Structural Texture And Numerical Modelling Of Bonded Granular Materials

Granular matter reserves extensively in nature and artificial structure.It consists of large number of distinct particle elements,among which exists complexed interaction mechanism and dynamic pattern.Various kinds of materials concerned by hydraulic engineers,such as rock,soil and debris flow,can all be described by granular system.Breakage and flowing of granular matter is due to its deformation and weakening during quasi-static procedure.Studying the mechanical and structural behavior of quasi-static granular assemblies can give insight to the failure of granular materials and predict its occurrence,thus provide guidance to engineering practice.This work adopts the discrete element method(DEM)to carry out research on bonded granular assemblies.Theoretically,we tried to analyze the microscopic and mesoscopic mechanical& structural signature of quasi-static granular system and establish relations to macroscopic responding including apparent stress and strain.The peak stress moment is used to distinguish the elastic and residual stage of multi-confining-pressure triaxial compression.In elastic stage,the granular packing shows a homogeneous compression pattern.In residual stage,the maximum principle stress declines and shear band emerges.In the shearing zone,cohesive bonds between the spheres are broken and local mechanical integrality is weakened.As confining pressure arises,more shearing micro-cracks appears than tensile ones.Force chain yield to the perpendicular direction of shear band.Strong and weak force network present significant contrast,with extreme distinction between stress level of individual particle elements.Average granular temperature among numerous local ensembles exhibits similar temporal trend with macroscopic stress and maintain a certain value in later shearing stage.Spatial extremum of granular temperature occurs also in shearing district.Radical tessellation method is applied to analyze system topological texture at mesoscale.Local fivefold symmetry(LFFS)is positively related to the compactness of granular packing,and district with a higher degree of LFFS is more likely to be occupied with plastic events.As an application of the DEM bonded particle model,we introduce the interaction range parameter to mend contact detection criterion and simulate the macroscopic character of methane hydrate bearing sediment(MHBS).We abandon the empirical relevance between bond length and methane hydrate(MH)saturation in common DEM models and establish an algorithm to calculate binding material saturation by regarding the expanded interaction range as its volume.Importing the interaction range parameter brings addition contacts in granular assembly and give rise to macroscopic elastic modulus and compression strength.We managed to build a relatively precise model to simulate the relationship between MH saturation and the peak stress of MHBS specimen,while the stress declining rate in numerical model appear to be higher than experimental results due to present mechanism simplification,which may be a promising issue for future investigations.