Study On The Influence Of Particle Gradation And Shape On The Critical State Of Gravel-Concrete Shear

It is inevitable that deep backfill gravel foundation will be encountered in the engineering construction in the filling engineering areas of sea reclamation and land reclamation and goaf backfilling,and the problem of contact surface is an important subject of pile-soil contact surface interaction.At present,the research on the critical state of pile-soil interface is limited to fine particles such as sand and clay,and there is little research on coarse particles such as gravel and gravel that need to consider the shape of particles,The in-depth study of the influence of the grading and shape characteristics of backfill crushed stone on the shear critical state of gravel concrete interface has important theoretical and practical significance for the load transfer problem of pile gravel interface.In this paper,the influence of gravel particle gradation and shape on the shear mechanical properties of gravel concrete interface under critical state is studied by using the research method of combining numerical test and theoretical analysis.The main research contents and conclusions are as follows:（1）Eight types of gravel materials are screened and photographed,and the particle shape indexes（aspect ratio,convexity and sphericity）are obtained with the help of computer image processing software.The parameter overall regularity（or）describing the shape characteristics of granular materials is calculated by taking the weight of the three shape indexes.By introducing the overall regularity into the grading formula,A calculation method of grading curve considering the shape of gravel particles based on image analysis is proposed.（2）The shear model of gravel concrete interface considering gravel gradation and shape is established in the discrete element software².The effects of nonuniformity coefficient,curvature coefficient and overall regularity on the critical state macro parameters(M,λ,_（8）,The theoretical formula of the relationship between the reaction particle gradation,shape parameters and the macro parameters of the critical state is obtained.（3）Based on the discrete characteristics of particles in software²,the shear mechanics mechanism of gravel concrete interface is further analyzed from the micro point of view,and the influence laws of different particle gradation,particle shape and normal stress on the thickness of interfacial shear band are obtained.By analyzing the movement state of particles,the deformation mechanism of gravel concrete interface shear is further discussed.