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袋装石墨尾矿承载性能及沿空留巷数值模拟研究

Research on bearing capacity of soilbagged graphite tailings and numerical simulation of along empty lanes

  • 摘要: 为分析袋装石墨尾矿的承载特性及破坏机理,验证袋装石墨尾矿柔性墙应用于沿空留巷的可行性。在土工袋半圆边界承载模型的理论基础上,考虑土工袋体积的变化,修正半圆边界模型公式推算;利用PFC2D颗粒流程序,根据直剪试验、拉拔试验确定石墨尾矿与土工布接触的细观参数,并开展袋装石墨尾矿的单轴压缩数值试验,获得不同因素下袋装石墨尾矿的应力−应变曲线,将理论计算与数值试验结果对比,验证数值参数选取的合理性,并从颗粒接触和颗粒运动趋势进一步研究土工袋堆叠体的承载机理和破坏形式;根据某煤矿沿空留巷工作面概况,通过PFC2D颗粒流程序建立纵横交错、横向无缝、横纵交错、纵向无缝排列方式下袋装石墨尾矿柔性墙体,以刚性墙体的运动模拟沿空留巷中顶板的下沉,对4种不同堆叠方式的柔性墙体的承载进行分析,验证袋装石墨尾矿柔性墙体用于沿空留巷巷旁支护应用的可行性。结果表明:在承载过程中,约束形成的张力是影响土工袋承载性能的主要因素,土工袋的初步破坏发生在袋与袋的界面接触处,初步破坏后土工袋堆叠整体并未发生失稳现象,受土工袋侧面约束影响,土工袋整体可继续承载至其侧面断裂;初步破坏处的袋子主要受剪切破坏,完全破坏时土工袋内中心位置的颗粒会产生压缩固结现象;修正后的土工袋半圆边界承载模型计算结果与数值计算结果接近;4种不同排列方式中横纵交错排列方式的柔性墙承载能力最大、沉降最小,满足沿空留巷的顶板下沉位移范围以及在土工袋发生初步破坏前均满足充填体的阻力要求。提出的建模方法和结果可为土工袋柔性墙技术应用于沿空留巷的巷旁支护提供一定的参考。

     

    Abstract: In order to analyze the bearing characteristics and failure mechanism of soilbagged graphite tailings, and to verify the feasibility of applying flexible walls in along empty lanes. The study based on the theoretical foundation of the soilbag semi-circular boundary bearing model. The model formula is modified to consider the variation of the geotextile bag volume. The microscopic parameters of the contact between graphite tailings and geotextile fabric are determined through direct shear tests and pull-out tests using PFC2D particle flow program. Numerical tests on uniaxial compression of soilbagged graphite tailings are conducted to obtain the stress-strain curves under different factors. The theoretical calculations are compared with the numerical test results to validate the rationality of the selected numerical parameters. Furthermore, the bearing mechanism and failure modes of the soilbag stack are further studied based on the contact between particles and their movement trends. Based on the overview of the working face in a specific coal mine, the flexible wall of soilbagged graphite tailings is established using PFC2D particle flow program in four different stacking arrangements: staggered in both vertical and horizontal directions, seamless in horizontal direction, seamless in vertical direction, and staggered in vertical direction. The movement of the rigid wall is simulated to represent the subsidence of the roof in the along-airway backfilling. The bearing capacity of the flexible walls in the four different stacking arrangements is analyzed to validate the feasibility of using soilbagged graphite tailings as flexible wall. The results show that during the bearing process, the tension formed by the confinement is the main factor affecting the bearing performance of the soilbags. The initial failure of the soilbags occurs at the interface between the soilbags. After the initial failure, the overall stability of the soilbag stack is not compromised. The soilbags can continue to bear load until they fracture on their sides due to the lateral constraints. The soilbags at the initial failure location primarily experience shear failure, and when complete failure occurs, the particles at the center of the soilbag experience compression consolidation. The results of the modified soilbag semi-circular boundary bearing model are close to the numerical calculation results. Among the four different arrangements, the staggered arrangement in both vertical and horizontal directions exhibits the highest bearing capacity and the smallest settlement. It meets the displacement range of roof subsidence in the along-airway backfilling and satisfies the resistance requirements of the filling material before the soilbags experience initial failure. The modeling method and results presented in this study can serve as a reference for the application of soilbag flexible walls in the side support of along empty lanes.

     

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