Roadway Backfill Research Articles

Classification and Design of Backfill Coal Mining Systems Based on Typical Engineering Cases

Backfill coal mining technology has drawn widespread attention due to its benefits of “controlling surface deformation and subsidence, reducing mining-induced disturbance in the stope, and recycling solid mine wastes”. However, the backfill coal mining technology is still progressing slowly in China. The geological environment of China’s mining areas is complex and highly diversified, and backfill coal mining is expected to fulfill different goals in a wide range of engineering scenarios. These facts explain the poor reproducibility of backfill coal mining projects. This study reviews the existing backfill coal mining systems in China. Based on findings from a survey of engineering cases, we summarize five types of new backfill coal mining methods classified by deployment style; namely, borehole grouting backfill, roadway backfill, borehole–roadway backfill, in situ backfill, and roadway-in-situ backfill. A total of 15 backfill coal mining methods falling into the above five categories are described. An engineering design workflow for backfill coal mining consisting of five steps is proposed; namely, identifying the targets of backfill, analyzing the feasibility of deploying the backfill system, comparing the engineering quantities of different engineering schemes, estimating the economic efficiency of backfill, and backfill performance tracking and monitoring. Real cases of backfill engineering design are analyzed to inform the fast and reasonable design of backfill strategy for specific working faces in certain coal mines.

Experimental study on roadway backfill mining of paste-like material

Roadway backfilling mining is vital for ensuring the safety of surface buildings while mining coal underneath buildings, railways, and water bodies. The technique and backfilling material, however, need to be optimized to ensure the long-term safety of the project and surface structures. Using a mine as the engineering background, reasonable strength, an optimal ratio of backfilling materials was determined by using numerical simulation and indoor testing. Displacement characteristics of the surface were analyzed after the roadway backfilling mining technology was completed using similar simulations. The research results showed that the overburden strata could be effectively controlled when the strength of the backfill material is 0.6 to 0.8 times that of the coal. The optimal ratio of the paste-like material is 80% fly ash, 5% mineral powder, 15% quicklime, 4% gypsum (external doping), 1% activator A1, and 0.02% expansion agent. The subsidence of the overburden strata in a similar model was characterized by two rapid sinking stages, with a final surface maximum horizontal deformation value of 0.011 mm/m and a maximum curvature value of 0.043. After performing an industrial test on a working face, the maximum subsidence of the surface of the filling area was 289 mm, indicating that the surface structures were within the range of I level damage.

Stability of Coal Pillar and Roof Movement Characteristics in Roadway Backfill Mining

In order to explore the stability of coal pillar and the characteristics of roof movement during the process of roadway backfill mining (RBM), the 301 backfilling test working face of Ordos Chahasu coal mine is taken as the background. Based on the expansive pressure arch theory, the evolution process of the stope expansive pressure arch in RBM is studied; by establishing a mechanical model for the stability of coal pillars, the interactions between the height, width, and the maximum number of branches are obtained. When the width and height of the branch are both 5 m, the optimal number of the branches is obtained. Then, by establishing a mechanical model for the subsidence of the immediate roof, the process of the immediate roof subsidence is divided into three stages, namely, the formation stage of the local pressure arch, the merge stage of the pressure arch, and the expansion stage of the pressure arch. In addition, using the numerical method, the alternate bearing process of coal pillars and filling bodies and the change of the maximum supporting stress are studied, and the evolution of the pressure arch bearing structure above the stope and the staged subsidence characteristics of the roof are analyzed. The on-site test showed that the coal pillar has a good stability during the mining process. The maximum stress of the coal pillar is 16.5 MPa, and the maximum stress of the filling body is 9 MPa. The maximum settlement of the immediate roof is 102 mm, indicating that the roof control effect is good. This research will play an important role on engineering practice.

Study on Overburden Stability and Development Height of Water Flowing Fractured Zone in Roadway Mining with Cemented Backfill

In order to explore the stability of overburden rock and the development height of water flowing fractured zone in roadway filling mining, based on the movement and deformation mechanism of overburden rock, the mechanical analysis of overburden stability and failure was carried out, and the mechanical model of main roof rock beam was established, and the ultimate span and limit deflection of rock beam fracture were deduced. Combined with the mechanical model of the main roof fractured rock, the basis for the judgment of overburden failure developing to fractured zone is given in this paper. Taking a coal mine roadway backfill under water-bearing stratum as an example, based on the equivalent mining height, the theoretical calculation and analysis are carried out on the stability of overburden rock and the height of water flowing fractured zone. The reliability of the theoretical analysis is verified compared with the empirical formula and the numerical simulation results. The results showed that the water flowing fractured zone developed to the bottom of no. 7 glutenite, with a height of 32.5 m, slightly less than the calculation result of the empirical formula. The thickness of the waterproof coal pillar was 39.8 m, which was much less than the distance from the aquifer to the coal seam and can be mined safely.

The segmental subsidence structure with immediate roof of gob side entry retaining in backfill mining

When gob side entry retaining is carried out in backfill mining, the roof will show different subsidence morphology due to the difference of compactness and supporting force of the backfill body at different positions. This paper analyzed the immediate roof subsidence structure under two extreme conditions, constructed the roof segmented subsidence structure and the mechanical model of roadside backfill body, and used FLAC3D software to investigate the roof migration and the force law of the roadside backfill body under the conditions of different goaf backfilled rates, different width and strength of roadside backfill body. Finally, the backfill practice of a mine in Shandong Province of China is taken as an example for analysis. The results show that the segmented subsidence structure of the immediate roof is related to the mechanical properties of the roadside backfill body and the goaf backfill body. When the backfilled rate of goaf decreases from 95% to 70%, the width of roadside backfill body decreases from 5 m to 1 m, and the elastic modulus decreases from 10 GPa to 0.5 GPa, the greater difference in the subsidence and inclination of the immediate roof on both sides of the roadside backfill body is, the more obvious the segmented subsidence structure characteristics of the immediate roof are, and the greater force on the roadside backfill body will be, the more unfavorable it is to maintain the stability of the roadway surrounding rock and the roadway backfill body. Therefore, when gob side entry retaining is carried out in backfill mining, the surrounding rock structure and the force on roadside backfill body should be considered comprehensively.

Destabilization mechanism and energy evolution of coal pillar in rockburst disaster

Rockburst disaster caused by coal pillar poses a serious threat to safety production in advanced mining technology, such as the technology of gob-side entry driving, which is employed to develop the mining rate of coal. In order to reveal the rockburst mechanism of coal pillar in mines from the view of energy evolution, the bursting liability of coal specimen is tested in a mine, where a rockburst of coal pillar happens in the third cycle of 6 # roadway excavation. The rockburst mechanism of the coal pillar is analyzed theoretically and simulated by FLAC. On this basis, an evaluation standard of energy density is proposed and realized for risk assessment of rockburst. Then, numerical models with two types are established, and the trend characteristics of energy density factor and vertical stress in two scheme types are studied. Based on research results obtained, the weak impact tendency of coal specimen and the moderate impact danger level of mining face are internal causes for rockburst disaster in roadway backfilling mining; meanwhile, the maximum value 51,351 J/m4 of energy density factor in coal pillar of 6 # roadway in un-backfilling mining scheme is 3.33 times that of 15,403 J/m4 in backfilling mining scheme, and the rockburst disaster happens in the 6 # roadway excavation when elastic deformation energy reserved in coal pillar is released suddenly. The research results could provide a theoretical reference for the prevention and control of the rockburst disaster in mining engineering.

Study on Numerical Simulation of Roadway Backfill under Freeway Based on FLAC3D

Based on the paste-like roadway backfill technology in the study of coal mining under the freeway in Tang’an Mine, the mining scheme of coal under the freeway is described. In order to grasp the change law of the stress and damage degree of coal pillars and surrounding rocks during the coal mining process of roadway backfill, analyze the stability of coal pillars and the amount of roof subsidence, using FLAC3D numerical simulation method, select the width of coal pillar elastic plastic zone, the vertical stress of the column and the vertical displacement of the roof are used as indicators. The influence of the 15m temporary coal pillar width on the stability of the coal pillar, the stress distribution of the surrounding rock and the sinking of the roof under the mining method are studied to verify the feasibility of the mining scheme.

Automatic Roadway Backfilling of Caving Gangue for Cutting Roofs by Combined Support on Gob-Side Entry Retaining with No-Pillars: A Case Study

Automatic roadways on gob-side entry retaining with no-pillars are used for longwall mining technology. The mining technology with no-pillars can recover coal pillar resources and reduce the amount and cost of roadway excavations. Automatic roadway technology for cutting roofs by combined support on gob-side entry retaining with no-pillars is adopted for the condition of thick immediate roof and medium-thick coal seam mining, cutting off the immediate roof and the main roof on the gob by combined support. The fractured roof forms gangue blocks to fill the gob and loads the overlying strata. The gangue control system is placed on the roadside, which controls the caving gangue to form a gangue rib. In this paper, the viewpoints and key technologies (the roof-cutting technology, the reinforcement and support technology, the gangue rib control technology, and the auxiliary support technology) of automatic roadway technology for cutting roofs by combined support on the gob-side entry retaining with no-pillars are introduced. Furthermore, the formation and control process are explained. The numerical simulation is used to simulate and analyze the roof hanging and the roof cutting structures. In addition, a field engineering test is performed. The field test shows that automatic roadway technology for cutting roofs by combined support on gob-side entry retaining with no-pillars is feasible. This process uses construction techniques and technologies to meet on-site production needs. The combined support has high resistance strength and is shrinkable. In engineering applications, the combined support has a low damage rate. The deformation of the automatic roadway with gob-side entry retaining is small, and the control effect is significant.

Roadway Backfill Mining with Super-High-Water Material to Protect Surface Buildings: A Case Study

As coal resources trapped under surface buildings in the Wangtaipu coal mine area impede the efficient mining of coal seams and constrain the sustainable development of coal mines, a super-high-water roadway backfill mining technique for preventing building damage was adopted. According to the control principle and theoretical calculations, an engineering design was established including the reasonable width of segment coal pillars in the working face and technical parameter design. The monitoring results after the implementation of the scheme showed that building deformation was controlled within grade I, protecting the surface buildings. A reasonable roadway design parameter was achieved, with a surface subsidence of 27 mm and horizontal deformation of 0.3 mm/m, indicating that it can ensure the safety of surface buildings from the State Bureau of Coal Industry. The practical trial can provide a reference for the extraction of coal resources under similar conditions and is vital for the sustainable development of the mining industry and economic growth.

Application of Roadway Backfill Mining in Water-Conservation Coal Mining: A Case Study in Northern Shaanxi, China

The mining induced subsidence and strata deformation are likely to affect the stability of the aquiclude, resulting in loss of water resources in the mining area. In order to reduce the disturbance of coal mining to the overlying strata and to preserve the water resources in the coal mining area, the roadway backfill mining (RBM) method was trialed in Yuyang coal mine in Northern Shaanxi, China. Based on pressure arch theory and ultimate strength theory, a mechanical model was developed to analyze the stability of coal pillars. Then the maximum number of vacant roadways between the mining face and the backfilling face was determined according to the stability of coal pillar and filling body. The method to calculate aquiclude subsidence and deformation was also proposed. Furthermore, as indicated by FLAC3D numerical simulations, the maximum tensile stress subjected by the aquiclude was 0.14 MPa, which is smaller than its tensile strength; the horizontal deformation was 0.24 mm/m, which is also smaller than the critical deformation of failure. Field monitoring data demonstrated a maximum of 2.76 m groundwater level drop in the mining area after mining. The groundwater level was determined to be 4.45~10.83 m below surface, ensuring the normal growth of surface vegetation and realizing the water-conservation coal mining (WCCM).

Wongawilli roadway backfilling coal mining method - a case study in Wangtaipu coal mine

The current backfilling coal mining methods still have many limitations, such as lack of filling time and filling space and poor coordination between filling time and filling space. On the basis, this paper proposed the Wongawilli roadway backfilling coal mining method (WRBCM). As a pattern of 'backfilling while mining', WRBCM gives fully play to the advantages of the Wongawilli mining method and the backfilling mining method. The research results have been put into practice in Wangtaipu coal mine. As the recovery ratio of coal resources in the panel reached 96.8%, the values of surface deformation were smaller than the indicators for building damage grade I in China. WRBCM also implements the safe and efficient coal mining deposited under 'buildings, railways and water bodies'. [Received: June 20, 2016; Accepted: January 28, 2017]

The Influence of the Backfilling Roadway Driving Sequence on the Rockburst Risk of a Coal Pillar Based on an Energy Density Criterion

The rockburst hazard has always been an important issue affecting the safety production of coal mines in China. The unreasonable sequencing of roadway driving can lead to the dynamic instability of coal pillars, which subsequently causes rockburst accidents in roadway backfilling mining engineering and poses a serious threat to the safety of the mines. Roadway backfilling mining technology is an effective approach with which to mine corner residual coal resources under buildings, railways, and rivers. An energy density criterion is established and programmed with FISH language using numerical analysis software for the rockburst risk evaluation of coal pillars. On this basis, a numerical simulation model is established based on four scheme types, namely, the sequential mining, one-roadway interval mining, two-roadway interval mining, and three-roadway interval mining schemes. The influence of the backfilling roadway driving sequence on coal pillar stability is investigated, and the change law of vertical stress and energy density factor of coal pillars in different driving sequences in roadway backfilling mining technology are analyzed. According to the research results, the maximum energy density factor value of 21,172 J/m4 for coal pillars in one-roadway interval mining is the lowest among the different schemes. Therefore, the one-roadway interval mining scheme is the optimal choice in roadway backfilling mining technology. The results can be treated as an important basis for the prevention and treatment of coal pillar instability and rockburst in roadway backfilling mining technology.

Roadway Backfill Coal Mining to Preserve Surface Water in Western China

In China’s western eco-environmental area, water resources are very valuable. Longwall mining can cause these shallow water resources to leak, so most mines in this area use room-and pillar mining to prevent water inrush and protect water resources. However, over time, coal pillars can become unstable and collapse. To protect water resources and improve coal recovery, roadway backfill coal mining was proposed for the Ershike Coal Mine. The mechanical properties of backfill materials with different ratios of aeolian sand, fly ash, and Portland cement were studied in the laboratory to obtain an optimal ratio. Also, a 2-D physical simulation model was established to explore the development of mining-induced fractures and to conduct a stability analysis of aquiclude strata. The results can be used to guide coal mining in the study area and to protect local water resources.

Stability analysis of surrounding rock and pillar design in roadway backfill mining method

Over the past few decades, the low recovery of resource coupled with the strong strata behavior has plagued the development of mines in Western China. To address these issues, an emerging and innovative technology- roadway backfill mining method was proposed in this paper on the basis of the compressive properties of backfill materials. A rational composition for backfill materials is obtained and the roadway layout and the backfill mining technology of this method are presented. Once placed, the backfill materials together with the barrier pillar have to satisfy certain mechanical stability requirement to ensure a safe underground working environment. In this respect, a mechanical model of roadway backfill mining method was developed using statics analysis. Formulas for predicting roof subsidence above mined out area and the stress distribution in barrier pillar are obtained. Furthermore, an instability criterion of coal pillars is proposed. Combined with the specific geological and mining conditions of 3101 working face in Changxing Coal Mine, the current study showed that the width of backfill mining roadway to be 7.0 m, the width of unexploited coal pillar to be not less than 3.0 m, and the elastic foundation coefficient of backfill body to be not less than 1.5 × 107 N/m3.

Roadway backfill method to prevent geohazards induced by room and pillar mining: a case study in Changxing coal mine, China

Abstract. Coal mines in the western areas of China experience low mining rates and induce many geohazards when using the room and pillar mining method. In this research, we proposed a roadway backfill method during longwall mining to target these problems. We tested the mechanical properties of the backfill materials to determine a reasonable ratio of backfill materials for the driving roadway during longwall mining. We also introduced the roadway layout and the backfill mining technique required for this method. Based on the effects of the abutment stress from a single roadway driving task, we designed the distance between roadways and a driving and filling sequence for multiple-roadway driving. By doing so, we found the movement characteristics of the strata with quadratic stabilization for backfill mining during roadway driving. Based on this research, the driving and filling sequence of the 3101 working face in Changxing coal mine was optimized to avoid the superimposed influence of mining-induced stress. According to the analysis of the surface monitoring data, the accumulated maximum subsidence is 15 mm and the maximum horizontal deformation is 0.8 mm m−1, which indicated that the ground basically had no obvious deformation after the implementation of the roadway backfill method at 3101 working face.

Research and application of roadway backfill coal mining technology in western coal mining area

In China’s western coal mining area, the traditional room mining technology is facing coal pillar instability, mine earthquake, large-area roof subsidence in the goaf, surface subsidence, water and soil loss, vegetation deterioration, and other environmental problems. To solve the aforementioned problems and to improve coal recovery, the roadway backfill coal mining (RBCM) method was proposed as a solution and its technical principle and key equipment were presented in this paper. In addition, the microstructure and mechanical behavior (strain-stress relation in confined compressive test) of aeolian sand and loess backfill materials were studied for a rational backfill design for underground mines. Further, coal pillar stress, plastic zone change, and surface deformation of the RBCM schemes were studied using the FLAC3D numerical simulation software, and a reasonable mining scheme of “mining 7 m and leaving 3 m” was determined. The engineering application in Changxing Coal Mine shows that the RBCM method with loess and aeolian sand as backfill materials allows a stable recovery of coal pillars with a recovery ratio of more than 70 %. The maximum accumulated surface subsidence and the maximum horizontal deformation were measured to be 15 mm and 0.8 mm/m respectively, indicating that the targeted backfilling effect can help protect the environment and also control surface subsidence.

The Influence of Roadway Backfill on Bursting Liability and Strength of Coal Pillar by Numerical Investigation

The observations developed in this paper are intended to provide researchers and mining engineers with initial estimate of the burst risk of coal pillar, as the study of bursting liability is of importance in forecasting and preventing the bump of coal pillar. Bursting Energy Index (WCF) is selected in this study to describe the influence of roadway backfill on bursting liability and strength of coal pillar. For the general study undertaken in this paper, a formula derived from the combined South African and Australian databases was used to analyze the bursting liability of coal pillar. Based on over 60 numerical models of various pillar height and backfill percentage, a series of average axial stress-strain curve of 5∼10m coal pillar with roadway backfill is attained. Modelling results suggest that the pillar strength will increase with increasing roadway backfill. It also can be seen that the Bursting Energy Index (WCF) will decrease with increasing roadway backfill while the percentage of decrease amount of WCF will increase versus the percentage of roadway backfill. The increase in pillar strength is greater for the tall pillars than squat pillars. It is also observed that the central portion of coal pillar defined as elastic pillar core plays a significant role on loading capacity of pillars, increasing coal pillar strength and decreasing Bursting Energy Index (WCF).

The influence of roadway backfill on the coal pillar strength by numericalinvestigation

Stability of coal pillars and immediate rock mass is of importance in the bord and pillar extraction method underlying critical surface infrastructure. This paper describes the influence of roadway backfill on the coal pillar stability. Based on over 120 numerical models of various pillar height and backfill percentage, it is indicated that the pillar strength will increase with increasing roadway backfill, while the increase in pillar strength is greater for tall pillars than squat pillars for both cohesive and non-cohesive backfill. Modelling suggests that cohesive backfill is more effective in increasing both peak and post-peak pillar strength than non-cohesive backfill. It is also observed that the post-peak response will change from softening to hardening at a certain percentage of either cohesive or non-cohesive backfill.

Cracking of Concrete Decks and Other Problems with Integral-Type Bridges

During the continuing evolution of integral and semi-integral bridges, some problems have been encountered by engineers not familiar with the peculiarities of these structures, or with standard bridge practices that have been developed over many decades for the achievement of trouble-free bridge construction. Problems that occasionally confront transportation engineers include early-age cracking of concrete bridge decks; erosion of roadway shoulders, embankments, and backfill adjacent to bridge abutments; casting connections between moving members; and stage construction errors. Those aspects of integral-type bridge construction that deserve particular care and attention are examined and discussed. Presumably, a better awareness of such background will aid transportation engineers to achieve the economy, quality, and outstanding durability that integral-type bridges make possible.

886268 Roadway backfilling with foam grout — method limitations (In German and English) : Pier, J; Pahl, M H Gluckauf V124, NJ], 9 June 1988, P606–616 (German), P316–320 (English)

886268 Roadway backfilling with foam grout — method limitations (In German and English) : Pier, J; Pahl, M H Gluckauf V124, NJ], 9 June 1988, P606–616 (German), P316–320 (English)