A calculation method of reasonable size of coal pillar in large mining height section based on elastic theory
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摘要:
不同工况下区段煤柱两侧支承压力分布及岩体变形存在显著差异,考虑煤柱两侧不同支承压力对煤柱整体稳定性的影响,基于大采高区段煤柱的弹性力学计算模型,分析了支承压力下煤柱任一单元岩体的应力应变分量。通过建立大采高煤柱弹塑性界面上岩体的柱条模型,确定在0.65倍煤柱高度处单元岩体将首先发生水平拉伸破坏,利用虎克定律提出了该单元岩体极限拉应变与煤柱极限平衡区宽度的关系式。依据煤柱破裂区岩体的受力特征,运用摩尔库伦准则推导了煤柱破裂区宽度的计算公式。结果表明:①煤柱极限平衡区宽度与岩体极限拉应变和弹性模量反相关,与煤柱埋深和煤柱高度正相关;②煤柱高度及其与顶底板的界面摩擦角是影响破裂区宽度的关键性因素;③煤柱两侧不同工况下,煤柱岩体极限拉应变与其所受侧压呈正变关系,区段煤柱采空区侧所受侧压较巷道侧偏大,采空区侧岩体的极限拉应变也相应较大,表现为采空侧极限平衡区宽度较巷道侧偏小。最后,将上述理论公式应用于陕北某矿30109工作面大采高区段煤柱极限平衡区和破裂区宽度的分析计算,给出了该工作面两侧区段煤柱的合理宽度及其支护方案。工程应用表明,30109工作面区段巷道围岩变形控制效果良好,满足现场生产需求。
Abstract:There are significant differences in abutment pressure distribution and rock mass deformation on both sides of section coal pillar under different working conditions, the influence of different abutment pressures on the overall stability of coal pillar is considered, based on the elastic mechanics calculation model of coal pillar in large mining height section, the stress-strain components of any unit rock mass of coal pillar under abutment pressure are analyzed. Through the establishment of large mining height pillar elastic-plastic interface on the rock column model, it is determined that unit rock mass will first undergo horizontal tensile failure at 0.65 times the height of coal pillar, based on Hooke's law, the relationship between the ultimate stretching strain of rock mass and the width of limit equilibrium zone of coal pillar is proposed. According to the mechanical characteristics of the rock mass in the coal pillar fracture zone, the calculation formula of the width of the coal pillar fracture zone is derived by using the Mohr-Coulomb criterion. The results show that: ①The width of limit equilibrium zone of coal pillar is inversely related to ultimate tensile strain and elastic modulus of rock mass and positively related to buried depth and height of coal pillar;②The height of coal pillar and the interface friction angle between coal pillar and roof and floor are the key factors affecting the width of fracture zone; ③Under different working conditions on both sides of coal pillar, due to the positive relationship between the ultimate tensile strain of coal pillar rock mass and its lateral pressure, the lateral pressure on the gob side of the section coal pillar is larger than that on the roadway side, and the ultimate tensile strain of the rock mass on the gob side is correspondingly larger, which shows that the width of the limit equilibrium area on the gob side is smaller than that on the side of the gateway. Finally, the above theoretical formula is applied to the analysis and calculation of the width of limit equilibrium zone and fracture zone of coal pillar in large mining height section of 30109 working face in a mine in Northern Shaanxi, and the reasonable width of coal pillar and its supporting scheme under different working conditions on both sides of the working face are given. The engineering application shows that the deformation control effect of surrounding rock along the working face is good, which can meet the demand of field production.
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0. 引 言
外排土场是露天开采的必然产物,其稳定性是影响露天煤矿安全生产的重要因素。由于特殊的地形地貌条件,我国中西部的一些露天煤矿将排土场建立在沟壑发育的黄土基底上,形成了基底软弱、形态极其复杂的黄土沟壑基底排土场[1-3]。在我国平朔安太堡露天煤矿南排土场、黑岱沟露天煤矿阴湾排土场等多个黄土沟壑基底排土场均发生过滑坡,黄土沟壑基底的空间演化机制成为这类滑坡的主控因素,严重威胁着露天煤矿安全、高效生产[4-5]。由于沟壑纵横交错的复杂基底形态使得无法准确判断排土场的潜在滑坡模式,更无法准确计算其稳定性[6-7],忽略基底形态与岩性因素设计的排土场边坡往往与实际有较大偏差。因此,随着我国中西部煤炭资源的逐步开发利用,这种特殊基底条件下的排土场对露天煤矿安全生产的影响日渐突出,其变形破坏的空间演化规律与稳定性已成为露天矿边坡工程领域的亟待解决的技术难题。
目前关于排土场稳定性研究仍广泛采用极限平衡法[8-11]与数值模拟技术[12-13],少量采用模型试验手段[14]和监测手段[15]。如曹兰柱等[16]基于极限平衡法与数值模拟方法,揭示了不同基底倾角条件下排土场边坡稳定性变化规律,分析了软弱倾斜复合基底排土场边坡失稳机理;赵洪宝等[17]利用块体堆积散体边坡稳定性模拟试验装置,对排土场稳定性进行相似模拟试验,对比分析了不同块体组成与振动频率条件下边坡稳定性状态及滑坡启动模式;崔春晓等[18]基于GNSS在线监测技术,综合分析边坡变形监测数据,对排土场边坡的安全状态及稳定性进行评价。在以往的排土场稳定性分析中,广泛采用二维极限平衡法,不适用基底形态复杂的排土场稳定性分析;边坡三维稳定性计算方法尽管考虑了边坡的空间效应,但各种方法适用条件严格;三维数值模拟方法不仅能动态模拟排土场边坡破坏过程,而且能大致确定滑面的位置和形态。因此,对于黄土沟壑基底排土场的变形破坏问题,采用三维数值模拟方法更合适。
笔者以准能公司黑岱沟排土场为工程背景,借助FLAC3D有限差分软件,研究排土场变形破坏的空间演化过程,确定黄土沟壑基底排土场的滑坡模式及滑坡区域,为黑岱沟排土场边坡治理提供技术参考,为类似条件排土场稳定性研究提供借鉴。
1. 排土场工程地质概况
黑岱沟排土场位于鄂尔多斯高原东北部,地表由厚层第四系黄土覆盖。本区树枝状河谷和冲沟非常发育,致使台状高原被严重切割,沟壑纵横,地形支离破碎,形成具缓梁沟谷和高梁谷地形的塬丘地貌。排土场境界内地势南高北低,由南向北形成箕斗状,内部冲沟向位于排土场南北中轴线的主沟汇集,由北口汇出,如图1a所示。基岩面总体产状为北倾,倾角5°左右,近似箕斗形态,如图1b所示。显然,基底与基岩的赋存条件不利于排土场的稳定,易向东北方向滑动。
排土场岩土层自下而上可划分为风化基底层,第四系粉土、黏土层,排弃物料。浅部风化基岩主要为砂岩、泥岩,表层有一层高岭土,厚度不等。第四系粉土层厚0~56.8 m,上部结构较松散,土质均匀,具大孔隙,垂直节理发育;下部块状结构,属干硬状态的中低压缩性土,遇水易崩解。黏土层厚0~4.0 m,块状结构,土质均匀、密实,黏土质胶结,水化能力较强。各地层岩土体物理力学指标见表1。
表 1 岩土体物理力学指标Table 1. Physical and mechanical indices of rock and soil mass岩层 容重γ/(kN·m3) 黏聚力c/kPa 内摩擦角φ/(°) 体积模量K/MPa 剪切模量G/MPa 排弃物料 19.9 9.7 17.0 5.125 0.886 第四系粉土、黏土 20.0 32.0 7.0 8.400 1.800 风化基底 23.0 154.0 30.3 66.670 45.900 排土场周围有重要的建、构筑物,排土场的东帮紧邻储煤场、北帮距选煤厂150 m、西帮附近设有矿山公路(图1c),一旦发生滑坡将直接影响着露天矿的安全生产,威胁着人员设备安全。
2. 黄土沟壑基底的破坏机理分析
排土场常见的滑坡模式有沿基底面、基底内弱层或基岩顶板发生的组合滑动,还有剪切基底内土层发生的圆弧滑坡[19](图2)。上述滑坡模式均是针对基底或基岩面形态较规则的常规条件下,对于黄土沟壑基底排土场,滑坡必然会有新的模式。按照岩体力学中的断续结构面理论[20],存在沟壑的基底面可视为一起伏无充填结构面(图3),且黄土本身抗剪强度小,黄土层较厚,各位置形态差异较大,在排土场载荷与剪切作用下会形成啃断与爬坡效应,即当排土场边坡发生滑坡时,沟壑基底凸出部分可能被剪断,滑面仅切过部分黄土形成非规则曲面滑动(图4)。
3. 排土场滑坡空间演化机制数值模拟
数值模拟采用FLAC3D有限差分元软件,该软件共内置了12种弹塑性材料的本构模型以及5种计算模式,将多种计算模式耦合可用来解决复杂工程力学特性问题[21]。鉴于研究对象是松散土体,在计算分析中选用摩尔-库伦本构模型,同时考虑剪切和拉伸2种破坏机制,以位移不收敛作为滑坡判据,基于FLAC3D内嵌的Fish语言程序自编强度折减命令流,保存每一步折减后的数据信息,设置折减步长为0.01。通过分析失稳过程中的位移、变形等信息揭示黄土沟壑基底排土场滑坡的空间演化机制。
3.1 模型建立
为尽可能真实反映黄土沟壑基底排土场滑坡的空间演化机制,三维模型按1∶1比例进行构建,模型东西宽1 200 m、南北长1 100 m,单元类型为8节点,四面体单元。模型的底部边界设置垂直约束,四周边界设置水平约束,即垂直、水平位移为0,模型的顶部和坡面为自由面,加载方式为重力加载。模型各地层岩性从下至上分别为:风化砂岩、第四系粉土及黏土、排弃物料,数值模拟模型如图5所示。
3.2 数值模拟结果及分析
边坡稳定性求解采用强度折减法,其原理是循环折减岩土体的抗剪强度指标直到边坡刚好处于临界破坏状态[22]。通过分析折减系数与边坡最大位移的关系曲线可知(图6),折减系数从1.7到1.8的过程中,排土场和基底的最大位移均发生了突变,边坡的稳定系数为1.8。
图7、图8分别为排土场和沟壑基底的最大位移云图与矢量场,可用于分析排土场滑坡的空间演化机制。由图6、图7、图8可知,当折减系数为1.0时,边坡整体未发生明显的位移变形,排土场和基底均受自重作用产生垂直位移,排土场下方的基底在排土场的挤压作用下位移相对较大;折减系数从1.0~1.4的过程中,边坡上部岩体发生变形,在排土场上部出现两个位移相对较大的区域,基底土体在南北中轴线两侧的坡脚处发生变形,但此时边坡的最大位移相对较小;折减系数从1.4~1.7的过程中,最大位移呈近线性增加,在边坡上部岩体变形的推动作用下,中、下部岩体发生变形,受沟壑基底形态的影响,南北中轴线两侧的变形区向北部坡底扩展,形成类椭球形的变形区,同时基底土体在中轴线上的坡脚处发生位移变形;折减系数从1.7~2.1的过程中,变形区的整体形态未发生较大变化,其范围进一步扩大,最大位移加速增加,位移突变折减结束,排土场和基底土体最终变形区范围分别如图7和图8所示。
分析各剖面基底最大位移云图可知(图9),剖面A、B、C的滑体均在基底黄土层内,其滑坡模式为剪断部分黄土形成非规则曲面滑动;由于黄土本身抗剪强度小,黄土层较厚,各位置形态差异较大,导致滑面切过各剖面的黄土层厚度不同,充分验证了理论分析过程中对黄土沟壑基底排土场滑坡机理的认识。
4. 结 论
1) 沟壑基底面可视为起伏无充填结构面,且黄土本身抗剪强度小,黄土层较厚,各位置形态差异较大,在排土场载荷与剪切作用下会形成啃断与爬坡效应,其潜在滑坡模式为剪断部分黄土层的非规则曲面滑动。
2) 黑岱沟排土场的稳定性系数为1.8;在初始应力状态下,边坡整体未发生明显的位移变形,排土场受自重作用产生垂直位移,随着折减系数的增加,边坡上部岩体先发生变形,并挤压中、下部岩体发生变形,受沟壑基底形态的影响,位于南北中轴线两侧的变形区向北部坡底扩展,形成类椭球形变形区,最终演化成推动式滑坡。
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表 1 煤帮各计算参数取值
Table 1 Value of calculating parameters of coal wall
γ/(kN·m−3) K/GPa λ φ/(º) c/MPa φu/(º) φd/(º) E/GPa μ εt,max/10−3 D 25 0.15 0.8 30 1.8 25 25 3.6 0.3 0.68 1.6 注:D为直接顶与煤层弹量比。 表 2 煤帮各计算参数取值
Table 2 Value of calculating parameters of coal wall
\gamma /(kN·m−3) K/GPa \lambda \varphi /(º) c /MPa {\varphi _{\rm{u}}} /(º) {\varphi _{\rm{d}}} /(º) E /GPa \mu {\varepsilon _{{\rm{t}}\;\max }}_{,{\rm{BC}}} /×10−3 {\varepsilon _{ {\rm{t} },\max } }_{,{\rm{EH} } }/10−3 D 25 0.18 0.8 32 2.0 27 27 3.4 0.3 0.63 0.68 1.6 -
[1] 侯朝炯,马念杰. 煤层巷道两帮煤体应力和极限平衡区的探讨[J]. 煤炭学报,1989(4):21−29. doi: 10.3321/j.issn:0253-9993.1989.04.001 HOU Chaojiong,MA Nianjie. Stress in in-seam roadway sides and limit equilibrium zone[J]. Journal of China Coal Society,1989(4):21−29. doi: 10.3321/j.issn:0253-9993.1989.04.001
[2] 高 玮. 倾斜煤柱稳定性的弹塑性分析[J]. 力学与实践,2001,23(2):23−26. doi: 10.3969/j.issn.1000-0879.2001.02.005 GAO Wei. Elastoplastic analysis of the stability of inclined coal pillars[J]. Mechanics and Practice,2001,23(2):23−26. doi: 10.3969/j.issn.1000-0879.2001.02.005
[3] 于远祥,洪 兴,陈方方. 回采巷道煤体荷载传递机理及其极限平衡区的研究[J]. 煤炭学报,2012,37(10):1630−1636. doi: 10.13225/j.cnki.jccs.2012.10.017 YU Yuanxiang,HONG Xing,CHEN Fangfang. Study on load transmission mechanism and limit equilibrium zone of coal-wall in roadway[J]. Journal of China Coal Society,2012,37(10):1630−1636. doi: 10.13225/j.cnki.jccs.2012.10.017
[4] 翟 锦. 倾斜煤层区段煤柱宽度留设研究[D]. 西安: 西安科技大学, 2012. ZHAI Jin. Research on the width of coal pillar in inclined coal seam section[D]. Xi'an: Xi'an University of Science and Technology, 2012.
[5] 王德超,李术才,王 琦,等. 深部厚煤层综放沿空掘巷煤柱合理宽度试验研究[J]. 岩石力学与工程学报,2014,33(3):539−548. doi: 10.13722/j.cnki.jrme.2014.03.012 WANG Dechao,LI Shucai,WANG Qi,et al. Experimental study of reasonable coal pillar width of fully mechanized top coal caving in deep thick seam[J]. Chinese Journal of Rock Mechanics and Engineering,2014,33(3):539−548. doi: 10.13722/j.cnki.jrme.2014.03.012
[6] 孔德中,王兆会,李小萌,等. 大采高综放面区段煤柱合理留设研究[J]. 岩土力学,2014,35(S2):460−466. doi: 10.16285/j.rsm.2014.s2.040 KONG Dezhong,WANG Zhaohui,LI Xiaomeng,et al. Study of reasonable width of full-mechanized top-coal caving with large mining height[J]. Rock and Soil Mechanics,2014,35(S2):460−466. doi: 10.16285/j.rsm.2014.s2.040
[7] 张念超,孙元田,蔡胜海,等. 基于统一强度理论的护巷煤柱尺寸与支护技术研究[J]. 煤矿安全,2016,47(6):209−213. doi: 10.13347/j.cnki.mkaq.2016.06.057 ZHANG Nianchao,SUN Yuantian,CAI Shenghai,et al. Research on coal pillar size and support technology of roadway protection based on unified strength theory[J]. Coal Mine Safety,2016,47(6):209−213. doi: 10.13347/j.cnki.mkaq.2016.06.057
[8] 魏 臻, 李晋平, 何富连, 等. 综放面单侧采空煤柱稳定性研究及实测[J]. 矿业科学学报, 2017, 2(4): 371-378. WEI Zhen, LI Jinping, HE Fulian, et al. Stability study and field observation of coal pillar between goaf and unmined top-coal caving face[J]. Journal of Mining Science and Technology, 2017, 2(4). 371-378.
[9] 赵 宾,王方田,梁宁宁,等. 高应力综放面区段煤柱合理宽度与控制技术[J]. 采矿与安全工程学报,2018,35(1):19−26. doi: 10.13545/j.cnki.jmse.2018.01.003 ZHAO Bin,WANG Fangtian,LIANG Ningning,et al. Reasonable width and control technology of coal pillars in high-stress fully mechanized caving face[J]. Journal of Mining & Safety Engineering,2018,35(1):19−26. doi: 10.13545/j.cnki.jmse.2018.01.003
[10] 邸 帅. 8.5 m超大采高综采面回采巷道合理煤柱宽度分析[J]. 地下空间与工程学报,2019,15(2):614−621. DI Shuai. Analysis of the reasonable coal pillar width of the mining roadway in a fully mechanized mining face with an ultra-large cutting height of 8.5m[J]. Chinese Journal of Underground Space and Engineering,2019,15(2):614−621.
[11] 宁 静. 深部大采高综采工作面区段煤柱宽度优化研究[J]. 煤炭工程,2019,51(3):13−17. NING Jing. Tranquility Study on optimization of coal pillar width in deep and large mining height fully mechanized mining face[J]. Coal Engineering,2019,51(3):13−17.
[12] 顾士坦,魏宝贞,蒋邦友,等. 双侧采空不规则煤柱稳定性分析[J]. 煤矿安全,2020,51(3):216−220. doi: 10.13347/j.cnki.mkaq.2020.03.046 GU Shitan,WEI Baozhen,JIANG Bangyou,et al. Stability analysis of irregular coal pillars in bilateral goaf[J]. Safety in Coal Mines,2020,51(3):216−220. doi: 10.13347/j.cnki.mkaq.2020.03.046
[13] 王东星. 浅埋煤层大采高综采面区段煤柱宽度留设理论及试验研究[D]. 西安: 西安科技大学, 2017. WANG Dongxing. Theoretical and experimental research on coal pillar width in the section of a fully mechanized mining face with high mining height in shallow coal seams[D]. Xi’an: Xi’an University of Science and Technology, 2017.
[14] 王宝石. 区段煤柱宽度合理留设研究[D]. 邯郸: 河北工程大学, 2013. WANG Baoshi. Study on the reasonable retainning of the width of the section coal pillar[D]. Handan: Hebei University of Engineering, 2013.
[15] 薛雄飞. 杭来湾煤矿工作面区段煤柱合理尺寸研究[D]. 西安: 西安科技大学, 2020. XUE Xiongfei. Research on reasonable size of coal pillars in working face section of Hanglaiwan Coal Mine[D]. Xi’an: Xi’an University of Science and Technology, 2020.
[16] 白进龙. 浅埋煤层大采高综采面区段煤柱宽度优化研究[D]. 西安: 西安科技大学, 2018. BAI Jinlong. Optimization of Section Coal Pillar Width on Full-mechanized Mining Face in Shallow Coal Seam[D]. Xi’an: Xi’an University of Science and Technology, 2018.
[17] 张艳军. 浅埋煤层大采高综采面区段煤柱合理宽度留设研究[D]. 西安: 西安科技大学, 2016. ZHANG Yanjun. Research on the reasonable width of coal pillars in the section of fully-mechanized mining face with large mining height in shallow seam[D]. Xi’an: Xi’an University of Science and Technology, 2016.
[18] 钱鸣高, 石平五. 矿山压力与岩层控制[M]. 徐州: 中国矿业大学出版社, 2003. [19] 王卫军,黄成光,侯朝炯,等. 综放沿空掘巷底鼓的受力变形分析[J]. 煤炭学报,2002,27(1):26−30. doi: 10.3321/j.issn:0253-9993.2002.01.006 WANG Weijun,HUANG Chengguang,HOU Chaojiong,et al. Mechanical deformation analysis of floor strata of roadway driving along next goaf in fully mechanized sub-level caving face[J]. Journal of China Coal Society,2002,27(1):26−30. doi: 10.3321/j.issn:0253-9993.2002.01.006
[20] 薛 强. 弹性力学[M]. 北京: 北京大学出版社, 2006. [21] 秦忠诚,王同旭. 深井孤岛综放面支承压力分布及其在底板中的传递规律[J]. 岩石力学与工程学报,2004,23(7):1127−1131. QIN Zhongcheng,WANG Tongxu. Abutment pressure distribution and its transfer law in floor of deep isolated fully-mechanized mining faces using sub-level caving[J]. Chinese Journal of Rock Mechanics and Engineering,2004,23(7):1127−1131.
[22] 黄庆享,刘建浩. 浅埋大采高工作面煤壁片帮的柱条模型分析[J]. 采矿与安全工程学报,2015,32(2):187−191. doi: 10.13545/j.cnki.jmse.2015.02.003 HUANG Qingxiang,LIU Jianhao. Analysis of the column model of the coal wall slab in the shallow burying and large mining height face[J]. Journal of Mining & Safety Engineering,2015,32(2):187−191. doi: 10.13545/j.cnki.jmse.2015.02.003
[23] 孙训方, 方孝淑. 材料力学(I)[M]. 北京: 高等教育出版社, 2009. [24] 尹希文,闫少宏,安 宇. 大采高综采面煤壁片帮特征分析与应用[J]. 采矿与安全工程学报,2008,25(2):50−52. doi: 10.3969/j.issn.1673-3363.2008.02.021 YIN Xiwen,YAN Shaohong,AN Yu. Characters of the rib spalling in fully mechanized caving face with great mining height[J]. Journal of Mining & Safety Engineering,2008,25(2):50−52. doi: 10.3969/j.issn.1673-3363.2008.02.021
[25] 宁 宇. 大采高综采煤壁片帮冒顶机理与控制技术[J]. 煤炭学报,2009,34(1):50−52. doi: 10.3321/j.issn:0253-9993.2009.01.010 NING Yu. Mechanism and control technique of the rib spalling in fully mechanized mining face with great mining height[J]. Journal of China Coal Society,2009,34(1):50−52. doi: 10.3321/j.issn:0253-9993.2009.01.010
[26] 沈明荣. 岩体力学[M]. 上海: 同济大学出版社, 2002 [27] 陈建君. 厚硬顶板特厚煤层孤岛煤柱应力集中程度及错层防冲研究[D]. 徐州: 中国矿业大学, 2016. CHEN Jianjun. Study on the stress concentration and the anti-scouring of the isolated island coal pillar in the thick and hard roof extra-thick coal seam[D]. Xuzhou: China University of Mining and Technology, 2016.
[28] 董方庭. 巷道围岩松动圈支护理论及应用技术[M]. 北京: 煤炭工业出版社, 2001. [29] 于远祥. 矩形巷道围岩变形破坏机理及在王村矿的应用研究[D]. 西安: 西安科技大学, 2013. YU Yuanxiang. Study on deformation mechanism of surrounding rock in rectangular roadway and its application in Wangcun coal mine [D]. Xi'an: Xi'an University of science and technology, 2013.
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