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1、Safety Analysis for Pillar of Ally Exploitation Laneway In Extreme Close Distance Coal SeamAbstract: According to the geological and mining conditions of ZhaoPo coalmine, and using the FLAC3D program which can describe the geometrical non-linear large strain character of rock mass, the paper perform
2、ed numerical simulation, analyzed the deformation characters and stress of the laneways, which is under the conditions of single excavation and working face mining and condition of ally exploitation laneway in extreme close distance coal seam, and drew the conclusions that 3m pillar of exploitation
3、laneway is conformed to the practical project, the safety is relatively fine, and it can be used for reference by other construction of the similar projects.Keywords: FLAC3D; non-linear large strain; extreme close distance coal seam; safety1 IntroductionThe design of pillars measure has been always
4、a technical problem of coalmine production safety under the condition of ally exploitation in extreme close distance seam. The reasonability of pillars measure design is directly associated with supporting effect of laneway, coalmine production safety and economic benefit of coalmine. According to o
5、n-the-spot observation, combining with underground press distributing rules in extreme close distance seam, stratum lithologies, thickness and so on, some people put forward several schemes to design the pillars measure, which obtained apparently technical and economical benefit in practice, but aut
6、hor consider that this way not only require great deal of manpower and financial also exist safety hidden trouble during the course of construction. At present, along with the rapidly develop of computer and software for rock and soil engineering numerical value computation, such as ANSYS, FLAC and
7、ABAQUS etc. The approximately feasible conclusion of pillars measure design can be gotten through computer numerical simulation. Numerical simulation usually simplified space problem to plane problem and applied two dimensional plane-strain models in the past. However, three dimensional numerical ca
8、lculation is an important method simulating stress and strain of special structure, which has such merits as more objective, accurate and visualized etc. FLAC3D is a three-dimension explicit finite-difference program developed by Itasca Consulting Group Incorporation, which can simulate three-dimens
9、ional mechanical behavior of rock and soil as well as other materials. FLAC3D divides the calculating area into several tetrahedron plane strain elements. Each of the elements conforms to appointed linear or non-linear constitutive equations under given boundary conditions. If element stress yields
10、the material or generates plastic flow, element network and structure can transform with the material, which is appropriate to simulate large strain problem. FLAC3D adopts explicit finite-difference to solve control differential equation of field, that is to say, firstly apply the differential princ
11、iple to solve node-unbalanced force and velocity based on the change of node stress and applied force (or velocity) and time step; Then according to constitutive equations of element, solve element strain increment, stress (or displacement) increment and the total stress by node velocity. Then enter
12、 new cycle, and use mixed elements discrete model to simulate material yield, plastic flow, soft and even large strain. Especially, it has obvious advantages in such fields as elastic-plastic analysis, large strain analysis and simulating construction process.2 Geometric Equation of Non-linear Large
13、 Strain The paper adopts FLAC3D program based on pulling coordinate method to numerical simulation research. Because there is large error and even mistake when calculating large-displacement plane problem using classical small strain theory, FLAC3D computes large strain using pulling coordinate meth
14、od. The kind of coordinate pulls, extends, shortens with the transformation of distorting body, and then leads to the change of coordinate curvature. Fig.1 shows the large stain and of rotation continuous distorting body. A0 transforms continuously with time, for example, A0(T0)A(T). At time T0, the
15、 pulling coordinatexi is the same with the fixed coordinate Xi, that is to say, Xi(0)=Xi(xi,T0)=xi(0), at time T0, Xi=Xi(xi, T).Obviously, the conclusions are very reasonable to set up non-linear large strain geometric equations using pulling coordinate.3 Computing Simulation3.1 Geological Condition
16、 of Simulating Working FaceZhaoPo Coalmine lies in the city of Tengzhou of Shandong Province, which borders on Beijing-Shanghai Railway in the east. The highway extends in all directions. No.16 and No.17 coal exploited belong to thin coal seam, and the mining depth is 330 to 370m. The thickness of N
17、o.16 coal is 1.05m, and No.17 coal thickness 0.7m. Interval of two coal seams is 6.5m. Considering the economic benefits, it is unable to adopt slice-mining method, so ally exploitation and laneway after mining are adopted. No.16 and No.17 coal laneways bear excavating influences from this working f
18、ace and the lower sub-lever working face; furthermore, interval of two coal seams is very little. In addition, excavation of No.17 coal is also influenced by No.16 coal. After repeat excavation of two coal seams, the cover rock of laneways deformed greatly, and destroyed severely, and constant maint
19、aining was needed, which severely affected normal production and safety. So it is much essential to research pillar measure design of laneway to reduce cover rock deformation, improve safe production environment, and guarantee economic benefits as much as possible.3.2 Calculating Model The computati
20、onal analysis planed 15 schemes, among which pillar measure design of laneway is respectively 2, 3, 4, 6 and 8m, and different pillar measure corresponds to exploiting distance of 30, 40 and 50m respectively. This paper only analyzed five schemes related to 50m exploiting distance, separately marked
21、 as Scheme , , and .3.2.1 Construct model and divide calculating area gridThe calculating model disregards the effects of geological structure and underground water etc.; Initial stress is ground static stress field; Each stratum is combined continuous medium which contacts each other. In order to d
22、ispel boundary influence, geometric measure of the model selects 300m slope (X), 140m stride (Y), 50m depth (Z), 3m span of laneway, 1.8m walls high. According to geological working condition, the stress is static stress state in 350m depth; vertical stress is 5.6MPa; horizontal stress is 2.8MPa; ho
23、rizontal limit is loaded in the stride and slope direction of mode; vertical limit loaded on bottom boundary. Mechanics properties of cover rock are showed in the Table 1. The constitutive equation adopts Mohr-Coulomb Hypothesis. Because the change of additional stress and displacement before and af
24、ter exploitation need analyzing, the method of disposable filling material excavation is adopted to simulate caving gob in the course of mining . The calculating object is naked laneway without support, and its computing range and grid division is showed in Fig 2.3.2.2 Process of numerical calculati
25、onFirstly, the initial stress state is imitated. Because the effect of mining stress is the only consideration in the calculation for this time, displacement is set up zero when the initial stress reached balance. Then laneways excavation begins, and the change of the main special stress and plastic
26、 area of laneway cover rock are observed carefully. Finally, the working face excavation is simulated, and the gob is filled when unsettled distance is equal to exploiting distance of ally exploitation. Circulate sequentially until the simulating excavation is over.3.3 Results of Numeric Calculation
27、Disposable excavation is considered in the calculation. The exploitation layout of the working face is set up 10m for each. Time step is adopted to control the computation, and each computing period of time is according to 2000 step.3.3.1 Calculating results of laneways before working face excavatio
28、nWhen the pillar measures of laneways are 3m, the figures of plastic areas and the main special stress chromatogram are respectively Fig.3(a) and Fig.3(b).From the above results, it can be found that the deformation outline of laneways distribute symmetrically, similar to the practical one. After ca
29、lculating 2000 steps, it can be observed that convergence is obvious of vertical displacement of the center top and the maximum unbalanced force between element nodes. Destruction area of peripheral rock mass of laneways is not very large, and the main special stress distributes symmetrically in bot
30、h sides of laneways, which is conformed to the actual.3.3.2 Calculating results of laneways after working face excavationAfter exploitation of the working faces, the curve graphs of displacement and the main special stress in the direction of stride of No.17 coal floor for five schemes are respectiv
31、ely showed just as Fig 4(a) and Fig 4(b).From the above figures, it can be obtained that for each scheme, both displacement and the main special stress of floor take on “saddle shape”distribution character, symmetrical to middle axle; both ends of the laneways have larger displacement and stress; Mi
32、ddle parts are relatively small and gentle. All the simulation results are well conformed to the project reality. From the displacement curve graph, it can be found that the displacement to the bottom of both laneway ends has a decreasing trend. However, displacement to the bottom for Scheme is larg
33、er than that of other schemes, so Scheme is not advisable. Fig 4(b) show that released stresses for Scheme , and are relatively large, and destruction of laneways for these schemes is relatively serious than others. Thus, Scheme is believed to be the optimum through this simulation.4 Conclusions(1)
34、FLAC3D can discretize elements which make elements many as much as possible, analysis more accurate, adaptability more perfect, has a strong ability to manage figure. It adopts explicit finite-difference Lagrangian algorithm, which make it have an original advantage in such respects as analyzing ela
35、stic-plastic mechanics behaviors of rock and soil engineering, and simulating project construction etc. Especially, under the conditions of plastic flow and project unsteadiness, adopting large strain model can reflect the objective reality even more.(2) The paper adopts large strain mode of FLAC3D,
36、 simulates and compares deferent intervals of laneways. It can be drawn that the laneway stress suffered increases with the measure of pillars within certain distance; 3m pillar of laneway is relatively conformed to the project reality under the geological conditions. The safety of production enviro
37、nment is relatively fine.(3) From the analysis about laneway before and after excavation, it can be found that the simulation results are basically accorded to the practical destruction of laneways, and discover the characters of stress and deformation of laneways. So it indicates the exactness of s
38、imulation.(4) The conclusions of the paper have certain directive significance and reference value as to the projects under the similar geological conditions.极近距离煤层联合开采巷道煤柱留设尺寸的优化设计摘要：本文采用能描述岩体大变形特征的几何非线形程序FLAC3D，以赵坡煤矿的地质采矿条件为依据，进行数值模拟研究，在极近距离煤层联合开采条件下，对巷道在单独开挖以及在工作面开采时巷道围岩的受力和变形特征进行了分析，得出了巷道煤柱留设尺寸为
39、3m时比较符合工程实际，对指导类似的工程施工有一定的借鉴意义。关键词：FLAC3D，非线形大变形，近距离煤层，优化1简介极近距离煤层联合开采条件下，巷道煤柱留设一直是困扰煤矿安全生产的一个技术难题，巷道煤柱留设的合理性直接关系到巷道支护效果、煤矿安全生产，以及煤矿的经济效益。目前，用于进行岩土工程的数值计算软件发展迅速，例如ANSYS、FLAC、ABAQUS等。以往的数值模拟通常把空间问题简化为平面问题，应用二维的平面应变模型。而三维数值计算具有更客观、准确、形象等诸多优点是模拟空间结构受力及变形的重要手段。FLAC3D是由美国Itasca Consulting Group Inc.开发的三维
40、显式有限差分法程序，它可以模拟岩土及其他材料的三维力学行为。FLAC3D将计算区域划分为若干四节点平面应变单元，每个单元在给定的边界条件下遵循指定的线性或是非线性本构关系，如果单元应力使得材料屈服或是产生塑性流动，则单元网格及结构可以随着材料的变形而变形，非常适合模拟大变形问题。FLAC3D采用显式有限差分格式来求解场的控制微分方程，即首先由节点的应力和外力（或速度）变化和时间步长利用差分原理求节点不平衡力和速度；再根据单元的本构方程，由节点速度求单元的应变增量、应力（或是位移）增量和总应力，进而进入新的循环，并应用混合单元离散模型，可以准确地模拟材料的屈服、塑性流动、软化直至大变形，尤其在材
41、料的弹塑性分析、大变形分析以及模拟施工过程等领域有明显优势。2非线性大变形几何方程本文采用基于拖带坐标系法的FLAC3D程序进行数值模拟研究。由于经典小变形理论在计算发生大位移的平面问题时误差较大，甚至发生错误，在FLAC3D中给出了应用拖带坐标系计算大变形。陈至达教授提出了采用采用两个参照系统的方法来描述变形体的运动，其中一个为固定在空间的定系；另一个为嵌含在变形体中的动系，称为拖带坐标系。这种坐标系随着变形体的变形而拖带伸展、缩短、并引起坐标系的曲率改变。图2.1给出了一个连续变形体的大变形和大转动。随着时间的推移，A0连续发生变形，例如A0(T0) A(T)。在T0时刻，拖带坐标系和固定
42、坐标系相同，即：，在T时刻， 。图2.1 拖带坐标系局部基矢。其中，分别为变形体A在T0时刻和T时刻每一点的局部矢量。基矢从未变形状态变为变形状态，变形张量为 (1)根据S-R陈矢分解理论，=应变张量+转动张量 (2)有限应变张量 (3)有限平均局部转动 (4)局部转动的平均角 (5) 局部转动轴 (6)对于图1所示的滑动变形，运用大变形理论式(1) (6)计算滑动体每一点的应变，进行合理性验证如下=显然，利用拖带坐标系法建立非线性大变形几何方程，所获得结论非常合理。3计算模拟3.1模拟工作面的地质条件赵坡煤矿位于山东省滕州市境内，矿井东临京沪铁路，公路四通八达。开采的16、17煤属于薄煤层，
43、采深为330370m，16煤厚度为1.05m，17煤厚度为0.7m，两煤层间距为6.5m，考虑到经济效益，不能采取分层开采的方式，故采用联合开采、沿空留巷的方式。16、17煤巷道不仅承受本工作面的采动影响，而且还承受下区段工作面的重复采动影响，而且两煤层间距很小，此外17煤的开采还受到16煤开采的影响。16煤与17煤重复采动后，巷道围岩变形量大，破坏严重，需要不断维修，严重影响正常生产与安全。为了尽可能减少巷道围岩变形量、提高安全生产环境、确保经济效益，故进行巷道煤柱留设尺寸的研究是十分必要的。3.2计算模型本计算分析中共设计15个计算方案：巷道的煤柱留设尺寸分别为2、3、4、6、8m，并且每
44、个不同的巷道煤柱留设尺寸分别对应30、40、50m的联合开采错距，本文仅对联合开采错距为50m时的5个方案进行分析，分别记为、方案。3.2.1模型建立与计算区域网格划分计算模型不考虑地质构造、地下水活动等的影响，原岩应力为大地静应力场，各岩层为整合接触的连续介质。为了消除边界影响，计算模型几何尺寸为沿走向（Y）取140m，深度（Z）取50m，倾斜方向（X）取300m，巷道跨度3m，墙高1.8m。根据现场地质生产条件，应力条件考虑埋深350m的静水应力状态，垂直应力取5.6Mpa，水平应力取2.8Mpa，模型走向、倾斜方向均施加水平约束，底边界施加垂直约束。围岩力学性质见表3.1，本构关系采用摩
45、尔库仑模型。由于要分析开采前后采动附加应力及位移的变化，因此开采过程采用一次性换填材料式开挖模拟采空区冒落矸石3。计算对象为无支护的裸巷，其计算范围和网格划分见图3.1。图3.1 计算模型的网格划分表3.1 围岩力学性质表岩层厚度/m体积模量K/Gpa剪切模量G/Gpa密度Kg/m3粘聚力C/Mpa抗拉强度t/Mpa摩擦角F/0C砂泥岩322.19e97.84e823500.50.540灰岩6.452.78e91.59e926502.30.848泥岩1.61.33e96.15e822000.20.2535煤1.753.81e83.48e815700.20.1531泥质砂岩8.21.73e91.
46、14e9230020.7548采空区3.6e61.9e610000.0350.05253.2.2数值计算过程首先模拟原岩应力状态，由于本次计算只考虑采动应力的影响，所以在达到原岩应力平衡时，进行位移归零，然后进行巷道开挖，观察巷道围岩的最大主应力变化及所产生的塑性区域变化，接着进行模拟工作面的开挖，等悬空距离等于联合开采错距时进行采空区充填，依次循环，直至模拟开挖结束。3.3 数值计算结果计算中考虑巷道为一次性开挖，工作面的开采以10m为一开采布局，计算以时步控制，按每2000时步为一个计算时段。3.3.1 工作面开采前巷道的计算结果巷道煤柱尺寸为3m时的16、17煤巷围岩的塑性区域图及最大主
47、应力色谱图分别为图3.2、3.3所示。图3.2巷道围岩的塑性区域图 图3.3巷道围岩最大主应力色谱图从上面的结果可以看出，巷道的变形轮廓成对称分布，与实际变形轮廓相近。在计算到2000时步时可以看出，顶部中心的垂直位移以及计算单元节点间的最大不平衡力都有明显的收敛迹象。巷道周边的破坏区域不是很大，并且最大主应力值对称分布在巷道的两帮，与实际结果相符。3.3.2 工作面开采后巷道的计算结果工作面开采后，五种方案下17煤巷道底板沿走向方向上的位移曲线图及最大主应力曲线图分别如图3.4、3.5所示。图3.4 17巷道底板的位移曲线图 图3.5 17巷道底板的最大主应力曲线图从图中可以得出，每种方案中
48、无论是底板位移还是最大主应力都成“马鞍型”分布及与中间轴呈对称分布，巷道的两端有较大的位移及应力，中间部分较小且比较平缓。模拟结果与工程实际能够很好的吻合。从位移曲线图可以看出，随着巷道间距的减少，巷道两端的底鼓位移有下降的趋势，但是第方案巷道中间部分的底鼓位移比其它方案的位移量都大，因此此种方案不可取。从图35 17巷道底板的最大主应力曲线图中可以看出，第、方案应力释放较大，巷道破坏也较严重，因此通过本次模拟认为第方案为最优方案。4结论(1)FLAC3D能够对单元进行离散化处理，使得单元尽可能多，分析更加精确，自适应性强，有强大的图形后处理能力，它采用了基于显示有限差分法的拉格朗日算法，使得它在分析岩土工程结构的弹塑性力学行为、模拟工程施工工程等方面有独到的优势，尤其在发生塑性流动或工程失稳的情况下，采用大变形模式，更能反映客观实际，这一点较其它方法有很大的优势。(2)本文采用FLAC3D中的大变形模式，对巷道间不同的间距进行对比模拟分析，得出了在一定距离内煤柱越宽巷道受力越大，以及在此种地