landslide can be determined based on the intensity of the geological structure on the slope of the CV. Inti Jaya open pit limestone mine, in Wahab Village, Nimbokrang District, Jayapura Regency. This research aims to provide information on the current condition of the slope whether it is by safety standards, make slope engineering improvements and redesign safe slopes if unstable slope conditions are found. Research on the stability of limestone slopes begins with the collection of field data and rock samples. Furthermore, sample testing was carried out to obtain physical and mechanical properties and weighting of rock masses, which were then analysed to obtain the characteristics and quality of rock masses that would be applied using the finite element method with Slide 6 from Rocscience to determine the Factor of Safety (FK) and the design of safe slope geometry. The RMR value for slope 1 is 62, slope 2 is 61, and slope 3 is 62. So it can be concluded that the rock is included in rock mass class 2 with good quality. Based on the analysis of potential avalanche types, the three slopes have non-arc avalanche types. From the analysis carried out using Rocscience Slide 6.0 software, the FoS value for slopes in original, dry, and saturated conditions is obtained, where on slope 1: FoS in original conditions is 0.935, FoS in dry conditions is 1.619, and FoS in saturated conditions is 0.671. Then slope 2: FoS in original condition is 0.896, FoS in dry condition is 1.457, and FoS in saturated condition is 0.806. Slope 3: FoS in original condition is 3.490, FoS in dry condition is 4.199, and FoS in saturated condition is 3.368. So it can be concluded that slopes 1 and 2 are unsafe or unstable in original and saturated conditions so that landslides can occur. In the analysis of the FoS value of the actual condition of the slopes in the field using the Hoek & Brown method, the FoS value of slope 1 is 0.387, the FoS value of slope 2 is 0.579, and the FoS value of slope 3 is 1.272, it can be seen that the actual condition of the slopes in the field is slopes 1 and 2 in an unsafe or unstable state. Improvements must be made to the slope geometry to maintain the stability of the slope to remain safe or stable. The recommended improvement is to create a new working level for slopes 1 and 2, with steep height and large rock porphyry.

Activity of Okgye Limestone Mine in South Korea Observed by InSAR Coherence and PSInSAR Techniques

The Okgye limestone mine, which is the largest open-pit limestone mine located in a mountainous area in Korea, suffered a collapse in 2012 that claimed four casualties. Restoration work on the rocky mined-out slopes, as well as mining and dumping activities, are still in progress. Monitoring slope stability is important to prevent the sudden collapse of slopes, which can be efficiently performed by satellite-based interferometric synthetic aperture radar (InSAR) techniques. Firstly, we obtained elevation changes using InSAR-generated Copernicus 30 m DEM in 2014 and an SRTM 1Sec DEM in 2000, through which the area was roughly classified into the mining area, tailings storage area, and the mined-out area. A time series of 12-day coherence images produced by Sentinel-1B SAR were averaged annually to produce an RGB-composite image to observe the change in mining activities during 2018, 2019, and 2020. We found many persistent scatterers (PS) when observing the ground displacement, both in the ascending and descending orbits, from which we decomposed this into the vertical and east components. The largest displacement of 63.6 mm/year was observed during 2019 and 2020 in the tailings storage area in the direction of the dumping slope. For the rocky outcrops and the transmission tower, we found a seasonal oscillation, which can be interpreted as the thermal expansion of limestone and iron. This paper demonstrated that the surface stability and deformation of open-pit mines could be effectively monitored by combining InSAR DEM, coherence, and PSInSAR techniques.

Dynamic numerical simulation and risk predictive assessment of the slope debris flow for the rear mountain at the management office of the Erlang Mountain Tunnel

The Erlang Mountain Tunnel Management Office is located in Luding County, Sichuan Province, China. A long-term open-pit limestone mine is located on the rear mountain, 1 km from the west entrance of the Erlang Mountain Tunnel Management Office for the Sichuan-Tibet Highway. Dangerous rock masses and a large accumulation of mine waste slag are present o-n the hillside, which can easily produce slope debris flow disasters. This paper analyzes the formation causes of slope debris flow through field investigation and uses RAMMS (Rapid mass movement simulation) software to study the influence of base friction coefficient μ and ξ on slope debris flow. Numerical simulation predicted level of danger of the movement process from the aspects of Velocity, deposition height, flow, topography. When the dry Coulomb friction value μ increased from 0.3 to 0.4, the debris velocity decreased and began to spread out along the slope. The flow process can be divided into four parts, and found that the velocity and discharge are different in the upstream and downstream of the slope constriction. The slope constriction has a significant amplification effect on the velocity and discharge. The velocity is amplified by 31.1%, and the discharge is amplified by 14.5%. In addition, based on the dynamic characteristics and the frequency of rainstorms, the risk of debris flow is divided into four levels: low, medium, high, and extremely high. The hazard map of slope debris flow in the rainstorm return period (20 years) is established, which provides a basis for the assessment and prediction of debris flow.

Non-deterministic load and dump behaviour in mining haul trucks: a case of study

ABSTRACT Complex load and haul cycles in mining are composed of individual steps, whose times could be better described by a statistical distribution than by the average value. In order to evaluate how loading times and dumping times behave, this paper tested a large dataset of loading and dumping times measured at an open pit limestone mine in Brazil against the distributions most commonly used to model these variables, Log-normal and Normal; as well as Gamma, Logistic, Weibull and Exponential distributions. None of the tested distributions provided statistically significant adherence to the data, but it was possible to identify that for most equipment, Logistic and Normal distributions would produce less error on stochastic modelling then the other tested distributions.

Simulation and Real-time Visualization of Truck-Loader Haulage Systems in an Open Pit Mine using AnyLogic

In this study, we proposed a method to simulate a truck-loader haulage system in open-pit mines and visualize the results in real time using the software AnyLogic. An open-pit limestone mine in Korea was selected as the study area. The time parameters for each unit operation of the haulage system were measured via a field survey. A discrete event simulation model for the mine was then developed using AnyLogic. We intuitively confirmed the simulation results with key production indicators and visualized the truck-loader haulage operation over time. This study was thus able to overcome the limitations of previous studies, which could not measure key production indicator values and the status of haulage systems in real time during simulations.

Three dimensional slope stability analysis of open pit limestone mine in Rembang District, Central Java

PT X is a limestone mine located in the district of Rembang, Central Java, which plans to expand and dig deeper. To ensure that the slope is stable, geotechnical study is needed. However, if it is done in 2 dimensional (2D) the result might not always be representative. This research was conducted to determine the stability of single slope using three dimensional limit equilibrium method (3D LEM). The data was collected by doing geotechnical mapping of the drill core sample and conducting laboratory test of rock samples, i.e. the test of physical and mechanical properties of rocks. The result shows that there is a significant difference between 2D and 3D FoS. The volume of sliding is also presented.

UNMANNED AERIAL VEHICLES FOR GEOLOGICAL APPLICATIONS

Remote Sensing and photogrammetric techniques have always been used in geological applications. Current advancements in the technology behind Unmanned Aerial Vehicles (UAVs), in accordance with the consecutive increase in affordability of such devices and the availability of photogrammetric software, makes their use for large or small scale land mapping more and more popular. With the UAVs being used for mapping, the problems of increased costs, time consumption and the possible accessibility problems -due to steep terrain-, are all solved at once. In this study, a custom-made UAV with 2 cameras onboard, is used to monitor two complex –regarding their topography- regions in Western Greece. One open pit limestone mine and a landslide occurring on sandy-clayous sediments. Both regions were mapped using surveying instruments like tachymeters and geodetic GPS, as well as using the aforementioned UAV system. 3D models of both regions were created using off-the-shelf photogrammetric software. For the creation of the 3D models, multiple targets were placed on the ground, to indicate GCPs with precisely known coordinates that could be identified in the high-resolution air photos, in order to maintain low Root Mean Square Error, while creating the DSMs and Orthophotos. In addition, the fish-eye effect caused by the cameras’ wide-angle lens was taken into consideration, regarding whether or not it affects the models’ overall geometric accuracy. Finally, the 3D models were compared to the survey measurements and the results are presented in this paper.

Analysis of the Potential for Use of Floating Photovoltaic Systems on Mine Pit Lakes: Case Study at the Ssangyong Open-Pit Limestone Mine in Korea

Recently, the mining industry has introduced renewable energy technologies to resolve power supply problems at mines operating in polar regions or other remote areas, and to foster substitute industries, able to benefit from abandoned sites of exhausted mines. However, little attention has been paid to the potential placement of floating photovoltaic (PV) systems operated on mine pit lakes because it was assumed that the topographic characteristics of open-pit mines are unsuitable for installing any type of PV systems. This study analyzed the potential of floating PV systems on a mine pit lake in Korea to break this misconception. Using a fish-eye lens camera and digital elevation models, a shading analysis was performed to identify the area suitable for installing a floating PV system. The layout of the floating PV system was designed in consideration of the optimal tilt angle and array spacing of the PV panels. The System Advisor Model (SAM) by National Renewable Energy Laboratory, USA, was used to conduct energy simulations based on weather data and the system design. The results indicated that the proposed PV system could generate 971.57 MWh/year. The economic analysis (accounting for discount rate and a 20-year operational lifetime) showed that the net present value would be $897,000 USD, and a payback period of about 12.3 years. Therefore, we could know that the economic effect of the floating PV system on the mine pit lake is relatively higher than that of PV systems in the other abandoned mines in Korea. The annual reduction of greenhouse gas emissions was analyzed and found to be 471.21 tCO2/year, which is twice the reduction effect achieved by forest restoration of an abandoned mine site. The economic feasibility of a floating PV system on a pit lake of an abandoned mine was thus established, and may be considered an efficient reuse option for abandoned mines.

고정익 무인항공기(드론)를 이용한 노천광산 지형측량 기술의 현장실증

본 연구에서는 고정익 무인항공기(드론, SenseFly eBee)를 이용하여 국내 대규모 석회석 노천광산에 대한 지형측량을 수행하였다. 비행고도 300 m, 비행속도 12 m/s 조건으로 약 30분간 자동모드 비행을 수행한 결과 현장에서 총 288장의 항공사진을 촬영할 수 있었다. 특이점 추출이 불가능한 37장의 항공사진을 제외한 251장의 항공사진 자료들을 보정하고, 정합한 결과 7 cm 해상도의 정사영상과 수치표면모델 자료를 생성할 수 있었다. 4곳의 지상기준점에 대하여 고정밀 위성측정시스템를 이용하여 측정한 위치 좌표와 고정익 무인항공기 사진측량시스템을 이용하여 추출한 위치 좌표를 비교한 결과 평균 제곱근 오차가 15 cm 내외로 분석되었다. 고정익 무인항공기는 회전익 무인항공기에 비해 상대적으로 비행시간이 길어 넓은 영역의 신속한 지형측량이 가능하므로 대규모 노천광산 현장에서 효과적으로 활용될 수 있을 것이다. This study performed an on-site demonstration of the topographic surveying technique at a large-scale open-pit limestone mine in Korea using a fixed-wing unmanned aerial vehicle (UAV, Drone, SenseFly eBee). 288 sheets of aerial photos were taken by an automatic flight for 30 minutes under conditions of 300 m altitude and 12 m/s speed. Except for 37 aerial photos in which no keypoint was detected, 251 aerial photos were utilized for data processing including correction and matching, then an orthomosaic image and digital surface model with 7 cm grid spacing could be generated. A comparison of the X, Y, Z-coordinates of 4 ground control points measured by differential global positioning system and those determined by fixed-wing UAV photogrammetry revealed that the root mean squared errors were around 15 cm. Because the fixed-wing UAV has relatively longer flight time and larger coverage area than rotary-wing UAVs, it can be effectively utilized in large-scale open-pit mines as a topographic surveying tool.

보급형 회전익 무인항공기(드론)를 이용한 소규모 노천광산의 지형측량

This study carried out a topographic survey at a small-scale open-pit limestone mine in Korea (the Daesung MDI Seoggyo office) using a popular rotary-wing unmanned aerial vehicle (UAV, Drone, DJI Phantom2 Vision+). 89 sheets of aerial photos could be obtained as a result of performing an automatic flight for 30 minutes under conditions of 100m altitude and 3m/s speed. A total of 34 million cloud points with X, Y, Z-coordinates was extracted from the aerial photos after data processing for correction and matching, then an orthomosaic image and digital surface model with 5m grid spacing could be generated. A comparison of the X, Y, Z-coordinates of 5 ground control points measured by differential global positioning system and those determined by UAV photogrammetry revealed that the root mean squared errors of X, Y, Z-coordinates were around 10cm. Therefore, it is expected that the popular rotary-wing UAV photogrammetry can be effectively utilized in small-scale open-pit mines as a technology that is able to replace or supplement existing topographic surveying equipments.

A new seismic well logging technique and its application

A new seismic well logging technique has been developed for identifying the damaged zone around the rock masses that was affected by the stability of rock structures due to excavation of underground. In this study, we firstly purpose to introduce a new seismic well logging technique, then to show the results of the examples applied on rock structures of open-pit limestone mine and an underground power station. Finally, we intend to verify its efficiency. A new seismic well logging technique consisted of trigger sensor, super-elastic probe and signal conditioner was found applicable to evaluate the state of rock mass. From the measured result of rock slope in an open-pit limestone mine due to blasting, we defined that it was able to quantitatively evaluate the extent of damages of rock structures as well as to determine the location of damaged zone. In addition, this technique can measure P- and S-velocities simultaneously. P-velocity measurement from an access tunnel closed underground power station was also successfully carried out for observing the state of rock mass. It is expected that the newly developed seismic well logging technique would be a useful method for evaluating the integrity of rock mass and for ensuring an efficient tunnel support members.

露天資源開発の現状と新たな展開を支える技術 高感度傾斜計による岩盤斜面モニタリングと挙動分析

A high-resolution borehole tilt-meter is introduced to measure the inclination of rock slope at an open pit limestone mine, and the movement of rock slope is analyzed based on the measured results from the tilt-meter and numerical results by a three-dimensional boundary element method (3D-BEM). Firstly, the applicability of tile-meter to monitor the movement of rock slope due to a bench-cut excavation is investigated by 3D-BEM and the required accuracy of a tilt-meter is made clear. Then a high-resolution borehole tilt-meter is introduced and explained. Secondly, based on the measured results for nine months in a limestone mine, the mechanical behavior of rock slope is analyzed. The general mechanical behavior of rock slope due to excavation of a bench is then analyzed by 3D-BEM. Finally, using the results of measurement and numerical analysis, the mechanical behavior of rock slope is made clear. It is concluded that a high-resolution borehole tilt-meter is applicable to monitor the movement of rock slope in a short period.

In-situ rock stress measurement at an open-pit limestone mine using the CCBO technique

In-situ rock stress measurement is performed to estimate the state of stress at the Torigata open-pit limestone mine in Japan using the compact conica-ended borehole overcoring (CCBO) technique. The significance of the state of in-situ rock stress to evaluate the stability analysis of rock slope is then discussed. The CCBO technique was applied to the two horizontal boreholes, Borehole BH-1 at location I and Borehole BH-2 at location II. As a result of in-situ rock stress measured from the two horizontal boreholes using the CCBO technique, the maximum horizontal principal stress is in the NNE-SSW direction at present. The measured average vertical normal stress (−6.50 MPa) for Boreholes BH-1 and BH-2 is in good agreement with the estimated average overburden stress (−6.60 MPa). The horizontal normal stresses σxx (−5.10 MPa) and σyy (−6.00 MPa) are 78.5–92.3% of the vertical normal stress σzz (−6.50 MPa) suggesting that large horizontal stresses exist in Mount Torigata. The ratio of the horizontal normal stress to the vertical normal stress is relatively large at the measured location. Accordingly, for an appropriate evaluation of the mining-induced rock slope stability, not only the vertical stress components but also the horizontal stress components component should be considered.

Estimation of horizontal regional stresses at an open-pit limestone mine by back analysis

A set of back and forward analyses is carried out to evaluate the states of regional and local in-situ rock stresses and the mining-induced rock slope stability using a three-dimensional finite element model and the state of local in-situ rock stress measured by the compact conical-ended borehole overcoring (CCBO) technique. The directions of the horizontal principal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal principal local in-situ rock stress measured by the CCBO technique. The magnitudes of the horizontal regional tectonic stress are more compressive than those of the horizontal local in-situ rock stress. This presumably results from the fact that the horizontal regional stress due to the gravity is not considered in the back-analyzed horizontal regional tectonic stress while it is included in the local in-situ rock stress measured by the CCBO technique. The local stress obtained by the forward analysis is also in good agreement with the horizontal local in-situ rock stress measured by the CCBO technique, and the magnitudes of the vertical normal stress increase more rapidly than those of the horizontal normal stresses with depth. The ratio of the horizontal normal stress to the vertical normal stress is largest at the current excavation level and decreases with depth. This suggests that the stress field within the mining-induced rock slope is affected by the horizontal components of the local in-situ rock stress.

Rock stress measurements and the state of stress at an open-pit limestone mine in Japan

A series of rock stress measurements is performed to estimate the states of local paleostress and present (in situ) stress at the Torigata open-pit limestone mine in Japan using the calcite strain gauge (CSG) technique and the compact conical-ended borehole overcoring (CCBO) technique, respectively. A set of back and forward numerical analyses is then carried out to evaluate the states of regional and local present stresses and the mine-induced rock slope stability using a three-dimensional finite element model and the state of local present stress measured by the CCBO technique. The results of rock stress measurements from this and other studies suggest that the maximum principal stress direction in the study area has rotated counterclockwise from the southeast (NW–SE trend) to the northeast (NE–SW trend) since the late Cretaceous period up to the present time. The results of the back analysis show that the directions of the horizontal principal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal principal local in situ stresses measured by the CCBO technique. However, the horizontal regional tectonic stresses are more compressive than the horizontal local in situ stresses. It results from the fact that the horizontal regional stress due to gravity is not considered in the back-analyzed horizontal regional tectonic stress, but it is included in the local in situ stress measured by the CCBO technique. The results of the forward analysis show that the local stress obtained by the forward analysis, especially its horizontal components, is in good agreement with the horizontal local in situ stress measured by the CCBO technique, and that the magnitude of the vertical normal stress increases more rapidly than those of the horizontal normal stresses with depth. As a result, the ratio of the horizontal normal stress to the vertical normal stress is largest at the current excavation level (ground surface) and decreases with depth. It means that the stress field within the mine-induced rock slope is strongly affected by the horizontal components of the local in situ stress.