The presence of multilayered thick and hard roof strata results in frequent mine tremors, significantly complicating prevention and control efforts and posing a formidable challenge to the safe and efficient operation of coal mines.Taking the multi-layer thick and hard roof working face of Hongqinghe Coal Mine as the engineering background, the occurrence risk of mine earthquakes is identified by combining the occurrence of roof strata and surface subsidence conditions. Based on the damage theory, the mechanism of ground fracturing mine earthquake prevention and control is revealed. A method for the optimization and adjustment of ground vertical well layout and fracturing layer position, suitable for multi-layer thick hard roof mine earthquake prevention and control, is proposed. Furthermore, a test on ground vertical well fracturing mine earthquake prevention and control for multi-layer thick hard roof has been conducted. Fracturing damage weakens the mechanical properties of the rock mass, increases energy dissipation, and en-hances the discontinuity of the rock mass, providing a pathway for the fracture, sliding, and shedding of the thick and hard roof. Based on the results of rock mechanics and comprehensive interpretation of anisotropic logging data, it is possible to accurately identify thick and hard rock formations, thereby optimizing and adjusting the fracturing horizons. At the same time, a well-distribution method that comprehensively considers factors such as fracture propagation size and mining-induced fractures has been developed. Introducing temporary plugging agents during the fracturing process can enhance the construction pressure and increase the complexity of the fracturing fracture network. The main fracture extension direction of the surface vertical well fracturing is approximately N38°E. The length, width, and height of the fracturing fractures are 333, 225 and 56 m, respectively, effectively achieving pre-splitting weakening of the thick and hard roof. Ground fracturing reduces the frequency of high-energy events with a magnitude of 104 J and above. The average advancement of the working face for high-energy events has significantly increased from 5 m per occurrence to 48 m per occurrence, and the proportion of high-energy events has decreased from 7% to 2%. After surface fracturing, the amount and rate of surface subsidence show an increasing trend, indirectly indicating that the thick roof overburden can collapse in a timely manner with the advancement of the working face, reducing the risk of mine earthquakes.

In view of the problems of strong mine pressure such as rapid shrinkage of hydraulic support column and easy support crushing in working face under the fully mechanized caving face with large mining height in multi-layer thick and hard roof of extra-thick coal seam in Yushen mining area,the support working resistance and roof subsidence during the mining period of the working face are systematically monitored by using column pressure sensor and displacement sensor,and the macroscopic characteristics of mine pressure behavior and the linkage between near and far field overburden movement and mine pressure are analyzed.The characteristics of mine pressure in fully mechanized caving face with large mining height and multi-layer thick and hard roof were clarified,the spatial form of multi-layer thick and hard roof break-ing and the evolution law of overburden structure were obtained,and the mechanism of mine pressure was expounded.The mechanical model of overburden structure in different layers of low,medium and high layers was established considering the bending deformation in front of the coal wall and the stress correlation between the layers of multi-layer thick and hard roof.The criterion of rock failure instability and the critical support strength of the support in different layers were given.The results show that the mining of fully mechanized top coal caving face with multi-layer thick and hard roof and large mining height not only has the characteristics of"obvious regional pressure,rapid increase of pressure resistance,large and small periodic pressure,periodic strong dynamic load pressure",but also presents the new characteristics of multiple continuous or short-distance intermittent large periodic pressure during strong dynamic load pressure.During the period of strong dynamic load,the degree of continuous large-period rock pressure shows a trend of increasing first and then de-creasing,the periodic strong dynamic load pressure of the working face is irregular,with 4 to 10 small cycles,an interval of 120.9-241.9 m and an average interval of 161 m.During the period of strong dynamic load pressure,the mine pressure ap-pears abnormally strong.The high-level rock stratum is located more than 70 m above the coal seam.After the thick and hard rock stratum in the middle is broken,the effective contact and support force of the high-level"hinged beam"is re-duced,resulting in the failure and instability of the high-level hinged beam,which in turn leads to the strong dynamic load pressure phenomenon of multiple continuous or short-distance intermittent large-cycle pressure in the working face.The reasonable support strength of the support is 1.897 MPa when the middle"non-articulated beam"structure is broken and unstable.The reasonable support strength of the support corresponding to the rotary deformation instability of the"hinged beam"is 2.470 MPa,and the reasonable support strength of the support corresponding to the sliding instability is 3.180 MPa.The existing high-strength support is difficult to effectively control the strong mine pressure of the roof.It is neces-sary to adopt the means of roof weakening to control the surrounding rock of the stope.The research results have import-ant guiding significance for the surrounding rock control of multi-layer thick and hard roof mining in extra thick coal seam.

Mine pressure appears extremely strong during mining in hard and thick roof working faces. The prevention and control of this type of roof disaster has always been a problem that has plagued the safe and efficient production of working faces in my country. Based on the analysis of roof disaster cases, the types and disaster-causing characteristics of hard thick and difficult roof in my country are sorted out, and research on the occurrence mechanism and influencing factors of strong dynamic load mine pressure in hard thick and difficult roof working faces is carried out. Targeted prevention and control measures have been proposed in three stages: pre-design, pre-mining weakening and mid-mining monitoring and early warning, and have been applied in practice. The research shows that the hard thick and difficult to collapse roofs have the characteristics of high strength, large thickness and strong integrity, and can be divided into three categories: thick roof with high compressive strength, thick roofs with good integrity, and roofs directly covering basic roofs. Large-area instantaneous collapse of hard thick and difficult to collapse roofs is often accompanied by strong pressure from the working face, hurricanes and other phenomena, which may easily cause equipment damage, gas overlimits or explosion, endangering personal safety. There are two types of roof failure types that induce strong mine pressure in the working face. One is that the roof bends and sinks under the state of long overhanging roof, resulting in back-frame fractures; the other is that the long overhanging roof fractures in front of the coal wall, causing rapid rotation. The mine pressure in the stope with hard thick and difficult to collapse roof conforms to the movement form of the I-II-III-IV zoning support model. The roof has a large thickness, high tensile strength, and long cyclic collapse steps. When breaking, it is easier to cause the subsidence at the coal wall to increase, and significantly increase the resistance of the support, which is the reason why the mine pressure appears strong in the working face with hard thick and difficult to collapse roof. Based on the above analysis, a roof disaster prevention and control method that combines roof weakening and mine pressure monitoring is proposed. Under the conditions of pre-verification of the occurrence characteristics of overlying rocks and reasonable support selection, microseismic monitoring is used to determine the fracturing target layer, and the working face support-pressure relief effect is evaluated based on mine pressure monitoring. This method has been successfully applied in the 10 m super-high mining face of Caojiatan Coal Mine. During mining, the first weighting step distance of the working face has been reduced from more than 100 m to 49.35 m, and the high-energy microseismic events above the fourth power accounts for only 1.2%, achieving good prevention and control effects.

Fully mechanized mining technology with extra-large shearing height is the optimal technical approach to achieve high-yield,high-efficiency and high-recovery mining for 6-10 m ultra-thick coal seam in Chinese coal mines.Based on the analysis of the current status of fully mechanized mining technology and equipment with extra-large shear-ing height at home,focusing on the geological condition of fully mechanized working face with ultra-large shearing height of 10 m in extra-thick coal seam in the Caojiatan Coal Mine,Shaanxi Coal and Chemical Industry Group Co.,Ltd.,the ex-isting technical problems were analyzed and the associated solutions were given from three aspects:surrounding rock con-trol,key mining equipment and intelligent collaborative control.After nearly five years of scientific research,a series of innovative achievements have been achieved:① The surrounding rock control strategy with coordination of support and destressing for ultra-large shearing height working faces,namely"active strong support and protection+regional hydraul-ic fracturing weakening and stress relief',was proposed,a complete set of underground hydraulic fracturing technology and equipment with large flow of 5 m3/min was developed.Effective prevention and control of strong mining-induced activities in ultra-large shearing height working face has been realized.② The strong hydraulic shields with ultra-large shearing height of 10 m were developed,and the"double-layer telescopic beam+three-level side guard"mechanism was innovatively designed to achieve safe protection of working face roof and ultra-high coal wall;the zoned lubrication and distributed cooling scheme improves the cutting reliability of the shearer with large angle of elevation and long rocker;the high-reliability middle trough,lower chain catenary and slow-changing power start-up improve the adaptability of the ultra-large capacity scraper conveyor to the coal flow transportation of the working face with ultra-large shearing height.The systematic integration has formed the global first set of comprehensive mining equipment with extra-large shearing height of 10 m.③ An innovative intelligent control strategy for the operation status of the hydraulic shields with 10 m ultra-large shearing height,and the automatic control strategy for the shearer were proposed.A coordinated control system for the shearer with ultra-large shearing height and the scraper conveyor was constructed by applying the rough neural network technology.An intelligent control mode and control logic for heavy equipment groups with ultra-large shearing height were formed.④ A multi-field and multi-parameter collaborative monitoring and integrated analysis system for the work-ing face with ultra-large shearing height based on"microseism-rock movement-stress-hydrology"was constructed,realiz-ing the multivariate heterogeneous data integrated analysis among damage of overburden rock above working face,sur-face movement and deformation,groundwater flow field and mining-induced activities.The research results were success-fully applied in the in Caojiatan Coal Mine,achieving high-yield,high-efficiency and high-recovery mining in 10 m ultra-thick coal seam,getting significant economic benefits,and leading the development direction of high-efficiency and intel-ligent mining for extra-thick coal seam at home and abroad.

The dynamic response characteristics of stope support include the information of support resistance increase and live column shrinkage, which is not only an important index to reflect the strength of mining pressure behavior in working face, but also the basis for studying the dynamic interaction between support and surrounding rock. Taking the 122108 working face of Caojiatan Coal Mine as an example, heoretical analysis and mathematical statistics were used to clarify the dynamic response characteristics of the support during the mining process, reveal the resistance increasing mechanism of the support in different bearing stages, and analyze the characteristics of mining pressure before and after fracturing of the working face, and carry out research and application of the resistance increasing characteristics of the support before and after pressure. The results show that: in continuous cycles, the support shows the characteristics of “high resistance and continuous shrinkage of the living column”, then the working face is pressed, and the information of support shrinkage can be used to evaluate the apparent strength of the previous pressure. When the roof is not broken, the generalized Kelvin model can be used to characterize the slow movement of the roof. After the roof fracture, the support shows a logarithmic resistance increase at a given deformation stage, and the resistance increase rate is determined by the support stiffness, the controlled roof distance and the unstable state of the broken roof, and the support resistance increases exponentially or linearly at the given load stage. The dual-factor analysis method of support resistance and height can accurately judge the characteristics of mine pressure behavior in the working face with strong mine pressure. After fracturing, the proportion of the pressure step distance of more than 30 m in the working face is greatly reduced, and the proportion of the continuous pressure distance of 10 to 28 m is reduced to 2%. The normal distribution curve of cumulative shrinkage and shrinkage speed of support decreases as a whole. The change of the type and rate of resistance increase of support is a remarkable feature to judge whether the working face is under pressure or not, and it can be used as a new method to predict the pressure of working face. The result of increasing resistance by homogenization of support can be used to predict roof pressure and invert the macroscopic subsidence change of roof. The above research results have certain reference significance for improving the interaction between support and surrounding rock and guiding the early warning and prevention of roof disasters in working face.

Entry stability in ultra-thick coal seam longwall mining is often challenged by high abutment pressures and the need for wide coal pillars. This study presents the design, implementation, and verification of a hydraulic fracturing pressure relief strategy to optimize pillar width and improve entry performance in the longwall panels of Buliangou Mine. A site-specific fracturing scheme was applied near the coal pillar, using staged multi-interval fracturing from angled boreholes in the roof strata. Field instrumentation, including borehole imaging, water pressure monitoring, and stress/strain sensors, confirmed successful fracture propagation and significant stress redistribution. Post-fracturing monitoring indicated a shift in peak pillar stress location and an expansion of the elastic core zone, with entry deformation (ribs and roof-floor convergence) reduced by up to 25%. Based on these results and comparative case studies, an optimized 26 m pillar width was proposed and subsequently implemented in a new longwall panel. Field verification demonstrated stable entry conditions, consistent support loading, and a notable increase in coal recovery. This study confirms that hydraulic fracturing, when combined with detailed field design and monitoring, provides a reliable solution for stress management and pillar size reduction in ultra-thick seam longwall mining.

The 10 m ultra-large mining height of Caojiatan Coal Mine is a world's first in terms of single mining height and mining intensity,and the effective control of surrounding rock in the stope is crucial for safe and efficient mining at the working face.Based on the analysis of the coal seam occurrence conditions and the characteristics of the ground pres-sure behavior of the already mined faces,and considering the ultra-large mining space and the ultra-high coal wall charac-teristics of the working face,the difficulties in controlling the surrounding rock of ultra-large mining height were clarified.A"superimposed arch-beam"structural model for the ultra-large mining height stope was established,and a three-in-one surrounding rock control strategy of"active support protection+regional pressure relief weakening+comprehensive monitoring and early warning"was proposed,verifying the effectiveness of the surrounding rock control for the 10 m ultra-large mining height.The research shows that:the occurrence characteristics of multi-layer thick and hard roofs cause ab-normally strong mine pressure manifestation at the working face,with large-area hanging roofs during initial mining and significant strong dynamic loading pressure at the working face during normal mining.The keys to controlling the sur-rounding rock in the 10 m ultra-large mining height stope are reducing the pressure step distance,weakening the dynamic loading pressure,preventing rib spalling,and preventing the working face from being crushed by the pressure.The"double-layer telescopic beams+three-stage rib protection"structure of the hydraulic support achieves independent opera-tion for the protection of the empty roof in front of the support and the ultra-high coal wall,solving the problem of incom-plete rib protection by the original split-type rib protection.The high initial setting force and high working resistance of the hydraulic support significantly reduce the risk of rib spalling and roof caving at the working face and effectively control the roof subsidence during the pressure period.The underground deep-hole 5.0 m3/min high-flow directional fracturing weakening technology achieves weakening of the multi-layer thick and hard roofs,effectively reducing the intensity of mine pressure at the working face,controlling the amount of rib spalling and significant roof subsidence during the pres-sure period,and preventing the working face from being crushed by the pressure.Comprehensive monitoring and early warning effectively ensures the support efficiency of the support during mining,realizing real-time tracking of roof frac-ture and real-time analysis of strong mine pressure.The problems of large-area hanging roofs and small hurricanes during the initial mining of the ultra-large mining height working face have been resolved.The initial pressure step distance is 49.35 m,the pressure duration distance is 5.75 m,and the opening ratio of the safety valve of the support column is 24.81％.The manifestation of mine pressure during the periodic pressure period has been significantly alleviated.The av-erage shrinkage of the hydraulic support column has decreased from 0.48 m to 0.32 m,a decrease of 33.3％,and the max-imum shrinkage has decreased from 1.88 m to 1.44 m,a decrease of 23.4％.The proportion of the average dynamic load coefficient of the working face periodic pressure greater than 1.5 has decreased from 39.6％to 14％.During normal pro-duction at the working face,rib spalling is within a controllable range,with the amount of rib spalling concentrated at 0.2-0.5 m.The research results have important guiding significance for the control of surrounding rock in ultra-large min-ing height mining.

Quantitative research on the structure of"combined short cantilever-articulated rock beam"in roof with large mining height stope,the increase of mining height will inevitably lead to the increase of the activity range of the overlying strata in the horizontal and vertical directions.According to the characteristics of bottom-up movement and caving expan-sion of the overlying strata in the stope,the caving space in the goaf will be close to zero at a certain time,it is proposed that the roof strata that product stress on the support are within a certain range,that is,there is a boundary strata in the roof,and the concept and judgment method of the boundary strata are given.With the continuous advancement of the stope,the falling gangue will continue to creep and compress again under the action of the overlying strata,which will cause the overlying strata to sink many times,and cause surface subsidence until it finally stabilizes.Therefore,the overly-ing strata from the stope to the surface are divided into near-field strata and far-field strata from the perspective of the in-fluence on the ground pressure behavior of the stope,the near-field rock strata refer to the composite rock strata that from the support to the boundary strata,and the far-field rock strata refers to the composite rock strata that from the boundary strata to the surface.The movement law of rock strata in the near-field is the focus of studying the ground pressure of the stope,and the movement law of rock strata in the far-field is the focus of studying the surface subsidence of the stope.Based on the characteristics that the lower composite roof of the large mining height stope cannot touch the gangue before it collapses and presents a"combined short cantilever beam"structure,and the upper composite roof rock strata present an"articulated rock beam"structure in the horizontal direction of the stope under the support of coal wall,the combined sup-port body of support and direct roof,and caving gangue in the goaf,the new concept of immediate roof and main roof in the near-field of large mining height stope is proposed and the quantitative judgment method of immediate roof and main roof is obtained.Therefore,the quantitative structure of"composite short cantilever beam-articulated rock beam"of roof in large mining height stope is formed.The main roof strata that form the"articulated rock beam"structure generally have one or more layers,depending on the mining height and the thickness,strength,and position of the roof strata.The basic conditions for the formation of the articulated structure are:① the possible subsidence of the main roof is less than its lim-it subsidence(△m＜△j),② the stress in the upper part of the middle section of the structural plane is greater than its tensile strength(σt＞[Rt]),the stress in the lower part of the middle section is less than its compressive strength(σc＜[Rc]),③ The fracture distance of the rock strata is greater than 2 times of its thickness.Taking the 10 m super large mining height longwall face of Caojiatan Coal Mine as the engineering background,the objectivity of the existence of boundary strata is obtained by the field measurement and analysis,as the application of the quantitative structure theory of"compos-ite short cantilever beam-articulated rock beam"of roof in large mining height stope,the support strength of the special stacking support for the longwall face retracement with the 10 m large mining height was determined.

The overall stability of cemented tailings backfill (CTB) false roof, as an important support structure in the quarry, is of great significance for realizing the safe recovery of the ore body. This paper aims at the practical problem of ore body mining under the condition of deep broken rock mass. By analyzing the typical process characteristics of underhand cut-and-fill mining method, the dangerous mechanical state of CTB false roof is determined, and the CTB false roof strength model based on the maximum tensile stress failure criterion and deep mining coefficient is established. Based on the measured load value of CTB false roof, the minimum required strength of CTB false roof is obtained. Through the performance tests of CTB under different proportioning schemes, the mechanical strength of CTB false roof (UTS：0.43MPa, UCS：6.22MPa) is designed，the proportioning parameters of CTB with "high strength, high fluidity, quick setting and low cost" are put forward. Finally, based on FLAC3D numerical simulation and field monitoring, the stability of CTB false roof with recommended ratio parameters is analyzed. The results show that the CTB false roof has not been violently displaced and destabilized in the process of service ore body mining, has good strength reserve, and is able to provide a safe workspace for mining, verifies the reliability and reasonableness of the CTB false roof proportioning parameter, and provides a new way for the study of false roof stability.

The research focused on addressing various challenges in intelligent top caving theory, intelligent perception and recognition key technology, intelligent caving comprehensive decision-making technology, and remote caving intelligent control technology of fully mechanized top coal caving face. This is being done under the “13th Five-Year” national key research and development plan, specifically designed for the key technology and demonstration of intelligent fully mechanized top coal caving mining method with annual production of 10 million of tons in extra-thick coal seam. The research has resulted in the following outcomes: ① Comprehensive experiments were conducted to understand the interaction process of crushing and migrating of roof and top coal combination (RTCC) and the fragmentation distribution of RTCC under different roof conditions. A three-dimensional laser goaf space detection technology has been developed, and the arching phenomenon of top coal blocks on contact, at coal discharge process with multiple coal discharge ports, has been validated. In addition, the numerical simulation of multi-port intelligent coal caving in extra-thick coal seam is carried out with the constraints of mining and caving coordination, high recovery rate, and low gangue ratio, and the number of coal caving ports is determined. those provide a reliable theoretical basis for optimizing intelligent coal-caving processes. ②The research has explored the geological information and physical characteristics of coal and gangue in the working face, along with full-cycle sensing elements of the top coal caving process. This has led to the development of a comprehensive sensing technology system, including real time detection of top coal thickness, accurate identification of coal and gangue, and dynamic measurement of coal flow, providing crucial data information support for decision making of intelligent coal top caving technology. ③A multi-source information database has been established for the man-machine-environment interface, and a decision-making model has been developed for fully mechanized top caving in extra-thick coal seams. An intelligent coal top caving decision-making software based on the Q-learning algorithm has been created, utilizing artificial intelligence for coal and gangue identification, top coal thickness detection, and coal quantity monitoring. ④A high-precision inertial navigation monitoring and control technology for intelligent fully mechanized caving faces has been developed, enabling real-time positioning, attitude monitoring, and action control for the shearer, hydraulic support, and scraper conveyor. An intelligent mine-integrated communication scheduling system and a remote-integrated control platform for fully mechanized caving have also been established. Those allow for the successful implementation of intelligent coal caving in remote one-button start mode. ⑤Advanced technologies such as ground-penetrating radar for top coal thickness detection, vibration-audio-hyperspectral for coal-gangue identification, and laser three-dimensional scanning for real-time coal caving monitoring are utilized in the 8222 Working Face of Tashan Mine. Intelligent coal caving decision software is applied in fully mechanized caving operations, leading to a control of errors within 10.71% for top coal thickness detection, 9.32% for mixed gangue rate, and 7.8% for coal caving amount. On average, each coal caving cycle now saves about 30 minutes, leading to intelligent and efficient coal caving operations with an annual output of 15 million tons.

综采工作面倾向长度的增加,对顶板破断及应力演化产生的影响效应是复杂的,导致工作面支架支护特性存在分区差异.为深入理解超长工作面支架与围岩相互作用关系,以小保当煤矿450 m超长工作面为工程背景,构建弹性基础岩梁力学模型,运用数理统计及均化循环分析方法,对工作面支架实测数据开展循环末阻力、工作阻力分布频率、支架增阻特性分析,明晰不同面长工作面倾向方向顶板运动及支架工作阻力分布特征,探究超长工作面支架倾向分区内支架增阻特性.研究结果表明:工作面倾向长度增加,导致两巷煤体对中部顶板的支承减弱,中部峰值区域向两巷移近,超长工作面支架工作阻力分布趋势呈M型三峰值分布;超长工作面上部、中部、下部三区域支架呈对数型增阻时,其均化曲线仍为对数函数,表现为先急增阻后趋于平缓,此种支架增阻情况反映了来压期间工作面顶板由快速下沉逐渐变为缓慢下沉;呈对数?指数型增阻时,中上部区域支架增阻均化曲线为对数函数,中部及中下部均化曲线为对数?指数型复合函数,表现出先急增阻然后趋于平缓最后急增阻的特征;当支架工作循环时间超过一定值,对数?指数复合增阻型支架会急速增阻,不利于顶板控制,通过优化工作面割煤速度,降低支架工作循环时间,可减小支架增阻量,避免高阻力状态下支架再次瞬时增阻,提升工作面支架支护效果.

To solve the problems of small local relief range, low continuity and high operational risk of rockburst, regional hydro-fracking and burst prevention system and engineering application research were carried out within thick and hard roof of a coal seam by well over thousand meters on and under the ground. The results show that, according to the loading conditions, the roof dominated rockburst can be divided into three types: superposed dynamic and static loading type, high static loading type and high static unloading type; The thick and hard roof is the main source of regional static and dynamic loading for rock burst initiation of mining surrounding rock. With the thick and hard roof as the target, which provides the source of dynamic and static load for rock burst initiation, a segmented fracturing pressure relief system for the roof with 1 000 meter horizontal holes on and under the ground was established and fracking was carried out in this area. By destroying the integrity of the overlying roof in the burst prone area in advance on and under the ground, the load is transferred to the more intact roof area, so as to provide a low stress operational environment for underground excavation and extraction, and also make the rock burst initiation conditions inapplicable. The fracking and burst control tests on the roof area using the horizontal well drilled on the ground before the extraction of the panel, and underground drilling from the entries during the extraction were carried out respectively.Remarkable results have been achieved in practice, forming a new disaster prevention and control mode of “fracking before construction”for burst prone coal mines under construction, and “fracking before tunneling, fracturing before mining” for the producing coal mines.

This paper reviews the major achievements in terms of mechanical behaviors of coal measures, mining stress distribution characteristics and ground control in China's deep underground coal mining. The three main aspects of this review are coal measure mechanics, mining disturbance mechanics, and rock support mechanics. Previous studies related to these three topics are reviewed, including the geomechanical properties of coal measures, distribution and evolution characteristics of mining-induced stresses, evolution characteristics of mining-induced structures, and principles and technologies of ground control in both deep roadways and longwall faces. A discussion is made to explain the structural and mechanical properties of coal measures in China's deep coal mining practices, the types and distribution characteristics of in situ stresses in underground coal mines, and the distribution of mining-induced stress that forms under different geological and engineering conditions. The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways. The use of combined ground control technology (e.g. ground support, rock mass modification, and destressing) has been demonstrated to be an effective measure for rock control of deep roadways. The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face. The ground control challenges in deep underground coal mines in China are discussed, and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.

The excavation thickness of the coal seam and the corresponding motion space of the overlying strata are so large in the fullymechanized top coal caving face, that roof accidents are occur easily. In order to understand the mechanism of roof disasters in fully-mechanized caving working face, some cases of roof disasters in fully-mechanized caving working face are statistically analyzed. According to the roof conditions and disaster characteristics, the roof disasters in fully-mechanized caving working face are divided into two types: largearea roof cutting and support crushing for soft roof, large-area roof collapse with roof cutting and support crushing for hard roof. Taking Cuimu Mine and Caojiatan Mine as examples, the characteristics of two types of roof disasters are analyzed, and the corresponding roof disaster mechanism is presented: The roof in soft roof working face is of weak cementation. If the actual support stiffness is insufficient,the roof will break at the coal wall, and is easy to be unstable after breaking. As the same time, the insufficient support strength eventually leads to the leads to cutting and support crushing disaster of roof. The roof in hard roof working face is of good integrity and is not easy to break. When the suspended roof area is enough, the sudden breaking of roof will cause an impact on the support. If the breaking line is at the coal wall, it will easily leads to cutting and support crushing disaster of roof. Combined with engineering practice, prevention and control measures for two types of roof disaster are presented. For the soft roof working face, the measures such as reasonably improving the support stiffness, the supporting efficiency and the advancing speed of the working face, and the early warning and so on are used to prevent the occurrence of large-scale roof cutting and support crushing. For the hard roof working face, in addition to support management and rational mining design, it is necessary to improving roof conditions. For examples, the regional hydraulic fracturing technology is used to weaken the roof and prevent large-area roof collapse and support crushing disasters.

The development of free layer（protective layer）mining in rockburst mines can fundamentally improve the stress concentration of mining face, and thus reduce the impact risk of mining activities in a large space. In order to achieve the regional pressure relief goal of a single coal seam with rockburst tendency that can be mined without a liberated layer, a method of “artificial liberated layer” for the pressure relief and prevention of rockburst in the thick and hard roof area of the main disaster zone above the coal seam created by hydraulic fracturing is put forward. The engineering mechanical model is established, and the regional pressure relief mechanism and engineering test research are comprehensively carried out by using theoretical analysis, engineering acceptance and other methods. The results show that in the load supply process of rockburst, the foundation static load concentration necessary for rockburst can be changed by the regional transformation of the structure and load of overlying strata of coal seam. For the roof controlled rockburst mines, in the different stages of development, preparation and mining, a regional hydraulic fracturing is carried out for the thick and hard roof, that affects the occurrence of rockburst, to transform the overburden structure and load distribution. Therefore, the roadway excavation and mining face are in the low stress area under the fracturing coverage, and the effect of “artificial liberation layer” is realized for mining a single coal seam under rockburst threat. The mechanism of hydraulic fracturing in the roof area to relieve pressure and prevent rock burst is that compared with that before fracturing, the thick hard roof plate overlying the coal seam is artificially fractured regionally, making its long beams become short beams and large blocks become small blocks in the strike, so it does not have the function of large-area cantilever and reduces the dynamic load brought by the roof fracture caused by the increase of suspended overburden volume. In the inclined direction, the overburden load changes from hard transmission to soft transmission, reducing the overall static load level of the coal seam under the fracturing area. The first surface regional fracturing test for creating an “artificial liberated layer” was carried out in No.401102 fully mechanized caving face at the Mengcun Coal Mine in China. After the fracturing operation, the micro-seismic events during mining presented a high-frequency and low-energy distribution, the fracture fragmentation of roof rock was reduced, the roof water fell evenly in the goaf, the water inflow of the working face was reduced, the pressure and deformation of the working face and two roadways were significantly reduced, and the pressure relief effect of the liberated layer was achieved.

针对软岩巷道受采动应力长时间高压影响易发生围岩大变形的问题,以风水沟煤矿典型软岩矿井胶带巷为工程背景,采用现场调研、围岩应力及变形监测、数值模拟等手段,分析了软岩动压巷道围岩变形机制.从巷道顶板深部阻断应力传递路径、浅部高强支护角度出发,提出了软岩高应力巷道双主动超前断顶卸压+U型钢支架配合锚索高强支护协同控制技术.在5煤胶带巷未受工作面动压影响前,通过实施煤柱顶板深部长短孔爆破、浅部锚索高强支护方案,优化了巷道围岩应力环境,提高了围岩稳定性.基于围岩应力、电磁波CT、钻孔窥视、围岩位移等监测手段,开发了以保护巷道顶板浅部围岩、破坏深部围岩的综合成套监测技术体系,保证了双主动超前卸压护巷效果.

为了探究深部厚硬岩层对冲击地压的影响以及分析岩层的可压裂性,提出了采用地面水平井压裂技术对采场上覆厚硬岩层进行压裂控制,通过改变厚硬岩层的破断特征,达到降低厚硬岩层的破断步距和能量释放强度,并通过试验分析,得到上覆厚硬岩层的脆性系数、脆性矿物含量、黏土矿物含量、成岩作用等参数,综合定量评价厚硬岩层的可压裂性大小.研究结果表明:在厚硬岩层中产生的水平或垂直裂缝面,均有助于减弱厚硬岩层破断失稳引起的下伏回采空间的矿压显现;红庆河煤矿顶板主控岩层脆性系数为67％、黏土矿物含量为28.46％,脆性矿物含量为60.82％,镜质体反射率Ro为0.52％,数据表明主控岩层具有较高的可压裂性,可为后续地面水平井压裂技术的实施提供参考.

为解决浅埋深工作面由突发切顶造成的大面积压架灾害监测预警滞后的问题,采用浅埋工作面现场实测矿压数据分析和相似材料模拟试验方法,从支架工作阻力增阻特性、覆岩应变演化规律、覆岩应变与顶板破断来压的关系方面进行浅埋深工作面覆岩应变特征研究.研究结果表明:浅埋深工作面支架工作阻力在非来压时微增阻,来压时急增阻,增阻速率提升了27～85倍,反映了覆岩应变的突变性;顶板来压前覆岩微应变,来压时覆岩应变突增,切顶时出现尖峰;覆岩应变具有灵敏性和超前性,可以此对顶板异常来压进行监测预警,并提出了以应变为指标的基于分布式光纤技术的切顶压架灾害现场监测预警方法.研究对浅埋煤层开采顶板灾害防控具有实用价值.

8.8m超大采高综采工作面一次开采高度及开采强度大,采场围岩控制困难.采用立柱压力传感器、位移传感器对工作面回采期间支架工作阻力、顶板下沉量进行了全程系统监测,对工作面矿压显现规律、支架工作阻力循环曲线、顶板下沉量及割煤循环内下沉曲线进行了分析,对支架工作阻力、初撑力、支架刚度与顶板下沉关系进行了研究.研究结果表明:超大采高工作面开采具有来压区域性明显、来压急增阻、非来压恒阻、大小周期来压的宏观特征;工作面顶板下沉具有明显的时空差异性,空间上呈现工作面"两端小-中部大"的特征,时间上呈现来压期间大、非来压期间小的特点;工作面支架ΔF-T和顶板下沉ΔS-T均化循环曲线具有高度的一致性,来压期间2者均呈对数-大斜率线性复合增长,非来压期间呈现近常数或小斜率线性增长;顶板下沉与支架工作阻力呈线性对应关系,随支架工作阻力的增加而增大,安全阀开启后,顶板下沉速度明显增大,最大下沉速度为安全阀开启前的4.3倍,安全阀长时开启时顶板下沉速度由急增逐渐过渡至缓增状态,ZY26000/40/88液压支架在来压期间一定时间内可以将顶板下沉控制在一定的范围内,但并不能阻止其继续下沉;初撑力及支架刚度大小对顶板控制影响较为明显,随着初撑力的不断增大,顶板下沉及下沉速度显著降低并趋于稳定,临界点为15 MN,顶板下沉与支架刚度呈现类双曲线关系,支架刚度达到14 Mpa/m以上时,支架刚度对顶板下沉的抑制作用减弱,顶板下沉趋于平稳状态.

为预测综放工作面压架灾害,在综放顶板分区支承力学模型基础上,提出了综放工作面大采厚顶板矿压演化计算方法和支架压架判据,编制了相应的计算程序,分析了综放工作面顶板矿压演化规律,研究结果表明:①综放工作面顶板矿压演化包括4个阶段,分别为缓慢增阻阶段、顶板断裂阶段、快速增阻阶段和失稳阶段.②缓慢增阻阶段顶板沉降量小,支架增阻量小,顶板来压不强烈;快速增阻阶段顶板沉降量大,支架增阻显著.③顶板断裂阶段是矿压从缓慢增阻向快速增阻转变的过渡阶段.顶板煤壁前方断裂时,顶板的边界条件改变,顶板来压剧烈,支架增阻量大,易于引起安全阀开启,若顶板沉降量超过支架活柱允许压缩量,引发大面积切顶压架事故.④当工作面推进至断裂线处,顶板失稳,支架急增阻,若垮落覆岩作用于支架上的荷载超过支架额定工作阻力,安全阀开启,易于引发大面积压架事故.⑤支架额定工作阻力和初撑力设计应遵循的原则是:在缓慢增阻和快速增阻阶段,支架承担的荷载不超过支架额定工作阻力;在顶板断裂阶段,支架应具有足够的可压缩空间卸位让压;在失稳阶段,支架应具有足够的额定工作阻力承担垮落覆岩作用荷载.⑥酸刺沟煤矿6105-2综放工作面采用ZF15000/26/42四柱支承掩护式支架,初撑力10 800 kN,支架额定工作阻力不足,易于发生大面积压架事故.