3D Fabric Spatiotemporal Evolution Characteristics And Transparent Characterization Of Gangue Solid Waste Backfilling Material During Compression

The piled broken gangue,serving as the backfill material,embraced a complicated inner fabric structure.The block shapes,block gradations,block coordination,block breakage,block movement,evolution of force chain,and interspace structure are the origin that determines its mechanical behaviour,such as bearing compression and deformation characteristics.Hence,it is crucial to figure out the intrinsic spatiotemporal evolution rules and mechanism of the fabric of the bearing gangue body to control the deformation of gangue blocks under compression effectively.However,the inner complicated fabric evolution characteristics of gangues are always referred to as a “black box” problem,which is invisible and unreachable.Making inner structure visible and precisely quantitived are fundamentspaals for solving such “black box” problems and understanding the intrinsic mechanism that determines the physical and mechanical behavior.This dissertation focused on the topic of "the spatiotemporal evolution and the transparent characterization of the three-dimensional(3D)fabric of gangue solid waste backfilling material",by using CT scanning,large-scale triaxial compression tests,the particle flow numerical simulation,and other data analysis methods including image processing,3D digital model reconstruction,and software secondary development.The 3D shape features of random gangue blocks were analyzed quantitatively.The research on the evolution characteristics of the inner structure and mechanical behaviour of gangue blocks under triaxial compression was carried out based on real shapes of gangue blocks.The 3D digital model of the fabric of gangue blocks under bearing compression condition was reconstructed.The transparent characterization of spatiotemporal evolution of the complicated inner structure was achieved.The relationship between the physical-mechanical behavior and the complicated inner fabric was established.The research results provide theoretical and technical support for the quantitive analysis and transparent characterization of intricate physical and mechanical process in “black box”,such as 3D structure and interspace structure of fractured rock mass,fluid seepage,the catastrophic failure of rock mass.The main innovative results are stated as follows:(1)A 3D reconstruction method to digitize the real shape of random gangue blocks was put forward in the research.Based on the genetic algorithm,a program was developed to obtain 3D shape parameters of irregular gangue blocks and achieved by Python programming.With those parameters,3D shape features of random gangue blocks could be analyzed quantitatively.The correlation between shape indexes frequency distribution of random gangue blocks and the block size was summarized.The comprehensive evaluation method for evaluating shape regularity of random gangue blocks was established using multiple shape indexes.(2)The combination of large-scale triaxial compression experiments and the particle flow numerical simulation was applied in the research.From the experiments,the characteristics of the apparent physical and mechanical behavior,such as axial strain,volumetric strain,bearing capacity and porosity of gangue blocks were systematically studied.The correlation between bearing capacity and confining pressure was established.The evolution rules of gradation and particle size distribution features of gangue blocks during confined compression were illustrated.The effect mechanism of confining pressure,gradation,block shapes on apparent and mechanical behavior,such as strain hardening and volumetric shrinkage,was revealed.(3)A 3D boundary surface software for gangue blocks with real shapes was firstly developed.Based on the real shape of gangue solid waste backfilling material,a visible continuous-discrete coupling element numerical simulation model for gangue blocks under large-scale triaxial compression tests was established.In order to achieve the reconstruction and visualization of the 3D fabric of gangue blocks during bearing compression,a compression apparatus with CT visualization function was developed before experiments.Thus,3D digital structure models and the interspace models of gangue solid waste backfilling material were reconstructed.(4)The 3D spatiotemporal evolution characteristics of gangue blocks during compression,including interspace structure,interspace distribution,block breakage,block movement and the evolution of force chains,was analyzed quantitatively and transparently.Furthermore,the visualization of the 3D inner structure change was achieved.The influence from block shapes,confining pressure and gradation on inner fabric were obtained.The intrinsic relationship between inner structure change,including interspace compression,block movement and coordination,the unstabilityreconstruction of mechanical chains,and block breakage,and macro deformation was established.The analysis revealed the intrinsic mechanism why the apparent mechanical behavior served as a critical control factor.There are 127 figures,15 tables and 175 references in this dissertation.