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混合顆粒體光彈力鏈定量提取方法

A quantitative extraction method of force chains for composite particles in a photoelastic experiment

  • 摘要: 巖土工程和采礦工程涉及大量的顆粒物質科學和技術難題,定量識別和提取光彈試驗顆粒體系的力鏈網絡結構和分布特征,對于認識和掌握其內部細觀力學機理和研究宏觀力學行為至關重要.采用彩色梯度均方值(G2)算法,建立了不同粒徑的圓形顆粒和方形顆粒的接觸力(F)和G2的關系;基于數字圖像處理技術,提出了識別和區分圖像中不同粒徑圓形顆粒和方形顆粒的方法,獲得了光彈圖片中力鏈網絡結構和力鏈分布方位.以煤礦綜放開采為實例,對所提出的力鏈定量提取方法進行了驗證分析,清晰揭示了綜放采面礦壓形成機理和本質特征.研究表明:單顆粒的F值與G2呈單調遞增關系,且粒徑越大,FG2值的增長速度越快;顆粒體系接觸力集中分布在0.5F~F (F為平均接觸力),方顆粒、Φ12 mm圓形顆粒平均接觸力較大,多為強力鏈;Φ10 mm、Φ8 mm圓形顆粒的平均接觸力較小,多為弱力鏈.綜放開采頂煤和覆巖中力鏈主要為樹狀力鏈,以豎向發育為主的強力鏈傳遞上部主要荷載,橫向發育的弱力鏈對強力鏈起到側向支撐的作用.頂煤放出口附近,由于顆粒側向移動弱力鏈喪失,導致強力鏈減弱甚至消失.

     

    Abstract: In geotechnical and mining engineering, numerous particle matters are involved in scientific and technical problems. Recognition and quantification of the structure and distribution of force chain networks using photoelastic experiments, for instance, are significantly important in understanding the internal mechanism of mesoscopic mechanics and studying the macroscopic mechanical behavior. Based on the algorithm of the mean square value of color gradient (G2), the correlations of G2 with the contact force (F) of different sizes of round and square particles were established and combined with digital image processing technology. A method was proposed for identifying particles in images and distinguishing square particles from round ones, and force chain structures and force chain distributions were obtained in photoelastic images. Using fully mechanized caving mining as an example, the proposed method was verified, and it elaborated the formation and characterization of mining-induced stress in a top-coal caving mining face. The study shows that F monotonically increases with increased G2, and larger particle sizes correspond to a faster growth of F. The contact forces of singular particle distribute primarily between 0.5 and 1.5 times average contact force. Also, the average contact forces in square particles and Φ12 mm circular particles are higher and mainly occur in strong force chains, whereas average contact forces in Φ10 mm and Φ8 mm circular particles are lower and primarily occur in weak force chains. In top-coal caving mining, force chains in top-coal and overburden strata are mainly displayed in tree-like forms. Strong force chains, which extend in a vertical direction, transmit majority overburden loads, whereas lateral-developed weak force chains play a role in supporting strong force chains. In the vicinity of the top-coal outlets, because of the lateral movement of particles toward the mined area, the weak force chains in top coal disappear, resulting in the strong force chains becoming weaker or completely disappearing.

     

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