DEM Study On Soil-Structure Interface And Its Microstructural Characteristics

The soil-structure interface is widely existent in large structures such as embankment,railway and highway,and thus it is meaningful and important to understand the mechanism of soil-structure interaction for the design of large structures.In this paper,the discrete element method(DEM)is used to simulate the cohesive soil-concrete interface tests and angular gravel-steel interface tests to explore the microstructural evolution(i.e.particle displacement,anisotropy and coordination number)of soil specimen under the effect of interface shearing behavior.Particle breakage is considered in the DEM simulations of angular gravel-steel interface tests and its influence on microstructural evolution is correspondingly studied.Some results show as follows:1.A series of 3D DEM models of soil-structure interface tests are successfully established.In this paper,the concept of DEM is introduced into experimental simulations of soil-structure interface tests and investigation on microstructural characteristics.The shear stress-shear displacement curves in the DEM simulations of cohesive soil-concrete interface tests are in good agreement with the physical test results,while the shear stress-shear displacement curves in the DEM simulations of angular gravel-steel interface tests are basically consistent with the physical test results despite the strain softening phenomenon when shear begins.The results in terms of macroscopic mechanical response show that the model can simulate and study the soil-structure interface successfully.2.The influence factors and laws of particle displacement under interface shearing behavior are revealed.Results of DEM simulations of soil-structure interface tests show that he alteration of shear direction will lead to the shift of particle displacement in terms of magnitude and direction on the interface itself and its adjacent zone.The magnitude of particle displacement decreases from the interface to the lower parts,showing a crescent shape on the whole.In addition,the normal stress positively correlates with the particle displacement and the particle displacement is closely related to the interface shear extent,i.e.the magnitude of shear stress.Particle displacement deflects more to the Y-axis direction with the increase in the shear stress in the Y-axis direction.3.The dynamic microstructural evolutions of soil-structure interface tests are studied and revealed.In DEM simulations of cohesive soil-concrete interface tests,normal force anisotropy negatively correlates with normal stress in general,while tangential force anisotropy positively correlates with normal stress.If the shear stress in the Y-axis direction increases,normal force anisotropy and tangential force anisotropy increase correspondingly.In DEM simulations of angular gravel-steel interface tests,there is a significant positive correlation between normal stress and contact normal anisotropy,normal force anisotropy and tangential force anisotropy.A phenomenon is found that the magnitudes of some anisotropic parameters firstly decrease followed by a rise after the shear direction changes,which is named as'adjustment phase'.The'adjustment phase' appears in the evolutions of different anisotropic parameters in DEM simulations of cohesive soil-concrete interface tests and angular gravel-steel interface tests.The forming reason for the 'adjustment phase' in the former simulations is that the alteration of shear direction causes the soil sample to become slightly loose first and then become compact again.However,the forming reason for the 'adjustment phase' in the latter simulations is the evolution of contact orientation distributions on the X-Z plane caused by the interface shearing behavior.It is worth noting that the fundamental forming reason for the'adjustment phase' in these simulations is the interface shearing behavior.4.The phenomenon and law of the variation of soil sample density caused by interface shearing behavior are obtained.Particle coordination number is a parameter that characterizes the density of the soil sample in the DEM model established in this paper.In DEM simulations of cohesive soil-concrete interface tests,the magnitude of particle coordination number significantly positively correlates with normal stress,and its evolution process also reveals an'adjustment phase'.If there is shear force in the Y-axis direction,the particle coordination number will be correspondingly smaller.The particle coordination numbers in DEM simulations of angular gravel-steel interface tests are greatly affected by the normal stress and show decreasing trend in the whole shear process.5.DEM is Adopted to investigate on the evolution of particle breakage and its effect on microstructural evolution under interface shearing behavior in both macroscopic and microscopic scales.Results of DEM simulations of angular gravel-steel interface tests show that particle breakage mainly occurs on the interface itself and its adjacent zone and is greatly affected by the interface shearing behavior.Particle breakage can reduce the magnitude of shear stress on the interface and significantly reduce the degrees of anisotropy parameters.The evolution of the bond coordination number,which is closely related to particle breakage,also indicates that there is an ultimate particle breakage state existing that the same soil specimen will reach an identical particle breakage state no matter what their normal stresses are.