Study On Macro-micro Numerical Simulation And Mechanism Of Deformation And Failure Of Cemented Granular Materials

The mechanical behavior of the cemented granular material(CGM)is strongly influenced by the morphology,strength and spatial distribution of the cement matrix,as well as the skeleton structure of the granular packing.In this paper,based on the discrete element method(DEM),a cementitious contact constitutive model was proposed which is built on the cohesive zone model(CZM).Simulation results have shown that the proposed model had promising progress on catching the post-peak softening behavior of CGMs.Meanwhile,this paper proposed a constant pressure-energy dissipation system to create random granular packings.By using the computed tomography(CT)as the source of 3-D reconstruction,combining with laboratory tests,this paper built the statistical correlativity between local morphology of cement matrix and particle arrangement.Based on the researches mentioned above,a numerical model which has a similar internal structure of the real CGMs was built up and applied to a series of simulation of the uniaxial compression test and structurized cementing test.The simulation work dedicates to investigating how the cement strength,shape and granular skeleton influences the CGM's macro-microscopic mechanical behavior and the failure mechanism.The research contents and innovations of the present paper are as follows:1.Proposed a constant pressure-energy dissipation system to create random granular packings.Based on the same statistical specification such as porosity and particle size distribution,the present paper found that the bearing capacity of the random packing mentioned above showed a significant difference from the packing generated by gravity.It is caused by the difference of the force chain density and orientation between these two models.Furthermore,the random model is adopted as its force chain property is closer to the real situation which is reconstructed by CT images.2.Based on the tomography and image recognition algorithm,the present paper reconstructed the skeleton structure and the morphology of the cement matrix.The cementitious connections are recognized as capillary bridges and interstitial cement matrix,whose morphological parameters were connected with the local arrangement of the grains as well.This statistical relation was then applied to guide the build-up of the cementing bonds in the numerical model.3.Following the upper-mentioned researches,a relatively complete DEM model were built and the model's sensitivity analysis were presented in this paper.The designed model was then used to carry out a group of simulation in uniaxial compression tests.By comparing the stress-strain curves and failure patterns obtained in the experiments,it's found that the proposed model had promising progress on catching the post-peak softening behavior of CGMs and reflecting the failure patterns and effect of strain localization.4.Carry out research about how the structurized cementation method influences the macroscopic mechanical behavior of the CGMs.The uniaxial test model was locally enhanced or weakened,artificially.The results showed that the specimen still maintained its bearing capacity if only discretized the core region.The cement clusters had a significant effect on increasing the post-peak strengths and the anisotropy of the cement bonds may change the peak strengths and failure patterns.