【作者】 石露；

【导师】 李小春；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2010， 博士

【摘要】 我国是露天矿开采较多的国家。许多大型露天矿山始建于50至60年代,且当前约有80%以上的露天铁矿将进入中晚期。随着每年以12～20m的速度开采,部分露天矿正处于转地下开采的过渡时期,主要有以下工程特点：1.露天开采接近晚期,产量下降,在地下开采投产之前必须开采替代矿体以满足选矿的需要。而这些多为赋存条件比较复杂的矿体,大多数为露天坑内的边缘矿。2.边缘矿或地下开采与露天开采同时进行。3.对于复杂边缘矿开采,通常会采用稳定结构的采矿方法,留有矿柱和保安矿柱,以防止其开采对边坡稳定性的影响。那么,面临的主要问题有：1.矿柱的稳定性分析。2.由矿体采动造成应力场扰动的边坡稳定性分析。3.塌陷区范围的确定。本文以峨口铁矿南西西边缘矿为工程背景,采用块体理论、矢量和法以及扩展有限元法对上述三个问题进行了系统研究,核心内容如下：。1.基于三维节理裂隙网络进行矿柱的几何稳定性和力学稳定性分析：(1)总结了目前关键块体搜索的两种主流方法,并分析了二者的优缺点。本文将二种方法结合起来,即采用砍树法找到矿柱开采自由面上的所有闭合环路,以每个闭合环路为基本单元生成闭合环路子区域,将组成该闭合环路的第一类节理和相关节理视为无限大平面切割此子区域,找到闭合环路相对应的块体。该方法既不需对复杂块体进行繁杂的判断,且避免了因视节理为无限大平面切割研究区域生成大量的块体从而造成计算量巨大,亦可以简单地实现凹面体的搜索。(2)分析了矿柱的岩体结构特征,认为矿柱与节理裂隙是同尺度的,不能简单地将矿柱岩体视为连续介质。将节理视为无限大平面,切割矿柱区域,生成具有凸性的子块体,而后进行子块体拼装,由此生成的块体能够准确地反应矿柱节理裂隙统计特征,随后将其导入3DEC中进行块体力学分析,避免3DEC自身生成块体须将节理视为无限大切割已有块体的局限性。当节理数目较多时,可将研究区域等分成一系列子区域,相应的节理切割和块体拼装都在子区域中进行,然后将子区域组装在一起完成研究区域块体的重构,能够有效降低计算量。2.分析了目前边坡安全系数计算的各种方法,认为基于边坡应力场的矢量和法更加适合矿体采动前后边坡安全系数的计算。改进了蚁群算法,将蚂蚁前进的关键判断量—信息素视为连续变量,使其在搜索边坡临界滑面时无需对边坡进行离散。本文还将改进的蚁群算法与遗传算法联合来搜索边坡临界滑面,较好地克服了遗传算法不利用空间信息反馈而易于陷入局部最优的缺点,同时也克服了蚁群算法在初始信息素匮乏而启动贪婪式搜索造成的求解效率低下的不足,在一定程度上达到了求解效率与时间效率相互平衡。3.开采沉陷是岩体的破坏过程。对于大规模的矿山开采,除Ⅲ级及其以上结构面外,其余的普遍节理应视为对岩体参数的弱化而反映到岩体力学参数中。目前,常用于开采沉降计算的有限元和离散元方法均不能很好的反映上述特点。本文采用扩展有限元方法评价开采沉陷,进行了显式解法推导,并进行了程序实现,避免了裂隙扩展后需要重新组总刚。采用接触面的切向与法向刚度来反映裂隙段上高斯点跳跃的位移与力之间的关系,实现了扩展有限元接触问题。根据子结构法由尖端单元与其相邻单元形成子结构刚度矩阵,使每步的尖端加强自由度可直接由常规自由度和跳跃自由度得到,从而避免了系统收敛指标过多以及由此带来的系统振荡。通过平板不同位置裂隙的拉伸、压剪以及扩展说明了本文方法的有效性。更多还原

【Abstract】 The open-pit mining is prevalent in China. Most large open pit mines were established in 1950-60’s, of which about 80% will step into advanced. With the rate of 12-20m mining annually, some open-pit mines are in the transition period of turning to underground mining. Currently, the main features of open-pit are as follows:1. Before the commissioning of the underground mining, some alternate ore-bodies must be exploited to meet the needs of dressing due to the production drawdown when the open pit is approach to be closed. They are always border ores with complicated geological conditions in the open pit.2. The marginal ores mining or underground mining is simultaneous with open pit mining.3. When exploiting the marginal ore-body, the pillars and safety pillars were kept to prevent the influence on open pit slope as mining method of stable structure was adopted.As a result, the main questions are:1. Evaluation on mine pillar stability.2. Analysis of slope stability under stress field disturbance due to mining.3. Determination of the scope of subsidence area.With the background of SWW marginal ore-bodies in Ekou iron mine, the Block Theory, Vector Sum Analysis and Extend Finite Element Method (XFEM) have been introduced to study the above-mentioned three problems systematically in this dissertation, of which the key contents are as follows:1. Study the geometric and mechanical stability of ore pillar based on 3D Joint Network.(1) There existing shortcomings of two popular methods in searching the key block, which are overcome by combining them in this dissertation. First of all, searching the closed loops on the free surface of mine pillar by Tree Cut Method; then, the sub-region of every single closed loop, which is a range box of typeⅠjoints, is cut by infinite plane of type I and other relevant joints to form many small blocks, the block which has the exact face of closed loop is the key block. The combined method has no requirement of intricate judgment when the block is complicated, also will not cause enormous computational cost when the joints are token as infinite plane, and can realize concave block searching without any special algorithm.(2) The material of ore pillar cannot be treated as continuative simply as the size of which is the same as or slightly bigger than joints. The pillar region was cut by infinite planes of joints to generate a series of convex polytopes, and then the non-exist face of polytope is deleted to make the combination of convex polytopes to form the blocks that can truly match the joints network. Sometimes, the joint cut and polytope combination take place only in sub-region which is generated by equally divided the pillar region to avoid forming large number of polytopes. The blocks of entire pillar region can be formed by piecing together all sub-region blocks. Mechanical analysis can be carried out once the formation of pillar block is finished. The block formation method is prior to 3DEC itself in which the joint is regarded as infinite plane to cut the blocks and lead to inconsistence with statistical parameters of the joint such as trace length.2. Calculating the FOS (factor of safety) of slip surface and searching the critical slip surface.(1) The Vector Sum Analysis can calculate the FOS of the slope based on the stress field without iteration, and it’s more suitable for analyzing the slope stability with stress disturbance due to mining.(2) The Ant Colony Algorithm (ACO) was improved to search the slope critical slip surface without the discretization of the slope body by taking the pheromone as a continuous distribution variable. In addition, to overcome low speed of ACO owing to absence of original pheromone, as well as multiple redundancies and low efficient solving of genetic algorithms as a result of no feedback ability, the ACO was integrated with genetic algorithm to complement each other’s disadvantages.3. Actually, mine subsidence is the failure process of the rock mass. Also, the ubiquitous-joint is equivalent to the weakness of the mechanical parameters of rock mass in large-scale mining except classⅢand above. The FEM and DEM which are commonly used to analyze the mine collapse can not reveal the above features very well. The XFEM was adopted to solve this subject. In order to avoid rebuilding the overall stiffness matrix, the XFEM was realized by explicit solution technique. The normal and shear stiffness of contact surface was used to reflect the relationship of jumping displacement and stress on Gauss points of the fracture segments. Moreover, the tip-enriched freedoms can be directly derived by normal and Heaviside freedoms using the sub-structural stiffness matrix which is based on sub-structure method and made up of tip element and its neighbor elements, in the prevention of too many convergence indicators and oscillation of system. Then, some numerical simulations of crack tensile, compression and shear as well as propagation in a plate were carried out to illustrate the effectiveness of the methods. Finally, the section of 18# prospecting line was used for analyzing the rock failure by exploitation of north ore-body.更多还原