Temporal and spatial evolution mechanism of deformation and failure of lower mining roadway in near residual coal pillar area

Temporal and spatial evolution mechanism of deformation and failure of lower mining roadway in near residual coal pillar area | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Temporal and spatial evolution mechanism of deformation and failure of lower mining roadway in near residual coal pillar area Xiao-He Wang, Jiang-Hao Wang, Qing-Long Yun, Yi-Qing Wang, Jing Wu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3807279/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In order to demonstrate the temporal and spatial evolution mechanism of deformation and failure of the lower mining roadway in the residual coal pillar area during the mining process of close coal seam, this paper takes the close coal seam mining of Tashan Coal Mine of China Coal Group as the research background, adopts the roof borehole and peeping technology to detect the failure situation of the roof surrounding rock of the roadway, and determines the approximate failure area of the roadway surrounding rock. The stress evolution law of roadway surrounding rock and the failure characteristics of plastic zone are studied by theoretical analysis and numerical simulation. The results show that there is a positive correlation between the size of the plastic zone and the deformation of the surrounding rock, that is, the larger the plastic zone, the more severe the deformation of the surrounding rock. The stress concentration area under the residual coal pillar and the new stress field in the mining face are superimposed on each other, resulting in asymmetric deformation and failure in the surrounding rock of the return air roadway, and the shape is approximately "butterfly". The stress on one side of the surrounding rock will be deflected, resulting in a significant difference in stress concentration on both sides of the roadway, and the extension of asymmetry in the plastic zone will also occur, which will lead to the large asymmetric deformation and failure of the surrounding rock of the roadway. Earth and environmental sciences/Solid earth sciences/Mineralogy Physical sciences/Engineering/Civil engineering Short distance coal seam Asymmetric failure Space-time evolution mechanism Non-uniform stress field Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 1 Introduction Nowadays, close-range coal seam mining has gradually become a common way of coal mine production in China. Different from single coal seam mining, close-range coal seam mining will be influenced by the mining of adjacent coal seams in many ways, resulting in a lot of ore pressure phenomena and significant characteristics [ 1 – 3 ] . Due to the influence of the goaf and residual coal pillar formed by the mining of the upper coal seam, the surrounding rock of the mining roadway of the lower coal seam presents plastic characteristics, so the stress in the roof rock stratum will shift and produce significant deformation [ 4 – 7 ] , which has a great impact on the excavation, maintenance of the roadway and the mining of the working face. Due to the mining disturbance of the working face, the internal stress of the surrounding rock of the roadway changes [ 8 – 11 ] , which leads to deformation and failure, which is the essence of the roadway disaster. In order to study the regional scope and characteristics of roadway surrounding rock failure, many scholars put forward the natural caving arch theory [ 12 ] , axial variation theory [ 13 – 14 ] , maximum horizontal stress theory [ 15 ], and other theories based on theoretical analysis and field engineering practice, and analyzed the deformation characteristics and development rules of roadway failure forms. The quantitative calculation method of the radius of the plastic zone around a circular hole under hydrostatic pressure was studied, that is, the Fenner formula and Castner formula proposed earlier were used for calculation [ 16 – 18 ] . Yue Xizhan et al. [ 19 ] built a structural mechanical model of the "elliptical stress arch" of the overlying coal seam based on the structure of the "elliptical stress arch" of surrounding rock near the coal pillar left over from the overlying coal seam, and the numerical simulation theory was used to calculate the additional stress of the roadway of the lower coal seam floor. Based on the basic research of surrounding rock deformation and failure, Liu Pengze et al. [ 20 – 23 ] demonstrated the reasonable layout of the mining roadway under the near residual coal pillar by means of theoretical tests and numerical simulation. When the coal seam is mined at a close distance, the internal stress of surrounding rock changes, and the roadway is in a non-uniform stress field, which will lead to deformation of surrounding rock, roof subsidence, floor heave, and failure of two sides moving closer [ 24 – 30 ] . Ma Nianjie and Zhao Zhiqiang et al. [ 31 – 34 ] established the physical model of butterfly failure of roadway based on the elastoplastic theory, put forward the butterfly failure theory, analyzed the butterfly failure mechanism of roadway under a non-uniform stress field, and then deduced the quantitative calculation formula for the range of butterfly failure plastic zone of roadway. Based on this, Guo Xiaofei [ 35 – 38 ] proposed the evaluation criteria for the plastic zone of circular roadway, the prediction of the potential danger zone of circular roadway, and the evaluation criteria for the dynamic hazard critical point of roadway based on the characteristic radius. Cui Feng et al. [ 39 ] analyzed the energy characteristics of coal and rock mass impact damage from the perspective of energy accumulation and release. Kong Linghai et al. [ 40 ] studied the impact failure law of deep coal roadway surrounding rock under the effect of incremental load through similar simulation tests with horizontal and vertical bidirectional incremental loading, and revealed the sudden change characteristics of surrounding rock stress during impact failure. The change of stress field is easy to causes the deformation and failure of the mining roadway and bring disaster to the mine production when the coal seam under the goaf is mined in the near residual coal pillar. Based on the engineering background of coal seam mining under the near residual coal pillar in Tashan Coal Mine, this paper analyzes the failure form of the roof under mining disturbance in detail, reveals the deformation mechanism of mining roadway under the near residual coal pillar, and provides a theoretical basis for the stability control theory of surrounding rock of roadway. 2 Methods 2.1 Engineering Background Zhongmei Tower Mountain mine is located in the Middle East margin of Datong coalfield, currently, the main mining 3–5# coal seam (No. 3, No. 5 coalbed, written as "3–5# coal" in this paper), the average thickness of 18m, the reserves account for more than 65% of the whole mine, its mining technology selects the mining technology of large mining high caving top coal. Above the coal seam is a 2# coal seam with an average thickness of 3m, which has been mined. The distance between the two layers of coal is 4.4m, and its spatial position is shown in Fig. 1 below. Since no other roadway is involved, only 30503 return air roadway is included in the profile. According to the coal mining continuation plan, the mining of 30503 face will start after the mining of 30501 face. Before the mining of the 30501 working face, the 30502 return air roadway was excavated to 860m, with a height of 4m and a width of 5.7m. The vertical side of the roadway is 15.2m away from the protective coal pillar of the upper coal seam, and the negative side is 25.4m away from the protective coal pillar of the 30501 working face, among which the width of the protective coal pillar is 20m. Due to the obvious deformation of 30503 return air roadway in the process of driving, in order to ensure the normal mining of 30501 working face, 30503 return air roadway is closed during the mining period. When the return air roadway 30503 was opened after the stoping of the working face 30501, it was found that the roadway was in a closed state. Therefore, the coal mine renovated the roadway. During the renovation process, large local deformation occurred in the roadway of the repaired section, and the displacement of the roof and floor and the two sides continued to increase, and the deformation of the two sides was significantly different, as shown in Fig. 2 . In order to study the failure pattern, the tunnel roof is drilled and peered, and the failure range of the roof is directly observed. 2.2 Field Test The roof peeping can detect the roof lithology and the failure form of surrounding rock more accurately and intuitively. According to the actual production conditions, the measuring points of the roadway section 40m away from the driving face of the return wind lane are selected for drilling and peeping. Seven measuring points are arranged on the roof of this section, evenly arranged on the roof, with a peeping depth of 12m, and the number of marked holes is 1–7, as shown in Fig. 3 . The borehole column diagram was obtained according to the borehole detection in the roof (Fig. 4). Taking the central hole of the roof 40m away from the driving head of the return air lane as an example, the observation shows that there are obvious crack distribution and serious breakage between 0.46m and 1.84m in the roof, and there are more separation layers during the period, the crack shape distribution is different, and the hole wall is rough but the shape is relatively complete. The deep cracks of the borehole are gradually reduced, and there is little breakage. Most fractures were found between 5.8m and 7.3m, but no serious fractures were found. In the range of 9.3m ~ 12m, the fracture distribution decreased, the overall integrity was high, and there was no separation phenomenon. From the above drilling peep analysis, it can be seen that the roof rock structure in the whole peep range is relatively simple, and some thin interlayers are occasionally seen in the coal seam, about 1 ~ 3 layers, the thickness is about 0.25 ~ 0.5m, the roadway roof is seriously broken between 0.4m and 1.8m, and the cracks are relatively developed in the 3m ~ 4.8m area, and the distribution range is wide. The distribution of cracks in the deep borehole is gradually reduced, there is little fracture phenomenon, and the integrity of rock strata is good. The damage area in the roof is drawn according to the breaking condition, damage degree and scope of the surrounding rock in the borehole, as shown in FIG. 5 and 6 below. It can be seen from the drawn failure area diagram that the roof of the roadway presents irregular and asymmetric failure characteristics, among which, the roof failure area near the residual coal pillar in the upper section is obviously larger and deeper, and the damage area presents a "convex" shape at the top corner of the positive side, gradually decreases in the middle of the roof, presenting a "concave" shape, and a smaller bulge appears near the roof at the negative side. However, the convex range of the front side is smaller, and the overall shape is approximately "butterfly". 2.3 Numerical simulation calculation Mining at the working face of a coal mine will break the original initial stress balance of coal and rock mass, and the internal stress of surrounding rock mass will be redistributed, resulting in stress concentration under the influence of mining. When the internal stress of coal and rock mass gradually increases and is higher than the strength of the surrounding rock mass, the surrounding rock mass will be deformed and damaged, and the surrounding plastic zone will also increase. When the surrounding rock is destroyed, the internal stress will continue to decrease, and the concentrated stress will gradually transfer to the deep area of the surrounding rock. When the high stress is transferred to the deep rock mass and higher than the strength of the rock mass, the deep surrounding rock deformation occurs and the surrounding rock failure is more severe. When the high stress continues to extend until the stress is less than the strength of the rock mass, the influence of the change of the internal stress of the surrounding rock is reduced until it is balanced. In the process of mining, the stress of the goaf roof surrounding rock will be transferred to the lower surrounding rock, the stress will be redistributed and concentrated, and the abutment pressure zone will be formed around. In order to study the variation law of the mining stress field caused by face mining and the corresponding surrounding rock control technology, this paper takes the 30503 return air roadway of Tashan Mine as the engineering background and studies the evolution law of mining stress field, and the maximum and minimum principal stress, ratio and direction characteristics through theoretical analysis and numerical simulation. A three-dimensional numerical model is established according to the actual situation of the 30503 return air roadway. The length, width, and height of the model are 500m, 500m, and 156m respectively, and 8.7MPa vertical stress is applied to the upper boundary, as shown in Fig. 7 . According to the actual site conditions and referring to the paper "Research on Mining Method of Close Ultra-Thick Coal Seam in Datong Tashan Coal Mine of SDIC", the physical and mechanical parameters of surrounding rock for numerical calculation of 30503 return air roadway are obtained, as shown in Table 1 below. Table 1 Rock mechanics parameter table Parametric lithology Density (kg/m 3 ) Bulk (GPa) Shear (GPa) Friction (°) Cohesion (MPa) Tension (MP) Siltstone 2560 11.69 10.67 38.57 6.4 3.34 Sandy mudstone 2500 10.2 8.4 36.4 3.72 1.73 Kernstone 2700 14 10.7 39.4 5.68 6.4 2#Coal 1400 3.48 0.78 34.45 2.13 0.92 3#-5#Coal 1500 3.48 1.61 34.45 2.13 0.92 Kaolinite 2100 8.2 7.6 35 5.5 1.73 6#Coal 1500 3.48 1.61 34.45 2.13 0.92 7#Coal 1500 3.48 1.61 34.45 2.13 0.92 8#Coal 1500 3.48 1.61 34.45 2.13 0.92 9#Coal 1500 3.48 1.61 34.45 2.13 0.92 Shan 4 Coal 1400 3.48 0.78 34.45 2.13 0.92 3 Results 3.1 Failure characteristics of residual coal pillar after mining of upper coal seam As shown in Fig. 8 , a 20m coal pillar is left between the two goaf areas, and the coal pillar is symmetrically damaged in the area near the goaf. The plastic damage depth of the coal pillar shows a roughly linear increase from the upper corner of the goaf to the center of the coal pillar. The area from the bottom of the coal pillar to the height of the roadway has good integrity, and no plastic damage occurs. A 6m-10m plastic failure occurs in a region of about 6m-9m. 3.2 Failure characteristics of roadway after mining of lower coal seam face As can be seen from FIG. 9 , asymmetric and non-uniform plastic failure occurs around the roadway when the working face advances at different positions. When the working face is pushed to the head position of the roadway, the plastic failure depth of the top of the roadway reaches 6.8m, and the plastic zone near the coal pillar side of the upper section of the roadway is more severe, and the maximum depth is 12.8m. At 20m in front of the working face, the maximum depth of plastic failure at the top of the roadway is still 6.8m, the depth of plastic failure near the coal pillar side is 10.4m, and the plastic failure of the floor and the normal side is relatively small. At 60m in front of the working face, the maximum depth of plastic failure on the negative side of the tunnel is 8.0m. At 100m in front of the working face, the deformation failure range around the roadway is small, and the main failure area is concentrated in the roof and the negative side. In summary, the farther the distance between the roadway head and the mining face, the smaller the damage depth of the plastic zone. With the continuous advance of the working face, the distance between the two gradually shrinks, the scope of the plastic zone around the roadway gradually expands, and the damage depth also increases. The depth of the plastic zone at the bottom of the roadway is relatively stable, and the maximum depth of the plastic zone is stable at about 1.6m. The negative side of the roadway is affected by the coal pillars left over from mining in the upper section, and its plastic damage degree is more severe than that of the positive side. However, with the increase of the distance from the working face, the influence of the goaf gradually decreases, and the overall depth of the plastic zone of the negative side of the roadway also shows a decreasing rule. From Fig. 10 , it can be seen that the plastic failure degree of the roof and negative side of the tunnel is still more severe than that of the floor and positive side. When the working face meets the roadway head-on, the maximum depth of the negative side plastic zone is 12.8m, and the plastic damage range at the top of the roadway can reach 6.8m. The plastic damage on the bottom plate and positive side is relatively small; At a distance of 20m behind the working face, the plastic failure depth of the negative side of the roadway reaches 8.4m, forming a connection with the plastic zone of the residual coal pillar in the upper section, resulting in severe plastic failure; At a distance of 60m behind the working face, the plastic zone on the negative side of the tunnel is more severely damaged, with a damage range of up to 14.2m. The maximum depth of the plastic zone at the top is 4.8m. The bottom of the positive side of the tunnel and the adjacent goaf are penetrated and destroyed, and there is almost no plastic damage at the bottom of the tunnel. The negative side of the tunnel experiences large-scale plastic damage; At a distance of 100m behind the working face, the deformation of the roof and floor of the tunnel is relatively small, and plastic penetration failure still occurs in the negative side. There is almost no plastic failure at the bottom of the tunnel, and penetration failure occurs between the bottom of the positive side of the tunnel and the adjacent goaf. In summary, with the continuous mining of the working face, the roadway head gradually moves away from the mining face, and the plastic failure depth of the roadway surrounding rock also decreases, finally stabilizing at 4.8m. There is almost no plastic failure at the bottom of the roadway, and slight penetrating failure occurs at the bottom of the positive side of the roadway and the adjacent goaf. Due to the double influence of the goaf and the upper coal pillar, almost all penetrating failure occurs at the rear of the working face. 3.3 Deformation characteristics of the roadway after mining of lower coal seam face It can be seen from the analysis of Fig. 11 that the stress changes of surrounding rock mainly occur in the positive and negative side areas of the roadway, and the whole is asymmetrical, in which the negative side and the upper corner of the negative side of the roadway have slight displacement. With the increase of the distance between the working face and the 30503 return air lane, the displacement of the negative side of the roadway decreases in a stepped way. The maximum displacement area is the middle of the negative side, and the maximum displacement amount reaches 33.4mm. The displacement amount of the positive side of the roadway decreases linearly, and the maximum displacement area appears in the middle of the positive side, and the maximum displacement amount is 14.1mm. Due to stress concentration, the displacement at the top and bottom of the roadway is relatively obvious, and the whole is asymmetrical. Slight displacement occurs at the top of the roadway, and the area with the largest displacement is the middle of the roof with the largest displacement of 24.5mm. Slight displacement also occurs at the bottom of the roadway and the lower corner, and the displacement is relatively uniform overall with the maximum displacement of 5.91mm. It can be seen from FIG. 12 that the displacement of the surrounding rock of the roadway at 20m in front of the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. The displacement of the negative side and upper corner of the roadway is small, and the displacement decreases in a step pattern as the distance from the roadway is longer, and the area with the largest displacement occurs in the middle of the negative side with the maximum displacement of 30.8mm. The displacement of the roadway side decreases linearly with the distance from the roadway position. The maximum displacement area is the middle of the roadway side, and the maximum displacement is 14.5mm. Due to stress concentration, the displacement at the top and bottom of the roadway is relatively obvious, and the overall displacement is asymmetrical. The displacement at the top of the roadway is small, and the displacement decreases in levels as the distance from the roof of the roadway increases. The displacement in the middle area of the roadway roof is up to 25.5mm, while the displacement at the bottom and lower corner of the roadway is generally uniform, and the displacement is up to 4.93mm. As shown in Fig. 13 , the displacement of the surrounding rock of the roadway at a distance of 60m in front of the mining work mainly occurs on the two sides of the roadway, showing an overall asymmetry. The displacement of the negative side and upper corner of the roadway is relatively small. As the working face is mined, the distance between the front of the roadway and the mining face increases, and the displacement of the roadway decreases in a stepped manner. The area with the highest displacement is the middle of the negative side, with a maximum displacement of 27.5mm. The displacement of the positive side of the roadway decreases linearly due to the influence of the goaf, and the area with the highest displacement is the middle of the positive side, with a maximum displacement of 14.3mm. Due to stress concentration, the displacement of the top and bottom of the tunnel is relatively obvious, showing an overall asymmetry. The displacement at the top of the tunnel decreases and decreases hierarchically. The area with the largest displacement is the middle of the tunnel roof, with a maximum displacement of 24.4mm. The bottom and lower corners of the tunnel have slight displacement, and the displacement is relatively uniform overall, with a maximum displacement of 4.79mm. It can be seen from Fig. 14 that the displacement of the surrounding rock of the roadway 100m in front of the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. With the distance of the working face, the stress of the surrounding rock of the roadway gradually decreases and eventually becomes stable. The negative side and upper corner of the roadway have slight displacement, the maximum displacement is 25.9mm, and the maximum displacement area of the roadway's positive side appears in the middle of the positive side, and the maximum displacement is 14.2mm. The vertical displacement mainly occurs at the top and bottom of the roadway, and the overall displacement is asymmetrical. The displacement at the top of the roadway is small, and the area with the largest displacement is the middle of the roadway roof with the maximum displacement of 23.8mm. The bottom and lower corners of the roadway have slight displacement, and the displacement is relatively uniform as a whole with the maximum displacement of 4.6mm. As shown in Fig. 15 , the displacement of the surrounding rock of the roadway at a distance of 20m behind the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. As the working face moves away, the displacement around the roadway decreases to varying degrees. The negative side and upper corner of the tunnel experience slight displacement, with the maximum displacement being in the middle of the negative side, with a maximum displacement of 32.8 mm. The maximum displacement of the positive side of the tunnel is in the middle of the positive side, with a maximum displacement of 10.5mm. The vertical displacement mainly occurs at the top and bottom of the tunnel, showing an overall asymmetry. There is a slight displacement at the top of the tunnel, and the area with the largest displacement is the middle of the tunnel roof, with a maximum displacement of 21.0mm. There is a slight displacement at the bottom and lower corners of the tunnel, and the displacement is relatively uniform overall, with a maximum displacement of 7.0mm. It can be seen from Fig. 16 that the displacement of the surrounding rock of the roadway 60m behind the mining face mainly occurs in the area of two sides of the roadway, showing an overall asymmetry. Slight displacement occurs in the negative side and upper corner of the roadway, mainly concentrated in the middle of the negative side, with a maximum displacement of 22.9mm. The displacement of the positive side of the roadway decreases linearly with the distance from the roadway, and the maximum displacement area is the middle of the positive side. The maximum displacement is 8.1mm. The vertical displacement mainly occurs at the top and bottom of the roadway, showing an overall asymmetry. Slight displacement occurs at the top of the roadway, and the displacement decreases with the distance from the roof. The largest displacement area is the middle of the roof, with a maximum displacement of 16.4mm, while slight displacement occurs at the bottom and lower corner of the roadway, and the displacement is relatively uniform overall, with a maximum displacement of 5.1mm. From Fig. 17 , it can be seen that the displacement of the surrounding rock of the roadway at 100m behind the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. There is slight displacement in the negative side and upper corner of the roadway, with a maximum displacement of only 16.3mm. The displacement of the positive side of the roadway decreases linearly with the distance from the roadway position, with a maximum displacement of 7.4mm. The vertical displacement mainly occurs at the top and bottom of the tunnel, showing an overall asymmetry. There is slight displacement at the top, and the displacement decreases hierarchically as the distance from the roof of the tunnel increases, with a maximum displacement of 13.8mm. There is slight displacement at the bottom and lower corners of the tunnel, and the displacement is relatively uniform overall, with a maximum displacement of 4mm. 3.4 Relationship between deformation and failure of surrounding rock of mining roadway Based on the numerical simulation results, the displacement of the top and bottom of the roadway and the size of the plastic zone are measured at 100m, 60m, 20m, the working face, 20m, 60m, and 100m in front of the working point respectively, and the relationship diagram between the displacement and the size of the plastic zone is drawn to analyze the relationship between the deformation of the mining roadway and the size of the plastic zone. The mechanism of large deformation in the mining roadway under the near residual coal pillar is revealed. From Fig. 18, it can be seen that the plastic zone at 100m behind the working face is significantly developed on the front and top sides, with maximum dimensions of 17.24m and 3.96m, respectively. The displacement is also relatively large on the negative side and bottom sides; Due to the formation of a plastic zone before excavation, the size of the plastic zone is abnormal near the bottom plate of the negative slope. Ignoring the abnormal value, the maximum plastic zone size is only 1.71m and the maximum displacement is 6.29mm; The displacement of the bottom plate is minimal and there is no plastic zone present. From the trend of change, the displacement of the bottom plate and the size of the plastic zone are both small and have little change. The maximum displacement and size of the plastic zone of the positive and negative sides both occur near the top plate. As can be seen from Fig. 19, the plastic zone at 60m behind the working face develops significantly in the front side and top plate, and the displacement is larger than that of the negative side and bottom plate. Due to the formation of the plastic zone before excavation of the negative side, the size of the plastic zone is abnormal near the bottom plate of the negative side, and the maximum size of the plastic zone is only 3.41m when the abnormal value is ignored. The displacement of the bottom plate is minimal and only 0.41m plastic zone appears. From the trend of change, the maximum displacement of the roof appears in the position of the negative side of the middle, and the maximum plastic zone size appears in the position of the positive side of the middle. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum displacement and the maximum plastic zone size of the positive and negative sides appear near the top plate. It can be seen from Fig. 20 that at 20m behind the working face, the maximum size of the plastic zone on the front side and the top plate is 16.32m and 6.16m respectively, and the displacement is larger than that on the negative side and the bottom plate. The displacement of the negative side and the plastic zone gradually increase. The maximum plastic zone size is 7.7m and the maximum displacement is 10.58mm. The displacement of the bottom plate is minimal and only 0.83m plastic zone appears. From the changing trend, the maximum displacement of the roof appears in the middle position, and the maximum plastic zone size appears in the middle position near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum displacement of the front side and the size of the maximum plastic zone appear near the top plate. Both the maximum plastic zone size and the maximum displacement of the negative side appear in the upper part of the negative side. As can be seen from FIG. 21, at the position of the working face, the plastic zone develops obviously in the front side and the top side and the maximum plastic zone size is 12.3m and 5.73m, respectively, and the displacement is larger than that of the negative side and the bottom floor. The displacement of the negative side and the plastic zone gradually increase, the maximum plastic zone size is 4.71m, and the maximum displacement is 14.12mm. The displacement of the bottom plate is minimal and only 1.25m plastic zone appears. From the trend of change, the displacement mainly occurs in the middle of the surrounding rock, and the maximum plastic zone size appears near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum plastic zone size occurs near the top plate. As can be seen from Fig. 22, the plastic zone at 20m in front of the working face develops significantly on the front side and top plate, and the maximum plastic zone size is 9.93m and 5.73m, respectively. The displacement of the negative side and the plastic zone gradually decrease, the maximum plastic zone size is 2.58m, and the maximum displacement is 14.57mm. The displacement of the bottom plate is the smallest and only 1.67m plastic zone appears. From the trend of change, the maximum displacement mainly appears in the middle of the surrounding rock, and the maximum plastic zone size appears near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum plastic zone dimensions of the positive and negative sides appear near the top plate. As can be seen from Fig. 23, at 60m in front of the working face, the plastic zone develops significantly on the front side and top plate, with the maximum plastic zone size of 8.06m and 5.28m respectively, and the displacement is also larger than that of the negative side and bottom plate, with the maximum displacement of 27.50mm and 24.40mm. The displacement of the negative side and the plastic zone also decreases gradually. The maximum plastic zone size is 2.14m and the maximum displacement is 14.33mm. The displacement of the bottom plate is the smallest and only 1.67m plastic zone appears. From the trend of change, the maximum displacement of the roof appears in the middle position, and the maximum plastic zone size appears in the position near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. Both the maximum displacement and the maximum plastic zone size appear in the middle of the face. The maximum displacement of the negative side occurs in the middle part of the negative side and the maximum plastic zone size occurs near the top. From Fig. 24, it can be seen that at a distance of 100m in front of the work, the plastic zone is significantly developed on the positive side and the top plate, with the maximum plastic zone size of 5.69m and 4.4m respectively, and the displacement is relatively large on the negative side and bottom plate; The negative displacement and plastic zone gradually decrease, with a maximum plastic zone size of 1.71m and a maximum displacement of 14.09mm; The displacement of the bottom plate is minimal and only a 1.25m plastic zone appears. From the trend of change, the maximum displacement of the top plate appears in the middle position, and the maximum plastic zone size appears near the front wall position; The displacement of the bottom plate and the size of the plastic zone are both small and have little change; The maximum displacement and maximum plastic zone size of the positive side both occur in the middle position; The maximum displacement of the negative side appears in the middle of the roof, and the maximum plastic zone size appears near the roof. To sum up, the size of the plastic zone of the surrounding rock of the roadway generally presents a positive correlation with the deformation of the surrounding rock, and the area with greater plastic failure usually has greater deformation. In the stress concentration area near the residual coal pillar of the upper coal seam, the deformation amount and the plastic zone size are both large. The maximum deformation amount of the roof is 25.55mm, the maximum plastic zone size is 6.61m, the maximum deformation amount of the normal side is 33.41mm, and the maximum plastic zone size is 17.24m. The deformation of the roof and negative side of the roadway is relatively small compared with the size of the plastic zone. The maximum deformation of the floor is 6.3mm, the maximum deformation of the plastic zone is 1.67m, and the maximum deformation of the negative side of the roadway is 14.57mm. Because the damage occurs before excavation, the maximum damage depth is 12.85m, and the maximum damage depth is about 7.7m when the damage before excavation is ignored. 4 Discussion According to the above analysis, it can be concluded that during the mining process of 30501 face in Tashan Coal Mine, the surrounding rock of 30503 return air roadway produces regional stress variation rules and plastic zone failure characteristics. During the mining under the near seam residual coal pillar, asymmetric deformation and failure occur in the return air roadway 30503, and the asymmetric expansion rule of the plastic zone of the surrounding rock of the roadway is consistent with the asymmetric deformation rule, and there is a positive correlation between the two, that is, the larger the plastic zone, the roadway deformation increases. From this, it can be concluded that the large deformation mechanism of non-uniform and non-symmetrical coal seam roadway in the lower coal seam mining near coal seam is as follows: The stress concentration area generated under the residual coal pillar and the new stress field mined at the working face are superimposed on each other, resulting in irregular and asymmetric failure in the return air roadway. Among them, the plastic failure area near the top Angle of the positive side of the upper coal pillar is large, and the plastic failure area tends to decrease in the middle of the roof. When it gradually approaches the negative side, the failure range increases in a small range, and the overall shape is approximately "butterfly". With the continuous mining of the working face, the stress on one side of the surrounding rock will be deflected, resulting in a significant difference in stress concentration on both sides of the roadway, and the extension of the asymmetry in the plastic zone, which will lead to the large asymmetric deformation and failure of the surrounding rock of the roadway. 5 Conclusions Through the roof drilling, theoretical and numerical simulation calculation and analysis, this paper studies the deformation and failure mechanism of the surrounding rock of the mining roadway under the residual coal pillar during the mining process of the near coal seam in Tashan Coal Mine. The conclusions are as follows: (1) Through roof drilling, the breaking law of the roof strata of the mining roadway is analyzed when the coal seam under the near residual coal pillar is mined. It is concluded that cracks and separated layers are more distributed in the roof of the roadway, but the overall integrity is good, showing irregular and asymmetric failure characteristics. Among them, the roof failure area near the side of the residual coal pillar in the upper section is larger and the damage depth is deeper. The destruction decreases from left to right. (2) After the mining of the near seam, the difference stress change law and plastic zone failure characteristics of the mining roadway in the lower seam are analyzed with the change of mining position of the adjacent working face. It is concluded that when the distance between the roadway and the working face increases, the stress concentration value in the surrounding rock and the depth of the plastic zone both show a decreasing law. However, the stress concentration and the failure depth of the plastic zone near the residual coal pillar of the upper coal seam are larger, that is, under the action of stress superposition, the principal stress direction of surrounding rock will be deflected, and the roadway will appear asymmetric deformation and failure. (3) The failure of the surrounding rock of the roadway is the result of the combined action of the strength of the surrounding rock and the regional stress. In the case of the principal stress deflection, the stress on both sides of the roadway is significantly different, and the plastic zone shows butterfly deformation and failure. The mechanical mechanism and asymmetric deformation mechanism of the butterfly failure in the non-uniform stress field under the deflection of the principal stress direction in the mining near the lower coal seam are obtained. Declarations Data Availability Statement The raw data supporting the conclusion of this article will be made available by the authors, without undue reservation.Xiao-He Wang ( [email protected] ) should be contacted if someone wants to request the data from this study. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contributions In this paper, Xiao-He Wang, Wu Jing and Qing-Long Yun conducted experiments and collected experimental data; the full text was co-authored by Xiao-He Wang and Jiang-Hao Wang. Wen-Bo Zhang and Yi-Qing Wang are responsible for the data analysis and graphics rendering. Wen-Bo Zhang and Yi-Han Wu, Ji-Qiang Wang is responsible for the data analysis and graphics drawing; Xiao-He Wang, Ji-Qiang Wang and Wu Jing is responsible for the editing of the article. Funding This research was funded by the Guizhou Province Science and Technology Support Plan Project of China (Qiankehe Support [2021] General 400). This support is gratefully acknowledged. The authors are grateful to the reviewers for discerning comments on this paper. Publisher ’ s Note All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher. References Li Y, Gao X, Wang Z et al. Research on failure characteristics and control of lower roadway in very close seam mining [J]. Coal Technology,2022,41(08):62-66. 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19","display":"","copyAsset":false,"role":"figure","size":179520,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between the displacement of 60m surrounding rock behind the working face and the size of the plastic zone\u003c/p\u003e","description":"","filename":"19.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/a91fcb97c68630e4306fa4b6.png"},{"id":49053646,"identity":"5fe52940-919d-45ca-be8f-acc3e618cee5","added_by":"auto","created_at":"2024-01-02 11:08:00","extension":"png","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":179169,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between displacement of surrounding rock behind 20m face and size of plastic zone\u003c/p\u003e","description":"","filename":"20.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/28c35dc546fc9f8e135b0506.png"},{"id":49053652,"identity":"8775feab-1c17-46de-9be3-1992d1e1d5cd","added_by":"auto","created_at":"2024-01-02 11:08:00","extension":"png","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":179916,"visible":true,"origin":"","legend":"\u003cp\u003eThe relation between the displacement of surrounding rock and the size of the plastic zone\u003c/p\u003e","description":"","filename":"21.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/4c5a7c6139ce386a7bcddfc6.png"},{"id":49053651,"identity":"0904747a-ee1f-4b9f-9775-347e4881cc0d","added_by":"auto","created_at":"2024-01-02 11:08:00","extension":"png","order_by":22,"title":"Figure 22","display":"","copyAsset":false,"role":"figure","size":182472,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between displacement of surrounding rock at 20m in front of working face and size of plastic zone\u003c/p\u003e","description":"","filename":"22.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/dcdbc9cdc7c84b1e81dbbf3d.png"},{"id":49054494,"identity":"d2a0f797-88af-4f75-9285-e2cae01330ee","added_by":"auto","created_at":"2024-01-02 11:32:00","extension":"png","order_by":23,"title":"Figure 23","display":"","copyAsset":false,"role":"figure","size":175917,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between the displacement of surrounding rock 60m in front of the working face and the size of the plastic zone\u003c/p\u003e","description":"","filename":"23.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/cad105dc22ddfe4a8eecacaa.png"},{"id":49053653,"identity":"c32acfd0-087d-4410-af98-ebfd3e841b41","added_by":"auto","created_at":"2024-01-02 11:08:00","extension":"png","order_by":24,"title":"Figure 24","display":"","copyAsset":false,"role":"figure","size":205109,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between the displacement of surrounding rock 100m in front of working face and size of plastic zone\u003c/p\u003e","description":"","filename":"24.png","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/b049e62d1cf28faa24341a77.png"},{"id":50704373,"identity":"0da67a82-c69e-4214-9061-655a235fb81d","added_by":"auto","created_at":"2024-02-06 05:32:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4908764,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3807279/v1/cb1500e9-6114-487a-9d59-dacfed95b215.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Temporal and spatial evolution mechanism of deformation and failure of lower mining roadway in near residual coal pillar area","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eNowadays, close-range coal seam mining has gradually become a common way of coal mine production in China. Different from single coal seam mining, close-range coal seam mining will be influenced by the mining of adjacent coal seams in many ways, resulting in a lot of ore pressure phenomena and significant characteristics\u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. Due to the influence of the goaf and residual coal pillar formed by the mining of the upper coal seam, the surrounding rock of the mining roadway of the lower coal seam presents plastic characteristics, so the stress in the roof rock stratum will shift and produce significant deformation\u003csup\u003e[\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e, which has a great impact on the excavation, maintenance of the roadway and the mining of the working face. Due to the mining disturbance of the working face, the internal stress of the surrounding rock of the roadway changes\u003csup\u003e[\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e, which leads to deformation and failure, which is the essence of the roadway disaster. In order to study the regional scope and characteristics of roadway surrounding rock failure, many scholars put forward the natural caving arch theory\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e, axial variation theory\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e, maximum horizontal stress theory\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e],\u003c/sup\u003e and other theories based on theoretical analysis and field engineering practice, and analyzed the deformation characteristics and development rules of roadway failure forms. The quantitative calculation method of the radius of the plastic zone around a circular hole under hydrostatic pressure was studied, that is, the Fenner formula and Castner formula proposed earlier were used for calculation\u003csup\u003e[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. Yue Xizhan et al.\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e built a structural mechanical model of the \"elliptical stress arch\" of the overlying coal seam based on the structure of the \"elliptical stress arch\" of surrounding rock near the coal pillar left over from the overlying coal seam, and the numerical simulation theory was used to calculate the additional stress of the roadway of the lower coal seam floor. Based on the basic research of surrounding rock deformation and failure, Liu Pengze et al.\u003csup\u003e[\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e demonstrated the reasonable layout of the mining roadway under the near residual coal pillar by means of theoretical tests and numerical simulation.\u003c/p\u003e \u003cp\u003eWhen the coal seam is mined at a close distance, the internal stress of surrounding rock changes, and the roadway is in a non-uniform stress field, which will lead to deformation of surrounding rock, roof subsidence, floor heave, and failure of two sides moving closer\u003csup\u003e[\u003cspan additionalcitationids=\"CR25 CR26 CR27 CR28 CR29\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. Ma Nianjie and Zhao Zhiqiang et al.\u003csup\u003e[\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e established the physical model of butterfly failure of roadway based on the elastoplastic theory, put forward the butterfly failure theory, analyzed the butterfly failure mechanism of roadway under a non-uniform stress field, and then deduced the quantitative calculation formula for the range of butterfly failure plastic zone of roadway. Based on this, Guo Xiaofei\u003csup\u003e[\u003cspan additionalcitationids=\"CR36 CR37\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e proposed the evaluation criteria for the plastic zone of circular roadway, the prediction of the potential danger zone of circular roadway, and the evaluation criteria for the dynamic hazard critical point of roadway based on the characteristic radius. Cui Feng et al.\u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e analyzed the energy characteristics of coal and rock mass impact damage from the perspective of energy accumulation and release. Kong Linghai et al.\u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e studied the impact failure law of deep coal roadway surrounding rock under the effect of incremental load through similar simulation tests with horizontal and vertical bidirectional incremental loading, and revealed the sudden change characteristics of surrounding rock stress during impact failure.\u003c/p\u003e \u003cp\u003eThe change of stress field is easy to causes the deformation and failure of the mining roadway and bring disaster to the mine production when the coal seam under the goaf is mined in the near residual coal pillar. Based on the engineering background of coal seam mining under the near residual coal pillar in Tashan Coal Mine, this paper analyzes the failure form of the roof under mining disturbance in detail, reveals the deformation mechanism of mining roadway under the near residual coal pillar, and provides a theoretical basis for the stability control theory of surrounding rock of roadway.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Engineering Background\u003c/h2\u003e\n\u003cp\u003eZhongmei Tower Mountain mine is located in the Middle East margin of Datong coalfield, currently, the main mining 3\u0026ndash;5# coal seam (No. 3, No. 5 coalbed, written as \"3\u0026ndash;5# coal\" in this paper), the average thickness of 18m, the reserves account for more than 65% of the whole mine, its mining technology selects the mining technology of large mining high caving top coal. Above the coal seam is a 2# coal seam with an average thickness of 3m, which has been mined. The distance between the two layers of coal is 4.4m, and its spatial position is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e below. Since no other roadway is involved, only 30503 return air roadway is included in the profile.\u003c/p\u003e\n\u003cp\u003eAccording to the coal mining continuation plan, the mining of 30503 face will start after the mining of 30501 face. Before the mining of the 30501 working face, the 30502 return air roadway was excavated to 860m, with a height of 4m and a width of 5.7m. The vertical side of the roadway is 15.2m away from the protective coal pillar of the upper coal seam, and the negative side is 25.4m away from the protective coal pillar of the 30501 working face, among which the width of the protective coal pillar is 20m. Due to the obvious deformation of 30503 return air roadway in the process of driving, in order to ensure the normal mining of 30501 working face, 30503 return air roadway is closed during the mining period. When the return air roadway 30503 was opened after the stoping of the working face 30501, it was found that the roadway was in a closed state. Therefore, the coal mine renovated the roadway. During the renovation process, large local deformation occurred in the roadway of the repaired section, and the displacement of the roof and floor and the two sides continued to increase, and the deformation of the two sides was significantly different, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. In order to study the failure pattern, the tunnel roof is drilled and peered, and the failure range of the roof is directly observed.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Field Test\u003c/h2\u003e\n\u003cp\u003eThe roof peeping can detect the roof lithology and the failure form of surrounding rock more accurately and intuitively. According to the actual production conditions, the measuring points of the roadway section 40m away from the driving face of the return wind lane are selected for drilling and peeping. Seven measuring points are arranged on the roof of this section, evenly arranged on the roof, with a peeping depth of 12m, and the number of marked holes is 1\u0026ndash;7, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe borehole column diagram was obtained according to the borehole detection in the roof (Fig.\u0026nbsp;4). Taking the central hole of the roof 40m away from the driving head of the return air lane as an example, the observation shows that there are obvious crack distribution and serious breakage between 0.46m and 1.84m in the roof, and there are more separation layers during the period, the crack shape distribution is different, and the hole wall is rough but the shape is relatively complete. The deep cracks of the borehole are gradually reduced, and there is little breakage. Most fractures were found between 5.8m and 7.3m, but no serious fractures were found. In the range of 9.3m\u0026thinsp;~\u0026thinsp;12m, the fracture distribution decreased, the overall integrity was high, and there was no separation phenomenon.\u003c/p\u003e\n\u003cp\u003eFrom the above drilling peep analysis, it can be seen that the roof rock structure in the whole peep range is relatively simple, and some thin interlayers are occasionally seen in the coal seam, about 1\u0026thinsp;~\u0026thinsp;3 layers, the thickness is about 0.25\u0026thinsp;~\u0026thinsp;0.5m, the roadway roof is seriously broken between 0.4m and 1.8m, and the cracks are relatively developed in the 3m\u0026thinsp;~\u0026thinsp;4.8m area, and the distribution range is wide. The distribution of cracks in the deep borehole is gradually reduced, there is little fracture phenomenon, and the integrity of rock strata is good.\u003c/p\u003e\n\u003cp\u003eThe damage area in the roof is drawn according to the breaking condition, damage degree and scope of the surrounding rock in the borehole, as shown in FIG. 5 and 6 below. It can be seen from the drawn failure area diagram that the roof of the roadway presents irregular and asymmetric failure characteristics, among which, the roof failure area near the residual coal pillar in the upper section is obviously larger and deeper, and the damage area presents a \"convex\" shape at the top corner of the positive side, gradually decreases in the middle of the roof, presenting a \"concave\" shape, and a smaller bulge appears near the roof at the negative side. However, the convex range of the front side is smaller, and the overall shape is approximately \"butterfly\".\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3 Numerical simulation calculation\u003c/h2\u003e\n\u003cp\u003eMining at the working face of a coal mine will break the original initial stress balance of coal and rock mass, and the internal stress of surrounding rock mass will be redistributed, resulting in stress concentration under the influence of mining. When the internal stress of coal and rock mass gradually increases and is higher than the strength of the surrounding rock mass, the surrounding rock mass will be deformed and damaged, and the surrounding plastic zone will also increase. When the surrounding rock is destroyed, the internal stress will continue to decrease, and the concentrated stress will gradually transfer to the deep area of the surrounding rock. When the high stress is transferred to the deep rock mass and higher than the strength of the rock mass, the deep surrounding rock deformation occurs and the surrounding rock failure is more severe. When the high stress continues to extend until the stress is less than the strength of the rock mass, the influence of the change of the internal stress of the surrounding rock is reduced until it is balanced. In the process of mining, the stress of the goaf roof surrounding rock will be transferred to the lower surrounding rock, the stress will be redistributed and concentrated, and the abutment pressure zone will be formed around.\u003c/p\u003e\n\u003cp\u003eIn order to study the variation law of the mining stress field caused by face mining and the corresponding surrounding rock control technology, this paper takes the 30503 return air roadway of Tashan Mine as the engineering background and studies the evolution law of mining stress field, and the maximum and minimum principal stress, ratio and direction characteristics through theoretical analysis and numerical simulation.\u003c/p\u003e\n\u003cp\u003eA three-dimensional numerical model is established according to the actual situation of the 30503 return air roadway. The length, width, and height of the model are 500m, 500m, and 156m respectively, and 8.7MPa vertical stress is applied to the upper boundary, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eAccording to the actual site conditions and referring to the paper \"Research on Mining Method of Close Ultra-Thick Coal Seam in Datong Tashan Coal Mine of SDIC\", the physical and mechanical parameters of surrounding rock for numerical calculation of 30503 return air roadway are obtained, as shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e below.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eRock mechanics parameter table\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eParametric lithology\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDensity (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eBulk\u003c/p\u003e\n\u003cp\u003e(GPa)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eShear (GPa)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFriction\u003c/p\u003e\n\u003cp\u003e(\u0026deg;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCohesion (MPa)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTension\u003c/p\u003e\n\u003cp\u003e(MP)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSiltstone\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2560\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11.69\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10.67\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38.57\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.34\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSandy mudstone\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e8.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e36.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.72\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.73\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eKernstone\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2700\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e39.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1400\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.78\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3#-5#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eKaolinite\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e7.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.73\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9#Coal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eShan\u003csub\u003e4\u003c/sub\u003eCoal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1400\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.78\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Failure characteristics of residual coal pillar after mining of upper coal seam\u003c/h2\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, a 20m coal pillar is left between the two goaf areas, and the coal pillar is symmetrically damaged in the area near the goaf. The plastic damage depth of the coal pillar shows a roughly linear increase from the upper corner of the goaf to the center of the coal pillar. The area from the bottom of the coal pillar to the height of the roadway has good integrity, and no plastic damage occurs. A 6m-10m plastic failure occurs in a region of about 6m-9m.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Failure characteristics of roadway after mining of lower coal seam face\u003c/h2\u003e\n\u003cp\u003eAs can be seen from FIG. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, asymmetric and non-uniform plastic failure occurs around the roadway when the working face advances at different positions. When the working face is pushed to the head position of the roadway, the plastic failure depth of the top of the roadway reaches 6.8m, and the plastic zone near the coal pillar side of the upper section of the roadway is more severe, and the maximum depth is 12.8m. At 20m in front of the working face, the maximum depth of plastic failure at the top of the roadway is still 6.8m, the depth of plastic failure near the coal pillar side is 10.4m, and the plastic failure of the floor and the normal side is relatively small. At 60m in front of the working face, the maximum depth of plastic failure on the negative side of the tunnel is 8.0m. At 100m in front of the working face, the deformation failure range around the roadway is small, and the main failure area is concentrated in the roof and the negative side. In summary, the farther the distance between the roadway head and the mining face, the smaller the damage depth of the plastic zone. With the continuous advance of the working face, the distance between the two gradually shrinks, the scope of the plastic zone around the roadway gradually expands, and the damage depth also increases. The depth of the plastic zone at the bottom of the roadway is relatively stable, and the maximum depth of the plastic zone is stable at about 1.6m. The negative side of the roadway is affected by the coal pillars left over from mining in the upper section, and its plastic damage degree is more severe than that of the positive side. However, with the increase of the distance from the working face, the influence of the goaf gradually decreases, and the overall depth of the plastic zone of the negative side of the roadway also shows a decreasing rule.\u003c/p\u003e\n\u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e, it can be seen that the plastic failure degree of the roof and negative side of the tunnel is still more severe than that of the floor and positive side. When the working face meets the roadway head-on, the maximum depth of the negative side plastic zone is 12.8m, and the plastic damage range at the top of the roadway can reach 6.8m. The plastic damage on the bottom plate and positive side is relatively small; At a distance of 20m behind the working face, the plastic failure depth of the negative side of the roadway reaches 8.4m, forming a connection with the plastic zone of the residual coal pillar in the upper section, resulting in severe plastic failure; At a distance of 60m behind the working face, the plastic zone on the negative side of the tunnel is more severely damaged, with a damage range of up to 14.2m. The maximum depth of the plastic zone at the top is 4.8m. The bottom of the positive side of the tunnel and the adjacent goaf are penetrated and destroyed, and there is almost no plastic damage at the bottom of the tunnel. The negative side of the tunnel experiences large-scale plastic damage; At a distance of 100m behind the working face, the deformation of the roof and floor of the tunnel is relatively small, and plastic penetration failure still occurs in the negative side. There is almost no plastic failure at the bottom of the tunnel, and penetration failure occurs between the bottom of the positive side of the tunnel and the adjacent goaf.\u003c/p\u003e\n\u003cp\u003eIn summary, with the continuous mining of the working face, the roadway head gradually moves away from the mining face, and the plastic failure depth of the roadway surrounding rock also decreases, finally stabilizing at 4.8m. There is almost no plastic failure at the bottom of the roadway, and slight penetrating failure occurs at the bottom of the positive side of the roadway and the adjacent goaf. Due to the double influence of the goaf and the upper coal pillar, almost all penetrating failure occurs at the rear of the working face.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Deformation characteristics of the roadway after mining of lower coal seam face\u003c/h2\u003e\n\u003cp\u003eIt can be seen from the analysis of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e that the stress changes of surrounding rock mainly occur in the positive and negative side areas of the roadway, and the whole is asymmetrical, in which the negative side and the upper corner of the negative side of the roadway have slight displacement. With the increase of the distance between the working face and the 30503 return air lane, the displacement of the negative side of the roadway decreases in a stepped way. The maximum displacement area is the middle of the negative side, and the maximum displacement amount reaches 33.4mm. The displacement amount of the positive side of the roadway decreases linearly, and the maximum displacement area appears in the middle of the positive side, and the maximum displacement amount is 14.1mm. Due to stress concentration, the displacement at the top and bottom of the roadway is relatively obvious, and the whole is asymmetrical. Slight displacement occurs at the top of the roadway, and the area with the largest displacement is the middle of the roof with the largest displacement of 24.5mm. Slight displacement also occurs at the bottom of the roadway and the lower corner, and the displacement is relatively uniform overall with the maximum displacement of 5.91mm.\u003c/p\u003e\n\u003cp\u003eIt can be seen from FIG. 12 that the displacement of the surrounding rock of the roadway at 20m in front of the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. The displacement of the negative side and upper corner of the roadway is small, and the displacement decreases in a step pattern as the distance from the roadway is longer, and the area with the largest displacement occurs in the middle of the negative side with the maximum displacement of 30.8mm. The displacement of the roadway side decreases linearly with the distance from the roadway position. The maximum displacement area is the middle of the roadway side, and the maximum displacement is 14.5mm. Due to stress concentration, the displacement at the top and bottom of the roadway is relatively obvious, and the overall displacement is asymmetrical. The displacement at the top of the roadway is small, and the displacement decreases in levels as the distance from the roof of the roadway increases. The displacement in the middle area of the roadway roof is up to 25.5mm, while the displacement at the bottom and lower corner of the roadway is generally uniform, and the displacement is up to 4.93mm.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e13\u003c/span\u003e, the displacement of the surrounding rock of the roadway at a distance of 60m in front of the mining work mainly occurs on the two sides of the roadway, showing an overall asymmetry. The displacement of the negative side and upper corner of the roadway is relatively small. As the working face is mined, the distance between the front of the roadway and the mining face increases, and the displacement of the roadway decreases in a stepped manner. The area with the highest displacement is the middle of the negative side, with a maximum displacement of 27.5mm. The displacement of the positive side of the roadway decreases linearly due to the influence of the goaf, and the area with the highest displacement is the middle of the positive side, with a maximum displacement of 14.3mm. Due to stress concentration, the displacement of the top and bottom of the tunnel is relatively obvious, showing an overall asymmetry. The displacement at the top of the tunnel decreases and decreases hierarchically. The area with the largest displacement is the middle of the tunnel roof, with a maximum displacement of 24.4mm. The bottom and lower corners of the tunnel have slight displacement, and the displacement is relatively uniform overall, with a maximum displacement of 4.79mm.\u003c/p\u003e\n\u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e that the displacement of the surrounding rock of the roadway 100m in front of the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. With the distance of the working face, the stress of the surrounding rock of the roadway gradually decreases and eventually becomes stable. The negative side and upper corner of the roadway have slight displacement, the maximum displacement is 25.9mm, and the maximum displacement area of the roadway's positive side appears in the middle of the positive side, and the maximum displacement is 14.2mm. The vertical displacement mainly occurs at the top and bottom of the roadway, and the overall displacement is asymmetrical. The displacement at the top of the roadway is small, and the area with the largest displacement is the middle of the roadway roof with the maximum displacement of 23.8mm. The bottom and lower corners of the roadway have slight displacement, and the displacement is relatively uniform as a whole with the maximum displacement of 4.6mm.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003e, the displacement of the surrounding rock of the roadway at a distance of 20m behind the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. As the working face moves away, the displacement around the roadway decreases to varying degrees. The negative side and upper corner of the tunnel experience slight displacement, with the maximum displacement being in the middle of the negative side, with a maximum displacement of 32.8 mm. The maximum displacement of the positive side of the tunnel is in the middle of the positive side, with a maximum displacement of 10.5mm. The vertical displacement mainly occurs at the top and bottom of the tunnel, showing an overall asymmetry. There is a slight displacement at the top of the tunnel, and the area with the largest displacement is the middle of the tunnel roof, with a maximum displacement of 21.0mm. There is a slight displacement at the bottom and lower corners of the tunnel, and the displacement is relatively uniform overall, with a maximum displacement of 7.0mm.\u003c/p\u003e\n\u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003e that the displacement of the surrounding rock of the roadway 60m behind the mining face mainly occurs in the area of two sides of the roadway, showing an overall asymmetry. Slight displacement occurs in the negative side and upper corner of the roadway, mainly concentrated in the middle of the negative side, with a maximum displacement of 22.9mm. The displacement of the positive side of the roadway decreases linearly with the distance from the roadway, and the maximum displacement area is the middle of the positive side. The maximum displacement is 8.1mm. The vertical displacement mainly occurs at the top and bottom of the roadway, showing an overall asymmetry. Slight displacement occurs at the top of the roadway, and the displacement decreases with the distance from the roof. The largest displacement area is the middle of the roof, with a maximum displacement of 16.4mm, while slight displacement occurs at the bottom and lower corner of the roadway, and the displacement is relatively uniform overall, with a maximum displacement of 5.1mm.\u003c/p\u003e\n\u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e17\u003c/span\u003e, it can be seen that the displacement of the surrounding rock of the roadway at 100m behind the mining face mainly occurs on the two sides of the roadway, showing an overall asymmetry. There is slight displacement in the negative side and upper corner of the roadway, with a maximum displacement of only 16.3mm. The displacement of the positive side of the roadway decreases linearly with the distance from the roadway position, with a maximum displacement of 7.4mm. The vertical displacement mainly occurs at the top and bottom of the tunnel, showing an overall asymmetry. There is slight displacement at the top, and the displacement decreases hierarchically as the distance from the roof of the tunnel increases, with a maximum displacement of 13.8mm. There is slight displacement at the bottom and lower corners of the tunnel, and the displacement is relatively uniform overall, with a maximum displacement of 4mm.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4 Relationship between deformation and failure of surrounding rock of mining roadway\u003c/h2\u003e\n\u003cp\u003eBased on the numerical simulation results, the displacement of the top and bottom of the roadway and the size of the plastic zone are measured at 100m, 60m, 20m, the working face, 20m, 60m, and 100m in front of the working point respectively, and the relationship diagram between the displacement and the size of the plastic zone is drawn to analyze the relationship between the deformation of the mining roadway and the size of the plastic zone. The mechanism of large deformation in the mining roadway under the near residual coal pillar is revealed.\u003c/p\u003e\n\u003cp\u003eFrom Fig.\u0026nbsp;18, it can be seen that the plastic zone at 100m behind the working face is significantly developed on the front and top sides, with maximum dimensions of 17.24m and 3.96m, respectively. The displacement is also relatively large on the negative side and bottom sides; Due to the formation of a plastic zone before excavation, the size of the plastic zone is abnormal near the bottom plate of the negative slope. Ignoring the abnormal value, the maximum plastic zone size is only 1.71m and the maximum displacement is 6.29mm; The displacement of the bottom plate is minimal and there is no plastic zone present. From the trend of change, the displacement of the bottom plate and the size of the plastic zone are both small and have little change. The maximum displacement and size of the plastic zone of the positive and negative sides both occur near the top plate.\u003c/p\u003e\n\u003cp\u003eAs can be seen from Fig.\u0026nbsp;19, the plastic zone at 60m behind the working face develops significantly in the front side and top plate, and the displacement is larger than that of the negative side and bottom plate. Due to the formation of the plastic zone before excavation of the negative side, the size of the plastic zone is abnormal near the bottom plate of the negative side, and the maximum size of the plastic zone is only 3.41m when the abnormal value is ignored. The displacement of the bottom plate is minimal and only 0.41m plastic zone appears. From the trend of change, the maximum displacement of the roof appears in the position of the negative side of the middle, and the maximum plastic zone size appears in the position of the positive side of the middle. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum displacement and the maximum plastic zone size of the positive and negative sides appear near the top plate.\u003c/p\u003e\n\u003cp\u003eIt can be seen from Fig.\u0026nbsp;20 that at 20m behind the working face, the maximum size of the plastic zone on the front side and the top plate is 16.32m and 6.16m respectively, and the displacement is larger than that on the negative side and the bottom plate. The displacement of the negative side and the plastic zone gradually increase. The maximum plastic zone size is 7.7m and the maximum displacement is 10.58mm. The displacement of the bottom plate is minimal and only 0.83m plastic zone appears. From the changing trend, the maximum displacement of the roof appears in the middle position, and the maximum plastic zone size appears in the middle position near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum displacement of the front side and the size of the maximum plastic zone appear near the top plate. Both the maximum plastic zone size and the maximum displacement of the negative side appear in the upper part of the negative side.\u003c/p\u003e\n\u003cp\u003eAs can be seen from FIG. 21, at the position of the working face, the plastic zone develops obviously in the front side and the top side and the maximum plastic zone size is 12.3m and 5.73m, respectively, and the displacement is larger than that of the negative side and the bottom floor. The displacement of the negative side and the plastic zone gradually increase, the maximum plastic zone size is 4.71m, and the maximum displacement is 14.12mm. The displacement of the bottom plate is minimal and only 1.25m plastic zone appears. From the trend of change, the displacement mainly occurs in the middle of the surrounding rock, and the maximum plastic zone size appears near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum plastic zone size occurs near the top plate.\u003c/p\u003e\n\u003cp\u003eAs can be seen from Fig.\u0026nbsp;22, the plastic zone at 20m in front of the working face develops significantly on the front side and top plate, and the maximum plastic zone size is 9.93m and 5.73m, respectively. The displacement of the negative side and the plastic zone gradually decrease, the maximum plastic zone size is 2.58m, and the maximum displacement is 14.57mm. The displacement of the bottom plate is the smallest and only 1.67m plastic zone appears. From the trend of change, the maximum displacement mainly appears in the middle of the surrounding rock, and the maximum plastic zone size appears near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. The maximum plastic zone dimensions of the positive and negative sides appear near the top plate.\u003c/p\u003e\n\u003cp\u003eAs can be seen from Fig.\u0026nbsp;23, at 60m in front of the working face, the plastic zone develops significantly on the front side and top plate, with the maximum plastic zone size of 8.06m and 5.28m respectively, and the displacement is also larger than that of the negative side and bottom plate, with the maximum displacement of 27.50mm and 24.40mm. The displacement of the negative side and the plastic zone also decreases gradually. The maximum plastic zone size is 2.14m and the maximum displacement is 14.33mm. The displacement of the bottom plate is the smallest and only 1.67m plastic zone appears. From the trend of change, the maximum displacement of the roof appears in the middle position, and the maximum plastic zone size appears in the position near the front side. The displacement of the bottom plate and the size of the plastic zone are small and have little change. Both the maximum displacement and the maximum plastic zone size appear in the middle of the face. The maximum displacement of the negative side occurs in the middle part of the negative side and the maximum plastic zone size occurs near the top.\u003c/p\u003e\n\u003cp\u003eFrom Fig.\u0026nbsp;24, it can be seen that at a distance of 100m in front of the work, the plastic zone is significantly developed on the positive side and the top plate, with the maximum plastic zone size of 5.69m and 4.4m respectively, and the displacement is relatively large on the negative side and bottom plate; The negative displacement and plastic zone gradually decrease, with a maximum plastic zone size of 1.71m and a maximum displacement of 14.09mm; The displacement of the bottom plate is minimal and only a 1.25m plastic zone appears. From the trend of change, the maximum displacement of the top plate appears in the middle position, and the maximum plastic zone size appears near the front wall position; The displacement of the bottom plate and the size of the plastic zone are both small and have little change; The maximum displacement and maximum plastic zone size of the positive side both occur in the middle position; The maximum displacement of the negative side appears in the middle of the roof, and the maximum plastic zone size appears near the roof.\u003c/p\u003e\n\u003cp\u003eTo sum up, the size of the plastic zone of the surrounding rock of the roadway generally presents a positive correlation with the deformation of the surrounding rock, and the area with greater plastic failure usually has greater deformation. In the stress concentration area near the residual coal pillar of the upper coal seam, the deformation amount and the plastic zone size are both large. The maximum deformation amount of the roof is 25.55mm, the maximum plastic zone size is 6.61m, the maximum deformation amount of the normal side is 33.41mm, and the maximum plastic zone size is 17.24m. The deformation of the roof and negative side of the roadway is relatively small compared with the size of the plastic zone. The maximum deformation of the floor is 6.3mm, the maximum deformation of the plastic zone is 1.67m, and the maximum deformation of the negative side of the roadway is 14.57mm. Because the damage occurs before excavation, the maximum damage depth is 12.85m, and the maximum damage depth is about 7.7m when the damage before excavation is ignored.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eAccording to the above analysis, it can be concluded that during the mining process of 30501 face in Tashan Coal Mine, the surrounding rock of 30503 return air roadway produces regional stress variation rules and plastic zone failure characteristics. During the mining under the near seam residual coal pillar, asymmetric deformation and failure occur in the return air roadway 30503, and the asymmetric expansion rule of the plastic zone of the surrounding rock of the roadway is consistent with the asymmetric deformation rule, and there is a positive correlation between the two, that is, the larger the plastic zone, the roadway deformation increases. From this, it can be concluded that the large deformation mechanism of non-uniform and non-symmetrical coal seam roadway in the lower coal seam mining near coal seam is as follows: The stress concentration area generated under the residual coal pillar and the new stress field mined at the working face are superimposed on each other, resulting in irregular and asymmetric failure in the return air roadway. Among them, the plastic failure area near the top Angle of the positive side of the upper coal pillar is large, and the plastic failure area tends to decrease in the middle of the roof. When it gradually approaches the negative side, the failure range increases in a small range, and the overall shape is approximately \"butterfly\". With the continuous mining of the working face, the stress on one side of the surrounding rock will be deflected, resulting in a significant difference in stress concentration on both sides of the roadway, and the extension of the asymmetry in the plastic zone, which will lead to the large asymmetric deformation and failure of the surrounding rock of the roadway.\u003c/p\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eThrough the roof drilling, theoretical and numerical simulation calculation and analysis, this paper studies the deformation and failure mechanism of the surrounding rock of the mining roadway under the residual coal pillar during the mining process of the near coal seam in Tashan Coal Mine. The conclusions are as follows:\u003c/p\u003e \u003cp\u003e(1) Through roof drilling, the breaking law of the roof strata of the mining roadway is analyzed when the coal seam under the near residual coal pillar is mined. It is concluded that cracks and separated layers are more distributed in the roof of the roadway, but the overall integrity is good, showing irregular and asymmetric failure characteristics. Among them, the roof failure area near the side of the residual coal pillar in the upper section is larger and the damage depth is deeper. The destruction decreases from left to right.\u003c/p\u003e \u003cp\u003e(2) After the mining of the near seam, the difference stress change law and plastic zone failure characteristics of the mining roadway in the lower seam are analyzed with the change of mining position of the adjacent working face. It is concluded that when the distance between the roadway and the working face increases, the stress concentration value in the surrounding rock and the depth of the plastic zone both show a decreasing law. However, the stress concentration and the failure depth of the plastic zone near the residual coal pillar of the upper coal seam are larger, that is, under the action of stress superposition, the principal stress direction of surrounding rock will be deflected, and the roadway will appear asymmetric deformation and failure.\u003c/p\u003e \u003cp\u003e(3) The failure of the surrounding rock of the roadway is the result of the combined action of the strength of the surrounding rock and the regional stress. In the case of the principal stress deflection, the stress on both sides of the roadway is significantly different, and the plastic zone shows butterfly deformation and failure. The mechanical mechanism and asymmetric deformation mechanism of the butterfly failure in the non-uniform stress field under the deflection of the principal stress direction in the mining near the lower coal seam are obtained.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe raw data supporting the conclusion of this article will be made available by the authors, without undue reservation.Xiao-He Wang ([email protected]) should be contacted if someone wants to request the data from this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this paper, Xiao-He Wang, Wu Jing and Qing-Long Yun conducted experiments and collected experimental data; the full text was co-authored by Xiao-He Wang and Jiang-Hao Wang. Wen-Bo Zhang and Yi-Qing Wang are responsible for the data analysis and graphics rendering. Wen-Bo Zhang and Yi-Han Wu, Ji-Qiang Wang is responsible for the data analysis and graphics drawing; Xiao-He Wang, Ji-Qiang Wang and Wu Jing is responsible for the editing of the article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded by the Guizhou Province Science and Technology Support Plan Project of China (Qiankehe Support [2021] General 400). This support is gratefully acknowledged. The authors are grateful to the reviewers for discerning comments on this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublisher\u003c/strong\u003e\u003cstrong\u003e\u0026rsquo;\u003c/strong\u003e\u003cstrong\u003es Note\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLi Y, Gao X, Wang Z et al. Research on failure characteristics and control of lower roadway in very close seam mining [J]. Coal Technology,2022,41(08):62-66.\u003c/li\u003e\n\u003cli\u003eHuang Q, Wang X, He Y et al. 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Journal of China Coal Society, 21,46(06):1847-1854.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Short distance coal seam, Asymmetric failure, Space-time evolution mechanism, Non-uniform stress field","lastPublishedDoi":"10.21203/rs.3.rs-3807279/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3807279/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn order to demonstrate the temporal and spatial evolution mechanism of deformation and failure of the lower mining roadway in the residual coal pillar area during the mining process of close coal seam, this paper takes the close coal seam mining of Tashan Coal Mine of China Coal Group as the research background, adopts the roof borehole and peeping technology to detect the failure situation of the roof surrounding rock of the roadway, and determines the approximate failure area of the roadway surrounding rock. The stress evolution law of roadway surrounding rock and the failure characteristics of plastic zone are studied by theoretical analysis and numerical simulation. The results show that there is a positive correlation between the size of the plastic zone and the deformation of the surrounding rock, that is, the larger the plastic zone, the more severe the deformation of the surrounding rock. The stress concentration area under the residual coal pillar and the new stress field in the mining face are superimposed on each other, resulting in asymmetric deformation and failure in the surrounding rock of the return air roadway, and the shape is approximately \"butterfly\". The stress on one side of the surrounding rock will be deflected, resulting in a significant difference in stress concentration on both sides of the roadway, and the extension of asymmetry in the plastic zone will also occur, which will lead to the large asymmetric deformation and failure of the surrounding rock of the roadway.\u003c/p\u003e","manuscriptTitle":"Temporal and spatial evolution mechanism of deformation and failure of lower mining roadway in near residual coal pillar area","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-02 11:07:55","doi":"10.21203/rs.3.rs-3807279/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2df0cd65-2280-4c67-a028-47c7357202af","owner":[],"postedDate":"January 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":27877989,"name":"Earth and environmental sciences/Solid earth sciences/Mineralogy"},{"id":27877990,"name":"Physical sciences/Engineering/Civil engineering"}],"tags":[],"updatedAt":"2024-02-06T05:24:10+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-02 11:07:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3807279","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3807279","identity":"rs-3807279","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}