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Monitoring of strata control parameters and behaviour of a powered support was carried out during an experimental trial of a mechanized longwall sublevel caving face for exploitation of a 7.5m thick coal seam. Field observations indicated that the requirement of support density for underwinning of top coal by sublevel caving under intact strata is...
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Context 1
... effective control of the roof, the ideal estimate of support density can be obtained in the field by gradually reducing the support thrust until the roof becomes critically stable. Such a practice, however, is lengthy, dangerous and expensive. The concept of a roof block (Fig. 3a) is used to estimate the rating of a powered support for soft rock conditions. Here the height of a detached block (t) is dependent upon the working height (h) and bulking factor (k) (Smart, 1989) and can be expressed as: In actual field conditions the height of caving is different due to the considerable amount of convergence of the ...
Context 2
... support for soft rock conditions. Here the height of a detached block (t) is dependent upon the working height (h) and bulking factor (k) (Smart, 1989) and can be expressed as: In actual field conditions the height of caving is different due to the considerable amount of convergence of the roof strata. Taking convergence of the face into account (Fig. 3b) the above relationship ...
Context 3
... of massive roof strata causes a drop in the value of the bulking factor (k) which increases the height and therefore weight of the roof block to be supported. For such heavier geomining conditions (which are frequently encountered in Indian coal fields), the location of a prominent parting plane within the roof strata plays an important role (Fig. 3c) in estimating the void between the caved waste and overhanging roof. Under this condition, the required support density is mainly influenced by the thickness of the immediate roof, the mechanism of roof failure and the limiting span of overhang. The values of limiting span of a clamped beam and cantilever (Fig. 3d) of the pertinent ...
Context 4
... strata plays an important role (Fig. 3c) in estimating the void between the caved waste and overhanging roof. Under this condition, the required support density is mainly influenced by the thickness of the immediate roof, the mechanism of roof failure and the limiting span of overhang. The values of limiting span of a clamped beam and cantilever (Fig. 3d) of the pertinent beds are given ...
Citations
... Unver et al. 16 analyzed the surface movement pattern resulting from thick coal seam mining. Singh and Singh 17 investigated the behavior of a support system and roof strata during sublevel caving of a thick coal seam. Ramesh and Ram 18 predicted subsidence due to coal mining in the Raniganj coalfield in West Bengal, India. ...
The Yangjiacun coal mine, located in western China, exhibits distinctive characteristics, such as its shallow depth, thick bedrock, thin loose layer, and unique roof strata breaking movement. In this research, a comprehensive analysis of previous exploration data, subsequent mechanical testing, key stratum theory, natural equilibrium arch theory, and simulation tests and numerical simulations has been conducted to investigate the failure behavior of the overlying rock strata in the Yangjiacun Coal Mine. Specifically, the load‐bearing capacity of the key stratum structure in the bedrock and the morphological properties of the arch‐beam structure have been thoroughly examined. A mechanical model of the roof rock arch‐beam structure has been established, and an analytical formula for the limit size and stability criterion of the arch‐beam structure has been derived. The mining‐induced rock arch‐beam structure plays a crucial role in transferring the load of the upper strata to the surrounding goaf, thereby preventing subsidence and deformation of the overlying strata. However, the arch‐beam structure periodically experiences instability during the advancement of the working face, gradually progressing towards the upper layer until the main key stratum is breached and the arch‐beam structure collapses. Based on the characteristics of weathered rock and the arch‐beam failure model in the Yangjiacun Coal Mine, quantitative backfilling mining methods have been proposed to either compensate for the mining void created by coal extraction or limit the size of exposed key strata through strip mining, ensuring the stability of the R6 key stratum. This study represents a significant contribution to understanding the intricate failure behavior of overlying rock strata in coal mines and provides a valuable framework for the responsible and efficient extraction of coal resources in similar environments.
... China is rich in coal resources and has extensive coal mining activities [1][2][3]. In recent decades, the fully mechanized technology with large mining height has become one of the main mining technologies for 3.5-5.0 ...
... The roadway was in the stage of slight deformation, during which the plastic zone of roadway begins to evolve. 2 Violent deformation stage. The range was from 30 m ahead of the coalface to 200 m behind the coalface (−30~200 m). ...
... The roadway deformation and velocity were all slight in this stage. 2 Slow deformation stage. The range was from 55 m to 25 m ahead of the coalface (−55~−25 m). ...
Reused roadways are increasingly adopted in fully mechanized coalfaces with large mining heights because of the ventilation and gas drainage problems. However, the forced mechanism and grouting control technology of the reused roadway was seldom studied. Hence, in this paper, field monitoring and numerical simulation were undertaken to investigate the distribution of stress and deformation of the reused roadway, and the reasonable grouting opportunities and technological parameters were determined accordingly. Engineering application of grouting control technology with self-developed inorganic double-fluid grouting materials was conducted. The field monitoring and numerical simulation revealed that the reused roadway was significantly affected by the lateral abutment pressure during the first mining operation and by the leading abutment pressure during the second mining operation. It was characterized by lagging stable deformation during the first mining operation and ceaselessly increasing deformation during the second mining operation. The deformation range of the reused roadway during the first mining operation can be divided into three stages: initial deformation, violent deformation and plateaued deformation, while the deformation range can be divided into three distinct stages: initial deformation, slow deformation and violent deformation during the second mining operation. On the basis of the roadway deformation law, two grouting opportunities were confirmed. The first grouting opportunity was suggested in the front part of the plateaued deformation stage during the first mining. The second grouting opportunity was suggested in the slow deformation stage during the second mining. Field engineering applications showed that both the deformation range and value of the reused roadway were decreased obviously after grouting.
... But the increased height of extraction influences the amount and nature of overlying strata movement during their caving. A physical modeling study (Singh and Singh 1999) demonstrated this influence and found it important for the design of underground mining structures. Strata mechanics around the working needs to be considered extensively (Singh & Singh 2010). ...
... Here, longwall top coal caving (LTCC) provides an edge over the other variants of these two popular mining methods. However, in India, the longwall route of thick seam mining in single lift remained limited to the sub-level caving of 7.5 m thick coal seam of east Katras colliery (Singh and Singh, 1999). A popular method like LTCC could not be practiced in Indian coalfields, mainly, due to: (a) scarcity of financial investment, (b) unavailability of indigenous longwall equipment and spare parts, (c) past failures of power supports and (d) existence of suitable geo-mining conditions for alternative technologies like opencast mining. ...
Engineering efforts need to be organized as per the rock mechanic conditions of the site for efficient underground extraction of a thick coal seam. Geo-mining conditions of Indian coalfields have favoured development of thick coal seams on Bord and Pillar (B&P) method, where single lift depillaring of total thickness (SLDTT) is vital for their final extraction. Competency of heightened pillar is an important factor for uncontrolled roof-pillar interaction during caving of the hard and massive overlying strata. An increase in extraction height by underwinning of roof coal band of the thick coal seam during retreat, developed along its floor horizon, is found to be the main reason for the strength deterioration. Conducted field studies also showed that the presence of competent overlying strata caused caving after a large overhang inside the goaf varying from 6000 m2 to 12500 m2. An attempt was made to control the roof caving by a proportional increase in width of the heightened pillars and it worked well but caused the issue of resource conservation. However, another field study with SLDTT working below laminated and weak overlying strata experienced a smooth strata control condition. This fortifies the idea of strength reduction of the competent overlying strata by fracturing for a controlled strata behaviour. This paper presents the result of the field investigations to demonstrate the role of strength reduction of overlying strata for underground extraction of total thickness of a thick coal seam in single lift.
... The study of the magnitude and nature of dynamic loads resulting from the impact of rock mass as tremors directly on powered roof supports has been the subject of numerous studies [43][44][45][46][47][48]. Many researchers from all over the world are conducting studies to identify the required dynamic resistance of the leg [49][50][51][52][53]. ...
This paper presents the results of a study conducted to determine the dynamic power of a hydraulic leg. The hydraulic leg is the basic element that maintains the position of a powered roof support. It is located in the structure between the canopy and the floor base. The analysis assumes that its power must be greater than the energy of the impact of the rock mass. The energy of the rock mass is generated by tremors caused mainly by mining exploitation. The mining and geological structure of the rocks surrounding the longwall complex also have an influence on this energy generation. For this purpose, stationary tests of the powered roof support were carried out. The analysis refers to the space under the piston of the leg, which is filled with fluid at a given pressure. The bench test involved spreading the leg in the test station under a specified pressure. It was assumed that the acquisition of dynamic power would be at the point of pressure and increase in the space under the piston of the leg under forced loading. Based on the experimental studies carried out, an assessment was made with the assumptions of the methodology adopted. The results of the theoretical analysis showed consistency with the experimental results.
... Many scholars contributed much to the first type of models. Singh [7,8] established a ground subsidence prediction model based on the elastic-plastic theory and field observation data. Liu et al. [9,10] combined the layered elastic slate controlling theory and stochastic medium theory to build the prediction model. ...
In the process of coal mining, when the buried depth is large and the loose layer is thick, the ground subsidence tends to be abnormal, thus causing great damage to the surface ecological environment. In order to reveal the mechanism of mining ground subsidence under ultrathick loose layer, taking 1305 working face of a mine as the background, the law of mining ground subsidence under ultrathick loose layer was analyzed through field measurement. The law of bedrock subsidence is analyzed by similar simulation test, and the role of ultrathick loose layer in bedrock subsidence is quantitatively analyzed. The hydrophobic settlement model of ultrathick loose layer is established by settlement theory calculation, and the law of ground subsidence caused by hydrophobic of ultrathick loose layer is analyzed. The results show that the ground subsidence is mainly composed of bedrock subsidence and hydrophobic settlement of ultrathick loose layer. The maximum ground subsidence measured in the field is 4.201 m, the bedrock surface subsidence obtained by the simulation test of similar materials is 3.552 m, and the subsidence of ultrathick loose layer obtained by hydrophobic settlement analysis is 0.58 m. Adding the subsidence of bedrock surface and the subsidence of ultrathick loose layer, the ground subsidence is 4.132 m. It is in good agreement with the total ground subsidence measured in the field, which verifies the rationality that the ground subsidence mainly includes bedrock subsidence and hydrophobic settlement of ultrathick loose layer.
... Stress meters are installed for observation of induced stress, auto warning tell tales (AWTTs) and single height tell tales (SHTTs) are installed for observation of roof sagging and instrumented roof bolts to record load developing over breaker-line supports. Experiences of working under varying Indian geo-mining conditions (Singh and Singh, 1999) helped in selection of these instruments for the roof sagging study in different panels. These instruments are installed at judicious location in a panel in order to monitor strata movement phenomenon. ...
... Overlying strata gets time to separate during slower rate of extraction, which creates strata control issues (Singh and Singh 1999), especially under weak and laminated roof strata. Faster rate of extraction by the CM proved to be a panacea for the depillaring operation at this mine. ...
A fully mechanised mining method using continuous miner (CM) for pillar extraction in single-pass is introduced in the year 2010 at Pinoura Mine of South Eastern Coalfields Limited, Bilaspur in India. Overall mining cycle time is reduced by single-pass pillar extraction as it does not require drivage of split galleries in pillars and support installation for such galleries. Further, inherent technical abilities of the deployed CM for faster cutting and quad-bolter for supporting, helped in faster recovery of pillars without creating any strata control issues. Rate of face advance varied between 5-15m/day with an average of 8m/day. Field observations found that CM based single-pass extraction is capable in dealing with the strata control issues during depillaring under weak and laminated (incompetent in nature) roof layers having rock mass rating value around 42. A total of eleven panels, have been depillared under the weak and laminated geology, ranging depth of cover from 59 to 149m in different panels of the mine. During field investigations in these panels, a maximum of 2.89MPa induced vertical stress is recorded and influence of caved roof over underground mining structures is observed up to 15m in the out-bye from the goaf edge. This paper deals with estimation of snook size and limiting roof movement value based on numerical simulation and field studies during the single-pass extraction below the incompetent geological formations.
... e majority of high-yield Chinese coal mines have thick coal seams, as the movement of overlying strata throughout mining in such mines has been a focus of research and has been thoroughly and extensively studied. Ju and Xu [31] studied the structural characteristics of key strata and the behavior of a fully mechanized longwall face with 7.0 m height chocks; furthermore, the behavior of both support systems and overlying strata was analyzed during sublevel caving of a thick coal seam [32]. Ma et al. [33] studied the deformation characteristics of and established mechanical model for overlying stratum deformation during backfilling with fully mechanized and retaining roadways along the gob area. ...
The basis of traditional ground pressure and strata control techniques is the key strata theory, wherein the position of the key stratum can easily be determined for coal seams with regular thickness and without goaf. However, in the case of mining ultrathick coal seams underneath goaf, the traditional methods used for the calculation of key stratum position need to be improved in order to account for the additional coal seam thickness and the presence of an upper goaf. This study analyzed the failure height and collapse characteristics of overlying strata during excavation for determining the structure of the failed overlying strata. The results indicate that the intercalation and overlying strata gradually evolve into a large “arch structure” and a small “arch structure” during longwall mining, respectively. A mechanical model of the bearing characteristics of the interlayer key strata structure was established according to the structure of the intercalation rock layer, which is a hinged block structure. The results of the model indicate that the maximum principal stress occurs when the key strata portion of the arch structure bears the overlying load. Consequently, the movement and position of the interlayer key strata can be evaluated throughout the mining process of the ultrathick coal seams underneath goaf. This method was used to determine the position of interlayer key stratum of overlying strata in Xiegou coal mine. And the results agree with that of the engineering practice. The results are significant to determine the key strata position during ultrathick coal seam underneath goaf longwall mining.
... The water-cement ratio is 1:1. According to the geometric parameters and the physical and mechanical indexes of the original rock combined with the selected geometric similarity ratio and strength similarity ratio, the amounts of various materials used in each rock stratum in the model and the thickness of the model layers are calculated (Singh and Singh 1999). The composition parameters of the specific model are shown in Table 4. ...
A study of the deformation of the surrounding rock and coal pillars near a fault under the influence of mining is conducted on a physical model for the design of coal pillars to support and maintain the roofs of adjacent fault roadways. This research is based on the 15101 mining face in the Baiyangling Coal Mine, Shanxi, China, and uses simulation tests similar to digital speckle test technology to analyse the displacement, strain and vertical stress fields of surrounding rocks near faults to determine the influence of the coal pillar width. The results are as follows. The surrounding rock of the roadway roof fails to form a balance hinge for the massive rock mass. The vertical displacement, vertical strain and other deformation of the surrounding rock near the fault increase steeply as the coal pillar width decreases. The steep increase in deformation corresponds to a coal pillar width of 10 m. When the coal pillar width is 7.5 m, the pressure on the surrounding rock near the footwall of the fault suddenly increases, while the pressure on the hanging wall near the fault increases by only 0.35 MPa. The stress of the rock mass of the hanging wall is not completely shielded by the fault, and part of the load disturbance is still transmitted to the hanging wall via friction. The width of the fault coal pillars at the 15101 working face is determined to be 7.5 m, and the monitoring data verify the rationality of the fault coal pillars.
... Wang and Pang [8,9] studied the process of roof stratum breakdown instability and dynamic evolution of hydraulic support load, putting forward the "stiffness-strength-stability coupling model" between hydraulic support and surrounding rock, which provides an approach for dynamic analysis and prediction of hydraulic support load on longwall mining face. Many other scholars [10][11][12][13][14][15][16][17][18][19] analyzes the fracture instability process of the overburden on working face in various mining conditions, proposes a method for calculating the suitable working resistance of the hydraulic support, and reveals the relationship between surrounding rock fracture instability and hydraulic support load. ...
Hydraulic support plays a key role in ground control of longwall mining. The smart prediction methods of support load are important for achieving intelligent mining. In this paper, the hydraulic support load data is decomposed into trend term, cycle term, and residual term, and it is found that the data has clear trend and period features, which can be called time series data. Based on the autoregression theory and weighted moving average method, the time series model is built to analyze the load data and predict its evolution trend, and the prediction accuracy of the sliding window model, ARIMA (Autoregressive Integrated Moving Average) model, and SARIMA (Seasonal Autoregressive Integrated Moving Average) model to the hydraulic support load under different parameters are evaluated, respectively. The results of single-point and multipoint prediction test with various sliding window values indicate that the sliding window method has no advantage in predicting the trend of the support load. The ARIMA model shows a better short-term trend prediction than the sliding window model. To some extent, increasing the length of the autoregressive term can improve the long-term prediction accuracy of the model, but it also increases the sensitivity of the model to support load fluctuation, and it is still difficult to predict the load trend in one support cycle. The SARIMA model has better prediction results than the sliding window model and the ARIMA model, which reveals the load evolution trend accurately during the whole support cycle. However, there are many external factors affecting the support load, such as overburden properties, hydraulic support moving speed, and worker’s operation. The smarter model of SARIMA considering these factors should be developed to be more suitable in predicting the hydraulic support load.
... Weak roof rock (e.g. laminated with RMR = 40-45) is present at the Pinoura Mine and creates uncertainties during development and depillaring, unless a favourable ground reaction can occur during depillaring [4,5] for controlled caving in goaf. In the occurrence of the ladder, coupled with shallow depth (i.e. ...
... Stress metres, single-height tell tales (SHTT), autowarning tell tales (AWTT) and instrumented roof bolts were installed in the panel so that the strata movement could be monitored during depillaring. Selection of these instruments was based on the experiences gained during strata monitoring at several depillaring panels in Indian coal mines [4]. In addition to measurement, efforts were made to monitor the caving behaviour. ...
This article offers an examination of a retreat mining method conducted at the Pinoura Mine in India from 2010 to 2017. The method is atypical for coal mines of India’s coalfields. The method executes depillaring in a single pass and does not require the formation of galleries and support installation in splits, thus, reducing the cycle time. A variety of observations are discussed throughout this work and emphasis is placed on field measurements and depillaring under weak roof (RMR = 40–45). This paper discusses design techniques, specifically the estimation of the snook (remnant pillar) size, and important practical observations after the fact. The execution of this method was eventually conducted in eleven panels.
