李浩,唐世斌,康志勤,等. 特厚煤层底板断层破坏与顶板垮断联动效应的CFDEM模拟研究[J]. 煤炭学报,2024,49(6):2615−2629. doi: 10.13225/j.cnki.jccs.2023.0887
引用本文: 李浩,唐世斌,康志勤,等. 特厚煤层底板断层破坏与顶板垮断联动效应的CFDEM模拟研究[J]. 煤炭学报,2024,49(6):2615−2629. doi: 10.13225/j.cnki.jccs.2023.0887
LI Hao,TANG Shibin,KANG Zhiqin,et al. CFDEM simulation on the linkage effect between floor faults failure and roof collapse in ultra-thick coal seam[J]. Journal of China Coal Society,2024,49(6):2615−2629. doi: 10.13225/j.cnki.jccs.2023.0887
Citation: LI Hao,TANG Shibin,KANG Zhiqin,et al. CFDEM simulation on the linkage effect between floor faults failure and roof collapse in ultra-thick coal seam[J]. Journal of China Coal Society,2024,49(6):2615−2629. doi: 10.13225/j.cnki.jccs.2023.0887

特厚煤层底板断层破坏与顶板垮断联动效应的CFDEM模拟研究

CFDEM simulation on the linkage effect between floor faults failure and roof collapse in ultra-thick coal seam

  • 摘要: 特厚煤层采场空间大、覆岩扰动范围广,顶板垮断产生的强扰动加卸荷载易导致底板断层破坏加剧。通过数值模拟研究特厚煤层底板断层突水与顶板垮断联动效应机理规律是开展水害防治的基础,关键在于掌握加卸载下岩体渐进破坏与裂隙流耦合特征。构建加卸载下拉、剪损伤演化方程,结合有效偏/球应力为基本变量的屈服准则与塑性势函数,得到完整岩块的塑性损伤本构;建立拉/剪、混合型加卸载过程中塑性位移与强度劣化关系,以平方拉剪应力与B-K准则为初始、完全断裂准则,形成非贯通裂隙断裂本构;提出岩块分离、压缩、剪切判据,结合实验数据建立离散块体间挤压、剪切摩擦本构与剪胀方程。基于质量/动量守恒、状态方程,并结合流体体积与浸没边界方法,形成裂隙岩体气−水二相流模拟理论。由此形成CFDEM数值计算程序,并将加卸载下塑性损伤、断裂、挤压/摩擦、流体属性分别赋予实体单元(岩块)、黏聚力单元(非贯通裂隙)、接触对(贯通裂隙)、欧拉单元(水和气)。根据宁武煤田北部矿区工程地质条件,建立特厚煤层底板断层突水与顶板垮断联动效应数值计算模型。结果表明:① CFDEM耦合程序及相应的理论模型可数值实现特厚煤层覆岩及底板断层从(准)连续体到离散体转化,以及地下水在裂隙中运移;② 模拟条件下特厚煤层含断层底板的采动裂隙包络线呈w形,最深处超过55 m位于断层及其上盘,最浅处23 m位于断层下盘,而无构造底板处的破坏深度为24~36 m,已导通奥灰含水层;③ 特厚煤层底板普遍出现二次破坏现象。表现为无构造底板在超前工作面处破坏深度为24.0~29.3 m,但在采空区内普遍增加至31.5~36.0 m;断层及其上盘在超前工作面处裂隙总开度为0.34~0.86 m,但在采空区内迅速增加至3.6 m,形成突水优势通道。④ 底板断层突水与顶板垮断联动效应的根源在于覆岩高位关键岩层垮断失稳、砌体梁下沉与二次断裂,并导致底板二次破坏,突水风险加剧。

     

    Abstract: The ultra-thick coal seam has a large mining space and a wide range of overburden disturbance. The strong disturbance of loading and unloading caused by the roof collapse can easily exacerbate the failure of floor faults. Studying the mechanism of the linkage effect between water inrush from the floor fault and roof collapse in ultra-thick coal seam through numerical simulation is the basis for water hazard prevention and control. The key lies in understanding the coupling characteristics of progressive rock failure and fracture flow under loading and unloading. In this study, the evolution equations of tension and shear damage under loading and unloading were constructed, and combined with the yield criterion and plastic potential function with effective partial/spherical stress as the basic variable, the plastic-damage constitutive model of intact rock was obtained. The relationship between plastic displacement and strength deterioration during tension/shear/mixed loading and unloading was established, using the square tensile shear stress and B-K criterion as initial and complete fracture criteria, the fracture constitutive model of non-penetrating fracture was formed. The separation, compression and shear criteria of discrete rock blocks were put forward, and the extrusion, shear friction constitutive and dilation equations between discrete blocks were established based on experimental data. Based on the conservation of mass/momentum, the equation of state, and combined with the method of fluid volume and immersion boundary, the simulation theory of gas-water two-phase flow in the fractured rock mass was formed. Thus, the CFDEM numerical calculation program was developed, and the plastic damage, fracture, extrusion/friction, and fluid properties under loading and unloading were assigned to solid elements (rock blocks), cohesion elements (non-penetrating cracks), contact pairs (penetrating cracks), and Euler units (water and gas) respectively. According to the engineering geological conditions in the northern mining area of Ningwu coalfield, a numerical calculation model of linkage effect between water inrush from floor fault and roof collapse in extra-thick coal seam was established. The results indicate that ① the CFDEM coupling program and corresponding theoretical models can numerically achieve the transformation of overlying rocks and floor faults in ultra-thick coal seams from quasi-continuous to discrete rock, as well as the migration of groundwater in fractures. ② Under simulated conditions, the mining fractures envelope line of the fault floor of the ultra-thick coal seam is w-shaped, with the deepest point exceeding 55 m located on the fault and its hanging wall, the shallowest point 23 m located on the footwall of the fault, and the failure depth at the intact floor is 24−36 m, which has already connected to the Ordovician limestone aquifer. ③ Secondary damage is commonly observed on the floor of ultra-thick coal seam. The failure depth of the intact floor at the advanced working face is 24.0−29.3 m, but it generally increases to 31.5−36.0 m in the goaf. The total cracks opening of the fault and its hanging wall at the advanced working face is 0.34−0.86 m, but it rapidly increases to 3.6 m in the goaf, forming a dominant channel for water inrush. ④ The linkage effect of water inrush from floor fault and roof collapse is rooted in the collapse instability of key strata in overlying strata, the sinking of masonry beams and the secondary fracture, which leads to the secondary damage of floor and aggravates the risk of water inrush.

     

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