Study On Three-dimensional Reconstruction And Crushing Behavior Of Calcareous Sand Particles Considering Shape Characteristics

The phenomenon of particle fragmentation is prevalent in geotechnical engineering,which greatly influences the mechanical behavior characteristics of the material and further affects its application in practical engineering.Compared with terrestrial source sand such as quartz sand and feldspar,calcareous sand particles are more prone to fracture,and among them,particle morphological characteristics are one of the main factors affecting particle fracture behavior.However,the influence mechanism of calcareous sand particle morphology on crushing behavior is not perfect,and the damage mode,damage size distribution,and contact force chain evolution characteristics of particle crushing need to be further investigated.To investigate the mechanism of particle morphology influence in the crushing behavior of calcareous sand particles,this paper reviews the influence of calcareous sand particle morphology in the basic physical force behavior,discusses the characterization method of single-particle shape and the three-dimensional reconstruction method of particles,and statistics the characteristics of damage mode of different materials.The macroscopic mechanical behavior characteristics such as particle crushing strength and damage mode are obtained through indoor tests of single particle crushing of calcareous sand,and the numerical simulation of realistic particle morphology is established and validated based on the indoor test data,and the fine mechanical behavior characteristics such as the evolution of contact force chain during the crushing of calcareous sand particles are analyzed.The association between particle crushing strength and crushing size distribution and crushing type was investigated by combining indoor tests and numerical simulations.Firstly,in order to improve the quantitative characterization of calcareous sand particle morphology and avoid duplicate parameters.The particle morphology parameters were divided into three categories according to their definitions: size parameters,contour parameters,and angular parameters.The quantitative characterization mechanism of particle morphology was established.The distribution range of the particle parameters of calcareous sand under different shapes was analyzed by the particle shape analysis test,and the changes in the particle shape of calcareous sand with the particle size were analyzed,and the statistical results showed that the aspect ratio of more than 90% of the particles was between 1-3,and all other morphological parameters showed a decreasing trend with the growth of the particle size,which showed a negative correlation between the regularity of the particle shape and the particle size.Based on the statistics of each morphological parameter,a sensitivity analysis was carried out to select the parameters with higher sensitivity in each type,which provides a basis for the reconstruction accuracy of the subsequent particle 3D reconstruction.Secondly,in order to obtain realistic particle shapes of calcareous sand and facilitate the construction of discrete element numerical experimental models,3D reconstruction of calcareous sand particles is performed.Based on the multi-view 2D images of the calcareous sand particles,a basic model of the pointing sphere is established,a 3D point cloud model of the actual particle shape is obtained through the point set rejection process,and the point cloud model is further materialized to obtain realistic reconstructed particles,and the reconstructed accuracy is evaluated by each morphological parameter so that the morphological error of the reconstructed model is within the predefined control range.The results show that the morphological errors of more than 90% of the particles are within 10%,the maximum error is 10.84%,and the minimum error is less than 1%.Finally,the effect of particle shape on the crushing behavior characteristics of calcareous sand particles was investigated by single-particle indoor tests as well as numerical simulations.The results show that the Weibull modulus of each shape of calcareous sand particles is between 1-2,among which the crushing strength of block-shaped particles is the highest,with a characteristic stress value of 4.97 MPa,while the strength of flaky particles is the lowest,with a characteristic stress value of 2.25 MPa,and the evolution characteristics of particle fine-scale behavior during the crushing of different shapes of particles are analyzed.It is found that the crushing process of block particles and spindle particles is relatively slow,and some of the particles are vicious when crushing,while strip particles,flake particles,and spindle particles,show obvious brittle damage characteristics.