摘要
在条带老采空区上方地表进行建设必须考虑地表残余沉降值和采空区内煤柱稳定性,目前地表残余沉降仍然较多采用基于概率积分法的沉陷预计方法,但其预计参数很难反映煤体随时间变化的蠕变性,而数值模拟方法对蠕变本构模型参数的选取也是一个难题。针对深部条带煤柱蠕变影响下地表残余沉降及煤柱稳定性,采集岱庄煤矿条带煤柱煤样开展实验室蠕变渗流试验,根据试验结果将煤体蠕变曲线分为两大类:稳定蠕变和非稳定蠕变。基于试验数据,采用曲线拟合方法,以开尔文体、三参量体、伯格斯体及改进伯格斯体反演得到了4组煤体蠕变本构方程组及其蠕变力学参数K,G_(0),G_(1),η_(1)和η_(2)。构建岱庄煤矿深部条带开采的FLAC3D数值模型,模拟得到开采结束时条带煤柱将进入非稳定蠕变。采用BURGERS蠕变模型和试验反演出的蠕变力学参数,对条带开采后13 a的地表残余沉降进行了模拟,获得了“深部条带开采—煤柱非稳定蠕变变形—覆岩移动—地表残余沉降”的地表沉降机制。得到:地表累计最大下沉量达到434 mm,最大下沉量与采厚比为0.167;开采结束后第1年下沉速率最大,达到91 mm/a,其余每年下沉速度均小于50 mm/a,下沉速率整体呈减小趋势并将最终稳定。根据Mohr-Coulomb剪切破坏和拉伸破坏准则建立了煤柱单元屈服接近度指标作为评价煤柱稳定性的量化指标,采用CVISC蠕变模型模拟条带开采结束1 a时,抗剪强度(黏聚力和内摩擦角)和采留宽变化对煤柱单元屈服接近度分布和煤柱稳定性的影响。研究认为深部条带煤柱稳定性主要受到开采因素、时间因素和煤体强度因素影响,深部条带开采引起煤柱内部出现应力集中,如果煤柱核区应力达到非稳定蠕变的阈值,煤体应变逐渐增大,应力状态点更接近Mohr-Coulomb屈服面,而煤体抗剪强度在采空区充水等因素影响下还可能降低,导致屈服面缩小,煤柱剪应力一旦在蠕变过程中到达屈服面,将使煤柱破坏区域增大,煤柱核区宽度缩小,直至煤柱发生完全破坏失稳。
Surface residual subsidence and coal pillar stability are two key factors for construction over strip mining gob.The prediction parameters of the probability integral method,widely used for residual subsidence,can hardly reflect the creep property of coal.The numerical simulation method can use the creep constitutive models,but it is hard to obtain the creep parameters of creep models.A creep and seepage test is carried out with coal samples from the Daizhuang Coal Mine.The creep curves of coal samples are classified into two types,that is,stable creep and unstable creep.With the test data,four creep bodies including Kelvin,Generalized-Kelvin,Burgers,and Modified-Burgers are used to obtain four groups of creep constitutive equations and their creep parameters K,G_(0),G_(1),η_(1) and η_(2) by the curve inversion method.A FLAC3 D numerical simulation model is set up to simulate deep strip mining in the Daizhuang Coal Mine and the results show that the coal pillar will enter an unstable creep state after strip mining.Using the Burgers creep constitutive model and creep parameters from inversion,the surface subsidence values within 13 years after strip mining are obtained.The mechanism of“strip mining-unstable creep of coal pillar-overlying strata movement-surface residual subsidence”is obtained.The accumulated maximum surface subsidence is 434 mm and the subsidence coefficient is 0.167.Among annual subsidence velocity values,a maximum value 91 mm/a occurs at the end of the first year,other values are below 50 mm/a,and subsidence velocity values take on a downtrend generally and will be stable at last.According to the Mohr-Coulomb failure criteria and tension failure criteria,the Yield Approach Index(YAI)of coal body unit is set up to be a quantitative evaluation index of coal pillar stability.Using the CVISC creep constitutive model,the influence of shear strength(cohesion and inner friction angle)and mining-pillar-width on coal pillar stability at the end of the first year after mining is analyzed with the YAI.The results show that the coal pillar stability of deep strip mining is mainly influenced by mining,time,and strength.Deep strip mining will result in the stress concentration of coal pillar,if stress in the core of coal pillar reaches the threshold value of unstable creep,coal strain will increase continually,and the shear strength of coal body will decrease increasingly under the influence of water flowing to the gob,which will shrink the Mohr-Coulomb yield surface.Once the shear stress of coal body reaches the yield surface,the range of coal failure area will increase and the core area will decrease further,till entirely unstable.
作者
蓝航
韩科明
韩震
LAN Hang;HAN Keming;HAN Zhen(Ecological Environment Science&Technology Co.,Ltd.,China Coal Technology&Engineering Group,Beijing 100013,China;Ecological Environment Science&Technology Department,Tiandi Science&Technology Co.,Ltd.,Beijing 100013,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2022年第S01期1-12,共12页
Journal of China Coal Society
基金
北京市科技计划资助项目(Z181100005118012)
中国煤炭科工集团有限公司科技创新创业资金专项重点资助项目(2018-02-ZD007)
关键词
条带开采
残余沉降
蠕变
煤柱稳定性
屈服接近度
strip mining
residual subsidence
creep
coal pillar stability
yield approaching index
