Pit Walls Research Articles

Influence of Foundation Pit Excavation and Precipitation on Settlement of Surrounding Buildings

With the large-scale development of urban underground space, foundation pit engineering has become one of the important geotechnical engineering topics in urban construction. In this paper, the effects of foundation pit excavation and precipitation on adjacent buildings are studied in detail. The main research work includes the following aspects: summarizing and analyzing the soil consolidation theory, foundation pit excavation, and precipitation process; the influencing factors of the adjacent soil layer displacement; the influence mechanism and influence types of foundation pit excavation and precipitation on adjacent buildings. The finite element model considering the whole process of foundation pit excavation is established, and the variation law of the upper layer displacement around the foundation pit is analyzed. The deformation law of the retaining structure, the calculation results of precipitation and nonprecipitation, and different excavation methods will be analyzed and compared. The calculation results show that the displacement of the soil layer around the foundation pit is also different between different excavation methods. As the distance between the foundation pits increases, the lateral displacement of the underground continuous wall near the frame structure gradually decreases. The distance from the foundation pit wall is 30 m. The maximum value of the lateral shift is reduced by 4.7% compared with 5 m. The foundation pit is studied, as well as the law of internal force variation of adjacent buildings caused by digging and precipitation, and checking the safety and adaptability of structural members. The calculation results show that a large additional internal force will be generated on the bottom floor of the adjacent building, and some structural members will be damaged by the bearing capacity.

Landslide stabilization experience in Urtui open pit mine

Instability of pit wall slopes is the most critical accident in open pit mining. The risk of damages to pit walls is proportional to the height of exposed surfaces and to the time of exposure. Among many factors governing pit wall stability, the major factor is geological structure and weakening zones in rock mass. Deformation processes are initiated in host rock mass of coal seams mostly because of undercutting of weak interlayers. Alongside with local undercutting, another cause of landslides is transition of coal mining from down-dip extraction to up-dip extraction. The sequence of mining and morphology of weak interlayers also have influence on initiation and evolution of deformations. The basic component of engineering solutions on pit wall stability control is optimization of mining sequence and methods of accessing working horizons in open pit mines. Large-scale deformation of Western and Southeastern pit walls in Urtui mine could be avoided using the optimized sequence of mining operations. For example, mining advance mostly along the curve of the Urtui centroclinal fold, with early access and destress of the eastern and, first of all, western wings of the fold could make it possible to evade from up-dip mining of coal seams and, as a consequence, to solve the major geomechanical problems in the open pit mine.

Moderate blasting technologies: Experience and prospects for introduction in Polyus mines

It is commonly known that rock fragmentation by blasting is the most economically efficient method to prepare large volumes of rock mass to excavation and handling. The drilling and blasting technology accepted by a mine governs both rock fragmentation quality and mining safety connected with slope stability. Therefore, optimization of drilling and blasting is an objective calling for the effective blast design and control. This article presents the main principles and methods of moderate blasting implemented at Polyus company towards minimization of impact on pit walls and benches. The main point is stagewise reduction of the dynamic effect exerted by blasting on rock mass when approaching the ultimate pit limits. Polyus company initiated the far and wide review and introduction of the best international practices for improvement of blasting operations near the ultimate pit limits. The article describes the activities undertaken within implementation of projects on drilling and blasting technology justification and improvement to enhance stability of pit walls and, as a consequence, to reduce geotechnical hazards. As a complimentary measure to abate seismic effect of explosions on adjacent rock mass, the nonelectric blasting is replaced by electronic blast initiation systems with more accurate delay intervals, which almost nullifies probability of simultaneous ignition of two or more charges and ensures, thereby, the acceptable and seismically safe modes of blasting of large rock blocks. Furthermore, the introduction of the electronic blasting cardinally changes the approach to blasting order and sequence per intervals in blast holes depending on the current task within a block to be blasted.

Justification of rockfall-and-rockslide protection screen design for open pit mines

The article discusses the general operation principle and design features of structural elements of a standard rockfill-and-rockslide protection screen. The main problems connected with operation of such structure and their causes are described. The recommendations on aspects to focus on during the analysis of a situation and selection of a proper solution are given. The list of initial data required for calculating the screen design variables and approximate cost at the project design stage is presented. By way of illustration, it is proposed to analyze the engineering protection systems manufactured by Geobrugg AG, Switzerland. The main advantages of these products include: – strength higher than the conventional analogs have; – design capable to uniformly distribute load; – approval by large-scale trials in association with independent institutions. Rockfall-and-rockslide protection screens are widely applied, including protection of benches and pit walls. The screens can be constructed and installed on the fly, need no constant attendance, are inexpensive and, above all, ensure safety and efficiency of mining. Adherence to the recommendations during planning of screen construction activities, namely, acquisition of specific information and engineering approach to the screen design and material can greatly enhance reliability of the structure and to extend its operating life.

Geotechnical prerequisites for safe and efficient accessing and mining of thick coal seam in highlands

Bel-Alma deposit is located in the Batken region in Kyrgyzstan. Orographycally, the deposit occurs on the south shoulder of the Kichik–Alai ridge, 1–1.5 km away from the cognominal river. The local relief is high-mountain, rocky and heavily broken. Geologically, the deposit is composed of the Upper Paleozoic rocks, which underlay the stratified Meso-Cenozoic deposits, and amorphous loose overburden. The productive strata is the bottom range of the Sogul series of the Jurassic system. The total thickness of the series in the cross-section is 102.7 m. The Sogul series rocks feature erosion and distinct structural unconformity in the Paleozoic residuum. The overlying strata are represented by red conglomerates and sandstone of the Upper Cretaceous age. The geotechnical estimation of the properties of rocks composing the study area in Bel-Alma deposit is performed. The rock mass structure is determined using geological exploration cores. The parameters of stable pit wall and benches are preliminarily optimized and will be included in the ultimate pit limit design.

Evaluation of Internal Fit and Marginal Adaptation of Provisional Crowns Fabricated with Three Different Techniques.

Different techniques have been used to construct provisional crowns to protect prepared teeth. The purpose of this in vitro study was to assess the internal fit and marginal discrepancy of provisional crowns made by different methods. A total of 48 provisional crowns were constructed and divided into three groups (n = 16) according to the fabrication methods: fabricated manually-group MAN; computer-aided design/computer aided manufacturing technology-group CAM; and 3-dimensional (3D)-printed technology-group 3DP. The same standard tessellation language (STL) file was used for both CAD/CAM and 3D-printed group. The silicone-checked method was used to measure the internal gap distance. The marginal discrepancy was measured by using the polyvinyl siloxane (PVS) replica method and swept-source optical coherence tomography (OCT) scanning technique. Data were analyzed with one-way analysis of variance (ANOVA) nonparametric Kruskal-Wallis and Tukey tests at α = 0.05. At the central pit and axial walls, the gap distance mean values of group CAM were higher than those from group MAN and 3DP. The group 3DP was statistically significantly higher in gap distance at the location of occlusion than group MAN and group CAM (p < 0.05). The total gap distances assessed by silicone-checked method revealed there were no statistically significant differences between the tested groups (p > 0.05). The total mean values of absolute and horizontal marginal discrepancy of the group 3DP obtained by using the PVS-replica method and OCT scanning technique were significantly higher than the group MAN and CAM (p < 0.05). Regression correlation results of marginal discrepancy indicated a positive correlation (r = 0.902) between PVS-replica method and OCT scanning technique. The manually fabricated provisional crowns presented better internal fit and a smaller marginal discrepancy. Between different assessment techniques for marginal adaptation, PVS-replica method and OCT scanning technique have a positive correlation.

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.

Slope Stability in a Mining Environment M&apos;haoudatt-Zouerate Site, Mauritania

The instability of the M'HAOUDATT pit is a major problem often encountered on the wall composed of a network of fractures located in unfavorable conditions for a very soft geological formation. Therefore, the trend in large open-pit mines is to use high-energy blasting to increase conveying performance and crusher throughput. The increase in blasting energy concentration can threaten the integrity of the pit wall. In this paper, we aim to find a suitable plan to stabilize the pit deposit, through analyses of structural and lithological data on the pit walls, with an interpretation of the lateral and depth extensions according to the geological complexity of the deposit. Followed by an analytical treatment of the current pit parameters. Data processing included core classification, kinematic assessment of failure mechanisms based on visual observations on the exposed faces of the expected pit. The results of the laboratory tests were also used to define the rock mass parameters used to establish a stable slope design. The analyses showed the need for an effective strategy to ensure that the slopes won’t be damaged by blasting. This wall control strategy aims to produce a fragmented bulk ore pile and a slope as designed and in good condition. A good understanding of the failure mechanisms is necessary to ensure better monitoring of the rock slopes of the M'HAOUDATT pit.

Analysis of 2D and 3D estimates of pit wall stability

Analysis of 2D and 3D estimates of pit wall stability

Effects of Sublevel Open Stope Underground Mining on Surface and Open Pit Slopes

Underground mining is an economically viable option for exploiting ore reserves deemed uneconomic after open pit mining. However, underground development can have adverse effects on the above existing open pit slope walls. As a goal of this paper, identification and assessment of potential slope instabilities prior to underground development is crucial for safe and sustainable mining. Towards goal achieving, this paper gives a comprehensive parametric study to investigate the influence of sublevel open stope (SLOS) underground mining on the surface and open pit slope walls. By means of numerical simulation, the SLOS design is tried against the existing open pit followed by adjustments of important slope parameters which are overall slope height (OSH) and overall slope angle (OSA). We found that underground mining may induce slope failure, particularly on the hangingwall side of the pit. Subsidence is prominent on the hanging wall and the surface, whereas, the uplift dominates the footwall and pit bottom. Pit wall closure is observed during underground mining. Although the assigned dimensions in the parametric study show a negligible effect of OSH and OSA, the high OSH experience low subsidence in comparison with low OSH. Overall, the results demonstrate that the slope walls on the hanging wall side are mostly affected by the underground mining and high-stress concentration prevails near slope toes and pit bottom. Additionally, slope deformation decrease from pit bottom towards the slope crest and surface. The results of this study add knowledge to open pit and underground mining interaction.

Seismic effects induced by large-scale blasts in isotropic and structurally complex pit wall rock masses

Seismic effects induced by large-scale blasts in isotropic and structurally complex pit wall rock masses

Method to make a shielding slot in pit wall rock mass using non-explosive destructive mixture

Method to make a shielding slot in pit wall rock mass using non-explosive destructive mixture

Development of a method for determining the stability reserve of iron ore pit board section

The purpose of this article is to develop a new methodology for assessing the stability margin of iron ore opencast sides sections. The sequence of work. To achieve this goal, at the first stage, high-resolution photography was carried out for characteristic sections of the pit wall, followed by computer processing of photographs to assess the fracturing of rocks. The next step was the calculation of the fractal dimension of the array section from the obtained images using the ImageJ and FracLac programs, including the MicroMod2015 plug-in package (add-ons). The next step was assess the disturbance of the massif due to fracturing, a study of the relationship between the fractal dimension and the coefficient of structural weakening was carried out (this coefficient is determined by the classical method through the ratio of the strength of rocks in the massif and in the sample). At the last stage of the work, after establishing the specified connection and calculating the coefficient of structural weakening of rocks that based on the results of determining the fractal dimension, an assessment of the stability margin iron ore opencast sides sections that carried out. The known dependence of the stability safety factor on the coefficient of structural weakening of the array was used. As a result of comparing the fractal dimension of the exposed massif areas based on photographs with the calculation by classical methods, the discrepancy in the structural attenuation coefficient was 5-10%. This indicates a satisfactory convergence and allows the use of this express technique for assessing the fracturing of a section of a pit flank on the basis of fractal dimension. The scientific novelty of the results obtained - for the first time, the analytical dependence of the structural weakening coefficient of rocks on the fractal dimension of the massif cracks was established, which made it possible to simplify the procedure for its calculation. The practical significanceof the work lies in the creation of a new methodology for assessing the stability margin of an iron ore opencast side sections that the basis of rock fractures fractal analysis.

Planetary fracturing and lineaments revealed in the Kovdor magnetite–apatite ore deposit by open pit mining

The analysis of the studies into fracturing of Zhelezny pitwall rock mass over the period from 1989 to 2019 proves that planetary fracturing is represented by faults, carbonatite dykes and single fractures oriented in the same direction as the prevailing regional lineaments on the Kola Peninsula. Planetary fracturing is assumed as a system of regular-oriented fractures. The planetary fracturing also includes lineaments of tectonic origin. The scientists think the faults registered in the pitwall rock mass and codirectional with the lineaments will accompany mining operations down to the full depth of the pit, up to the full extraction of magnetite–apatite ore reserves. While preparing this article, the authors have collected, generalized and analyzed the data of geological and structural mapping implemented by VIOGEM’s experts over the period from 1989 to 2019. VIOGEM’s procedure of geological and structural mapping ensures continuous documentation of extensional tectonics at high referencing accuracy (to 50 cm), as well as determination of inaccessible azimuths and angles of fractures by remote assessment of their orientations in pit walls using a laser scanner and photographic techniques to study the structure of hard rock mass and the behavior of permanent benches.

Deformation Behavior of Deep Foundation Pit under Both Overloading and Unloading Conditions

A deep foundation pit in a station of the Hangzhou subway is adjacent to new high-rise residential buildings on the north side and to the Evergrande foundation pit being excavated on the south side. This work considers the excavation of the foundation pit in the subway station as the research subject, focuses on the difference of the deformation and Earth pressure between the north side and the south side of the foundation pit under these special working conditions through the analysis of the measured data, and compares it with an ordinary foundation pit. Analyzing the measured data reveals that the horizontal displacement of the retaining wall and the ground settlement are far larger on the north side than on the south side, and both often exceed the deformation alarm value; the deformation of the ordinary foundation pit is between the deformation of the overloaded (north) side and that of the unloaded (south) side of the foundation pit. Moreover, the maximum rate of the horizontal creep of the soil and the maximum rate of the creep caused by the ground settlement on the north side of the foundation pit are larger than those on the south side of the foundation pit; the maximum rate of the horizontal creep of the ordinary foundation pit is between the two. The active Earth pressure on the pit wall on the north side is higher than that on the south side of the foundation pit, and because of the surrounding unloading, passive Earth pressure is generated at the bottom of the pit wall on the south side of the foundation pit, which causes it to shift to the outside of the foundation pit. The settlement of the surrounding high-rise buildings and the settlement of the columns are all within the range of the alarm values; also, the buildings settle evenly. Due to the excavation and unloading on the south side of the foundation pit, the uplift of the columns is not considerable.

Evaluation of the possibility of manifestation of deformations from the position of disturbance of the massif (using the Kamagan field as an example)

Introduction. The main task in the development of mineral deposits by open and underground methods is to ensure the safety of mining operations. As a result of long-time standing of the pit walls in the near edge zone massif, changes in natural stresses can occur, which lead to deformations. Prediction and prevention of deformation processes of the near-rock massif largely depend on reliable information about its structural features, including the structure of the massif and the degree of its disturbance. Purpose of research is to assess the possibility of manifestation of deformations from the position of disturbance of the massif. Methods of research. When assessing the possibility of deformation manifestation, a set of methods was used, including: full-scale measurements of fracturing; methods of mathematical statistics using the Stereonet program for processing measurement results; analysis of the spatial position of cracks relative to the direction of strike of the slopes and sides of the open pit with the identification of the most dangerous ones; kinematic analysis, allowing to determine potential types of loss of stability from the position of disturbance of the massif. Result of research. In the southeastern, northern and western sides of the Kamagan open pit, 41 fracture systems have been identified; the prevailing systems are northwestern dip systems at angles of 50 ° –85 °; south-east - at an angle of 50 ° and south-west - at an angle of 50 °. For example, for the northern side (Ap = 90 °; n = 60 °), it was found that potential types of destabilization are: wedge formed by systems of cracks with spatial characteristics Ap = 65 °; n = 45 ° and Apr = 150 °; n = 90 °, and planar sliding formed by systems of cracks with the parameters Ap = 90 °; n = 55 ° and Apr = 100 °; n = 42 °. Conclusions. Studies have proven the need to study and identify weakening surfaces in the process of mining and determine the parameters of their occurrence in order to assess the possibility of deformations and further assess the stability of slopes.

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.

Ensuring Wall Stability in the Course of Blasting at Open Pits of Kyzyl Kum Region

Involvement of deep deposits in mining predetermined the trend of development of open pit mining towards increasing the depth of open pits. The main limitation imposed on drilling and blasting in the near-contour zone of an open pit is the need to protect the pit walls and engineering structures on the walls from seismic effects of huge blasts. As practice shows, the most effective and proven method of protecting pit walls is the use of blasting by presplitting method, creation of a shielding gap and a shielding layer of blasted rock mass, i.e. pre-splitting of the pit walls, preceding the huge blast. Therefore, the study of stress-strain state of the near-contour rock mass, determination of the parameters of blastholes for edge pre-splitting (preliminary shielding gap formation) in open pits is an urgent task. The analysis of the pit wall design and stress-strain state of rock mass at Kokpatas deposit exploited by Navoi Mining and Metallurgical Combine allowed to determine the model, as well as the method for calculating stress-strain state of the rock mass. When assessing stability of the pit walls, an approach known as the displacement method was used. Applying the boundary integral equations method allowed to develop an algorithm for calculating stresses in the rock mass for the conditions of Kokpatas deposit. A technique has been developed for experimental studies of blasting contour blasthole charges (blasting by pre-splitting method) using models, allowing to study fracturing on volumetric models and wave interaction by the method of high-speed video recording of the blasting process in transparent models, as well as to determine the parameters of stress waves during blasting in samples of real rocks. A method for formation of stable pit wall slopes, an excavator method for bench pre-splitting on ultimate envelope (contour) of a pit, and a method for initiating blasthole charges in the near contour zone of a pit have been developed and implemented in the industry.

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).