混合颗粒体光弹力链定量提取方法
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摘要
岩土工程和采矿工程涉及大量的颗粒物质科学和技术难题,定量识别和提取光弹试验颗粒体系的力链网络结构和分布特征,对于认识和掌握其内部细观力学机理和研究宏观力学行为至关重要.采用彩色梯度均方值(G~2)算法,建立了不同粒径的圆形颗粒和方形颗粒的接触力(F)和G~2的关系;基于数字图像处理技术,提出了识别和区分图像中不同粒径圆形颗粒和方形颗粒的方法,获得了光弹图片中力链网络结构和力链分布方位.以煤矿综放开采为实例,对所提出的力链定量提取方法进行了验证分析,清晰揭示了综放采面矿压形成机理和本质特征.研究表明:单颗粒的F值与G~2呈单调递增关系,且粒径越大,F随G~2值的增长速度越快;颗粒体系接触力集中分布在0.5F~F(F为平均接触力),方颗粒、φ12 mm圆形颗粒平均接触力较大,多为强力链; φ10 mm、φ8 mm圆形颗粒的平均接触力较小,多为弱力链.综放开采顶煤和覆岩中力链主要为树状力链,以竖向发育为主的强力链传递上部主要荷载,横向发育的弱力链对强力链起到侧向支撑的作用.顶煤放出口附近,由于颗粒侧向移动弱力链丧失,导致强力链减弱甚至消失.
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(G~2),the correlations of G~2 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 G~2,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 mmcircular 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.
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(G~2),the correlations of G~2 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 G~2,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 mmcircular 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.
引文
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[17]Wang J A,Liang C,Pang W D.Photoelastic experiment on force chain evolution of particle aggregate under the conditions of biaxially loading and bilaterally flowing.Rock Soil Mech,2016,37(11):3041(王金安,梁超,庞伟东.颗粒体双轴加载双向流动力链演化光弹试验研究.岩土力学,2016,37(11):3041)
[2]Zhang D,Liu Y,Wu S C,et al.Failure mechanism analysis of tailing dams based on coupled discrete and continuous method.Chin J Geotech Eng,2014,36(8):1473(张铎,刘洋,吴顺川,等.基于离散-连续耦合的尾矿坝边坡破坏机理分析.岩土工程学报,2014,36(8):1473)
[3]Han T C,Qiu Z Y,Dou H Q.Soil arching effect between antislide piles based on YADE discrete element method.J Cent South Univ Sci Technol,2016,47(8):2715(韩同春,邱子义,豆红强.基于颗粒离散元的抗滑桩土拱效应分析.中南大学学报(自然科学版),2016,47(8):2715)
[4]Behringer R P,Daniels K E,Majmudar T S,et al.Fluctuations,correlations and transitions in granular materials:statistical mechanics for a non-conventional system.Phil Trans R Soc London A,2008,366(1865):493
[5]Kramar M,Goullet A,Kondic L,et al.Persistence of force networks in compressed granular media.Phys Rev E,2013,87(4):042207
[6]Sun Q C,Jin F.The multi-scale structure of granular matter and its mechanics.Physics,2009,38(4):225(孙其诚,金峰.颗粒物质的多尺度结构及其研究框架.物理,2009,38(4):225)
[7]Wang D M,Zhou Y H.Statistics of contact force network in dense granular matter.Particuology,2010,8(2):133
[8]Cheng Z L,Wu L P,Ding H S.Research on movement of particle of fabric of granular material.Rock Soil Mech,2007,28(Suppl):29(程展林,吴良平,丁红顺.粗粒土组构之颗粒运动研究.岩土力学,2007,28(增刊):29)
[9]Majmudar T S,Behringer R P.Contact force measurements and stress-induced anisotropy in granular materials.Nature,2005,435(7045):1079
[10]Kramar M,Goullet A,Kondic L,et al.Quantifying force networks in particulate systems.Physica D,2014,283:37
[11]Kondic L,Goullet A,O'Hern C S,et al.Topology of force networks in compressed granular media.EPL,2012,97:54001
[12]Liu Y,Miao F X,Miao T D.Force distributions in two dimensional granular packs.Chin J Geotech Eng,2005,27(4):468(刘源,缪馥星,苗天德.二维颗粒堆积体中力的传递与分布研究.岩土工程学报,2005,27(4):468)
[13]Yang R W,Cheng X H.Direct shear experiments of photoelastic granular materials.Rock Soil Mech,2009,30(Suppl):103(杨荣伟,程晓辉.光弹颗粒材料的直剪实验研究.岩土力学,2009,30(增刊):103)
[14]Zheng H.Experimental study on deformation of geo-granular materials based on photoelastic techniques.J Eng Geol,2014,22(5):851(郑虎.基于光弹测试技术的颗粒材料细观变形试验研究.工程地质学报,2014,22(5):851)
[15]Wang J A,Han X G,Pang W D,et al.Photoelastic experimental study on the force chain structure and evolution in top coal and overlaying strata under fully mechanized top coal caving mining.Chin J Eng,2017,39(1):13(王金安,韩现刚,庞伟东,等.综放开采顶煤与覆岩力链结构及演化光弹试验研究.工程科学学报,2017,39(1):13)
[16]Wang J A,Pang W D,Liang C,et al.Photoelastic Experiment Apparatus of Aggregates with Bilateral Flowing:China Patent,CN204556449U.2015--08--12(王金安,庞伟东,梁超,等.一种双向颗粒流动光弹实验装置:中国专利,CN204556449U.2015--08--12)
[17]Wang J A,Liang C,Pang W D.Photoelastic experiment on force chain evolution of particle aggregate under the conditions of biaxially loading and bilaterally flowing.Rock Soil Mech,2016,37(11):3041(王金安,梁超,庞伟东.颗粒体双轴加载双向流动力链演化光弹试验研究.岩土力学,2016,37(11):3041)