| The problems of uneven settlement and instability of buildings caused by temperature have gradually increased with the development of temperature-related engineering projects such as geothermal energy development,cold and hot foundation treatment,and nuclear waste treatment.It has been regarded as an important subject in the field of geotechnical engineering to investigate the effect of temperature on granular materials such as sand and soil.At present,laboratory experiments and field experiments are used by a large number of researchers to explore the effect of temperature changes on the macroscopic mechanical properties of granular materials.However,the effect of temperature on the mesoscopic interparticle contact force and anisotropy of granular materials has been neglected.Therefore,in this paper,a series of coupled thermalmechanical experiments are simulated by particle flow software(PFC)based on the discrete element method(DEM).The effects of heat source boundary,temperature cycle,compaction degree,and other factors on the macro-and micro-mechanical properties of granular materials in the process of temperature change were studied.The main research contents and results are as follows:(1)The monotonic heating-up consolidation test was simulated for granular materials by the temperature coupling method.The effect of the initial heat transfer boundary on granular materials was investigated.The simulation results show that the heating rate and the degree of compaction increase with the increase of the contact area between the initial heat transfer boundary and the particle.The reflection at the micro-level is that the increase of the normal contact force in the horizontal direction makes the overall distribution of the normal contact force tend to be isotropic;The inter-particle movement is limited by the densification of the material,which results in a reduction in the tangential contact force.(2)The process of temperature transfer in the real thermal coupling method is simplified,and a simplified thermal coupling method considering volume expansion is proposed.The thermal cycle consolidation test and the direct shear test were simulated for granular materials using the simplified thermal coupling method.Macroscopically,the bulk deformation accumulation and mean stress decay with temperature cycling are quantified.Microscopically,the increasing trend of the contact number,the normal contact force,and its anisotropy in temperature cycling are described.The weakening of shear strength and dilatancy properties caused by stress decay is described by direct shear tests.(3)Based on the simplified thermal coupling method,the effects of the initial state and the temperature change path on the temperature effect of granular materials during the temperature cycle consolidation were investigated.The denser the initial state of the granular material,the greater the normal contact force and the number of internal contacts,and the resulting effective stress also increases.The increase in the temperature cycle amplitude induces a larger volumetric cumulative strain of the particles,resulting in a more pronounced densification characteristic.With the decrease of the temperature cycle amplitude,the disturbance to the interior of the granular material decreases,which increases the structural stability and reduces the magnitude of the tangential contact force.(4)Combined with the correction of the thermal expansion coefficient,the warm consolidation test,and the direct shear test were simulated in three-dimensional space.The simulation results of the simplified thermal coupling method on the behavior of temperature-body strain and shear stress-shear strain are verified by the existing laboratory test data.At the same time,the thermally induced bulk strain and structural stability enhancement behaviors exhibited by the simplified thermal coupling method in the heating temperature consolidation test are consistent with the simulation results of the real thermal coupling method. |
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