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In order to effectively control the large deformation of coal pillar and roadway during entry retained along gob side with small coal pillar, taking 1311 and 1312 working faces of a coal mine in Shanxi Province as engineering background, the structural characteristics of overlying rock are studied, and the stress source of entry retained along gob side with small coal pillar and the principle of roof cutting and pressure relief are analyzed, then the roof cutting and pressure relief technology of shaped charge blasting with combined and grouped of deep and shallow holes is put forward. According to the geological conditions of 1311 working face, through the calculation of caving zone and crack zone height of the working face, the analysis of roof breaking and instability conditions and the calculation of crack zone blasting radius, the key parameters of roof cutting by deep and shallow hole combined blasting are determined. Through the numerical simulation and analysis of roof cutting and pressure relief in different key strata, the variation law of vertical stress acting on small coal pillar is obtained, as follows: no roof cutting > only cut layer 2 > only cut layer 1 > cut layer 3 + partial layer 2 > cut layer 1 ~ 3; Based on these, a cooperative control scheme of “roof cutting and pressure relief by shaped charge blasting with combined and grouped of deep and shallow holes” + “anchor-cable combined support” + “coal pillar strengthened” is put forward. The field industrial test results show that the control effect of small coal pillar and roadway surrounding rock is good. [ABSTRACT FROM AUTHOR]

The extraction of thick coal seams at high intensity inevitably leads to more severe strata pressure, especially when influenced by adjacent goaf areas. The combination of multiple strata pressures results in significant deformation of the surrounding rock along the goaf roadway. In order to the problem of large deformation of the surrounding rock of the gob-side roadway, this study proposes a novel method for protecting gob-side roadway using energy-gathering blasting (EGB) to cut roof and relieve pressure, which combines parallel pull-rods fracture theory with the Weibull strength of rock microelements to establish a new energy-gathering blasting model. The optimal spacing of blast holes is determined and the correlation between damage degree and energy-absorbing coefficient as well as explosive center distance is analyzed. Numerical simulation methods are employed for validation, and the results demonstrate that the EGB technique effectively blocks the transmission of stress in non-energy-absorbing directions, further enhancing energy accumulation in the energy-gathering direction. This leads to slower attenuation of effective stress and particle vibration velocity in the energy-gathering direction, promoting the directional expansion of energy-gathering fractures and revealing the mechanical mechanism of energy-gathering fracture directional expansion. Based on this technology, a method for relieving overburden pressure in the surrounding rock is proposed. Through EGB technique cutting the long cantilever structure of thick and hard rock layers is snapped, force them to collapse and expand, thereby supporting the overlying structure and reducing stress concentration in the roadway's surrounding rock. This method reveals the mechanism of pressure unloading in the mining area after roof cutting. Furthermore, based on theoretical analysis, the parameters for roof-cutting pressure unloading are designed, and engineering practice confirms the successful reduction of stress on both sides of the roadway ahead of the working face, optimizing the stress environment of the roadway and achieving the goal of protecting the tests have validated the effectiveness of the method, significantly reducing stress and deformation in the surrounding rock of the roadway. The research findings provide a scientific basis for controlling roadway deformation under similar conditions. Highlights: A new EGB method is proposed based on characteristics of rock. A novel damage model for EGB has been constructed by combining the rock micro element strength with the tension rod fracture theory. The application of EGB method in coal mining can effectively reduce mine pressure and protect roadway. [ABSTRACT FROM AUTHOR]

Abstract In order to effectively control the large deformation of coal pillar and roadway during entry retained along gob side with small coal pillar, taking 1311 and 1312 working faces of a coal mine in Shanxi Province as engineering background, the structural characteristics of overlying rock are studied, and the stress source of entry retained along gob side with small coal pillar and the principle of roof cutting and pressure relief are analyzed, then the roof cutting and pressure relief technology of shaped charge blasting with combined and grouped of deep and shallow holes is put forward. According to the geological conditions of 1311 working face, through the calculation of caving zone and crack zone height of the working face, the analysis of roof breaking and instability conditions and the calculation of crack zone blasting radius, the key parameters of roof cutting by deep and shallow hole combined blasting are determined. Through the numerical simulation and analysis of roof cutting and pressure relief in different key strata, the variation law of vertical stress acting on small coal pillar is obtained, as follows: no roof cutting > only cut layer 2 > only cut layer 1 > cut layer 3 + partial layer 2 > cut layer 1 ~ 3; Based on these, a cooperative control scheme of “roof cutting and pressure relief by shaped charge blasting with combined and grouped of deep and shallow holes” + “anchor-cable combined support” + “coal pillar strengthened” is put forward. The field industrial test results show that the control effect of small coal pillar and roadway surrounding rock is good.

Currently, research and practice on roadway floor heave mainly explore the deformation mechanism and control technology of roadway floor. The mechanical analysis of floor before and after roof cutting and pressure relief in gob-side entry retaining is not comprehensive. In order to solve the above problem, mechanical models of the surrounding rock and floor of the roadway before and after roof cutting are constructed based on the features of coal partition failure. The effects of solid coal, roadway support, and goaf on the floor are analyzed. The analytical solutions for the floor heave of the roadway before and after roof cutting are obtained. The conclusion is drawn that the elastic-plastic zone of the coal wall beside the roadway, the support structure of the roadway, and the load on the floor of the subsidence zone jointly affect the magnitude of the roadway floor heave. Numerical simulation is used to verify the features of rock mass failure, stress distribution, and changes in floor heave in gob-side entry retaining before and after roof cutting and pressure relief. The results show that roof cutting and pressure relief technology can effectively reduce the damage area on the solid coal side and top of the roadway, and maintain the stability of the roadway rock mass structure. The maximum stress of the roadway floor, the resistance of the roadway side support, and the amount of roadway floor heave all decrease, with an average decrease of 25.78%, 56.14%, and 54.07%, respectively. The on-site application results show that the amount of floor heave of thick hard top in gob-side entry retaining is reduced from 709.345 1 mm to 320.965 8 mm. The roof cutting and pressure relief technology can optimize the stress structure of the surrounding rock of the roadway, suppress the floor heave of the roadway, and effectively improve the floor damage.

According to the engineering geological characteristics and production technology level of Qianyingzi Coal Mine, the stability control technology of surrounding rock of the cutting roof and pressure relief roadway is proposed. For the advanced section, lagging section and stable section of the mining roadway, technical measures of advanced reinforcement support, side wall protection and lagging temporary support were proposed. Through the real-time monitoring system, the stress of anchor cable and surrounding rock deformation of goaf roadway are monitored, the deformation characteristics of roadway and stope surrounding rock are studied, and the law of mine pressure development in self-formed roadway without coal pillar is revealed by the comparison and analysis with the existing goaf roadway. The results show that the deformation rate of surrounding rock reaches the maximum at the position of 170 m away from the working face, and the deformation of surrounding rock is the most intense at this stage, and then tends to be gentle, and the deformation of surrounding rock reaches the stable stage when the working face lags 220 m. The application effect of the pre-cracking blasting cutting roof for gob-side entry retaining in the W3233 working face of Qianyingzi Coal Mine has reached the expected goal.

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Aiming at the problem of cutting roof and retaining roadway on the right third working face of 16#, east second mining area of Jixian Coal Mine in Shuangyashan city, the mechanical model of surrounding rock of cutting roof and retaining roadway is established, and the theoretical calculation formula of key parameters such as cutting height and cutting angle is given; the influence of roof cutting parameters (roof cutting height and angle) on the stress distribution and deformation characteristics of the surrounding rock is further analyzed. The numerical simulation results show that the greater the roof cutting height is, the better the relief effect is; with the increase of the cutting angle, the side stress of solid coal shows an increasing trend, which also creates certain conditions for the caving of gangue. The similar simulation results show that when the coal seam is mined to a certain distance, the upper rock stratum in the goaf collapses at the same time, and the rock mass in the slit range and caving rock mass form a hinged joint, that is, the side filling of the roadway is basically completed, and the structure of “low cantilever beam + high hinged rock beam” is formed above the roadway. The engineering practice show that the cutting height is 8.0 m (2.39 m medium sandstone), the cutting angle is 10°, and the spacing of the drilling holes is 600 mm. When it is about 60 m away from the working face, the roof subsidence is 168 mm, the solid coal wall displacement is 212 mm, the deformation of the gangue wall is almost 0, and the bottom heave is 120 mm.

Aiming at the problem that roof deformation of cross fault roof cutting and pressure relief self-formed roadway is large and difficult to support, the mechanism of roof deformation of self-formed roadway in cross fault roof cutting and pressure-relieving roadway is studied based on the engineering background of the transport channeling of No. 11101 face in the eastern district of Qipanjing Coal Mine, and the effect of the support method of “roof cutting and pressure relief + constant resistance anchor cable” on roof deformation control of self-formed roadway in cross-fault roof cutting and pressure relieving roadway is studied. A mechanical analysis model was established to study the influence of the relevant parameters of the roof on the direct roof stress of the roadway, and the deformation process of the roof of the roadway was divided into four stages. The calculation method of each stage and the total vertical displacement of the roof of the roadway were studied and the calculation formula was given, and the relevant parameters were substituted into the formula to solve the vertical displacement of the roof of the roadway across the fault. 3DEC numerical simulation software was used to establish the numerical calculation model of self-formed roadway with cross fault roof cutting and pressure relief, and the stress-strain evolution law of roadway roof near the fault and the control effect of constant resistance anchor cable were studied. The research results show that the error between the numerical simulation and theoretical analysis data of roadway roof deformation is 1.14% and 4.04%, respectively. The constant resistance anchor cable can effectively reduce the deformation of roadway roof. Compared with the non-constant resistance anchor cable model, the vertical displacement of roof on slit side of upper wall roadway is reduced to 16.8%, and the vertical displacement of roof on slit side of lower wall roadway is reduced to 50.7%. The roof of upper and lower wall roadway will have different degree of stress concentration in the process of mining through the measurement section of roadway, and the vertical stress concentration value of upper wall roadway roof is larger than that of lower wall roadway, which is 5.72 MPa and 4.48 MPa respectively. The constant resistance anchor cable can reduce the deformation rate of roadway roof near the fault, and control the deformation of roadway roof jointly with the gravel wall after the filling is completed. By comparing the displacement monitoring data of surrounding rock along the channel of No. 11101 face transport with the calculation results of the theoretical model, the error is less than 10%, which proves that the support method of “roof cutting and pressure relief + constant resistance anchor cable” has a good control effect on the roof deformation of cross fault roadway.

To address stress concentration in mining roadways, particularly in the inclined, thick, and hard roof, and lessen the impact of sudden overlying strata collapse, a comprehensive study was conducted on the 1301N transport roadway in No.6 Great Wall Mine. The research utilized various methods such as theoretical analysis, numerical simulation, and field monitoring to optimize the key parameters of roof cutting and roadway retaining, leading to improved control of the surrounding rock and reduced risk of impact disturbance. Firstly, based on field geological data, the theoretical minimum roof-cutting height and angle of the 1301N transportation gateway were calculated using the coefficient of rock crushing and swelling and masonry beam theory. Furthermore, in order to confirm and enhance the accuracy of the theoretical findings, we utilized PFC2D numerical software to create a model of the roof-cutting retaining roadway situated in the No.1301N working face. By employing the control variable approach, we studied the response characteristics of roof stress, displacement, and surrounding rock fabric tensor of the retaining roadway at various roof-cutting heights and angles. The analysis results indicate a logarithmic relationship between cutting height and pressure relief effect. The effect increases with height, but growth amplitude decreases. There is an “S” growth relationship between the roof-cutting angle and the pressure relief effect. The pressure relief effect first increases and then decreases with the increase of the roof-cutting height. The change law between pressure relief parameters and pressure relief effect reveals that there is an optimal value for the selection of the roof-cutting height and an optimal solution for the selection of the roof-cutting angle. Based on the results of theoretical analysis and numerical simulation, it is determined that the most suitable roof-cutting height is 13 m, and the optimal roof-cutting angle is 10°. The field monitoring shows that the control effect of the surrounding rock under the roof-cutting parameters is good, and the deformation of the surrounding rock of the retaining roadway is small. It can effectively meet the mining demand of the next working face and verifies the effectiveness of optimizing the roof-cutting parameters. This provides a theoretical basis and practical reference for the selection of the parameters of roof cutting and retaining roadway under similar geological conditions.

Abstract Though the recovery rate of coal resources can be effectively improved by adopting the gob‐side entry longwall face, which is also easy to cause tension between mining and excavation. Therefore, a new type of roadway layout, narrow coal pillar entry retained (NCPER), was invented in the study. The NCPER is excavated together with the tailgate of next longwall face before the mining of prior longwall face, which is retained and reused during the mining of the next longwall face. The layout is based on the advantages and successful experience of the double roadways excavation, the gob‐side entry retained, and the roadway driven along gob‐side and heading for adjacent advancing coal face; moreover, the NCPER significantly shortens the preparation time of the longwall face while improving the recovery rate. Taking the production geological conditions of Yushuling Mine as the engineering background, the influence of factors such as roof‐cutting pressure relief and coal pillar width on the stability of the narrow coal pillar from the perspective of improving the stress environment of the roadway and strengthening the weak structure support of the surrounding rock was studied, and reasonable suggestions for selecting parameters of roof cutting and coal pillar width were given. Furthermore, the bidirectional grouting cable and its joist were used to strengthen the narrow coal pillar and the roadway roof, respectively, and a good effect of roadway control has been obtained. The invention and application of NCPER provided a new approach for the longwall face roadway layout and effectively eased the strained relationship between mining and excavating, which has a strong popularization and application value.

In order to solve the problem of large deformation of roadway under strong mining conditions, taking 1806N working face auxiliary transport channel of No. 1 mine of New Shanghai as engineering background, the causes of deformation and destruction of strong mining roadway and the mechanism of large deformation of surrounding rock were analyzed by field exploration, theoretical analysis and numerical simulation methods, and corresponding control strategies were put forward for engineering application. The results show that the main reasons for deformation and failure of surrounding rocks are low rock strength, heavy water-rich roof and strong mining stress. Based on the control mechanism of large deformation roof cutting of surrounding rocks, the design scheme of deep directional roof cutting combined with tunnel reinforcement was formed. By means of numerical simulation, the stress variation law of the roadway with broken roof and the roadway without broken roof is compared and analyzed. The maximum vertical stress at the end of the roadway with broken roof is 14.6 MPa, the maximum vertical stress at the end of the roadway with broken roof is 12.5 MPa, and the vertical stress at the end of the roadway with broken roof is reduced by 14%. It is considered that broken roof has certain effect of cutting stress transmission and reducing tunnel shrinkage. Through field industrial tests, the displacement of the top and bottom slab at the end of the broken roof is reduced by 41. 5%, the deformation of the two sides is reduced by 12. 5%, and the development length of the bottom heave is reduced by 92%. The results show that the broken roof can effectively reduce the deformation of the end tunnel and the development length and height of the advanced bottom heave, which can provide reference for tunnel construction under similar engineering geological conditions. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Though the recovery rate of coal resources can be effectively improved by adopting the gob‐side entry longwall face, which is also easy to cause tension between mining and excavation. Therefore, a new type of roadway layout, narrow coal pillar entry retained (NCPER), was invented in the study. The NCPER is excavated together with the tailgate of next longwall face before the mining of prior longwall face, which is retained and reused during the mining of the next longwall face. The layout is based on the advantages and successful experience of the double roadways excavation, the gob‐side entry retained, and the roadway driven along gob‐side and heading for adjacent advancing coal face; moreover, the NCPER significantly shortens the preparation time of the longwall face while improving the recovery rate. Taking the production geological conditions of Yushuling Mine as the engineering background, the influence of factors such as roof‐cutting pressure relief and coal pillar width on the stability of the narrow coal pillar from the perspective of improving the stress environment of the roadway and strengthening the weak structure support of the surrounding rock was studied, and reasonable suggestions for selecting parameters of roof cutting and coal pillar width were given. Furthermore, the bidirectional grouting cable and its joist were used to strengthen the narrow coal pillar and the roadway roof, respectively, and a good effect of roadway control has been obtained. The invention and application of NCPER provided a new approach for the longwall face roadway layout and effectively eased the strained relationship between mining and excavating, which has a strong popularization and application value. [ABSTRACT FROM AUTHOR]

The goaf at the side of the roadway pillar (lateral roof) often encounters thick and hard roof, which will not collapse naturally in a short period of time, and is easy to cause mine earthquake and roof fall. Taking the 113105 working face of Bojiang Haizi Coal Mine as the research background, aiming at the strong ground pressure phenomenon caused by the lateral long cantilever, based on roof fracture mechanics, a mechanical model of lateral long cantilever of goaf is established to analyze the fracture length of rock mass between the roof before and after roof cutting. The results show that when the tensile strength, thickness and friction coefficient of rock mass are large, the front beam length after fracture is longer; when the unit weight and cutting angle of rock mass increase, the back beam length after fracture is longer. Through physical test, the long cantilever broke into two 5-8 m long blocks after roof cutting, and the roof collapsed periodically, realizing the purpose of active pressure relief on the lateral cantilever rock layer of the roadway. The field test shows that the surrounding rock stress is transferred after the blasting roof cutting, the ground pressure manifestation is reduced, and the roadway deformation can meet the normal mining demand of the working face, ensuring the high production and high efficiency of the mine.

To address the support difficulties caused by the dynamic pressure from the adjacent working face in gob-side entry driving, this study, taking the 8103 working face of the Jinhuagong Coal Mine in Shanxi Province as an example, adopted methods such as theoretical analysis, physical experiments, numerical simulations, and field practices to explore roof-cutting and pressure-relieving techniques to control the surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure. Fractures of the lateral roof, stresses on the surrounding rock, and deformations with different cutting-roof parameters were analyzed to determine the reasonable parameters for applications. The following results have been obtained. The longer the lateral cantilever length of the roof, the greater the load borne by the surrounding rock. Therefore, the key to reducing the confining pressure in a roadway is reducing the lateral cantilever length of the roof. After roof cutting, the roof of the gob area collapsed more completely. The stress on both sides of the coal pillar and that on the ribs of the solid coal dropped by 7.72 MPa and 4.16 MPa, respectively. The key roof-cutting parameters were analyzed by the UDEC numerical software, and the reasonable roof-cutting angle and height were determined to be 12° and 14 m. A support scheme combining "steel strip + bolt + anchor cable + roof cutting" was proposed. With the scheme applied, the displacement of both sides of the coal pillar was 61 mm shorter than that in the non-test section, and the duration in which the roadway was affected by mining was 11 days shorter. Therefore, the rationality of the selected roof-cutting and support parameters in this study is verified. The proposed scheme can effectively control the stability of surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coal is the principal energy of China, and the coal industry is an important basic industry related to the energy security. For a long time, the underground coal resources mining in China has always been based on the longwall 121 mining method. This mining system has many problems such as waste of coal resources, high rate of entry excavation and concentrated stress of coal pillars. In order to solve the three bottlenecks and prominent problems of “safety, mining cost and coal recovery rate” existing in the current mining system, we established a mining engineering model based on the mining damage invariant equation, analyzed the mechanical principle of automagical entry formation without coal pillars. On this basis, the key technologies of 110 and N00 mining method, such as directional presplitting and pressure relief of roof, NPR bolt/cable support are developed. The technical objective of “being able to control the roof, cut off the roof, make the roof easy to collapse and protect the entry rib” has been achieved. The 110 mining method of automagical entry formation without coal pillars and the N00 mining method at different development stages have been formed. The 110 mining method unifies the two sets of processes of coal mining and excavation initially, so that each coal mining face can dig one less mining entry, and no pillar mining is realized. The N00 mining method is based on the 110 mining method, which completely unifies the two processes of coal mining and excavation. The mining pressure is used to automatically form the roadway, thus eliminating the excavation of roadways and thoroughly eliminating the long-standing problem of strained relations of mining and excavation. The field practice shows that the 110 mining method cuts off the stress transmission between the roof of the goaf and the roof of the entry. The mine pressure and self balance of the surrounding rock of the retained entry is realized by using the crushing and swelling property of the collapsed gangue. The N00 mining method innovates the original mining technology, changes the layout of the traditional mining system, and realizes no entry digging and automatic entry formation in the whole mining area.

In order to improve the recovery rate of coal resources in general, Chengzhuang Coal Mine has carried out and implemented the technology of gob-side entry retaining in 5309 large height mining face. In view of the complex conditions such as 6 m thick coal seam and hard thick rock stratum in the roof, the application of directional blasting presplitting and flexible formwork concrete technology in the mining face of “thick coal seam and hard roof” is emphatically discussed by means of theoretical analysis and field test. The results show that the deformation of gob side entry retaining roadway develops rapidly within 10-90 m behind the working face; the wall pressure of gob-side entry retaining reaches the maximum within 50-100 m behind the working face; the cooperative application of blasting presplitting, roof cutting and pressure relief and flexible formwork concrete wall not only reduces the influence of periodic pressure on the roof of the roadway reserved along the goaf, but also enhances the bearing capacity of the roadway side, which obviously improves the overall stability and reliability of the roadway.

IntroductionSoft rock mining roadways are severely deformed and damaged during coal mining. Blindly increasing the support strength not only has little effect but also wastes material resources.MethodsMaintaining the original support parameters, model experiments were conducted to investigate the mechanism of pressure relief protection of the front soft rock mining roadway by cutting the roof behind the longwall face. The roof-cutting height was 2.5 times the coal thickness, the angle was 10°, and the advance distance is 0. ResultsThe study found that the abutment stress borne by the roof of the original roadway was transferred to the coal seams to be mined. The average stress of the coal seams increased by 10%, while the average stress of the surrounding rock in the front roadway decreased by 12.57%. The roof cutting weakened the influence of the overlying strata in the gob on the rear roadway. The stability of the rear roadway also weakened the traction effect on the front roadway. The vertical convergence of the front roadway decreased by 27.3%, and the deformation of the coal pillars decreased by 15.7%.DiscussionThe roof cutting reduced the stress of the front roadway to the peak failure stress, fundamentally weakening the main factor that induced the deformation of the front roadway. Numerical simulations were performed to research the deformation and stress distribution properties of the surrounding rock after roof cutting, and the model experimental results were validated. Finally, engineering recommendations are presented, which are expected to provide a reference for controlling the roadway stability of soft rock masses.

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• Analysis the mining-induced failure, stress, and pore water pressure evolution rule before and after roof cutting. • A multi-factor fusion prediction model for floor failure depth of OPWF mining. • A water prevention technical guarantee system of ultra-wide OPWF mining on confined aquifer. The floor failure depth of the ultra-wide opposite pulling working face (OPWF) mining on the confined aquifer is larger, and the risk of water inrush is higher. Based on the engineering background of Binhu Coal Mine (BHCM) in North China Coalfield, this paper analyzes the distribution rule of floor support pressure in OPWF mining, carries out numerical simulation before and after roof cutting, and microseismic-electrical joint dynamic monitoring. The results show that the failure depth, vertical stress, maximum principal stress, maximum shear stress, and pore water pressure of floor after roof cutting are decreased by 28.6 %, 15.5 %, 12.1 %, 30.9 %, and 41.7 %, respectively, the stress concentration coefficient is also decreased by 19.5 %. Roof cutting blocks the propagation path of mining stress, reduces the mine pressure concentration and controls the floor failure depth. Using the optimal univariate function between the floor failure depth and mining width, mining depth, mining height, roof cutting height, working face stagger distance, a multi-factor prediction model for the floor failure depth of the OPWF mining is established, and the accuracy of the model is more than 90 %. Combined with the methods of exploration, treatment, and monitoring, the water disaster prevention technical guarantee system in the ultra-wide OPWF mining on the confined aquifer is constructed, which provides a new method for the prevention and control of floor water disasters during mining. [ABSTRACT FROM AUTHOR]

• The mechanism of roof failure in close-distance coal seams are analysed. • The calculation model considers rotational sinking and roof separation deformation. • Numerical simulation was conducted to study the roof control parameters in CDCSs. • The optimization scheme avoids failure to the roadway roof in CDCSs. Multiple mining operations in close-distance coal seams (CDCSs) can reduce the integrity and bearing capacity of the surrounding rock, leading to roof fracturing and widespread subsidence in gob-side entry retaining (GER). This highlights the critical need for research on roof control technology. For this purpose, adopting the panel of the Xinchazhuang Coal Mine (the distance between two coal seams is 7.3 m) as the engineering background, a theoretical model of GER of CDCSs was established on the basis of the surrounding rock structure and roof rock movement characteristics, and the roof failure deformation mechanism was examined. The roof failure deformation encompasses two parts: rotational sinking of roof rock blocks and roof separation deformation. To achieve roof control, a strategy involving optimized roof cutting and higher preload cables was suggested. The impacts of key roof control parameters on roadway deformation were examined and compared by numerical simulation studies. The findings showed that optimized roof cutting resulted in a 21.1 % reduction in the roof stress, whereas the use of roof cables with higher preload levels resulted in a 55.1 % decrease in roadway deformation, effectively mitigating rotational sinking and roof separation deformation. The field tests demonstrated that the optimized scheme facilitated roof integrity preservation, and the maximum deformation of the roof reached 98 mm, a decrease of 68.5 % on average from that in the original scheme. These research results could provide a reference for roof support in CDCSs roadways under similar geological conditions. [ABSTRACT FROM AUTHOR]

To address the support difficulties caused by the dynamic pressure from the adjacent working face in gob-side entry driving, this study, taking the 8103 working face of the Jinhuagong Coal Mine in Shanxi Province as an example, adopted methods such as theoretical analysis, physical experiments, numerical simulations, and field practices to explore roof-cutting and pressure-relieving techniques to control the surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure. Fractures of the lateral roof, stresses on the surrounding rock, and deformations with different cutting-roof parameters were analyzed to determine the reasonable parameters for applications. The following results have been obtained. The longer the lateral cantilever length of the roof, the greater the load borne by the surrounding rock. Therefore, the key to reducing the confining pressure in a roadway is reducing the lateral cantilever length of the roof. After roof cutting, the roof of the gob area collapsed more completely. The stress on both sides of the coal pillar and that on the ribs of the solid coal dropped by 7.72 MPa and 4.16 MPa, respectively. The key roof-cutting parameters were analyzed by the UDEC numerical software, and the reasonable roof-cutting angle and height were determined to be 12° and 14 m. A support scheme combining “steel strip + bolt + anchor cable + roof cutting” was proposed. With the scheme applied, the displacement of both sides of the coal pillar was 61 mm shorter than that in the non-test section, and the duration in which the roadway was affected by mining was 11 days shorter. Therefore, the rationality of the selected roof-cutting and support parameters in this study is verified. The proposed scheme can effectively control the stability of surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure.

In Lianghuai area of China, due to the influence of the large buried depth of the mine and the complicated roof conditions, when gob-side entry is retained, the roof deformation of the gob-side entry retaining is large, the coal side is easily extruded and the floor heave is serious. In order to solve this problem, taking the 360804 fully mechanized working face of Xinji No.1 Mine as the research object, the technology of gob-side entry retaining supported by flexible formwork wall with roof cutting and pressure relief is proposed. The bilateral cumulative energy blasting technology is used in the advance working face to carry out pre-splitting of the roof of the gob-side entry retaining to reduce the roof stress of the gob-side entry retaining effectively. With the continuous mining of the working face, when the working face coal wall is lagged a certain distance, the flexible formwork wall made of concrete is used to support the roadway side in order to achieve strong support for the roof of the gob-side entry retaining. The field application results show that there are two obvious fractures at different heights of blasting hole, which indicates that the blasting roof cutting effect is good. The maximum separation of the shallow part of the roadway roof is 7 mm, the maximum separation of the deep part is 19 mm, and the roadway roof support is relatively intact. The roadway roof and floor deformation is 430 mm, the two sides deformation is 487 mm, the roadway surrounding rock deformation is within the allowable range, and the roadway retaining effect is good.

To study the influence of roof cutting and pressure relief on the surrounding rock control effect of gob-side entry retaining, numerical simulation was carried out by UDEC software, and the stress and deformation characteristics law of roadway surrounding rock under two states of whether the lateral roof collapsed or not were analyzed. The results show that compared with the state of the direct roof hanging, the vertical stress concentration coefficient of the coal seam on the coal side and the supporting wall beside the roadway are reduced by 0.19 and 0.49 respectively when the direct roof collapses. Under the condition of direct roof caving, the roof settlement, floor heave, coal wall internal displacement and wall internal displacement of roadway are reduced by 73%, 60%, 27% and 75% of that of direct roof hanging respectively. The direct roof hanging is an important reason for the large deformation of surrounding rock in gob-side entry. Cutting the roof will make the direct roof above the goaf collapse effectively, and the weight of overlying strata can not effectively transfer to the surrounding rock, and the collapsed rock stratum will play a certain supporting role on the roof, and also help to reduce the surrounding rock pressure.

In order to solve the application problem of gob-side entry retaining formed by roof cutting (GERRC) technology of working face under goaf in close-distance coal seams, the 9101 working face and its return air roadway of Xiashanmao Coal Mine were taken as engineering background. The key parameters of GERRC were studied by means of theoretical analysis, numerical simulation and field test. The results show that: The roof cutting height (RCH) should be not less than the height of stope caving, meanwhile, when the rock strata collapsed, broke and expanded within RCH, it should meet the support effect on basic roof. And the RCH should be less than the distance between coal seams. The roof cutting angle (RCA) should meet the mechanical conditions of rock mass failure along the structural plane, and it should meet the geometric condition of not squeezing the roadway roof during the rotation and subsidence of the stope basic roof. When the RCH was 7.5m, the RCA was 15 degrees and the blasting charge structure was 4+3+3+2, the stress distribution and roof subsidence were most optimal. Three rows of constant resistance with large deformation (CRLD) anchor cables were used to strengthen roadway roof. The unit support, hydraulic prop and π-shaped beam were carried out as temporary support in roadway. The surrounding rock of roadway tended to be stable when lagged behind 100m, and the effect of GERRC was good after the temporary support measures were withdrawn. [ABSTRACT FROM AUTHOR]

Aiming at the rapid and precise construction requirements for a large number of directional pre-borehole of roof cutting and pressure relief in coal mines, ZDY2-300LM full hydraulic drilling rig with double working arms is developed by means of variable amplitude mechanism with multiple degrees of freedom. LUDV hydraulic system is used to solve the problem of mutual interference when the two power heads work. AMESim software is used to build the simplified model and carry out the simulation research. The results show that the output flow and pressure are independent from each one and do not affect each other. The water way of two position three-way valve is adopted to solve the problem of backwater in the hole of loading and unloading drill pipe and increase the comfort of construction personnel. The test results show that the drilling rig has the advantages of fast angle adjusting speed, more freedom of luffing mechanism, accurate drilling positioning, good hole forming quality, and the construction efficiency meets the requirements of working face advance, which is 67.5% higher than that of other conventional non special drilling rigs.

The application of gob-side entry retaining(GER) in steeply dipping seam with hard roof has always been a difficult problem.Based on the characteristics of gangue slide accumulation in gob with steeply dipping seam, aim at make full use of the self bearing capacity of the gangue, the technology of the gob-side entry retaining with roof cutting(GERRC) in steeply dipping seam is proposed.Through the theoretical analysis and numerical simulation, the roof structures and surrounding rock stresses of the GERRC and the traditional GER were compared.According to the stability and deformation characteristics of roof in different stages of GEERC, the cutting angle and supporting technology were optimized, and field tests were carried out.This research finds that, when the roof structure of the GERRC is in a statically indeterminate state, it is more favorable for roadway stability.The stability of the surrounding rock in the dynamic section is the worst.Roadway strengthening support and blocking gangue support can be coordinated with the roof deformation.The field tests were successful.The cumulative deformation of the roof and floor is 177 mm.The supporting resistance of pillars is less than 28 MPa without obvious bending pillars.

To solve the problem of large deformation of concrete wall caused by large bearing capacity of gob-side wall retaining in large mining height working face, the concrete bearing structure of gob-side brick retaining was determined for the site conditions of Wangzhuang Coal Industry. We calculated the load-bearing capacity of concrete wall and its maximum load-bearing capacity, and proposed roof cutting and pressure relief technology to reduce the load on the wall. Through numerical simulation, it is concluded that the peak stress of lateral support of the working face can be effectively reduced, the load on the concrete wall can be reduced, the stress concentration on the coal side of the mining roadway can be reduced, and the pressure can be relieved. Based on the numerical simulation results, the blasting top cutting technology was determined to be adopted, and the height of the roof cutting was 15 m, and the blasting scheme was designed. The practical results show that the blasting roof cutting scheme has successfully played the role of pressure relief and roadway protection.

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although no pillar coal mining technology can improve coal production, roof instability and collapse will seriously affect underground personnel safety and surface ecological environment. Therefore, the stability analysis model of surrounding rock in gob side entry retaining without coal pillar mining operation with roof cutting and pressure relief is constructed, and its applicability is verified. The results show that the difference between the experimental results and simulation results of the maximum roof deformation is small, which are 10.96cm and 11.24cm, respectively. Based on the model, the influence of roof cutting height and other parameters on the stability of roadway roof is analyzed. The results show that the roof deformation will deteriorate with the increase of cutting height, but the cutting angle has little effect on it. In addition, the plastic yield area of roof decreases with the increase of cutting height. When the cutting height is 4.0m, the area of roof plastic yield area is 16.87m², but when the cutting height is 10m, the area of roof plastic yield area decreases to 0.33m². However, the plastic yield area of roof increases rapidly with the increase of cutting angle. The area of plastic yield area is 16.87m² when the cutting angle is 20° and 65.69m² when the cutting angle is 80°, respectively. Therefore, in order to prevent uncontrollable collapse and deformation of roof during coal mining, it is suggested to design the height and angle of roof cutting as 6m and 40°, respectively. [ABSTRACT FROM AUTHOR]

The gas concentration of No.8 coal seam in north 3 panel of Duerping Coal Mine is high, the direct roof and the basic roof are both hard limestone, and it is easy to form a large area of hanging roof in the upper corner after stoping on working face, which is not easy to collapse naturally in a short time, resulting in a high degree of stress concentration in the protective coal pillar of the adjacent working face. In the process of stoping of working face, floor gas drainage roadway arranged under the coal pillar is often affected by advance and lateral supporting pressure, which often results in large deformation and seriously affects ventilation and gas extraction of the roadway. Under influence of strong dynamic pressure, the floor gas drainage roadway shows intense pressure, which cannot satisfy the dual-use of one roadway. In view of the above problems, taking 68306 working face as research object, application research on roadway protection (floor gas drainage roadway) technology by hydraulic fracturing roof cutting pressure relief was carried out. The roadway protection technology by hydraulic fracturing roof cutting pressure relief was adopted on roof near the coal pillar side in air return way to cut off the connection between the roadway and the basic roof above the coal pillar, and minimize the length of side cantilever beam, weaken or transfer high stress of overlying coal pillar, reduce the load of coal pillar,so as to make 68306 floor gas drainage roadway be in a low stress area, fundamentally change the stress state of roadway surrounding rock,which achieves the effect of pressure relief and protect the roadway. The test results show that the deformation of surrounding rock of floor gas drainage roadway is obviously reduced after implementation of roadway protection technology by hydraulic fracturing roof cutting pressure relief, the deformation of the two sides and the roof and floor are controlled within 12% and 20% respectively. After using hydraulic fracturing roof cutting in air return way, the area of hanging roof in the upper corner of the working face is effectively controlled, and the gas accumulation in the upper corner is avoided.

Take the background of hard roof support problem of Qiuji Coal Mine 1102 working face haulageway, the cantilever beam model of uncutting roadway roof and the deformation and stress model of gob-side entry retaining are established. The maximum cantilever length of roadway roof cantilever beam structure is 4.68 m by theoretical calculation; the support resistance of the roadway roof with unit length suspended is 166.74 kN. Based on this, the parameters of roadway are designed, the specification of constant resistance and large deformation anchor cable is determined as ?准17.8 mm × 10 300 mm, and the spacing of two columns of anchor cable to be 1 000 mm and 2 000 mm respectively, and the roadway mine pressure is monitored. Monitoring results show that: within the range of 75 m to 173 m from the open-cut hole in 1102 haulageway, the maximum displacement of roadway roof and floor is about 36 mm, the roof abscission layer occurs at the junction of mudstone and limestone, the accumulative amount of abscission layer amount is 25 mm, the maximum stress of roof anchor cable is 150 kN, both deformation and stress are within a safe range, meet the stability requirement of roadway.

Affected by high in-situ stress and mining activities, In the original support scheme, entry of guotun coal mine is seriously deformed. The side of the head entry bulges out seriously and the roof sinks seriously. In order to solve the problem of large deformation of roadway, guotun coal mine adopts the technology of a nonpillar mining method with entry automatically retained in 4306 mining face. First, taking method of theoretical analysis, the stress model of blasthole under the deep condition is established, the mechanical conditions of crack propagation under the action of directional detonation wave and high surrounding rock binding force are obtained theoretically. Next, the mechanical model of roof cutting and pressure relief is established. Afterwards, The mechanical model of directional blasting under the condition of stress constraint is established by using LS-DYNA numerical calculation software, the evolution characteristics of effective stress and the law of crack growth are analyzed. In the end, the field test was carried out in 4306 mining face, and the blasting effect was observed by drilling peep, and the deformation of the head entry before and after pressure relief was monitored and analyzed. The results show that directional fracture blasting can produce a continuous crack, and the effect of pressure relief is remarkable, effectively controlling the deformation of surrounding rock under high in-situ stress. [ABSTRACT FROM AUTHOR]

The application of roof-cutting and pressure-relief gob-side entry retention plays a critical role in controlling the stability of the surrounding rock at the entry, easing continuity tension and improving resource recovery ratio. The excavation of the 360,803 airway in Xinji No. 1 Mine is affected by intense mining of the 360,805 working face. Hence, to address the stability problem of surrounding rock in the 360,803 airway, rock mass blast weakening theory was used in this study to analyze the blasting stress of columnar charged rock mass and obtain the radiuses of crushed, fractured, and vibration zones under uncoupled charging conditions. The reasonable array pitch, length, and dip angle of boreholes were determined according to the pressure-relief range of the blasting fracture. The migration laws of roof strata were explored based on a mechanical model of overlying roof strata structure on the working face. Subsequently, the horizon, breaking span, and caving sequence of hard roof strata were obtained to determine the roof-cutting height of this entry. On the basis of the theory of key stratum, the number of sequences at the roof caving limit stratum and hanging roof length in the goaf were calculated, the analytical solution to critical coal pillar width was acquired, the evaluation indexes for the stability of entry-protecting coal pillars were determined, and the engineering requirements for the 25 m entry-protecting coal pillars in the 360,803 airway were met. Moreover, various indexes such as roof separation fracture, displacement of surrounding rock, and loose circle of surrounding rock in the gob-side entry were analyzed. The stability and cementation status of surrounding rock in the 360,803 airway were evaluated, and tunneling safety was ensured.

Gob-side entry retaining by roof cutting (GERRC) is a new technique regarding a non-pillar mining method based on the "cutting cantilever beam theory" proposed in recent years. In this technology, the composition, formation mechanism, load transfer mode and stability mechanism of roadways are quite different from those of traditional coal mining methods. Based on the technical principle of the GERRC, the formation mechanism of the sidewall composed by collapsed gangues is clarified. Also, on basis of the observation of engineering site, the movement characteristics of the gangues in goaf are analyzed, and the movement processes are mainly divided into two stages, i.e. the rapid collapse stage and the slow compaction stage. Then, the interaction between the gangues and retaining structures in different movement stages is revealed. Meanwhile, a mechanical model of the roadside gangues was established, and the mechanical characteristics of the retaining structures were analyzed. Besides, a control concept, considering both dynamic and static pressure in the lateral direction and making it extensible to release pressure in the axial direction, was put forward to support the gangues in goaf based on the interaction characteristics of the gangues and the retaining structures. At last, three different retaining structures for the gangues were proposed in view of different mining heights, and the roadside gangues control system was established, which has been proved to be of good practicality in the engineering site. The research results can provide technical guidances for the control of roadside gangues in the GERRC and accelerate the process of popularization and application of the GERRC, which is of positive significance. [ABSTRACT FROM AUTHOR]

• Study of roof cutting parameters for soft-rock coal pillar mining roadway. • A similar rock bolt-mesh-cable-strip-shotcrete roadway is built as a simulation model. • The protection mechanism of roof-cutting to the front roadways are studied. • The stability of mining roadway can also be improved without adding support members. In the confinement of traditional supports, reinforced supports are often used to control the deformation of roadways constructed in soft rock. Due to the failure to weaken the factors that induce deformation at the source, the roadway remains damaged after the restoration period. To this end, taking inspiration from roof cutting and pressure relief concepts, the protection mechanism of stress transfer in mining roadways constructed in soft rock of longwall remaining coal pillars was studied in the context of a typical coal mine. Unlike the technical scheme of gob-side entry retaining, no components are added in this study. The roof cutting and coal mining progress are consistent to ensure the integrity of the roadway in front of the longwall coal mining face (LCMF). The effect of the roof-cutting parameter on the roadway is studied via numerical simulations, and the optimal parameters are subsequently applied to similar material simulation experiments. It was found that roof cutting relieved the mechanical connection between the gob roof and the roadway roof, and the high-stress area was transferred from the roadway roof to the front of the LCMF. Roof cutting diminished the abutment stress in the surrounding rock in the area of intense dynamic pressure in front of the LCMF (average reduction of 12.57 %), which effectively improved the stability of the roadway. The roof cutting impaired the traction effect of the roadway roof deformation behind the LCMF on the strata ahead and effectively reduced the roadway deformation (27.3 % reduction) and coal pillar deformation (15.7 % reduction). On-site practice has demonstrated the effectiveness of this research, and the results of this research provide a new idea for preventing the destruction of roadways constructed in soft rock. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Non-pillar mining technology plays an important role in sustainable exploitation of coal resources. Gob-side entry retaining by roof cutting (GERRC) is a new technique regarding a non-pillar mining method based on the "cutting cantilever beam theory". In order to study the distribution and evolution characteristics of macroscopic stress field of surrounding rocks in GERRC, and find out differences from traditional pillar retained mining method (PRMM), some key issues about abutment pressure and stress concentration shell were analyzed by numerical simulations. Results show that: (1) distribution characteristics of lead abutment pressure for the two mining methods are basically the same during the primary mining stage; (2) during the secondary mining stage, peak stress in front of mining face of the two modes is close, while the abutment pressure can be transferred more evenly to coal and rock mass far away from goaf when using GERRC, and that is more likely to cause high stress concentration in the coal mass near the goaf when mining with PRMM; (3) for the PRMM, lateral abutment pressure will produce a higher stress concentration in section coal pillar and a high residual stress will be maintained in it when coal masses on both sides of the pillar are extracted; (4) adjacent goafs can be connected to form a wide range of pressure relief region when using GERRC, and shape of distribution of the maximum principal stress appears a semi-space ellipsoidal shell in three-dimensional space, and it is a single arch shape in the section perpendicularly to the mining direction, however, it looks like a "m" shape in that section when mining with PRMM because of the high stress concentration in the coal pillar. [ABSTRACT FROM AUTHOR]

Affected by mining activities, 3−1103 tailgate of Hongqinghe coal mine is seriously deformed. The floor of tailgate cracking and tilting, and two ribs appearing in the net bag, which affects normal transportation and pedestrians. To solve this difficulty, this paper study on the technology of directional fracturing blasting for pressure relief of dynamic pressure roadway. First of all, taking method of theoretical analysis, the mechanical mechanism of directional blasting and the relevant calculation formula are expounded. Afterwards, the mechanical model of roof cutting of roadway is established. In order to analyze the evolution and propagation of effective stress, directional blasting model is established by using LS-DYNA numerical calculation software. In the next part, the roof control technology of directional cut blasting is put forward. In the end, the blasting effect is observed, and the deformation of the roadway before and after pressure relief is monitored and analyzed. The results shows that directional fracture blasting have obvious effect of joint formation, and the effect of pressure relief is remarkable, effectively controlling the deformation of surrounding rock under dynamic pressure. [ABSTRACT FROM AUTHOR]

With the increasing tension of current coal resources and the increasing depth of coal mining in China, Non Coal Pillar Gob-side Entry Retaining Technology has become a preferred coal mining method in underground coal mines. In the current study of the non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing, the theory and design of roof cutting under near-level conditions have formed a certain system. However, there is a lack of systematic research on the design of the roof cutting and the connection requirement of the cutting seam and other aspects about the inclined coal seam. Therefore, choosing the concrete representative target mines as the research foundation, using mechanics analysis, geometric analysis, numerical simulation and other means, on the basis of considering the change of mining height, this paper mainly studies about the effect of coal seam inclination on roof slit depth and angle, then get the three steps of the cutting height design, the three considerations of the roof cutting angle design and the connection rate requirement of the roof cutting. At last the key roof cutting parameters of the three target mines are calculated accordingly. Based on the existing research, this paper puts forward the concept and design method of roof cutting connectivity rate. The design system of roof cutting seam parameters of non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing is further improved, and the corresponding calculation method is deduced for the design of the key parameters of the inclined coal seam and the gently inclined coal seam, and proposing the second roof cutting scheme of the upper side gob-side entry retaining. [ABSTRACT FROM AUTHOR]

Affected by high ground stress, the surrounding rock control of a roadway is one of the most important factors restricting the utilization of deep resources. Therefore, it is necessary to propose a method to improve the stress environment of the deep-buried roadway and reduce its deformation. The article focuses on the 121,302 machine roadway in Kouzidong coal mine to analyze the large deformations of roadways near goafs (RNGs) in deep coal mines and reveal the mechanisms related to pressure relief via roof cutting. Through physical simulation, overburdened structures and the migration laws of RNGs in deep coal mines are studied, and the overburdened RNGs will eventually have a double short-arm “F”-type suspended roof structure. The superposition movement of the structure is the prime cause for the large deformation of the RNGs considered here. Artificial roof cutting can weaken the superposition effect of the double “F” structure and induce the roof to produce a new fracture. Meanwhile, sliding deformation along the fault line releases greater stress, and the cut roof can better fill the goaf. The stress distribution ratio between goafs and the coal pillar is improved. Here, a mechanical model of key block B’ (KBB’) is considered and the stability criterion of KBB’ is obtained. According to the theoretical calculation here, the stress of a coal pillar could be reduced by 19.14% when KBB’ is cut along the edge of the coal pillar in the 121,302 machine roadway. After engineering verification, the field observation result shows that the deformation of the 121,302 machine roadway is reduced by more than 50% after roof cutting.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In terms of the fact that the traditional mining method causes the high drivage rate and low resource recovery rate, a new mining technology, mining without coal pillars and gateroad excavation, was put forward based on the idea of roof cutting and automatically formed roadway. The concrete mining method of working face and the principle of roadway formation were explicated by comparing with traditional coal mining technology. Through the analysis of the movement characteristics of roof rock, a mechanical model of surrounding rock structure was established, and the formula for calculating the resistance of roof support is derived. Supporting technology matching with the new mining technology was studied on the basis of the characteristics of surrounding rock movement. Besides, the zoning supporting concept was proposed and applied in the field, which means that different support measures should be taken in different areas. Field test results show that the new mining technology has achieved the goal of mining without coal pillars and gateroad excavation in advance. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The application of roof-cutting and pressure-relief gob-side entry retention plays a critical role in controlling the stability of the surrounding rock at the entry, easing continuity tension and improving resource recovery ratio. The excavation of the 360,803 airway in Xinji No. 1 Mine is affected by intense mining of the 360,805 working face. Hence, to address the stability problem of surrounding rock in the 360,803 airway, rock mass blast weakening theory was used in this study to analyze the blasting stress of columnar charged rock mass and obtain the radiuses of crushed, fractured, and vibration zones under uncoupled charging conditions. The reasonable array pitch, length, and dip angle of boreholes were determined according to the pressure-relief range of the blasting fracture. The migration laws of roof strata were explored based on a mechanical model of overlying roof strata structure on the working face. Subsequently, the horizon, breaking span, and caving sequence of hard roof strata were obtained to determine the roof-cutting height of this entry. On the basis of the theory of key stratum, the number of sequences at the roof caving limit stratum and hanging roof length in the goaf were calculated, the analytical solution to critical coal pillar width was acquired, the evaluation indexes for the stability of entry-protecting coal pillars were determined, and the engineering requirements for the 25 m entry-protecting coal pillars in the 360,803 airway were met. Moreover, various indexes such as roof separation fracture, displacement of surrounding rock, and loose circle of surrounding rock in the gob-side entry were analyzed. The stability and cementation status of surrounding rock in the 360,803 airway were evaluated, and tunneling safety was ensured. [ABSTRACT FROM AUTHOR]

Affected by high ground stress, the surrounding rock control of a roadway is one of the most important factors restricting the utilization of deep resources. Therefore, it is necessary to propose a method to improve the stress environment of the deep-buried roadway and reduce its deformation. The article focuses on the 121,302 machine roadway in Kouzidong coal mine to analyze the large deformations of roadways near goafs (RNGs) in deep coal mines and reveal the mechanisms related to pressure relief via roof cutting. Through physical simulation, overburdened structures and the migration laws of RNGs in deep coal mines are studied, and the overburdened RNGs will eventually have a double short-arm "F"-type suspended roof structure. The superposition movement of the structure is the prime cause for the large deformation of the RNGs considered here. Artificial roof cutting can weaken the superposition effect of the double "F" structure and induce the roof to produce a new fracture. Meanwhile, sliding deformation along the fault line releases greater stress, and the cut roof can better fill the goaf. The stress distribution ratio between goafs and the coal pillar is improved. Here, a mechanical model of key block B' (KBB') is considered and the stability criterion of KBB' is obtained. According to the theoretical calculation here, the stress of a coal pillar could be reduced by 19.14% when KBB' is cut along the edge of the coal pillar in the 121,302 machine roadway. After engineering verification, the field observation result shows that the deformation of the 121,302 machine roadway is reduced by more than 50% after roof cutting. [ABSTRACT FROM AUTHOR]