1. Research Institute of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100038, China; 2. State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China; 3. College of Civil and Transportation Engineering, Hohai University, Nanjing 210024, China
Abstract：Based on the computer three-dimensional scanning and stochastic simulation technologies, the three-dimensional random meso-structure models and discrete element models for soil-rock mixture (S-RM) samples with different stone contents and spatial distributions are established. Considering the flexible loading of confining pressure, the large-scale numerical triaxial tests on the S-RM samples under different confining pressures based on the flexibly-bonded particles method are conducted by particle flow code, and the effects of the stone content and spatial distribution on their mechanical properties and deformation and failure characteristics are studied. The numerical simulation results show that the strengths and deformation resistibility capacities of the S-RM samples increase with the increase of stone content and confining pressure, and their internal friction angles and cohesions vary to a certain extent under the same content but different spatial distributions of stones. However on the whole, the internal friction angle increases linearly with the increase of stone content, while the cohesion decreases. Under the flexible loading of confining pressure, the S-RM samples show bulging deformation and failure mode, and the shear band formed after failure is a meandering strip with an asymmetric X-shaped distribution, whose thickness is about 1/3~1/2 times the height of the S- RM samples. Moreover, the failure mode and the thickness and shape of shear band are affected by the stone content and spatial distribution and the confining pressure. The shear band formation is accompanied by the rotations of the local particles in the S-RM sample. When the strain reaches the peak strain, the locally rotating particles are connected to each other, indicating that the shear band has basically formed at this time. Since then, as the axial strain increases continually, the rotations of the internal particles still change because of the effect of the bulging deformation after the peak, and the thickness and shape of the shear band also change accordingly.
 油新华. 土石混合体的随机结构模型及其应用研究[D]. 北京: 北京交通大学, 2002. (YOU Xin-hua.Stochastic structural model of the earth-rock aggregate and its application[D]. Beijing: Beijing Jiaotong University, 2002. (in Chinese))  孙华飞, 鞠杨, 王晓斐, 等. 土石混合体变形破坏及细观机理研究的进展[J]. 中国科学: 技术科学, 2014, 44(2): 172-181. (SUN Hua-fei, JU Yang, WANG Xiao-fei, et al.Review of the study on deformation, failure and the mesomechanisms of rock-soil mixture (RSM)[J]. Scientia Sinica: Technologica, 2014, 44(2): 172-181. (in Chinese))  王宇, 李晓, 赫建明, 等. 土石混合体细观特性研究现状及展望[J]. 工程地质学报, 2014, 22(1): 112-123. (WANG Yu, LI Xiao, HAO Jian-ming, et al.Research status and prospect of rock and soil aggregate[J]. Journal of Engineering Geology, 2014, 22(1): 112-123. (in Chinese))  夏加国, 胡瑞林, 祁生文, 等. 含超径颗粒土石混合体的大型三轴剪切试验研究[J]. 岩石力学与工程学报, 2017, 36(8): 2031-2039. (XIA Jia-guo, HU Rui-lin, QI Sheng-wen, et al.Large-scale triaxial shear testing of soil rock mixtures containing oversized particles[J]. Chinese Journal of Rock Mechanics and Engineering, 2017, 36(8): 2031-2039. (in Chinese))  王江营, 曹文贵, 蒋中明, 等. 不同应力路径下土石混填体变形力学特性大型三轴试验研究[J]. 岩土力学, 2016, 37(2): 424-430. (WANG Jiang-ying, CAO Wen-gui, JIANG Zhong-ming, et al.Large-scale triaxial tests on deformation and mechanical behavior of soil-rock aggregate mixture under different stress paths[J]. Rock and Soil Mechanics, 2016, 37(2): 424-430. (in Chinese))  金磊, 曾亚武, 张森. 块石含量及形状对胶结土石混合体力学性能影响的大型三轴试验[J]. 岩土力学, 2017, 38(1): 141-149. (JIN Lei, ZENG Ya-wu, ZHANG Sen.Large scale triaxial tests on effects of rock block proportion and shape on mechanical properties of cemented soil-rock mixture[J]. Rock and Soil Mechanics, 2017, 38(1): 141-149. (in Chinese))  金磊, 曾亚武, 李欢, 等. 基于不规则颗粒离散元的土石混合体大三轴数值模拟[J]. 岩土工程学报, 2015, 37(5): 829-838. (JIN Lei, ZENG Ya-wu, LI Huan, et al.Numerical simulation of large-scale triaxial tests on soil-rock mixture based on DEM of irregularly shaped particles[J]. Chinese Journal of Geotechnical Engineering, 2015, 37(5): 829-838. (in Chinese))  王新. 土石混合体力学特性影响因素及破坏机制研究[D]. 武汉: 长江科学院, 2010. (WANG Xin.Research on influence factors of mechanical characteristics and failure mechanism of soil-rock mixture[D]. Wuhan: Yangtze River Scientific Research Institute, 2010. (in Chinese))  张强, 汪小刚, 赵宇飞, 等. 不同围压加载方式下土石混合体变形破坏机制颗粒流模拟研究[J]. 岩土工程学报, 2018, 40(11): 2051-2060. (ZHANG Qiang, WANG Xiao-gang, ZHAO Yu-fei, et al.Particle flow modelling of deformation and failure mechanism of soil-rock mixture under different loading modes of confining pressure[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(11): 2051-2060. (in Chinese))  ZHAO X L, EVANS T M.Discrete simulations of laboratory loading conditions[J]. International Journal of Geomechanics, 2009, 9(4): 169-178.  DE B J P, MCDOWELL G R, WANATOWSKI D. Discrete element modelling of a flexible membrane for triaxial testing of granular material at high pressures[J]. Géotechnique Letters, 2012, 2(2): 199-203.  CIL M B, ALSHIBLI K A.3D analysis of kinematic behavior of granular materials in triaxial testing using DEM with flexible membrane boundary[J]. Acta Geotechnica, 2014, 9(2): 287-298.  金磊, 郑亚武. 基于三维柔性薄膜边界的土石混合体大型三轴试验颗粒离散元模拟[J]. 岩土工程学报, 2018, 40(12): 2296-2304. (JIN Lei, ZHENG Ya-wu.Numerical simulation of large-scale triaxial test on soil-rock mixture using DEM with three-dimensional flexible membrane boundary[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(12): 2296-2304. (in Chinese))  XU W J, HU L M, GAO W.Random generation of the meso-structure of a soil-rock mixture and its application in the study of the mechanical behavior in a landslide dam[J]. International Journal of Rock Mechanics & Mining Sciences, 2016, 86: 166-178.  张强. 大型冰水滑坡堆积体工程力学特性及应用研究[D]. 南京: 河海大学, 2016. (ZHANG Qiang.Study on engineering mechanical properties of large-scale outwash landslide deposits and its application[D]. Nanjing: Hohai University, 2016. (in Chinese))  徐文杰, 王识. 基于真实块石形态的土石混合体细观力学三维数值直剪试验研究[J]. 岩石力学与工程学报, 2016, 35(10): 2152-2160. (XU Wen-jie, WANG Shi.Meso- mechanics of soil-rock mixture with real shape of rock blocks based on 3D numerical direct shear test[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(10): 2152-2160. (in Chinese))  MEDLEY E W.The engineering characterization of mélanges and similar block-in-matrix rocks(bimrocks)[D]. Berkeley: University of California, 1994.  Itasca Consulting Group Inc. PFC 5.0 help manual[M]. Minneapolis: Itasca Consulting Group Inc, 2014.  XU W J, XU Q, HU R L.Study on the shear strength of soil-rock mixture by large scale direct shear test[J]. International Journal of Rock Mechanics & Mining Sciences, 2011,48(8): 1235-1247.  HALL S A, BORNERT M, DESRUES J, et al.Discrete and continuum analysis of localized deformation in sand using X-ray CT and volumetric digital image correlation[J]. Géotechnique, 2010, 60(5): 11-20.