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Longwall extraction of coal seam disturbs the whole overburden strata, from the coal seam to the surface, and forms a subsidence basin. This paper investigated the mechanism of the overburden strata bending deformation, the alluvium mechanical parameters, and their effect on surface subsidence by the theoretical analysis and numerical simulation analysis. The dynamic processes of overburden failure and surface subsidence due to longwall mining was analyzed by a novel two-dimensional trapezoidal-area method. A “π-shaped” model was first developed to reveal that surface subsidence consists of the overburden strata bending deformation and the subsidence of the alluvium. The process and mechanism of the overburden strata bending transfer were analyzed, and two mechanical models of the strata bending deformation were established, i.e., the strata suspended bending model and the strata overhanging bending model. The maximum subsidence equation of the overburden strata bending basin was derived based on the theoretical analysis. Also, the effect of the alluvium mechanical parameters on the surface subsidence was investigated by numerical simulation analysis. The rationalities of the numerical simulation were validated by the field measurements. The results show that surface subsidence increases logarithmically during increased alluvium thickness and decreases exponentially and logarithmically during increased internal friction angles and increased cohesions, respectively.

Using abandoned salt caverns for the disposal of solid wastes is one of the most effective and safest methods to deal with potential hazards caused both by the abandoned caverns and by the solid wastes. To investigate the geomechanical behavior of abandoned salt caverns used for solid waste disposal (alkali wastes), a discrete-continuous coupled method is proposed. In the proposed method, alkali wastes (discrete materials) are simulated using the discrete element method (DEM) while the caverns are simulated using the finite difference method (FDM). This method can overcome the shortcomings of the traditional method of treating the alkali waste as continuous materials with low strength, which cannot accurately depict the interaction between the cavern and alkali waste. Using the proposed method, a 3D geomechanical model is built to investigate the long-term mechanical behaviors of the cavern and alkali waste. The results show that the alkali wastes have significant effects on reducing the cavern convergence while the cavern convergence compacts the alkali wastes. Consequently, the surface subsidence induced by the convergence of the cavern is much smaller than that of a cavern which does not contain alkali wastes. This study provides a prerequisite to evaluate the effect of filling abandoned salt caverns filled with alkali wastes and also can serve as a reference for stability analysis of gas storage salt caverns that contain insolubles.

One task facing by the geotechnical engineers is to protect the workspace in an underground construction/excavation site from various forms of geological disasters, such as the water inrush, rock burst, and collapse of the surrounding rock/soil. In this paper, a combined controlling measure was proposed based on underground mining and water environment: the method of strip mining has been initially proposed as an effective measure against underground workspace floor failure when mining above confined aquifer in the Bucun coal mine, China, and however, its ability to avoid floor water inrush has yet to be demonstrated; in the next step, field trials using caving zone backfill technology to prevent underground workspace floor failure and excavate retained strip coal pillars were implemented based on the theoretical calculation and numerical simulation results. Engineering practice showed that the failure depth of the underlying strata of the workspace had no growth without the possibility of water inrush, and the safety of the underground space was achieved. Thus, this study represents a successful attempt to develop the combined strip mining and caving zone backfilling technique to ensure the safety of the underground workspace and control surface subsidence when excavating the retained strip coal pillars above confined aquifer. The proposed combined technique can also be used in other underground excavation activities with similar problems.

When using a Terrestrial 3D laser scanning (TLS) to monitor the mining subsidence in a mining area, the conventional methods are to set up the public target manually, or to set up the ground control network in advance. However, these have the disadvantages of high labor intensity and low efficiency. In order to overcome the shortcomings of the conventional methods, this paper presents the subsidence monitoring method using TLS without a target in the mining area. Feature points are used to splice the multi-station point clouds in the same phase, and a few station coordinates are used to uniformly transform the multiphase data into a geodetic coordinate system. Afterwards, the surface digital elevation model (DEM) is established by using the point clouds after coordinate transformation, and the dynamic subsidence value and subsidence basin during the period of observation are obtained by DEM subtraction. Compared to traditional methods, this method simplifies the field measurement process, reduces the labor intensity, and transfers the main work to the internal industry. It is suitable for surface subsidence monitoring with a harsh external environment and complicated topographic conditions. Surface deformation values are important basic data for mining area subsidence parameters acquisition, mining area environmental assessment, land reclamation, and ecological restoration. As a consequence, it is of great value to popularize and apply in mining area for subsidence monitoring.

Shallow coal seam exploitation not only causes serious surface subsidence but also induces extensive ground fissures, which severely threaten the safety of underground mining and the surface eco-environment. We use the Daliuta coal mine of the Shendong mining district in China as a case study to investigate and characterize the influence of underground coal mining on the development of ground fissures. A new comprehensive impact parameter K of geology and mining for ground fissure development is introduced to explain the effects of mining speed on the developmental features of ground fissures. The results show that ground fissures often develop in the surface tensile zone ahead of the working face advancing position and show an inverted C-shape on the surface, which is similar to periodic fracturing of the basic roof. The ground fissure angle increases linearly with mining speed and logarithmically with K, while the developmental cycle decreases linearly with mining speed. We propose a technical measure to control ground fissure disasters by adjusting mining speed, which provides a theoretical reference for eco-environmental governance in shallow coal seam mining districts.

Intensive and massive coal mining causes a series of geological hazards and environmental problems, especially surface subsidence. In recent years, backfill-strip mining has been applied to control mining subsidence in order to realize sustainable development of the mining environment. To accurately predict the surface subsidence of backfill-strip mining, a prediction method of subsidence superposition of backfill-strip mining is proposed on the basis of the traditional probability integral method prediction model. In analyzing the distribution of the actual subsidence space, the surface subsidence problem of backfill-strip mining can be regarded as the superposition of surface subsidence caused by backfill mining and strip mining. Then, the appropriate prediction parameters will be chosen, and the surface subsidence caused by the backfill mining and strip mining will be predicted separately. The surface subsidence values of the backfill-strip mining are equal to the superposition subsidence values predicted by the backfill mining and strip mining prediction method at the same surface location. A similar material model and a numerical simulation model have been built to verify the feasibility and accuracy of the superposition prediction method. The comparison results of the surface subsidence values show that the superposition surface subsidence prediction method is reasonable. The average relative error of this superposition prediction method is less than 6.7%, and its accuracy is 3.9%~11.4% higher than that of the conventional prediction method. The superposition prediction method can satisfy the precision requirement of engineering applications. This study provides a scientific technical reference for safe mining engineering design and surface disaster protection for backfill-strip mining.

Due to the continuous development of underground mining methods, technical equipment, the Internet and intelligent technology, a new energy revolution will be of great significance in years to come. Meanwhile, the high-intensity mining (HIM) of thick coal seams has become an important development direction of China’s underground coal mining technology. By summarizing the current situation and analyzing the characteristics of underground HIM using the analytic hierarchy process (AHP) method in thick coal seams in China, negative externalities are proposed, which are mainly reflected in the three aspects of overlying strata, ground surface, and ecological environment under the premise of standard operating procedures and underground mining safety. Considering the negative externalities of overlying strata and surface damage in HIM, geological disasters under HIM are divided into mine production disasters and ecological environment disasters, which have cluster, suddenness, and chain characteristics. Based on the types and characteristics of geological disasters caused by HIM, coal mining technology for preventing major geological hazards and environmental damage has been formed, providing a theoretical guidance and technical support for the development goals of HIM and environmental protection in China.

In consideration of the high filling costs and backfill material shortage at present, backfill–strip mining, which combines the advantages of strip mining and backfill mining, has gradually been adopted to control surface subsidence. In this study, similar material modeling is established to simulate strata movement characteristics of backfill–strip mining. The displacement and deformation values of this similar material modeling are precisely acquired through close-range photogrammetry and optical image methods, respectively. On this basis, structural and movement characteristics of the overlying strata are investigated in different stages to reveal the strata subsidence control mechanism of backfill–strip mining. The dynamic deformation characteristics of the overlying strata in mining are also explored. This study provides a scientific technical reference for safe mining engineering design and surface disaster protection for backfill–strip mining.

Historical global coal resource exploitation has resulted in goaf abandonment at most mines, which, during the life of the mine, exerts a strong influence on the ability to exploit new working faces adjacent to any abandoned goaf. Thus, the distribution law of the surface subsidence basin above the new working face differs from the general law. Given the lack of research on this distribution law, this study uses a similar material simulation method to examine the influencing mechanism(s) of abandoned goafs on the subsidence basin in the same coal seam. Synthetic aperture radar (SAR) monitoring results of the 9310 working face in the Nan Tun coal mine, Yanzhou, China, are used to verify analytical results, followed by numerical simulation to study the influence of the abandoned goaf on the subsidence basin. Finally, to accurately predict surface subsidence influenced by the abandoned goaf, inflection point deviations are selected and discussed in terms of the probability integral method. This allows for prediction of the distribution of the surface subsidence basin, and moreover, the predicted results are found to be consistent with the SAR monitoring results when the derivation of inflection points is revised.

Alluvial soil plays an important role in ground subsidence caused by coal mining and groundwater extraction. Coal mining areas covered with thick alluvial soil (CMATASs) are widely distributed in China, and ground subsidence in these areas exhibits unique features—for instance, the maximum subsidence is greater than the extracted coal seam thickness. Consequently, studies on the regularity and mechanism of mining subsidence in CMATASs have gained much attention. However, current research methods mainly involve numerical/physical simulation and theoretical analysis, while convincing verification using field data is lacking, leading to limited research results and weak practicability. This paper proposes a new approach for studying the spreading process of mining subsidence in rock mass and alluvial soil, as well as the response of alluvial soil to mining subsidence in these areas, through the use of field data. This approach includes the following steps and assumptions: First, the overlying rock mass and alluvial soil are regarded as a dual medium; subsidence data obtained in coal mining areas covered with thin (non-)alluvial soil (N-CMATASs) are taken as the bedrock surface subsidence in the CMATASs (the lower boundary condition of thick alluvial soil). Second, ground subsidence data obtained in CMATASs are taken as the upper boundary condition of the thick alluvial soil. And lastly, by considering the measured mining-induced overburden fracture datum and geo-mining conditions in CMATASs, we can study the spreading process of mining subsidence in rocks and soils and determine the underlying mechanism as well as the response of the soil to mining subsidence in CMATASs. A major feature of the proposed approach is that the overlying rock mass and alluvial soil can be separated and the measurement data can be obtained in different boundaries, thus compensating for the shortage of measured data in current study methods. This approach was successfully applied in the Huainan coal mining area in China, and can provide a basis for accurate calculation of ground subsidence in similar mining areas.

Mine collapse is a common geological hazard associated with mining areas. This study analyzes mine collapse above the Yongcheng mining area located on the Huanghuai Plain in eastern Henan Province, China. The aim is to predict surface subsidence and evaluate associated disaster risks in goaf with thick alluvial cover. The surface deformation above seven mined coalfields and six unmined coalfields was calculated using the probability integration method. The results showed that the final maximum ground subsidence would be 7.25 m for the Suburban mine and 5.3 m for the Xinzhuang mine. As part of a broader study, land subsidence was also measured over a 1-year period in 2012–2013 by interferometric point target analysis using Radarsat-2 satellite synthetic aperture radar. Interferometric displacement maps were validated with leveling data. Based on the principles of fuzzy mathematics and the analytical hierarchy process, a susceptibility assessment system was developed to define the risk from mine collapse for the coalfields across the mining area. A hazard-zoning map was also produced using the spatial analysis function of ArcGIS. These research results can serve as a reference for farmland reclamation, town planning, and the restoration of the natural environment in this area.

With the continuous development of the technology of underground coal gasification (UGC), it gradually moves into commercial development. However, there is limited measured data and related research on the overlying strata and surface movement rule caused by underground coal gasification, which has severely restricted the further application of underground coal gasification. In order to solve the problem of surface subsidence prediction of underground coal gasification, this numerical simulation software, FLAC3D, is adopted to study the differences of overlying strata and the surface movement rule of UGC strip mining (UCG mining) and strip mining, and the differences of prediction parameters under different recovery ratios. The model is established according to the geological and mining conditions of the underground coal gasification experiment area in China. The research results show that overlying strata and surface movement rules of UCG mining and strip mining are similar. So, the surface subsidence prediction of UCG mining can refer the prediction method of strip mining. Meanwhile, the difference values of surface movement extrema under different recovery ratios are less than 5 mm and the difference values of surface subsidence boundary are not more than 10 m. Therefore, the surface subsidence prediction parameters of UCG mining can be chosen as the corresponding prediction parameters of strip mining. Finally, the surface subsidence prediction method of UCG mining is proposed based on the above research results and prediction software is compiled for engineering application. Research results have important theoretical and practical significance for promoting the application of underground coal gasification.

The influence of abandoned mine subsidence on transportation facilities is a growing concern due to rapid urbanization and industrialization in China. Transportation infrastructures are being or will be developed in many areas with potential subsidence problems. Consequently, it is necessary to assess and mitigate the long-term and progressive residual subsidence effects on transportation facilities in such regions. This paper presents an integrated framework to identify and mitigate the risks of abandoned mine subsidence on highway infrastructures. The framework comprises four steps: comprehensive investigations of abandoned mine features; identification of subsidence mechanisms, conceptual model construction and risk assessment; optimization of remedial solutions and development of a management strategy. A case study that demonstrates a successful application of the framework is also presented in this paper. In this example, a technique that integrates remote-sensing analysis throughout surface features with conventional investigation methodologies is proved to be a potential tool to detect and understand areas that might be at risk of surface subsidence. Based on the analysis of the representative failure mechanisms observed in situ and the influencing factors, a methodology has been developed to assess the geohazards associated with mine subsidence. Moreover, the proposed criteria for stability classification allowed us to define three geohazard levels on a regional scale. Subsequently, based on a brief review of remedial works made in China, the paper gives some recommendations to identify the most appropriate solutions to mitigate residual subsidence risk on transportation infrastructures. Such integrated decision-making framework will assist practitioners and regulators in identifying the potential risks of residual subsidence on transportation routes, optimising the most appropriate alignments, and assessing risk management practices.

In coal mining, a poorly sealed borehole is one of the channels that can lead to an inrush of water and quicksand movement, seriously compromising the safety of the coal mine. In this paper, we used the water inrush and quicksand incident at Longde Coal Mine as an example in order to investigate the mechanism of water inrush and quicksand movement induced by a borehole, as well as to develop measures for the prevention and remediation of such problems. Two sand funnel models and a water inrush outlet model are introduced from which to calculate the flow of the water and quicksand; a comparison of the two shows that the flow predicted by the water inrush outlet model is more consistent with observations from the accident than the sand funnel models. Based on the water inrush outlet model, the aquifer thickness and borehole diameter are the two key factors affecting the flow. The aquifer channel is inferred as tubular, with its diameter gradually decreasing from ground surface to underground, and a time-dependent surface subsidence model is constructed. Finally, we develop a prevention method, “Prior to mining development, borehole should be investigated and plugged for prevention,” and propose a remediation method, “Changing the pipeline flow into fracture flow, followed by changing the fracture flow into pore flow, and finally grouting and plugging.”

The block cave mining mechanism and associated subsidence present one of the most challenging engineering problems in rock mining. Although block caving has been in use for many years, there has been limited research on the impact caving angles have on surface settlement and failure profiles, specifically when associated with deep caves and surface propagation (i.e., not as part of caving into an existing open pit). We analyse in this study block caving-induced step-path failure development in a large-scale demonstration model utilizing a numerical code based on a finite element technique that incorporates an elasto-brittle fracture mechanics constitutive criterion. Fracture initiation, propagation and coalescence, as well as the breaking of the intact rock bridge and the evolution of a pressure-balancing arch in the stressed strata, are represented visually during the whole caving process. Based on numerical results, surface impacts of block caving, such as subsidence profiles, break angles, fracture initiation angles and subsidence angles at different initial caving depths, are illustrated in this study.

A number of areas worldwide are suffering from the land subsidence, including the southern Yangtze River delta, the most developed area in China. Land subsidence is mainly induced by excessive groundwater pumping and has caused numerous problems, for example, flooding, structural cracking, and ground fissuring. Although several countermeasures have been adopted to mitigate the land subsidence problem in the southern Yangtze River delta, commonly using groundwater recharge, land subsidence is still developing even when groundwater levels are rising. The observation data of land subsidence in each stratum show that the deformation of the pumped aquifer is even greater than that in the adjacent aquitards when groundwater levels are recovering. Laboratory test results on the aquifer sand in Shanghai and Changzhou (two cities in the studied area, which have the most sufficient observation data about the land subsidence and groundwater level developing with time) proved that sand creep deformation is significant and is partially responsible for the land subsidence without groundwater level drawdown. Considering the difficulty and cost of collecting borehole samples from deep pumped aquifers to obtain the essential parameters for the existing sand creep calculation models, a simplified method was then proposed to calculate the sand creep deformation in the pumped aquifer. The relationship between the sand creep rate and the time can be recognized as linear using double logarithmic coordinates and the slope can be assumed to be one. In the proposed method, the laboratory test data are not necessary. Finally, case histories from Shanghai and Changzhou were used to verify the effectiveness of the proposed method.

Unlike the symmetrical surface settlement trough of a single tunnel which can be described using the Gaussian function, surface settlement over twin tunnels can be symmetric with respect to the mid-point between two tunnels or asymmetric. The paper reports the settlement troughs which developed when earth pressure balance (EPB) machines were used to excavate twin tunnels at shallow depth in the soft ground conditions beneath a developed part of Istanbul. An attempt is made to evaluate the effects of different factors on the surface subsidence. Detailed monitoring was undertaken when one tunnel was advanced ahead of the other and when only one tunnel was being driven. It was found that the shapes of the subsidence troughs over the two tunnels were different and varied with the excavation of the second/subsequent tunnel. It is concluded that changes in the subsidence trough are related to disturbance in the geo-material when an excavation is advanced ahead, as well as the nature and thickness of the overburden.

An analytical method has been developed to predict the location, depth and size of caverns created at the interface between salt and overlying formations. A governing hyperbolic equation is used in a statistical analysis of the ground survey data to determine the cavern location, maximum subsidence, maximum surface slope and surface curvature under the sub-critical and critical conditions. The regression produces a set of subsidence components and a representative profile of the surface subsidence under sub-critical and critical conditions. Finite difference analyses using FLAC correlate the subsidence components with the cavern size and depth under a variety of overburden strengths and deformation moduli. Empirical equations are proposed which correlate the subsidence components with the cavern configurations and overburden properties, allowing prediction of cavern configurations from the subsidence components.

The preparation and compilation of a 1:10,000 scale engineering geological map of the wider Thessaloniki area is discussed. This map includes the range of values of the geomechanical characteristics of the 13 engineering geological units distinguished. Greater detail was available in the inhabited and industrial areas where many of the 1,300 boreholes studied had been drilled. Particular emphasis was given to the earth fill unit, which in places is up to 20 m thick. Some of the underlying Quaternary units are aquifers and severe pumping has resulted in both a lowering of the groundwater level and surface subsidence. The subsidence was most prominent in the Sindos–Kalohori–Axios River zone and required the construction of an embankment along the coast.