Study On Discrete Element Biaxial Test Simulation Of Glass Fiber Reinforced Soil By Discrete Element Method And Its Microscopic Characteristics

As a special granular material,Loess is widely distributed in China.Its special mechanical properties lead to frequent geological disasters in the loess area,restricting the rapid economic and social development of the loess area in China under the background of"One Belt and One Road".Fiber-reinforced soil is an ideal improved soil technology,which effectively improves the strength of the soil,and has great potential for development in roadbed improvement,slope support and other projects.Fiber-reinforced soil is a typical geotechnical material whose application is greater than theoretical research.The study of its internal microstructure characteristics during the deformation process has important application value for solving complex geological disasters and geotechnical engineering problems.In this study,Yan’an loess was used as the research object,and glass fiber was used as the reinforced material,combined with field investigations,laboratory tests,and electron microscope scanning.An exploratory study was conducted on the macro-mechanical properties and micro-structure characteristics of glass fiber reinforced soil.Based on the PFC^2D numerical simulation program,the programming method is employed to construct a discrete element model of fiber reinforced soil with particle geometric characteristics,and the biaxial test of flexible boundary servo is performed to conduct a microscopic study of the deformation and failure process of fiber-reinforced soil.The specific conclusions are as follows:1.An increase then a decrease of the peak strength of glass fiber reinforced soil samples appear,influenced by the increase of fiber doping,withξ=0.6%as the optimal fiber doping.The fiber’s strength increase rate and the reinforcement rate show a quadratic relationship.The cohesion of the soil is increased by incorporating fiber,which shows little effect on the angle of internal friction.2.Scanning electron microscope is employed to obtain the microstructure characteristics of the sample shear band under different reinforcement ratios:the unreinforced remolded soil particles have a stable contact relationship,while the granular particles and the massive particles form point-to-point and Point-to-surface contact relationship.The framework of the soil is composed of massive and flake-like large particles in an inlaid manner,and the bonding particles and the framework particles form a cemented contact relationship.The inlaid particles form a relatively stable three-dimensional structure and are able to bear a certain external force.The fibers present a disorderly distribution state in the sample,and the main mechanism of fiber-reinforced soil is embodied by the bonding and friction formed between the fibers and the soil particles.The bond strength between fiber and soil is lower than the bond strength between the soil particles at the edge of the hole.The soil particles inside the hole formed after fiber pulled out are in an independent distribution state,and the surface of the fiber is not plastically deformed.When the fiber content exceeds the optimal reinforcement ratio,the fiber agglomeration structure of the sample will increase,which leads to a significant increase in the porosity of the nearby soil and various degrees of cracking.3.The generation of the sample shear band results from the differentiation of the particle velocity vector.Before the peak intensity comes,the particle displacement speed is low and the movement direction tends to be the same.After the peak intensity comes,the speed direction and size change rapidly,and the direction of change ultimately determines the failure mode of the sample.The lock-up effect produced by the geometry of the particles seriously affects the development process of the shear zone.The rotation angle of the particles in the shear zone:the geometric block particles inside the shear zone<the spherical particles inside the shear zone<the geometric blocks around the shear zone Particles<Spherical particles around the shear zone.4.The curve of sample crack number divides the deformation and failure process of the sample into three stages:compression stage-damage stage-failure stage.The internal tensile fissures of the sample are obviously lower than the shearing fissures,but with the increase of confining pressure,the number of fissures gradually tends to be equal.The formation process of shear bands can be divided into three stages:fiber deformation and tension-reinforcement and soil structure failure-shear band formation.As the reinforcement rate increases,the shear surface of the sample is gradually transitioned from a single shear surface to a multi-forked type when the sample is broken.Under the optimal fiber doping amount,the overall fiber distribution of the sample is relatively uniform,and a close contact structure between the fibers and the soil particles is formed.The fibers are bent in the soil body and overlap each other to form a network structure to prevent the relative displacement between the soil particles,which will reduce the overall deformation.As for samples with excessively high fiber reinforcement rate,there exist excessive overlaps of fibers in the soil,which will break the bond between the soil particles and affect the macroscopic mechanical strength of the soil.