Underground coal mining leads to land subsidence, which, in turn, results in damage to buildings and infrastructure, disturbs the original ecological environment, and hinders the sustainable ...development of coal mining cities. A reasonable estimation of land subsidence, on the other hand, is the foundation for building protection, land reclamation, and ecological environment reconstruction. However, when we applied the existing land subsidence estimation theory to the deep mining areas of the Ordos coalfield in western China, there was a significant deviation between the estimations and the measurements. To explain such unusual case, we propose using the overburden's average GSI (Geological Strength Index) value instead of the compressive strength (UCS) of rock specimens for a better representation of the overburden's overall properties. By using on-site subsidence monitoring results and historical data, we provided evidence which supports that the overburden's average GSI value has a much greater impact on subsidence rates than the UCS. Subsequently, we investigated the relationship between three typical overburden's GSI values and the subsidence rates via a calibrated numerical model, revealing the variation patterns of maximum surface subsidence when the overburden's average GSI value is set at 30, 50, and 75, respectively. Finally, on the basis of the measured and simulated results, we discussed a non-conventional strip mining method for mining subsidence control in the deep mining areas of the Ordos coalfield in western China, and explained why it is possible and what are the significant advantages behind. The proposed methods, findings, and suggestions in this paper are therefore quite helpful for researchers and engineers who wish to estimate and control the mining-induced land subsidence, as well as for those who are particularly interested in the study of environment science related to land subsidence.
Determining the strata and surface movement of deep mining can provide a scientific basis for wellbore protection and mine land utilization. In this paper, numerical simulation methods were employed ...to investigate the stratum and surface movement boundary curves of deep caving and backfilling mining. The findings can be concluded in three aspects. First, the stratum and surface movement boundaries of deep caving and backfilling mining were all curved and conformed to an exponential function, but the influence range of strata and surface movement of deep different mining methods were different. Second, the backfilling rate of deep backfilling mining had an impact on movement boundary boundaries of strata and surface. With the backfilling rate decreasing, the influence range of strata and surface movement boundary were increased. Last, the research results were applied to a case to confirm the new approach of determining the influence range of strata and surface movement of deep mining. The example application shows that it not only can ensure the safe production of the wellbore, but also can enhance the reuse area of the mine field.
The heterogeneity of a rock mass under high temperature and its thermo-mechanical coupling characteristics are difficult problems to investigate. This situation brings considerable difficulties to ...the study of underground coal gasification under thermo-mechanical coupling. The development of a numerical simulation method for the thermo-mechanical coupling of heterogeneity rock mass under high-temperature burnt conditions can provide an important foundation for related research. On the basis of the variation of mechanical properties of rock mass with temperature, a thermo-mechanical coupling simulation method, which considers the heterogeneity of a rock mass under high temperature, is proposed in this study. A test block experiment is implemented and then applied to the strata movement and failure of underground coal gasification. The results are as follows: (1) The proposed method can truly reflect the heterogeneity of a rock mass under high-temperature environment, providing an effective method for the numerical simulation of geotechnical engineering in high-temperature conditions. (2) The variation of mechanical properties of rock mass after an increase in temperature is the main reason for the change law of strata movement and failure of underground coal gasification. These factors should be considered in the investigation of underground gasification strata movement andfailure. The present study can provide an important means for the research on geotechnical engineering in high-temperature environments.
Coal is one of the fundamental fossil energy supporting the world’s economy. The synergistic development between efficient coal mining and ecological environment protection is the inevitable ...requirement for the preservation of global harmony. As the world’s largest coal producer, China has conducted a strategic shift from east to west in terms of the exploitation of its energy resources, posing a serious threat to the fragile ecological environment of the western region. In particular, the surface subsidence caused by coal mining is the root of the ecological deteriotation and the destruction of ground structures. However, it is difficult to reveal the law of large-scale surface subsidence in western mining areas merely by conventional measurement methods such as leveling, on account of the high intensity of coal seam mining, the weakness of the lithology of overlying rock and the large thickness of wind-blown sand strata. In view of this, small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technology was used in this study to obtain the time series of surface vertical displacement during the whole mining process of the 2401 working face in the Yingpanhao coal mine, Inner Mongolia. Based on the deformation data, the dynamic evolution characteristics of surface subsidence under high intensity mining in the western mining area were analyzed exhaustively. It was found that the surface subsidence is characterized by an extensive coverage range (48.52 km2) with minimal ground settlement (250 mm) in the study area. Meanwhile, the boundary shape of the subsidence basin followed a “circular-parallelogram-trapezoid” changeable process and the coverage area of the basin experienced three stages: a linear increasing period, a temporary stagnation period, and a re-expansion period. Furthermore, there existed an abnormal uplift phenomenon on the east side of the open-off cut in the 2401 working face. Combined with the structure of overlying strata, this paper carried out a preliminary analysis on the reasons of the abovementioned phenomenon. The research results are of vital realistic significance for ground buildings and ecological environmental protection in the aeolian sand mining area in Western China.
Backfill-strip mining is proposed as a sustainable mining method to address the shortage of backfill material and high filling costs at present. The overlying strata in backfill-strip mining are ...mainly supported by the combined support pillar (CSP) of the residual coal pillar and the filling body. The stability of the CSP in backfill-strip mining is important to control the surface subsidence and reduce surface environmental damage. The particle flow code (PFC) simulation method is used in this study to investigate the deformation characteristics, failure behaviours, and stress distribution of the CSP for assessing its stability. The different influencing factors of the stability of the CSP, including geological mining factors, backfilling mining techniques, and the sizes of the residual coal pillar and the working face, are discussed. The results show that the shape of the CSP looks similar to a saddle. The vertical stress of the coal pillars is larger than that of the filling body. The subsidence value of coal pillars is smaller than that of the filling body, but the horizontal movement value of the coal pillars is large. Among these influencing factors of the stability, the residual coal pillar width has the greatest influence on the CSP. The different widths of the residual coal pillar lead to changes of the support formation and the bearing stress weight of the CSP, which make a big difference in the stress distribution characteristics, the movement deformation characteristics, and the stability of the CSP. On this basis, the CSP is divided into four types according to the stability and the support characteristics of the CSP, and their deformation characteristics and stability are summarised. The research results are important for guiding the stability assessment of CSP in backfill-strip mining and preventing the subsidence disaster whilst promoting sustainable extraction of coal resources.
Underground coal-mining-induced ground subsidence deformation is a common geological disaster impacting buildings, transportation and water supplies. Models predicting ground subsidence dynamically ...with high precision are important for the prevention of damage derived from ground subsidence. In this paper, the Hook function is utilized to develop a model describing the velocity of ground subsidence due to underground coal mining. Based on the subsidence velocity model, a dynamic subsidence model is established by taking an integral of the velocity model. Coefficients of the model, which depend on maximum subsidence, maximum subsidence velocity and the time corresponding to the maximum subsidence velocity, are related to the geological and mining conditions of the coal seam being investigated. A Levenberg–Marquardt-algorithm-based method is also proposed to calculate the optimal model coefficients based on subsidence velocity observations. Four continuously operating Global Navigation Satellite System (GNSS) stations were constructed above a typical longwall coal mining working face in the Jining mining area, China. These GNSS stations collected subsidence observations over two years, which were used to validate the developed prediction model. The results show that the root-mean-square (RMS) of the model-predicted ground subsidence error is 56.1 mm, and the maximum relative error is 2.5% for all four GNSS stations, when the ground subsidence is less than 6000 mm.
Solid backfill mining is a filling mining method that integrates subsidence control and solid waste disposal and is an effective way to extract coal under buildings, railways and water bodies. In ...this study, we propose a prediction model to accurately predict the surface dynamic subsidence process of solid backfill mining and assess mining damage. First, a dynamic subsidence function of roof in solid backfill mining was established, whose validity was verified using in situ measured subsidence data from the roof of two backfill working faces. Then, this function and the Knothe time function were combined to create a dynamic surface subsidence prediction model of solid backfilling mining, which accumulates surface subsidence caused by backfilling materials’ compression deformation at different times. Finally, an engineering case study demonstrates that the model is effective. This prediction model provides scientific reference for guidance in the design of solid backfill mining and the reduction in mining damage.
Considerable coal resources are buried under buildings in No. 5 mining area of Hengjian Coal Mine, which greatly shortens its service life. Working on the premise that the degree of mining-induced ...damage to surface buildings should not exceed the protective indicator, the mine proposes to use super-high water backfill technology so as to ensure maximum exploitation of these resources. However, according to monitoring of observations of surface movement in the first-mined 2515 working face, mining-induced damage to the surface buildings will exceed level I if this technology is also used to exploit other working faces. A technology combining super-high water backfilling with strip mining is proposed. Numerical simulation is used to study the influence of different retaining pillar widths on surface subsidence characteristics. A reasonable design of these combined technologies is achieved based on the numerical simulation and theoretical analysis. Predicted results indicate that the designed scheme can ensure the safety of the surface buildings. These research results provide a reasonable and reliable technical solution for mining of coal resources buried under buildings.
Underground coal gasification (UCG) is an important part of the low-carbon green coal mining technology system. With the implementation of the carbon peaking and carbon neutralization and the ...maturity of UCG, UCG will inevitably perform large-scale and industrialized production, which will certainly cause some issues such as serious waste of UCG sites caused by large-scale surface residual subsidence and poor foundation of fractured rocks. The key to the reuse of the surface site after UCG is to ensure that the surface residual subsidence does not exceed the design index of the building (structure). However, there is still a lack of methods for predicting residual subsidence on the surface of UCG. Under such background, combined with the characteristics of the UCG process, this paper analyzed the mechanism of the surface residual subsidence after UCG, and concluded that the root resource of the surface residual subsidence after UCG was the stripping and yielding of the hyperbolic coal pillars. Next, a calculation model of the maximum stripping width and yielding zone width of the “hyperbolic” coal pillar for UCG was established by the theoretical analysis method, and a method for predicting the surface residual subsidence with the consideration of coal pillar stripping and yielding was proposed and applied to Ulanqab UCG test site. The research findings have important theoretical and practical significance for the UCG site stability evaluation and land resource reuse.
Under the action of high temperature, the mechanical properties of coal will change significantly. After gasification, different types of coal will form different surrounding rock mechanical ...characteristics, which may have different impacts on the movement characteristic of combustion space areas overlying strata and surface. Without considering the influence of coal types or degree of coalification, the actual underground coal gasification (UCG) projects may have issues, such as instability of surrounding rocks in the combustion space zones, damage to surface buildings and structures. At present, the surface subsidence prediction method for UCG and underground gasifier design haven’t considered the effects of different coal types. Therefore, this paper studies the influence of coal types on the movement characteristics of the combustion space area overlying strata and surface through field measurement, theoretical analysis and numerical simulation. The research results are as follows: 1) The principle of the mechanical property change of different types of coal is different after UCG; 2) Different types of coal have an effect on the surrounding rock movement and deformation around combustion space area, the vertical stress distribution of coal pillar and the surface subsidence. The strong-caking coal underground gasification is more useful for controlling overlying strata movement in the combustion space area and reducing the surface subsidence; 3) The prediction method of surface subsidence for UCG without shaft is proposed and the method is applied to the Ulanqab UCG industrial experiment field; 4) Suggestions for the design of gasifiers and isolated coal pillars considering the impacts of different coal types are proposed. The research results have important guiding significance and practical value for underground gasifier and isolated coal pillar design, surface subsidence prediction and UCG industrialization development.
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