Surface Subsidence Prediction Research Articles

Ground cracks development and characteristics of strata movement under fast excavation: a case study at Bulianta coal mine, China

Field examples of fast exploitation from underground coal seams in Bulianta mines, China, show that unexpected developmental rules of settlement and cracks can occur. In situ observation and a physical model consisting of sand, plaster, mica, and calcium carbonate were jointly employed to study the movement of strata, as well as the developmental characteristics of surface cracks. The physical model was observed with a high-precision industrial photogrammetric system. The results indicate that ground cracks are caused by strata deformation, but the formation of ground cracks can, in turn, promote the deformation of strata. Moreover, by contrast with coal mining at a speed of about 2 m/day, we found that the ground does not achieve full subsidence until the advancing distance exceeds 2.2 times the mining depth under rapid excavation (approximately 12 m/day), which would cause large errors for surface settlement prediction. OCF (opening and closing fractures) above gobs are self-closing, but the duration of the closing phase is 3.6 times that of the opening phase, different from the symmetric distribution caused by mining with slower speed. The whole developmental cycle is inversely proportional to mining speed, and fast excavation can shorten development time of OCF. However, the horizontal tension deformation is the most stable factor for predicting ground cracks regardless of excavation speed. The research results can provide theoretical basis for dynamic prediction of ground subsidence and cracks development caused by underground coal mining.

Prediction and analysis of surface settlement due to shield tunneling for Xi’an Metro

This study describes a new modified prediction method of surface settlement (SS) for Xi’an Metro. The estimation method of SS and its characteristic parameters, volume loss (VL), maximal SS, and settlement trough width (STW) are reviewed and discussed in this paper. The gap parameter (GP) is applied to estimate VL; however, the calculation method of GP and its influence factors have not been clarified entirely. In this study, six influence factors are introduced into the new GP model, and the detailed solutions are presented. This estimation method is able to take into account the support pressure of the shield head at the tunnel face, the lining support pressure around the tunnel opening, the filling effect of tail grouting, yawing, and pitching of the shielding machine, and the long-term deformation of the remoulded surrounding soil. Based on Xi’an Metro line 2, the soil behaviors and measured SS characteristics are deeply investigated. The upper and lower bounds of the total GP of the 15 cases are predicted. Comparison of the predicted SS troughs with field observations can show reasonable agreement. It is suggested that the new estimation method can be used effectively in estimating the SS induced by the shield tunneling method.

Prediction of maximum surface settlement caused by earth pressure balance shield tunneling using random forest

Due to urbanization and population increase, need for metro tunnels, has been considerably increased in urban areas. Estimating the surface settlement caused by tunnel excavation is an important task especially where the tunnels are excavated in urban areas or beneath important structures. Many models have been established for this purpose by extracting the relationship between the settlement and the factors that influence it. In this paper, Random Forest (RF) is introduced and investigated for the prediction of maximum surface settlement caused by EPB shield tunneling. Various factors that affect this settlement, including geometrical, geological and shield operational parameters were considered. The results of RF model has been compared with the available artificial neural network (ANN) model. It is shown that the proposed RF model provides more accurate results than the ANN model proposed in the literature.

Prediction methods on tunnel-excavation induced surface settlement around adjacent building

With the rapid development of urban underground traffic, the study of soil deformation induced by subway tunnel construction and its settlement prediction are gradually of general concern in engineering circles. The law of soil displacement caused by shield tunnel construction of adjacent buildings is analyzed in this paper. The author holds that ground surface settlement based on the Gauss curve or Peck formula induced by tunnel excavation of adjacent buildings is not reasonable. Integrating existing research accomplishments, the paper proposed that surface settlement presents cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics when the tunnel is respectively under buildings, within the scope of the disturbance and outside the scope of the disturbance. Calculation formulas and parameters on cork distribution curve and skewed distribution curve were put forward. The numerical simulation, experimental comparison and model test analysis show that it is reasonable for surface settlement to present cork distribution curve characters, skewed distribution curve characteristics and normal distribution curve characteristics within a certain range. The research findings can be used to make effective prediction of ground surface settlement caused by tunnel construction of adjacent buildings, and to provide theoretical guidance for the design and shield tunnelling.

Surface settlement prediction for EPB shield tunneling in sandy ground

Ground volume loss induced by shield tunnel construction is the major factor leading to ground settlement and deformation. The general equations predicting surface settlement based on ground volume loss involve a settlement trough width coefficient (parameter i) which in previous models was set as a constant in both the transverse and longitudinal directions. In this work, the equations predicting surface settlement during the construction were modified by introducing the parameter j – the width coefficient in the longitudinal direction, assumed to be different from that in the transverse direction. A model shield machine was adopted to carry a laboratory test under 1 g to investigate surface settlement induced by earth-pressure-balance shield tunnel construction in unsaturated sandy soil. The surface settlement during the excavating observed in the test was compared with that predicted by general equations from previous studies and the modified. The results showed that surface settlement above shield machine obtained by the modified equation proposed here fits the test data better than those obtained by the general equations because of the introduced longitudinal width coefficient.

Control of surface settlement by considering shield tunneling technology

With the high-speed development of subway construction of China, the prediction and control of surface settlement induced by shield tunneling construction is a hot research topic. In this study, the modified Peck formula was established based on the modified gap parameters that concerned with three factors of the shield construction technology, which were included in the fill rate of grouting and shield eccentricity ratio and support pressure ratio. The control limits of Shield Tunneling Parameters (STP) were presented on the basis of the Maximum Surface Settlement (MSS), the allowable partial incline and curvature of settlement trough. With the background of the Xi’an Subway line No. 2, the MSS and partial incline of transverse settlement trough near the ancient structures is less than 15 mm and 0.5‰, for the ordinary sections, the value of which is less than 30 mm and 3.0‰, respectively. The STP near the ancient structures are controlled as follow: λ ≥ 0.64, β ≥ 0.81, κ ≤ 0.59%, and the control limits of STP are λ ≥ 0.60, β ≥ 0.77 and κ ≤ 0.71% for the ordinary sections.

Numerical analysis of surface subsidence in asymmetric parallel highway tunnels

Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels (Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and in-equidimensional noncircular tunnel.

Strata movement and surface subsidence prediction model of dense solid backfilling mining

Surface subsidence is the most common disaster in coal mining areas, which threatens human lives and assets. In this study, a prediction model is proposed to predict the surface subsidence caused by dense solid backfilling mining. Firstly, the surface subsidence is monitored by high-resolution survey and its static and dynamic characteristics are analyzed. Then, the universal law of strata movement and load distribution on the main roof are analyzed by similar material simulation and numerical simulation, respectively. The strata movement and deformation of dense solid backfilling mining are totally different from caving mining. There is no caving zone but a limited height of fractured zone developed in the strata. The load distribution on main roof follows the piecewise function. Finally, the prediction model is created based on the combination of elastic foundation beams and volume invariant transfer principle, and the prediction values basically coincide with measured values. This prediction model can provide reference data for the evaluation and management of coal mining hazards.

The influence of an abandoned goaf on surface subsidence in an adjacent working coal face: a prediction method

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.

Tools for Predicting Damage to Archaeological Sites Caused by One-Dimensional Loading

Tools are developed to predict damage to archaeological remains caused by the construction of line infrastructure on soft soil. They are based on numerical modelling and laboratory testing supported by X-ray microcomputed tomographic observations, and micromorphological analyses of thin sections. They have been validated for one-dimensional (1D) loading at two sites in the Netherlands where soil has been placed on top of organic layers rich in ecofacts and overlaying Pleistocene sands.Numerical prediction of the deformation of soft layers underneath an embankment remains a challenge for geo-technical engineers. Errors on surface settlement prediction reach ±15% of the measured total settlement.Laboratory observations show that vulnerable artefacts can get crushed when packed loosely in pure assemblies under 1D loading equivalent to less than 5 m of sand. Fragmentation is assimilated to loss of archaeological value as it compromises recovery during sieving. Embedment in a sandy or a very compressible organic matrix has a beneficial effect on the resistance of ecofacts. Embedded ecofacts can resist a load of more than 12 m of sand. Flattening and re-orientation of soft plant remains occur during 1D loading without microscopic damage of tissues.

Surface dynamic subsidence prediction model of solid backfill mining

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.

A new method of surface subsidence prediction for natural gas storage cavern in bedded rock salts

The surface subsidence above underground natural gas caverns in salt formations is mainly induced by the volume shrinkage of the cavern. In this paper a new method, based on the Mogi model, to predict the subsidence above bedded rock salts gas storage cavern is proposed. Firstly, the equivalent elastic boundary deformation of the cavern volume decrease is assumed to be the first-order approximation of the real subsidence induced by creep shrinkage. Secondly, the cavern shape is simplified to be a spherical one with the same depth and volume, subjected to the pressure change of hydrostatic pressure in the sphere. And then, solving for the subsidence above, the storage is analyzed as the boundary displacement problem of the spherical cavern subjected to pressure change of hydrostatic pressure in the sphere in semi-infinite space. Based on the equivalent elastic model, the Mogi model, which has been developed for subsidence prediction in volcano seismology, is introduced to solve the boundary displacement problem. Then the expressions for subsidence and for horizontal displacement are obtained. The advantage of the new method is that the ground displacements can be calculated directly from the cavern volume shrinkage, thus the calculation has much been simplified. The validity of the method is verified by comparing to numerical simulation results, which show that the Mogi model has high validity for subsidence prediction for the gas cavern in salt formations. In the end, some constructive discussions on the application and improvement of the Mogi model are presented for its further applications.

Geomechanics of subsidence above single and multi-seam coal mining

Accurate prediction of surface subsidence due to the extraction of underground coal seams is a significant challenge in geotechnical engineering. This task is further compounded by the growing trend for coal to be extracted from seams either above or below previously extracted coal seams, a practice known as multi-seam mining. In order to accurately predict the subsidence above single and multi-seam longwall panels using numerical methods, constitutive laws need to appropriately represent the mechanical behaviour of coal measure strata. The choice of the most appropriate model is not always straightforward. This paper compares predictions of surface subsidence obtained using the finite element method, considering a range of well-known constitutive models. The results show that more sophisticated and numerically taxing constitutive laws do not necessarily lead to more accurate predictions of subsidence when compared to field measurements. The advantages and limitations of using each particular constitutive law are discussed. A comparison of the numerical predictions and field measurements of surface subsidence is also provided.

Research on the surface movement in a mountain mining area: a case study of Sujiagou Mountain, China

Landslides caused by underground mining are very common in mountain mining areas, and thus threaten human lives and assets. Under the superposed influence of underground mining and landslides, surface movement in mountain areas is different from that in flat areas. Further understanding of the law of surface movement in mountain mining areas can protect the locals and their assets. In this study, an improved survey technique called spherical fitting real-time kinematic was employed to monitor surface movement regularly, and similar material simulation was used as a supplement to reveal the process of strata failure. Results showed that the ground would uplift during underground mining in the valley bottom areas, an action that caused the subsidence velocity curve to appear as a skewed distribution instead of a Gaussian distribution. To improve the prediction accuracy, the prediction model of surface subsidence in mountain mining areas was updated. The mountain surface subsidence prediction system was developed using Visual Basic. Finally, the mechanism of mining landslide was studied. This work is of general interest to the professional public and it will contribute to a more objective knowledge of understanding the surface movement in mountain mining areas.

New Method of Surface Settlement Prediction for Saint-petersburg Metro Escalator Tunnels Excavated by EPB TBM

The article describes a new technology of escalator tunnel construction using earth pressure balance tunnel-boring machines (EPB TBM) in complex geological conditions of St. Petersburg soils. The results of field surveying observations of settlements and strain calculations arisen from the construction of the escalator tunnels of the St. Petersburg metro “Obvodny kanal”, “Admiralteyskaya”, “Spasskaya” stations are presented. It is established that the evolving strain can be dangerous for undermining buildings and structures. The method of escalator tunnel construction numerical modeling based on the finite element method is used to evaluate the qualitative relations of the geomechanical processes. A new method of surface settlement prediction is based on the results of complex processing of field data and results of construction numerical modeling. This method involves determination of the following characteristics of the displacement process: the position of the point of the maximum settlement in a subsidence trough, the size of a subsidence trough, the value of the maximum settlement, distribution of displacements and strains in the trough. The developed method for calculation of the settlements was tested on Saint-Petersburg metro escalator tunnels. Comparison of results for predicted and observed data indicate the reliability of the developed settlement and deformation prediction method in the construction of the escalator tunnels using the TBM in St. Petersburg.

Subsidence prediction and susceptibility zonation for collapse above goaf with thick alluvial cover: a case study of the Yongcheng coalfield, Henan Province, China

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.

Research on the surface movement rules and prediction method of underground coal gasification

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.

Numerical Study of Mine Site Specific Multiseam Mining and Its Impact on Surface Subsidence and Chain Pillar Stress

This paper investigates various multiseam mining related parameters using mine site specific data and numerical simulations. Two important mining effects—subsidence and stress—are analysed for different possible mining layouts. A geological mine dataset has been used to generate a numerical model. The predicted surface subsidence magnitude and surface profile have been compared under different scenarios to assess potential options in multiseam mining strategies. The effects that seam separation distances, mining offset, panel layout and panel orientation each have on surface subsidence and chain pillar stress magnitude have been investigated. The numerical simulation shows that ascending or descending mining directions have little impact on controlling the surface subsidence in multiseam mining and predicted an almost identical maximum stress development at the chain pillars. Numerical simulations infer that the orientation of the top panels control the subsidence profile.

Determining The Minimum Distance Between Centers of Two Parallel Tunnels to Apply The Law of Super Position in Order to Calculate Subsidence by Using The Software FLAC 3D

Due to the development of cities as well as rapid population growth, urban traffic is increasing nowadays. Hence, to improve traffic flow, underground structures such as metro, especially in metropolises, are inevitable. This paper is a research on the twin tunnels Of Isfahan's metro between Shariaty station and Azadi station from the North towards the South. In this study, simultaneous drilling of subway's twin tunnels is simulated by means of Finite Difference Method (FDM) and FLAC 3D software. Moreover, the lowest distance between two tunnels is determined in a way that the Law of Super Position could be utilized to manually calculate the amount of surface subsidence, resulted by drilling two tunnels, by employing the results of the analysis of single tunnels without using simultaneous examination and simulation. In this paper, this distance is called "effective distance". For this purpose, first, the optimum dimensions of the model is chosen and then, five models with optimum dimensions will be analyzed separately, each of which in three steps. The results of analyses shows that the proportions (L/D) greater than or equal 2.80, the Law of Super Position can be applied for prediction of surface subsidence, caused by twin tunnels' construction

Deficiencies in 2D Simulation: A Comparative Study of 2D Versus 3D Simulation of Multi-seam Longwall Mining

The reliable prediction and management of mining-induced surface subsidence is one of the environmentally challenging issues for the coal mining industry. Because coal mining companies operate under strict environmental accountability, the absence of robust and reliable analysis tools may significantly affect the industry’s ability to gain approval and licenses when significant surface subsidence issues are involved. This issue becomes even more critical in multi-seam mining conditions, where high-stress concentration and large amounts of surface subsidence are expected to generate during multi-seam mining, hence could affect the feasibility and safety of all seams being mined. To obtain mining approval, it is, therefore, imperative to understand the geomechanical effect of mining in one seam on the mining of the underlying/overlying seams, and to accurately predict the magnitude and profile of surface subsidence. Various computer programs using empirical or numerical approaches have been developed to estimate the stresses at pillars and coal seams during multi-seam mining (Bigby et al. 2007; Ellenberger et al. 2003; Mark et al. 2007; SCT 2010; Sears and Heasley 2013). However, empirical-based models have severe limitations, which often make them inapplicable for assessing the feasibility of multi-seam mining at green field sites. Instead, numerical simulations are widely employed for this purpose. Due to the complexity of the problems and the computational times, researchers and engineers generally resort to twodimensional (2D) simulations. The present study assesses the performance of 2D and 3D numerical simulations and presents comparisons of subsidence profiles and stresses in pillars obtained during multi-seam mining. We modeled two different seams, each with four mining panels, using an in-house, 3D, finite element code called COSFLOW (Adhikary et al. 1996; Adhikary and Guo 2002). A unique feature of COSFLOW is the incorporation of Cosserat continuum theory in its formulation (Cosserat and Cosserat 1909). In the Cosserat model, interlayer interfaces (i.e., joints, bedding planes) are considered to be smeared across the mass. In other words, the effects of the interfaces are incorporated implicitly in the choice of stress–strain model formulation. The Cosserat model incorporates the bending rigidity of individual layers in its formulation, unlike other conventional implicit models. COSFLOW produced very accurate results when simulating surface subsidence due to longwall mining at Appin Colliery in New South Wales in Australia (Guo et al. 2004).