Macro And Micro Research On Compressibility Of Soil Based On Laboratory Experiment And Discrete Element Numerical Simulation

On the basis of the close relationship between microstructure and macroscopic mechanical of soil,the analysis of field land subsidence project,the innovative design of experimental consolidation test and the numerical simulation research of discrete element method were carried out respectively.The following results are obtained:(1)A series of experiments were carried out in this study.In order to study the mechanism of land subsidence,the experiment combines the quantitative analysis of soil microstructure with the macroscopic mechanical properties test and the soil samples are taken from a 200 m borehole drilled in Shengze,Suzhou.A larger number of SEM images were obtained after using the method of vacuum freeze-drying.The imaging analysis software PCAS was used to acquire the parameters of soil microstructure and the fiber optic monitoring techniques were used to monitor the soil layers in the borehole.The results indicate that the moisture content,the liquid index and the compression coefficient get smaller and the microstructure orientation become more clearly with the depth of strata increasing;There is a large number of microscopic pore structures in the water-bearing sand layer of the second confined and the volume is big enough,which causes a great potential of subsidence in the future and it remains to be investigated.(2)Based on the approach of fixing and extracting the microstructure of sand specimens during the traditional consolidation test,the apparatus detailed herein combines a redesigned consolidation container and an automatic stepping motor for impregnating sand specimens with blue epoxy.A series of test results independently confirmed the optimum range of particle size,appropriate proportion of blue epoxy,and ultimate impregnation resistance force of the apparatus.The microstructure of three kinds of sand specimens with different particle size were obtained.The results show that coarse specimen exists larger compression potential.In microcosm,the destruction of sand particle is main reason of compression phenomenon in coarse specimen.The integrity of find specimen is better.The microstructure results obtained by software PCAS also indicates the internal structure of coarse specimen changes greatly(3)In order to study the failure characteristics in sand particle,rounded quartz sand was used.The results show that the failures in specimen are regional and framework structures appear under the vertical stress.In a single particle,the most serious broken is contact point.The stress concentration can be seen in contact point and the combination of broken networking make the destruction in microstructure and instability in macroscopic mechanical.(4)A series of laboratorial test were conducted with spherical quartz sand and standard laboratorial sand.The results show that while the range of particle size distribution increases,the compressibility of specimen increases.The stress history effects the compressibility and decreases the subsequent compression potential.The increasing of the find sand in specimen,the compressibility decreases.(5)Based on the particle size distribution and particle morphology,a series of discrete element method research were conducted.The conclusion of numerical simulation and test are accordant.the discrete element method is introduced to simulate hydraulic fracturing processes.The rules of energy calculation and energy conversion in the models are proposed and a 3D discrete element model was built.The results show that with the increase of particle size distribution,the compressibility of sand specimen increased;The irregular element caused the increase of compressibility in numerical simulation Furthermore,force chain and the phenomenon of stress concentration were observed in simulation;The energy curves was calculated in this paper.