J. Cent. South Univ. (2020) 27: 3103-3117

DOI: https://doi.org/10.1007/s11771-020-4532-6

Dynamic disaster control of backfill mining under thick magmatic rock in one side goaf: A case study

XUE Yan-chao(薛彦超)^{1, 2}, XU Tao(徐涛)^{1, 2}, WASANTHA P L P³,YANG Tian-hong(杨天鸿)^{1, 2}, FU Teng-fei(付腾飞)^{1, 2}

1. Center for Rock Instability and Seismicity Research, Northeastern University, Shenyang 110819, China;

2. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China;

3. College of Engineering and Science, Victoria University, Melbourne, Australia

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract: In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock (TMR), a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed. The simulation results were then compared with field monitoring data. The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects, i.e., displacement field, stress field and energy field. The results show that in comparison to the full caving mining method, the bearing capacity of the goaf after backfilling was enhanced, the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body, and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture. Before TMR fracture, the subsidence displacement of TMR was reduced by 65.3%, the front abutment stress of panel decreased by 9.4% on average and the high energy concentration zone around panel was also significantly reduced. Overall, the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.

Key words: backfill mining; thick magmatic rock; one side goaf; dynamic disaster; numerical simulation

Cite this article as: XUE Yan-chao, XU Tao, WASANTHA P L P, YANG Tian-hong, FU Teng-fei. Dynamic disaster control of backfill mining under thick magmatic rock in one side goaf: A case study [J]. Journal of Central South University, 2020, 27(9): 3103-3117. DOI: https://doi.org/10.1007/s11771-020-4532-6.

1 Introduction

The control of dynamic disasters due to the extraction of underground coal seams is a significant challenge in underground mining engineering [1-6]. This task is further compounded by the growing trend for coal to be extracted under special geological conditions such as thick magmatic rocks (TMRs) known as key strata. During the high-intensity underground coal mining, the sudden destruction of overlying TMRs on the roof of panel brings a series of dynamic disaster issues such as rock burst, surface subsidence [7-12]. From 2013 to 2017, there were 32 roof casualty accidents in China, accounting for 19% of coal mine casualty, and 116 roof deaths, accounting for 9%. The severity is second only to gas accidents (Figure 1). Therefore, controlling the dynamic disaster caused by the movement of roof overlying the strata to ensure the safety of coal mines has become an important issue.

Figure 1 Statistics of coal mine casualty accidents in China from 2013 to 2017:

The backfill mining method has been widely used since it can maximize the recovery of mineral resources and protect the underground and surface environment [14-18]. The dynamic disasters under TMRs are mainly caused by the special laws of rock movement and breaking during mining and the special stress field morphology [19, 20]. Numerous studies in the literature have investigated safe mining procedures of coal resources under TMRs. Due to the inaccessibility of the waste area, some researchers put forward assumptions to understand the stress and deformation state of the caved zone on the basis of indirect prediction methods, rather than in-situ measurement. YAVUZ [21] assumed that the goaf material could be compacted to its original volume under infinite pressure, and proposed an equation describing the stress-strain behavior of the filling material. Through the use of a mechanical model, ZHANG et al [22] determined the deformation characteristics of the hard roof and the energy evolution of the panel for different roof-controlled filling rates, and revealed the effectiveness of solid filling in reducing the energy storage of coal seams. The probability integral method was used to estimate surface subsidence after solid backfill mining based on strata movement after backfill mining [23-25]. Experimental tests have also been conducted on deformation characteristics of mining-induced overlying strata. Backfill structure is strongly affected by the external coupling environment (thermal, hydraulic, mechanical, and chemical), and GHIRIAN et al [26] carried out an experiment with insulated-undrained high columns to understand these coupling environmental factors. CHEN et al [27] investigated the strength characteristics of cement paste backfill in a similar stope model, and explained the strength difference of backfill under in situ and laboratory conditions from microstructure to macrostructure and LAN et al [28] proposed a new controlled low-strength filling material for the copper slag from a mine in Africa, and orthogonal test method and data visualization were used in the experiment to study the factors affecting the structural strength of the material.

In recent years, due to the advantages of low cost and good repeatability, numerical simulation is increasingly used for backfill-related research. For example, the influence of particle size distribution of cemented backfill [29, 30], solid filling rate [22, 31], and filling materials of different constitutive models [32, 33] on overburden movement and stress distribution in backfill mining has been investigated using numerical simulations. However, these previous studies have mostly focused on backfill mining under general geological conditions (single face mining with relatively small main roof thickness), and there have been only few studies on the dynamic disaster control effect of backfill mining under the cover of TMR, despite mining accidents related to the deformation of the TMR occur frequently.

The purpose of the present paper is to present a practical model considering the permanent volume change of backfill materials and to discuss its control effect on mine dynamic disasters. The software FLAC^3D (3-dimensionl Fast Lagrangian Analysis of Continua) was used to establish a three-dimensional numerical model of two mining methods (caving method and backfill method) based on the special geological mining conditions of overlying TMR in panel of one side goaf in Yangliu Coal mine. Then the Tecplot software was used for post-processing analyses of the model calculation results. The dynamic disaster control effects of backfill mining and the full caving mining were comparatively analyzed from displacement field, stress field and energy field. The results of the present paper are expected to be of great importance for deep understanding of the effect of backfill mining on dynamic disaster control.

2 Geological setting

Yangliu Coal Mine is located in Huaibei city, Anhui Province, south of China. It measures 3-9 km in the east-west direction and 9 km in the south-north direction, with an area of 60.4 km². The shallow part is closer to the north-south direction, and the structure is a monoclinic sloping eastward, with a formation inclination of 15-20°; the deep part contains mostly first-order folds, and the folds extend eastward, and the formation dip angle is 5-10°. Through drilling, it is revealed that the underlying strata of Cenozoic loose layer from top to bottom are upper Shihezi Formation, Lower Shihezi Formation and Shanxi Formation of Permian system, Taiyuan Formation and Benxi Formation of Carboniferous system, and Majiagou Formation of Ordovician system. Carboniferous and Permian are all coal bearing strata, and only Permian coal bearing strata are explored in this mine field. Stratigraphic column of 104 mining area in Yangliu Coal Mine has been shown by XUE et al [11]. In the early Yanshanian era, the magma in the deep crust ejected along the Subei fault and invaded the Yangliu coalfield along the Daniujia Fault. The Daniujia Fault, the Daimiao Fault and other connected faults in the Yangliu coalfield controlled the occurrence of magmatic rocks. The intrusive magmatic rocks are characterized by large thickness (tens of meters or even hundreds of meters), high strength (uniaxial compressive strength 87.6-114.8 MPa), and high occurrences of horizons (tens of meters to more than one hundred meters away from the mining coal seam).

The 104 mining area of Yangliu coal mine is mainly composed of #10 coal seam, with a thickness of 0-9.97 m and an average of 3.05 m, belonging to medium to thick coal seams. The floor elevation of panel is from -570 m to -610 m, with dip angles of coal seam ranging from 0° to 5°. The 104 mining area is divided into 8 panels, of which panel number 10414 is the first mining face. After the panel number 10414 is mined, the adjacent panel (panel number 10416) is mined immediately, so that the panel number 10416 is under the stress state of one side goaf [11], which increases the difficulty of mining, and once the overlying TMR breaks and loses its stability, it is easy to cause dynamic disaster accidents.

3 Numerical model

3.1 Double yield constitutive model for backfill

Disaster reduction can be achieved by controlling the movement of rock strata, and the best way to control the movement of TMR is to eliminate its movement space. Combining the mining conditions in the mining area, the measures for controlling dynamic disasters by backfill mining in the goaf are proposed as shown in Figure 2.

Figure 2 Mechanical schematic diagram of backfill mining:

Selecting a reasonable constitutive model is a prerequisite for studying the mechanical properties of engineering materials. The Mohr-Coulomb model is generally used to simulate the yield of geotechnical materials under shear stress. For non-linear materials, the deformation of the backfill is affected by the load and loading stress path, and the stress and strain are obviously non-linear. An elastoplastic model could be adopted for this material. In the model, the strain increment △ε is divided into the elastic part △ε^e and the plastic part △ε^p, and △ε can be expressed as

△ε=△ε^e+△ε^p                                              (1)

Double yield model is an extension of strain softening model. In addition to the shear and tensile failure envelopes in the FLAC^3D strain-softening/ hardening model, it can be used to simulate the irreversible compression deformation. Permanent volume changes are caused by the application of isotropic pressure, which are taken into account by including a volumetric yield surface (or “cap”) in the model [34]. The double yield model is more suitable for backfill materials with lower preconsolidation requirements [35].

In the double yield model, the plastic contributions of shear, tensile, and volumetric yielding are additive, the principal strain increments are [34]

   (2)

The incremental expression of Hooke’s law in terms of principal stress and strain has the form

                  (3)

                  (4)

                   (5)

The shear and tensile yield functions, referred to as f ^s and f ^t, have the form

                   (6)

f ^t=σ^t-σ₃                                         (7)

                           (8)

The volumetric yield function f ^v is defined as

                     (9)

where p_c consists of a vertical line on a plot of shear stress versus mean stress. The hardening behavior of the cap pressure is activated by volumetric plastic strain.

3.2 Numerical model setup

Based on the above analysis and the geological conditions of the panel number 10416 of Yangliu coal mine, a three-dimensional numerical model of 800 m (length)×780 m (width)×288 m (height) was established as shown in Figure 3, which contained 326349 grid nodes and 305760 zones. The Mohr-Coulomb model and double-yield model were adopted in simulating the rock strata and backfill, respectively. The mechanical parameters of rock stratum and backfill are shown in Table 1, where the rock mass properties are based on laboratory testing of rock and backfill. The thickness and strength of the TMR in the model were much higher than those of other strata, which was 70 m, and the distance from the coal seam was 80 m. The buried depth of the simulated coal seam was 600 m and the coal seam inclination was 0°.

The lateral displacement in X and Y directions was constrained in horizontal direction, the bottom was fully constrained, and the top boundary was free. The uniform compressive load applied on the top of the model was 8.8 MPa to simulate the 345 m overburden load. The lateral pressure coefficient (the ratio of horizontal stress to vertical stress) was 0.5, and the horizontal stress was applied as a trapezoidal uniform load, which allowed the applied stresses to vary linearly in the vertical direction.

Figure 3 FLAC^3D numerical model:

Table 1 Model strata and mechanical parameters [11]

3.3 Simulation scheme

The #10 coal was mined in steps along the strike of the coal seam, with a mining height of 6 m and a width of 160 m. In order to eliminate the influence of boundary effect, 200 m and 255 m wide coal pillars were set up along the strike and inclination of the panel. A small coal pillar with a width of 5 m was reserved between I₁ (panel number 10414 in Yangliu coal mine) and I₂ (panel number 10416 in Yangliu coal mine) of the two adjacent panels.

Scheme 1: Panel I₁ was excavated by longwall caving mining method to form mining conditions for one side goaf to prepare for the mining of the next panel I₂.

Scheme 2: After the mining of panel I₁ was completed, two mining methods (backfill mining and caving mining) were used to excavate the adjacent panel I₂. The displacement, stress and energy of coal/rock body of the two mining methods were compared, and the control effect of backfill mining on dynamic disaster was analyzed.

4 Results

4.1 Effects of backfilling on preventing overburden movement

During the mining process of the panel, the overlying strata gradually collapsed, and with the development upwards of the bed separations and fissures, the TMR bottom gradually lost its supporting role and suddenly broke and sank [36]. One of the mechanisms for backfilling to control dynamic disasters under TMRs is that the backfill eliminates the space for further movement of the TMRs and prevents their sudden breaking.

As shown in Figure 4(a), the maximum subsidence of the TMR after longwall caving mining of panel I₁ was only 0.79 m, which was relatively small compared to the mining height of 6 m, indicating that the TMR had not been broken at this time, only bending subsidence movement took place. The displacement of the rock mass at 60 m overlying the TMR is shown in Figure 4(b). The sinking movement was consistent with the TMR due to the control by the underlying TMR. Owing to the excavation of the panel I₁, the adjacent panel I₂ would be in a condition of one side goaf when mining. As the support range at the bottom of the TMR becomes smaller and the bed separation range becomes larger, the TMR is easy to break and settle suddenly in the mining process. When the failure movement of overburden develops to the surface, it could cause land subsidence disaster, and even the destruction of the buildings, river beds and so on.

Figure 5 shows the displacement monitoring data of the surface during the longwall caving mining of panel number 10416. It can be seen from Figure 5 that before November 21, 2012, the surface subsidence displacement and speed were relatively small, and after November 21, the surface subsidence displacement and speed increased sharply. The key stratum theory [36] pointed out that before the TMR fracture, the deformation of the upper strata was small. However, as the key stratum bore the weight of the overlying strata, the failure of the TMR caused the overlying strata to sink, move and deform, and the settlement increased rapidly. Under general geological conditions, as the panel was mined, the movement and deformation of the overlying strata was a continuous development process. However, when mining under TMRs, there were obvious differences,and the movement and deformation were abrupt. When the overhang length of the TMR reached the maximum span, breakage occurred, the overburden movement intensified, and when the destruction movement developed to the surface, the surface movement deformation increased sharply. The surface subsidence monitoring data of panel number 10416 of Yangliu Coal Mine shows that after November 21, the TMR broke and the structure was unstable.

Figure 4 Overburden movement of panel I₁ caving mining:

Figure 5 Change curve of surface subsidence during mining of panel number 10416 (Data taken from [9])

In view of the failure and instability of TMR in Yangliu Coal Mine, we take the measures to control the dynamic disaster by backfill mining. Figure 6 shows the comparison of overburden movement between caving and backfill mining in panel I₂. As shown in Figure 6(a), after the completion of caving mining in panel I₂, the vertical subsidence displacement of TMR rapidly increased to 3.4 m, and the maximum value was 5 m, indicating that the TMR had broken and destabilized. Affected by the breaking of the TMR, the rock mass at 60 m overlying the TMR also drastically subsided as a whole, with the maximum subsidence displacement of 4.94 m, as shown in Figures 6(c) and 7. As the data monitored in Figure 5, when the larger overburden migration develops to the surface, it could also cause the surface to sink sharply and form basins and fractures on the surface [37].

As shown in Figure 6(b), after the completion of backfill mining in panel I₂, the vertical subsidence displacement of TMR was 1.18 m, which was 65.3% lower than that of caving mining by 3.4 m. At this time, due to the active support of the lower backfill, the bending deformation of the TMR was greatly reduced and no fracture movement occurred. As shown in Figures 6(d) and (7), the subsidence amplitude of the rock mass at 60 m above the TMR was also greatly reduced, which proved that the backfill mining method can effectively control the movement of TMR, inhibit the deformation of the rock mass and reduce the risk of accidents such as rockburst, coal and gas outburst, and surface subsidence caused by the fracture of TMR.

4.2 Effects of backfilling on reducing mining stress concentration

Another mechanism for backfilling to control dynamic disasters under TMRs is to reduce the mining stress concentration on the coal/rock body, which is mainly reflected in two aspects: one is that the supporting effect of the backfill on the TMRs effectively shares the load of the coal/rock body and reduces the risk of production in the subsequent panel; the other is that the abutment stress in the subsequent mining activities is reduced under the supporting effect of backfill [20].

Figure 6 Comparison of overburden movement between caving and backfill mining in panel I₂:

Figure 7 Plots of maximum vertical displacement of rock mass at 60 m above TMR with different excavation lengths under two mining methods in panel I₂

Figure 8 shows the comparison of mining stress distribution between caving and backfill mining in several typical mining lengths of panel I₂ with the caving mining on the left and backfill, mining on the right. During caving mining, as shown in Figure 8(a), the maximum stress in front of the panel was 25.67 MPa at an advance of 120 m; the maximum stress was increased to 27.9 MPa at 320 m, reaching the peak stress, as shown in Figure 8(c); at 360 m, the maximum stress was sharply reduced to 23.04 MPa, indicating that the overlying TMR breakage occurred, and the stress accumulated in the coal/rock body was released, as shown in Figure 8(e). After the fracture of TMR, affected by the side goaf, the face end along goaf side was still in high stress state, which was easy to induce dynamic static combination type impact ground pressure under the disturbance of the fracture impact of TMR [36].

Figure 8 Comparison of mining stress distribution between caving and backfill mining in panel I₂:

Figure 9 shows the change of working resistance of hydraulic support during mining of panel number 10416. It can be seen from Figure 9 that from November 15 to 21 (311.7 to 343.7 m), the resistance of the hydraulic support was relatively small. From November 21 to 25 (343.7 to 375.7 m), the support resistance increased significantly, indicating that the TMR was damaged and unstable, resulting in a large area of pressure on the face hydraulic support. After November 25, with the release of stress, the support resistance gradually decreased.

Through the comparison and analysis of the above numerical simulation and field monitoring data, when the panel I₂ (10416) advanced to 343.7 to 375.7 m (360 m in numerical simulation), the TMT broke and lose stability, the working resistance (mining stress) and the settlement of the overburden rock increased sharply. The numerical simulation results were in good agreement with the field monitoring results.

Figure 9 Working resistance curve of hydraulic support in panel number 10416. Redrawn after [9]

During backfill mining, as shown in Figures 8(b) and (d), at 120 and 320 m, the maximum abutment stresses in front of the panel were 23.35 and 25.43 MPa, with a reduction of 9.03% and 8.85%, respectively, compared with the caving mining. As shown in Figure 8(f), the maximum stress was 25.46 MPa at 360 m, with a slight increase compared with that at 320 m, indicating that the TMR was still in a stable state without fracture. In order to show the evolution law of abutment stress in front of the panel, the maximum abutment stress in front of panel with different excavation lengths in two mining methods was plotted, as shown in Figure 10. Before TMR fracture, the abutment stress in front of the panel in the backfill mining was significantly lower than that in the caving mining, with an average reduction of 9.4%, indicating that the backfill shares the load of the coal/rock body and prevents the rapid release of stress caused by TMR fracture.

However, the vertical stress in the goaf generally increased. As shown in Figure 11, relative to caving mining, when backfill mining, the average vertical stress in goaf increased by 2.98 MPa, indicating that the bearing capacity of the goaf after backfilling was enhanced, and the load was shared more, which played a role in reducing the stress concentration in the mining process of the follow-up panel, alleviating the abutment stress of the roadway, and reducing the possibility of dynamic disasters in mining activities [21].

Figure 10 Plots of maximum abutment stress in front of panel I₂ with different excavation lengths in two mining methods

Figure 11 Plots of abutment stress of two mining methods in goaf of panel I₂ at 320 m

4.3 Effects of backfilling on reducing mining energy concentration

Figure 12 shows the comparison of elastic energy distribution between caving and backfill mining in several typical mining lengths of panel I₂, with the caving mining on the left and backfill mining on the right. The change of elastic energy of coal/rock body was consistent with the change trend of mining stress. With the advance of the panel, the elastic energy stored in the coal/rock body increased continuously before the fracture of TMR, from 81.46 kJ/m³ at 120 m to 93.62 kJ/m³ at 320 m, as shown in Figures 12(a) and (c).

When advancing to 360 m, as shown in Figure 12(e), the TMR was structural instability,and the elastic energy of coal/rock body was reduced to 65.41 kJ/m³, which was still in a high energy concentration state. During the energy release process, it may be accompanied by vibration, wall caving, coal and gas outbursts, and other dynamic phenomena.

Figure 12 Comparison of energy distribution between caving and backfill mining in panel I₂:

Figure 13 shows the energy release of microseismic activities during the mining period of panel number 10416. From July to October 2012, the underlying strata of the TMR collapsed periodically, and the bed separations and the fissures developed upward and ended at the bottom of the TMR [9]. Microseismic activities remained at a low level, and the total monthly accumulated energy remained relatively stable. During the stoping period in November, the microseismic energy increased sharply, while total energy decreased in December. The TMR experienced a process from energy accumulation before fracture to energy rapid release after fracture.

Figures 12(b), (d) and (f) show the distribution characteristics of elastic energy of I₂ backfill mining.

Figure 13 Total energy released every month during mining of panel number 10416. Redrawn from [9]

Compared with I₂ caving mining, the energy concentration degree in front of the coal wall was significantly reduced, the area of high energy concentration zone was also reduced, and the energy accumulated in the middle coal pillar was significantly lower than that of caving mining. As shown in Figure 12(b), the maximum elastic energy of coal body in front of panel I₂ was 78.21 kJ/m³ at an advance of 120 m, which was 3.25 kJ/m³ lower than that of caving mining. At 320 m, as shown in Figure 12(d), the maximum value was 91.54 kJ/m³, which was 4.78 kJ/m³ lower than that of caving method, and at 360 m, the energy continued to increase to 93.3 kJ/m³, without rapid energy release caused by TMR fracture. The evolution law of elastic energy in front of panel I₂ with different excavation lengths in two mining methods is shown in Figure 14. In addition, the elastic energy stored in the goaf continued to increase, with a maximum of 2.3 kJ/m³, which was significantly greater than that of the caving mining, indicating that the backfilling can effectively carry the load of the overlying strata and reduce the accumulation of the elastic energy of the coal and rock mass.

5 Discussion

Coal mine dynamic disaster is the process of energy accumulation, transformation and re-release from roof exposure to fracture. The precondition of the TMR-roof-induced dynamic disasters is the stress concentration in the coal and rock mass, which is accompanied by the accumulation of strain energy and the rapid release of energy when the TMR roof breaks [38]. According to the energy type of triggering disaster, the coal mine dynamic disaster can be divided into three types, namely, coal-body-compression, coal-body-bounce, and roof-fracture disasters [22]. However, no matter which type, the key to control the TMR-roof- induced dynamic disasters is to reduce the accumulated strain energy in coal and rock mass and the energy released during roof caving [39-43]. The placement of backfill material directly affects the energy accumulation of the main roof of the backfilling face. Therefore, in the description of filling effect, roof-controlled backfilling rate should be considered, that is, the ratio of filling height to mining height. Depending on the interaction between the roof and the backfill body at different roof-controlled backfilling ratios, ZHANG et al [22] classified the backfilling status as follows: no contact between the backfilled body and the roof before roof caving; contact between the backfilled body and roof before roof caving; no roof caving. In this study, contact between the backfilled body and roof before roof caving was selected. To build on the work presented herein, we consider it is also necessary to consider the other two situations.

Figure 14 Plots of elastic energy in front of Panel I₂ with different excavation lengths in two mining methods

GHIRIAN et al [26] reported a considerable body of experiment work that studied coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) properties of underground paste backfill. These experimental results showed that strongly coupled THMC processes control backfill behavior (unconfined compressive strength, shear strength parameters, microstructural properties etc.), and coupled THMC effects should be taken into account in field conditions to understand backfill behavior where stronger interplay reactions take place. In this study, the control of dynamic disaster under TMR by backfill mining was carried out under constant temperature and humidity. Future research could focus on the influence of the temperature and humidity of the backfill on the prevention and control of dynamic disasters using the model presented herein.

6 Conclusions

Based on the geological mining conditions in the 104 mining area of Yangliu Coal Mine, the mining effects of two different mining schemes were systematically studied using FLAC^3D numerical simulation, and on-site testing data was used to compare and analyze the simulation results. The displacement, stress, and energy fields were compared to analyze the control effect of backfill mining with double-yield material constitutive model on dynamic disaster under TMR in one side goaf. The following conclusions can be drawn:

Under the condition of one side goaf, after the completion of caving mining in panel I₂, the TMR had fracture instability, and the vertical subsidence displacement of the TMR increased rapidly to 3.4 m with a maximum value of 5 m. Affected by the breaking of the TMR, the overburden also subsided rapidly and synchronously. However, after I₂ backfill excavation was completed, the vertical subsidence displacement of TMR was only 1.18 m, which was 65.3% lower than the subsidence displacement of caving mining.

During I₂ caving mining, the abutment stress and elastic energy of the face increased with the increase of mining distance, and reached the maximum value before the TMR was broken. After breaking, the abutment stress and elastic energy decreased rapidly, and the violent release of energy was easy to cause accidents such as rockburst, wall caving and gas outburst. After the fracture of TMR, affected by the side goaf, the face end along goaf side was still in high stress state, which was easy to induce dynamic static combination type impact ground pressure under the disturbance of the fracture impact of TMR.

Stress and energy concentration was prone to occur at the coal/rock body in front of panel. When panel I₂ was mined by backfilling method, the bearing capacity of the goaf was enhanced, the front abutment stress of panel decreased by 9.4% on average and the area of high energy concentration area around panel was also significantly reduced, indicating that the backfilling can effectively carry the load of the overlying strata and reduce the stress and energy accumulated inside the coal/rock body.

Nomenclature

e

Elastic part

p

Plastic part

p^s

Plastic shear strain

p^t

Plastic tensile strain

p^v

Plastic volumetric strain

K_c

Tangential bulk moduli

G_c

Shear moduli

Φ

Angle of internal friction

c

Cohesion

σ^t

Tensile strength

p_c

Cap pressure

Contributors

XU Tao led the project and expanded the manuscript. Initial draft, numerical modeling and analysis were carried out by XUE Yan-chao. YANG Tian-hong also led the project. WASANTHA P L P improved the language and provided valuable suggestions. FU Teng-fei edited the draft of manuscript. All authors contributed to the writing of the manuscript.

Conflict of interest

XUE Yan-chao, XU Tao, WASANTHA P L P, YANG Tian-hong and FU Teng-fei declare that they have no conflict of interest.

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(Edited by HE Yun-bin)

中文导读

一侧采空厚层岩浆岩条件下充填开采对动力灾害的控制：案例研究

摘要：为了研究充填开采对上覆厚层岩浆岩特殊地质开采条件下动力灾害的控制效果，建立了杨柳煤矿工作面一侧采空条件下双屈服充填材料本构模型的三维数值模型，并将数值模拟结果与现场监测数据进行了对比。从位移场、应力场和能量场三个方面分析了垮落开采法和充填开采法的动态灾害控制效果。结果表明，与垮落开采法相比，充填后采空区的承载能力得到了提高，充填开采法能有效地降低煤岩体中积聚的应力和能量，消除了厚层岩浆岩的进一步移动空间，防止了厚层岩浆岩的突然破断。厚层岩浆岩断裂前，其沉降位移减少了65.3%，工作面前支承应力平均降低了9.4%，工作面周围的高能量集中区也明显减少。总的来说，本研究的结果为矿山充填采矿动力灾害的控制提供了深入的见解。

关键词：充填开采；厚层岩浆岩；一侧采空区；动力灾害；数值模拟

Foundation item: Project(2017YFC1503100) supported by the National Key Research and Development Program of China; Projects(51974062, 41672301, 51811530312) supported by the National Natural Science Foundation of China; Project(N180101028) supported by the Fundamental Research Funds for the Central Universities, China

Received date: 2020-06-11; Accepted date: 2020-08-27

Corresponding author: XU Tao, PhD, Professor; Tel: +86-24-83687705; E-mail: xutao@mail.neu.edu.cn; ORCID: https://orcid.org/ 0000-0001-8971-674X