Search

Abstract This study aimed to investigate the formation mechanism of the mud-inclusion-type underground debris flows of natural caving underground mines. The characteristics of fine moraine particles flowing through the coarse-grained ore bed were used to analyze the formation process of mud inclusions in the caving ore bed through a physical model test. Based on the movement behavior of the mud inclusions of moraine in the caving ore bed, a formation-mechanism generalized model of underground debris flows with mud inclusions was established. The model was used to examine the formation mechanism of mud-inclusion-type underground debris flows in natural caving. The results showed that the fine moraine particles had good cross-flow characteristics in the process of drawing coarse-grained ore. The accumulation of fine moraine in the ore bed was a prerequisite for the formation of mud inclusions, and the fluid inclusions were formed by a mixture of the particles with the infiltrated water. When mud inclusions in moraine are affected by many factors, such as ore-drawing vibrations, blasting vibrations, and groundwater, the inclusions undergo multiple migration–stop–migration cycles, resulting in separation or fusion. However, the inclusions are released along the optimal random pore path to the outlet, forming a certain scale of underground debris flows accidents. The accuracy and reliability of the formation mechanism were verified through geophysical explorations based on the equivalent inverse flux transient electromagnetic method. This study not only broadens the research on debris flow, but also provides theoretical guidance for the prevention and control of underground debris flows.

Goaf has become one of the most significant sources of hazard affecting the safety of metal and nonmetal mines. Evaluation of goaf stability is of paramount importance for mine safety production. First, 13 indices such as rock mass structure, geological structure, and goaf volume are selected based on engineering experience and literature review to assess the stability of goaf. These indices are classified according to the characteristics of each factor, and a stability evaluation system for underground mine goaf is constructed. Second, the analytic hierarchy process method based on group decision theory is utilized to calculate the subjective weight of each index. Additionally, the CRITIC method is used to calculate the objective weight of each index. Finally, game theory is used to combine the subjective and objective weights, thereby improving the accuracy of the index weight. The stability grade of the goaf is calculated using the normal cloud model. The FLAC3D numerical simulation is used to analyze the stability of the goaf and verify the accuracy of the model. The abovementioned model is utilized for assessing the stability of the goaf in the Duimenshan mine section. The results indicate that 90% of the goaf area is in a stable or relatively stable condition, while the remaining 10% is unstable. The evaluation outcomes were compared with FLAC3D numerical simulations, highlighting a scientific and reliable method with an accuracy rate of 90%.

In slopes where a mixture of coarse and fine particles is present, the infiltration of rainfall can cause the migration of fine particles. This migration alters the hydraulic properties of the soil and has implications for slope stability. In this study, the slope under investigation is a tailings dam composed of loosely consolidated soil with a wide particle size distribution. Due to rainfall infiltration, fine particles tend to migrate within the voids of the coarse particle framework, leading to changes in hydraulic properties and inducing slope instability. The classical internal erosion constitutive model, known as the Cividini and Gioda erosion criterion, is commonly used to predict the behavior and effects of fine particle erosion in geotechnical engineering. However, certain parameters in this erosion criterion equation, such as long-term density, are challenging to obtain through experiments. To investigate the coupled evolution of seepage and erosion within landfill slopes under the influence of rainfall infiltration and to understand the mechanisms of slope instability, this research assumes the erosion of fine particle suspension and adopts the Worman and Olafsdottir erosion criterion to establish a coupled model of unsaturated seepage and internal erosion. The developed model simulates the coupled response of seepage and erosion in unsaturated landfill slopes under three different rainfall intensities. It is then combined with the infinite slope model to quantitatively analyze the impact of fine particle migration on soil permeability and slope stability. The numerical simulations provide the following findings: The Worman and Olafsdottir erosion criterion, unlike the Cividini and Gioda erosion criterion, only requires the determination of the soil’s gradation curve to estimate the erosion rate. Internal erosion primarily occurs within the leading edge of moisture penetration, accelerating the advancement of the wetting front and reducing slope stability. When the rainfall intensity is lower than the saturated permeability coefficient, the influence of internal erosion can be disregarded. However, under rainfall intensities equal to or greater than the saturated permeability coefficient, considering internal erosion results in a difference in the depth of the wetting front of up to 34.2 cm after 6 h in the R2 scenario. The safety factor without considering internal erosion is 1.12, whereas considering internal erosion yields safety factors between 1.08 and 1.09. In the R3 scenario, the difference in the depth of the wetting front reaches 53.8 cm after 6 h, with a safety factor of 1.12 without considering internal erosion and safety factors between 1.06 and 1.07 when considering internal erosion.

Subsidence of the earth’s surface induced by mining activities has always been a critical concern in the relevant research fields. This subsidence disrupts the original geological structures and can lead to secondary geological hazards, environmental degradation, and threats to human lives and property. An in-depth investigation of this issue led to us using the three-dimensional finite-difference numerical simulation software FLAC3D 6.0 in this study. The research focuses on the Prang Copper Mine subsidence area in Yunnan Province, China, with a particular emphasis on the comprehensive analysis of the formation mechanisms of a large-scale crack appearing on the south side of the subsidence area. The study also includes a predictive analysis of the future development trends of this crack. The simulation results indicate that the crack formation was a consequence of the combined effects of uneven surface subsidence induced by underground structural interfaces and underground mining activities. As mining activities continued, the non-uniform subsidence of the surface intensified. The northward (Y-axis) displacement difference of characteristic points A and B on both sides of the crack continuously increased, signifying the widening of the crack. Mining activities also influence the displacement in the X-axis direction, potentially posing risks to support structures on either side of existing drainage channels. Therefore, effective control measures are warranted. Furthermore, this study highlights the possibility that new mining activities may further exacerbate subsidence on the south side of the subsidence area. This research provides valuable insights into the complexity of surface subsidence and its associated risks, offering guidance for mining activity planning and safety measures.

Underground mining in Karst Plateau landform area may cause the loss of support for the upper rock stratum, resulting in rock collapse and large-scale subsidence of the ground surface. Also, the formation of a large-scale goafs may further lead to geo-hazards such as collapse, water gushing, slope instability and so on in the area. To reduce the impact of goaf settlement on local strata stability, this paper established a standardized safe mining detection model for goafs based on the geological safety characteristics of mining goafs. With reference to the statistical analysis of the geological conditions in the mining area, a numerical model with 358 goafs and the proposed mining area was established using FLAC3D numerical software. The surface subsidence and variations of plastic zone in the mining area were comprehensively analyzed. The results indicated that there was a correlation between the stability of the mining area and the geological occurrence conditions of the goafs. By quantitatively taking the values from standardized safety mining detection models, the standardized safety mining detection and warning technique was finally established. The findings can provide technical guidance for safety detection and early warning in the whole process of underground goaf mining in Karst Plateau karst development zone.

The nature of fine particulate matter is caused by the deterioration of the lean ore loss index and the important influence factors of a mine disaster accident. In this paper, fine moraine particles and coarse-grained ore from the Pulang Copper Mine are studied. The flow of fine particles in mixed particles under the condition of uniform ore drawing was studied by using the laboratory 3D physical model test method. This experiment explored the flow of hybrid particles in the system and characteristics of the particle size of fine particles passing through, and suggested a transit index to quantify the draining effect of fine particles. The experimental results show the following: ①Hybrid particles in the flow system of fine particulate matter under their own gravity use mixed ore particles flow in the process of formation of the pore to implement down through sports. ②The fine particles with the particle sizes of 2.5–1.25 mm, 1.25–0.63 mm, 0.63–0.315 mm, and 0.315–0.16 mm all have the flow-through characteristics, and the smaller the particle size, the more significant the flow-through degree. ③The cumulative ore drawing height of fine particles with different particle sizes increases, while the permeability index of the appropriate discharge decreases. ④The relative motion of coarse and fine particles is the internal control factor that leads to the flow of fine particles. The more significant the relative motion of coarse and finely mixed particles is, the more pores are randomly generated in the particle flow system and the larger the pores are, resulting in the more obvious fine particle flow effect. This study provides some theoretical reference value for revealing the flow-through characteristics of the fine particulate matter in the mixed particle flow system. At the same time, it has practical engineering significance for ore lean loss index control and mine disaster accident prevention and control in caving mining.

The shear factor of ore drawing is an important factor affecting the formation of underground debris flows. The aim of this study was to investigate the effect of the mining shear factor on underground debris flows in natural caving. The research background was the underground debris flow in the Plan copper mine, and we analyzed the characteristics of the slurry material structure of the underground debris flow, as well as the influence of the ore-drawing shear factor on the formation mechanism of the underground debris flow. The results showed that the slurry of the underground debris flow in the Plan mine is both a pseudoplastic and thixotropic fluid. Shearing force induced in drawing deforms the slurry and decreases its viscosity with the increase in shear rate and time. The shear force produced by the flow of ore particles first produces shear action on the paste in the shear boundary region of the ore drawing, reducing the paste viscosity while increasing its fluidity. Consequently, the “activation” makes the paste flowable, which flows along with the bulk ore flowing through the drawing mouth. The continuous ore-drawing process continuously shears the new moraine slurry in the ore-drawing channel and continuously “activates” the moraine slurry in the ore-drawing channel. Finally, destructive underground debris flow accident of a certain scale occurs. To our knowledge, this study thoroughly investigated the effect of the ore-drawing shear factor on the formation mechanism of underground debris flows, which not only broadens the research field of debris flow but also covers the deficiency of systematic research on underground debris flows, providing theoretical guidance for the prevention and control of underground debris flows.

Considering the pressure-bearing mechanism of the safety helmet and as an anchored net is subjected to the surrounding rock mass, researchers should regard the support force as a safety criterion. Thus, a method for calculating the anchored mesh support parameters (mesh width and reinforcement diameter) is proposed in this paper. The method can provide a theoretical basis for selecting the technical parameters of an anchored mesh in active support in underground engineering. Calculation results show that a strong power relationship exists between the mesh width a of the anchor net and the distance h3 from the anchor net to the top of the worker’s safety helmet, that is, a=12.891e−0.065h3, and the correlation coefficient is R2=0.947. Moreover, the mesh width of the anchored mesh decreases with an increase in the distance from the anchored mesh to the top of the worker’s safety helmet. The anchored mesh parameters designed and selected by this method ensure that the rocks falling from the anchored mesh pose no safety threat to the workers wearing helmets. The parameters also prevent an excessively large steel wire/steel bar diameter of the anchored mesh, which lowers support costs and makes the selected technical parameters of the anchored mesh economical and safe.

To effectively manage the heterogeneous and discrete knowledge of the bridge maintenance domain, this study adopts knowledge graph technology to build a knowledge base of bridge maintenance, called the bridge maintenance knowledge graph (BMKG). The BMKG uses an ontology as the knowledge organization and representation framework and a graph database as the knowledge storage tool. To facilitate the construction of the BMKG, a hybrid method combining a top-down approach and a bottom-up approach is proposed. Firstly, a bridge maintenance domain ontology (BMDO) is coded with Protégé and represented in Web Ontology Language. Secondly, rule reasoning and ontology reasoning are implemented on the BMDO in Protégé in order to automatically complete missing relations or attribute values. Thirdly, ontology reasoning is adopted to perform consistency check on the BMDO. Lastly, the BMDO model is stored in the Neo4j graph database through data format conversion, thus completing the construction of the BMKG. The BMKG is applied in a typical scenario of bridge maintenance to demonstrate its application value. Results show that the proposed hybrid method can create a knowledge graph that can realize the transformation from discrete data into interconnected knowledge. Knowledge graph offers a novel idea to create a knowledge base in the bridge maintenance domain.

The occurrence of downhole debris flows in caving mines has burst, concealment, and destruction characteristics. This study aimed to investigate accurate prevention and control measures for downhole debris flows. The research background was a downhole debris flow in the Plan copper mine. The disaster chain theory was applied to study prevention and control methods for downhole debris flows. Using a model of source generation, chain breaking, and disaster reduction, we proposed accurate prevention and control measures for downhole debris flow disasters, which prevent and control the downhole debris flows at the source. The results showed that the disaster chain type of downhole debris flow disasters is the compound periodic cycle chain, which has the characteristics of the branch basin chain and the periodic cycle chain. Based on the chain-effect nature of disasters caused by downhole debris flows, active and passive prevention and control methods for downhole debris flow disasters were proposed. The active prevention and control measures for chain breaking and disaster reduction involve isolating the generation conditions from the source, inducing a downhole debris flow disaster. This prevention and control method is difficult to implement during the actual production process. The idea of disaster reduction through passive defensive chain breaking is based on the fact that if the three essential types of conditions for the downhole debris flow formation are not present at the same time, then a disaster accident of a downhole debris flow can be effectively prevented and controlled. Accordingly, the following measures are proposed for preventing and controlling downhole debris flows: (1) reinforcement measures applied to the slope body of the landslide material source in the collapse pit; (2) adopting comprehensive flood control measures such as locking, intercepting, dispersing, draining, and blocking under hydraulic conditions; (3) blocking the formation of the channel by adjusting the ore drawing conditions; (4) addressing the inducing factors by blasting with a small amount of explosive. According to the disaster chain theory, prevention, and control methods for downhole debris flow in caving mines were investigated in this study, which not only broadens the research of the debris flows but also fills the gap in the systematic research on downhole debris flows.

In order to study the influence of elevation on the slake durability index of the quartz mica schist, the quartz mica schist with different elevations on the east slope of the Manjiazhai open-pit mine is taken as the research object, and based on laboratory tests and statistical analysis, the variation of negative correlation between the slake durability index and elevation is obtained. The disintegration mechanism of quartz mica schist at different elevations is also discussed. The test results show that the disintegration characteristics of quartz mica schist at different elevations are related to its mineral composition, fissure channel size, and rock damage effect. As the slope height increases, the ratio of mica to quartz in the rock increases, and the greater the porosity of the rock, the more fissures in the rock, the greater the permeability coefficient, and the more obvious the change of effective stress of rock under osmotic pressure. At the same time, the higher the slope elevation of open-pit mine, the longer the weathering time of rock, the higher the cumulative damage of rock, and the lower the rock slake durability index. This study provides a new idea for guiding the research on the disintegration characteristics of similar soft rock slopes in the elevation direction.

In order to verify the universal applicability of the fluid structure coupling model to the analysis requirements of deep tunnels under the MIDAS-GTS geotechnical simulation environment, the study, together with several mining enterprises, carried out verification and analysis on the measured data of 107 deep tunnels in recent years. The reference group selects the mean value of the analysis results generated by the analysis model using the preferred nonfluid structure coupling model in the MIDAS-GTS environment. Finally, it is confirmed that the fluid structure coupling model group data have significant advantages over the reference group data within the buried depth of 550 ∼ 1450 m and the tunnel cross-sectional area of 45 ∼ 102 m2. Finally, it is considered that the fluid structure coupling model has universal applicability within the analysis range. It is suggested that, in the future work, for example, when the tunnel construction project within the above analysis scope needs to carry out the simulation analysis of roof displacement and anchor bolt tension, the fluid structure coupling model should be directly selected as the analysis model.

The integrated disposal of surface subsidence pits and surface solid waste can be realized by backfilling a surface subsidence area with a paste made from the solid wastes of mines, such as tailings and waste rock. The microstructures of these wastes determine the macroscopic properties of a paste backfill. This paper presents an experimental study on the internal structure evolution of pasty fluid mixed with different waste rock concentrations (10%, 30%, and 50%) and cement dosages (1% and 2%) under damage. To this end, a real-time computed tomography (CT) scan is conducted using medical CT and a small loading device. Results show that UCS (uniaxial compressive strength) increases when the amount of cement increases. Given a constant amount of cement, UCS increases first and then decreases as waste rock content increases. UCS is maximized at 551 kPa when the waste rock content is 30%. The paste body is a typical medium used to investigate initial damage, which mainly consists of microholes, pores, and microcracks. The initial damages also exhibit a high degree of random inhomogeneity. After loading, cracks are initiated and expand gradually from the original damage location until the overall damages are generated. The mesostructure evolution model of the paste body is divided into six categories, and this mesostructure is reasonable when the waste rock content is 30%.

Taking the Xinshan iron ore mine as an example, this paper, based on collecting and analyzing the actual production data and similar simulation test data of this iron ore mine, analyses various factors affecting ore depletion by bottomless column segmental chipping method by using hierarchical analysis method (AHP) and fuzzy comprehensive evaluation method (FCE), and establishes an evaluation system for comprehensively assessing the depletion of the ores. The results show that structural parameters, blasting parameters, loading parameters, and geological conditions are the main factors affecting ore depletion. The structural parameters are the most important factors, accounting for 35%. With the increase of the released amount, the released grade gradually decreases, the depletion rate gradually increases, and the comprehensive evaluation value gradually decreases. The released body is an approximate ellipsoidal block with a wide upper and narrower lower part. The end wall plays an obstructive role in the flow of the bulk body, which makes the end of the released grade higher and the middle of the released body higher. At the same time, due to the influence of blasting and shovel loading, the particles in the release body show some sorting phenomena. This paper provides a scientific basis and reference for predicting and controlling ore depletion in the bottomless column segmental chipping method. [ABSTRACT FROM AUTHOR]

Analysis of slope stability is of critical importance in any open cast. A slope failure is a potential hazard as it can cause loss of lives of workers and economic losses that may lead to complete closure of the mine. The fundamental modes of failure are however varried and complex thus need for their indepth analysis. Such slope failure modes are guided by engineering geological condition of rock mass which differs from site to site, from sample to sample. This work was focussed at studying slope stability using numerical modells. The aim of the project is to know how and assess the usability of FLAC/slope and OASYS geoengineering software in determination of slope stability. Usage of these two softwares were a bit complicarted at the start of the analysis, however, with time we understood clearly how to use them and it can be concluded that they are user. Parametric studies led to a conclusion that angle of the slope plays a critical role and governs stability of slopes. Safety factors ranged from a value 0.64 way up to a value 1.38, for a depth variation from 10M110M while keeping the slope angle constant 45 degrees. This clearly elucidated that increase in bench height or depth of the mine leads to a significant decrease of safety, hence decreased stability of the respective slope. It could be recommended that the overall slope angle should be maintained at about 35 degrees or less since at an elevation of 100M, safety factors were found to exceed 1.2, which is deemed to be safer. Objectives of this study were therefore achieved, and we could recommend that in order to improve reliability of the model results, the models should first undergo field callibration through piezometric monitoring techniques in varried mining sites and varried conditions. [ABSTRACT FROM AUTHOR]

Wet shotcrete technology is being gradually used in roadway support in frigid mining areas. Thus, problems such as low strength, fragility, and high repair rate have also emerged. This study focuses on low strength, cracking, and other problems in the wet shotcrete support of a mine. It introduced the fishbone diagram to investigate the effects of temperature, cement content, and water-cement ratio (W/C) on the strength of the shotcrete layer. The microscopic morphology of wet shotcrete based on scanning electron microscopy (SEM) is observed. Results demonstrated that temperature was the main influencing factor of wet shotcrete in frigid mining areas. When the curing temperature was lower than 10°C, the early strength of wet shotcrete dropped significantly. Temperatures above 15°C were favorable for later gain in strength. W/C was of a complementary relationship with strength development at different ages. Temperature was the essential factor that influenced the microscopic morphology of wet shotcrete. Furthermore, internal initial porosity and aggregate interface bonding strength had a direct effect on macro-mechanical properties of wet shotcrete. [ABSTRACT FROM AUTHOR]

As a low-cost grouting material, clay-cement grout has been increasingly applied to grouting construction and other aspects. The current research on its properties is, however, limited to physical mechanical properties such as the compressive strength of its hardened body, permeation coefficient, setting time and stability. As a comparison, there are few studies of the deformability and mobility of grouting materials. To enrich this research area, we used NXS-11A rotational viscometer to gauge the relationship between the change of intermolecular shear force and the change of intermolecular shear rate as our test method. The corresponding results show that the clay-cement grout can be regarded as a type of viscoplastic fluid because its' deformability and mobility curves resemble the viscoplastic fluid counterparts to a large extent. [ABSTRACT FROM AUTHOR]

In order to characterise the concentration variations of gaseous pollutants and their pollution level in Beijing downtown, the complete time series data were get by using muti-point real time monitoring system based on 12 stations in 6 districts of Beijing from March 2013 to February 2014. Using mathematical statistics methods, frequency distributions, correlations and hourly variation laws of gaseous pollutants were analysed. Results show that there was obvious linear negative correlation between CO and O3, linear positive correlation between CO, NO2 and SO2, and linear positive correlation between NO2 and SO2 on their 1 h average concentrations, and their correlations had no significant changes during the recent years. The annual average values of CO, O3, NO2 and SO2 were 1.92 mg m-3, 47.1, 57.4 and 26.7 μg m-3, respectively. Seasonal variation was obviously influenced hourly variation laws of gaseous pollutants concentrations, the average concentrations of CO, NO2 and SO2 were the highest in winter and the lowest in summer while O3 was the highest in summer and the lowest in winter. Preliminary analysis showed the influence factors on concentrations were the meteorological factors (monsoon, daily radiation, temperature, humidity, wind speed, etc.), surrounding environment, boundary layer and the regular artificial source. [ABSTRACT FROM AUTHOR]

In order to explore the characteristics of airflow field in flat chamber stopes, via combining the similarity theory, we have established the similar experimental models and analysed the time-averaged characteristics of flow field of turbulent jet in flat chambers. Thus, the following results have been obtained: the flow velocity ratio of ambient jet in chambers is the major parameter affecting the jet flow characteristics; the average maximum jet width increases linearly with the increase of flow velocity ratio; the average maximum jet length has a linear relationship with flow velocity ratio; the flow velocity of jet axis decays along the jet; the jet flow at high flow velocity ratio decays more slowly than it at low flow velocity ratio. The research results of experiment play an important practical significance and reference value for ventilation and dust extraction in flat chamber stopes. [ABSTRACT FROM AUTHOR]

This research aimed to reduce excessive dust concentration in flat chambers and to explore the main factors affecting dust motion. Based on the theory of gas-solid two phase flow and airflow field, a physical model was established. Numerical simulation results of dust concentration distributions in flat chambers, which came from fluent, fluid mechanics computational software, were basically concordant with experimental data. Research results showed the following aspects. (1) The main factors affecting dust motion in flat chambers laid in the jet flow zone and reflux zone. (2) When mean flow velocity in flat chambers ranged from 1.0 m/s~3.0 m/s, increases in the mean flow velocity resulted in decreases in dust concentration. (3) With the increase in distance away from working faces, air flow velocity and dust concentrations undulated and appeared to have a downward trend in cross sections. Circulation between the jet flow and reflux resulted in the elimination of dust in flat chambers. [ABSTRACT FROM AUTHOR]