沿空留巷下位岩层断裂特征数值模拟及控制技术研究

为解决沿空留巷直接顶松软破碎,严重影响基本顶和沿空留巷稳定性的问题,以新元煤矿3414工作面为研究对象,建立UDEC Trigon模型,通过模拟不同支护条件下沿空留巷下位岩层断裂特征,分析其对围岩稳定性的影响。数值模拟发现,沿空留巷围岩以剪切裂隙为主;充填区顶板张拉裂隙较为发育,是沿空留巷围岩控制的薄弱环节;沿空留巷下位岩层沿充填体外侧断裂,抑制了剪切裂隙在实体煤帮发展,增加了巷旁充填体和实体煤帮的承载结构的稳定性。工程实践表明:采用高预应力、高刚度锚索及时支护充填区直接顶的围岩综合控制技术,沿空留巷下位岩层沿充填体外侧断裂,巷道围岩顶底板最大变形量为900 mm,两帮最大变形量为800 mm,能够满足通风和瓦斯排放的要求。

层间作用对岩层断裂的影响

运用弹性力学基本理论分析了采场顶板岩层层间作用对岩层应力状态的影响；根据最大拉应力准则，建立了岩层破断位置的确定方法。结果表明，岩层中最大拉应力并非一定发生在最大弯矩所在的截面上，因而岩层也并不一定沿煤壁发生断裂。这一结论很好地解释了采场上覆岩层塌落范围自下而上逐层收敛的现象。

岩层断裂的最大转动梯度准则及其在构造地质中的应用

认为微观转动不协调是产生断裂的原因。在现代有限变形力学Ｓ（应变）－Ｒ（转动）分解定理基础上提出了断裂扩展的最大转动梯度准则，可直接确定断裂产生的位置和扩展方向。初步应用该准则对雁行裂纹的形成过程进行了数值模拟。

全套管全回转钻机在断裂带软硬交互岩层大直径超深成桩中的应用

云南省昭通市镇雄县鱼洞乡特大桥5号主墩部分桩基位于断裂带软硬交互岩层,桩基直径达2.8 m,最大深度达94 m,冲击钻成孔和旋挖钻成孔技术难以满足成桩质量和工期要求,本文提出利用DTR3205H型全套管全回转钻机进行成桩施工,介绍了全套管全回转钻机施工工艺,分析了施工流程和关键技术。全套管全回转钻机依靠冲击锤和冲抓斗反复冲击和抓取破碎岩体,可避免出现塌孔、卡钻、埋钻现象,有效阻隔地下承压水的影响,可满足大直径超深桩基施工;双套管分级钻进部分套管取出钻进技术工法成熟,成桩质量高,成桩速度较快,同时节约了工程投入。相关工程经验可为类似桩基工程施工提供借鉴。

基于支承压力估算的合理开切眼位置确定方法

针对开切眼附近冲击地压事故,通过理论研究和现场勘查,探索了开切眼附近冲击地压发生的原因,提出了基于支承压力估算的合理开切眼平面位置确定方法。研究结果表明:开切眼布置在上覆岩层自重应力、采空区传递应力、构造应力等叠加区域内,叠加应力超过煤岩体冲击临界值是导致发生冲击的主要原因。基于现场微地震实测数据剖面分析,估算了关键岩层的断裂角。结合覆岩空间结构,建立了支承压力估算模型,估算了叠加总应力,并绘制了支承压力分布曲线。以动应力比d=σ/σc为冲击危险性判断标准,根据经验d值,在支承压力影响范围内划分冲击危险区,指导合理开切眼平面位置或现场防冲强度的确定。研究成果经河南某矿现场应用,效果良好。

冲击矿压电磁辐射前兆规律的初步研究

在实验研究具有冲击倾向煤样变形、破坏电磁辐射特征的基础上 ,对综放工作面冲击矿压的电磁辐射前兆进行了现场测定 ,探讨了冲击矿压电磁辐射前兆与老顶岩层断裂、运动的关系 。

辽宁地区中等地震活动增强与后续最大震级的关系探讨

傅承义先生早在1971年就提出“红肿”假说：“在一个较大地震（例如，Ms≥4．5）发生前，地壳上层在很大地区内部都已经起了变化，并不局限于岩层断裂的地区；断层不过是最后的爆发点而已。地震过程就象人身上长疮一样，在一大片红肿的地方，疮口的面积只占一个很小的比例”。笠原庆一指出：“震源尺度与震级有关，震级越大则震源体积越大”。郁曙君对大华北地区的研究结果也表明，中等地震的活动规律可作为ML≥5．0地震的震兆，

大同矿区永定庄煤矿4#煤层开采支承压力分布规律研究

永定庄煤矿8106工作面由于受火成岩侵入导致煤层变质,厚度不稳定,通过采用极限分析方法和现场实测,得出了工作面支承压力的相关参数、顶板岩层断裂运动规律及岩层破坏波及范围。

层状岩体构造形成过程的力学机制

根据实验结果和理论计算，确定岩层断裂块的尺寸。从理论上阐述了块体结构的形成过程，并提供相应的实验资料。

Focal mechanism caused by fracture or burst of a coal pillar

As a regional, real-time and dynamic method, microseismic monitoring technology is quite an appropriate technology for forecasting geological hazards, such as rock bursts, mine tremors, coal and gas outbursts and can even be used to prevent or at least reduce these disasters. The study of the focal mechanisms of different seismic sources is the prerequisite and basis for forecasting rock burst by microseismic monitoring technology. Based on the analysis on the mechanism and fracture course of coal pillars where rock bursts occur mostly, the equivalent point source model of the seismicity caused by a coal pillar was created. Given the model, the seismic displacement equation of a coal pillar was analyzed and the seismic mechanism was pointed out by seismic wave theory. The course of the fracture of the coal pillar was simulated closely in the laboratory and the equivalent microseismic signals of the fractures of the coal pillar were acquired using a TDS-6 experimental system. The results show that, by the pressure and friction of a medium near the seismic source, both a compression wave and a shear wave will be emitted and shear fracture will be induced at the moment of breakage. The results can be used to provide an academic basis to forecast and prevent rock bursts or tremors in a coal pillar.

Experimental research on overlying strata movement and fracture evolution in pillarless stress-relief mining

In multiple seams mining, the seam with relatively low gas content （protective seam） is often extracted prior to mining its overlying and/or underlying seams of high gas content and low permeability to minimize the risk of high gas emission and outbursts of coal and gas. A key to success with this mining sequence is to gain a detailed understanding of the movement and fracture evolution of the overlying and underlying strata after the protective seam in extracted. In Zhuji mine, the No. 11-2 seam is extracted as a protective seam with the pillarless mining method by retaining goal-side roadways prior to its overlying No. 13-1 seam. An investigation has been undertaken in the panel 1111 （1） of Zhuji mine to physically simulate the movement and fracture evolution of the overlying strata alter the No. 1 I-2 seam is extracted. In the physical simulation, the displacement, strain, and deformation and failure process of the model for simulation were acquired with various means such as grating displacement meter, strain gauges, and digital photography. The simulation result shows that： （1） Initial caving interval of the immediate roof was 21.6 m, the first weighting interval was 23.5-37.3 m with the average interval of 33.5 m, and the periodic weighting interval of the main roof was in a range of 8.2-20.55 m and averaged at 15.2 m. （2） The maximum height of the caving zone after the extraction of No. 11-2 seam was 8.0 m, which was 4 times of the seam mining height and the internal strata of the caving zone collapsed irregularly. The mining-induced fractures developed 8-30 m above the mined No. 11-2 seam, which was 7.525 times of the seam mining height, the fracture zone was about 65° upward from the seam open-off cut toward the goaf, the height of longitudinal joint growth was 4-20 times of the mining seam height, and the height of lateral joint growth was 20-25 times of the mining seam height. （3） The ＂arch-in-arch＂ mechanical structure of the internal goaf was bounded by an expansion angle of broken strata in the lateral direction of the retained goaf-side roadway. The spatial and temporal evolution regularities of over- burden＇s displacement field and stress field, dynamic development process and distribution of fracture field were analyzed. Based on the simulation results, it is recommended that several goaf drainage methods, i.e. gas drainage with buried pipes in goaf, surface goaf gas drainage, and cross-measure boreholes, should be implemented to ensure the safe mining of the panel 1111 （1）.

Study on fault induced rock bursts

In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.

MECHANICAL BEHAVIOUR OF MAIN FLOOR FOR WATER INRUSH IN LONGWALL MINING

In this paper a new mechanica1 medel indicating the mechanical behaviour of main floor in longwall mining is proposed. In the medel the unfractured rnain floor is considered as an elasto plastic plate, and the combination of fractured blocks as a voussoir beam. Using the plastic hmit theory of plates, th limit load acting on rnain floor and the position of its largest deformation are gotten. The stability conditions for the key blocks of the voussoir beam are analysed by "S-R" stability theory. The results of the theoretical analysis are important for the study on the water inrush from seam floor.

Study on first caving fracture mechanism of overlying roof rock in steep thick coal seam

Based on the elastic plate theory, a mechanical model of thin plate for the first caving of overlying roof rock in steep mining face was established. The analytical solution of the deflection and stress distribution of roof rocks was obtained. According to the specific geological conditions of the 5-103 panel in Shanxi,the failure of roof rocks and the influence of seam dip on it during the exploitation were theoretically investigated. Meanwhile, the first caving characteristics of the overlying rock in the steep coal seam were investigated based on its stress contour. The results show that the dip angle has a distinct influence on the caving interval and the first caving interval for the 5-103 panel is 37 m in theory. Finally, a systematic monitoring on the behavior of rock pressures was conducted. The measured results agree well with the theoretical prediction, which provides a good reference for practical steep coal seam mining.

Relationship between the rock mass deformation and places of occurrence of seismological events

Static effort of rock mass very rarely causes of rock burst in polish coal mines. Rock bursts with source in the seismic tremor within the roof rock layers are prevailing. A seismic tremor is an effect of rupture or sliding in roof layers above the exploited panel in coal seam, sometime in a distance from actual exploitation. Sliding, as a rule occurs in fault zone and tremors in it are expected, but monolithic layer rupture is very hard to predict. In a past few years a practice of analyzing state of deformation in high energy seismic tremors zones has been employed. It let gathering experience thanks to witch determination of dangerous shape of reformatted roof is possible. In the paper some typical forms of roof rocks deformations leading to seismic tremor occurrence will be presented. In general these are various types of multidirectional rock layers bending. Real examples of seismic events and rock bursts will be shown.

An early warning method for water inrush in Dongjiahe coal mine based on microseismic moment tensor

Dongjiahe Coal Mine belongs to the Carboniferous Permian coal field which has a high degree of karst and fissure development.This paper takes the working face of Dongjiahe Coal Mine as an example;through the microseismic(MS)monitoring system arranged on the working face,the moment tensor theory was used to invert the focal mechanism solution of the anomalous area of the floor MS event;combining the numerical simulation and field data,the underlying floor faults were identified by the stress inversion method.The results show that:1)Moment tensors were decomposed into three components and the main type of rupture in this area is mixed failure according to the relative criterion;2)The hidden fault belongs to the reversed fault,its dip angle is approximately 70°,and the rupture length is 21 m determined by the inversion method of the initial dynamic polarity and stress in the focal mechanism;3)The failure process of the fault is divided into three stages by numerical simulation method combined with the temporal and spatial distribution of MS events.The results can provide a reference for early warning and evaluation of similar coal mine water inrush risks.

STRUCTURE AND STABILITY OF MAIN ROOF AFTER ITS FRACTURE

A series of physical modelings in which a main roof is considered as a Kirchhoff plate supported or clammed by Winkler elastic foundation were performed to simulate the fracturing process of the main roof in longwall mining. Based on these modelings spatial structures of the main roof after its fracture are described, blocks of the fractured main roof are classified and their behaviors are analyzed in this paper. Additionally, two stability indexes of the structures are defined, and the factors affecting stability of the structures with different boundaries and geometric conditions are discussed.

Surface borehole synthesis tension deformation fracture time-space rule

In order to release the tension and shear effect of the superjacent rock strata movement during excavation in coal mine,protect the surface borehole case from fracturing fast and make a good use of the surface borehole during goaf methane drawing,a common synthesis tension deformation fracture model was set up based on the synthesis tension effect of the rock strata,and the deformation rule of the surface borehole case with time and space was researched.The results suggest that,to reduce the deformation the surface borehole should be built between the boundary of the stope and the knee of subsidence curve.At the same time,a 3DEC simulation model and an engineering example were carried out to examine the rules of theoretical model.The result suggests that the model and the rules accord to the test and have good building and protection engineering application values to the surface borehole.

Fracture mechanism of inversed trapezoidal shaped tunnel excavated in 45° inclined rock strata

In order to understand failure mechanisms of the tunnel excavated in the stratified rock masses in deep mine, the physical modeling experiment by using the large-scale model was carried out. The field case simulated in the experiment is a main connection tunnel located at depth of 1000 m in Qishan coal mine,Xuzhou mining district. Tunnel deformation was monitored by using strain gauges and a video camera simultaneously. Crack initiation and propagation process during the test were analyzed based on image analysis of the captured video photographs. At the same time, deformation process of the key monitoring points around the tunnel section is given by the monitored strain plots. Under the increasing external loads, crack initiation occurs firstly on the left wall of the tunnel, then on the immediate roof.Complete failure of the tunnel occurs as a result of the slippage of the rock layers along the interfaces.

Active velocity tomography for assessing rock burst hazards in a kilometer deep mine

Active velocity tomography was used to determine the stress state and rock burst hazards in a deep coal mine. The deepest longwall face, number 3207 in the Xingcun colliery, was the location of the field trials. The positive correlation between stress and seismic velocity was used to link the velocity data with stratum stresses. A GeoPen SE2404NT data acquisition system was used to collect seismic data from 300 g explosive charges fired by instantaneous electric detonator and located in the tail entry. The geophones were installed on the rock bolts in the head entry of LW3207. Velocity inversion shows an inhomogeneous distribution of stress in the longvvall face that could not be obtained from theory or numerical simulations. Three abnormally high P-wave velocity regions were identified that were located on the corners of the two roadways and at the face end near the rail entry side. The maximum velocity gradient is located at the open cut off near the rail entry and is the area most dangerous for rock burst. Mining-induced tremors recorded by a micro-seismic monitoring system demonstrated that the position of energy release during mining coincides with the high velocity gradient area. This technology aids technicians in the coal mine as they design measures to weaken or eliminate potential danger during subsequent mining.