Study On Bearing Capacity Of Reinforced Foundation Of Strip Foundation Based On Discrete Element Method (PFC)

Soil is a complex aggregate of granules,which is neither an ideal elastic material nor an ideal plastic material in terms of material properties.and the soil has three phases of solid,liquid,and state,which makes it have complex mechanical behavior when it is subjected to force.For a long time,scholars have worked hard to understand the internal structure of the soil and gradually realized that the discretization of the continuum is an effective method of calculation and analysis.The idea of discrete element and the appearance of discrete element software have made contributions to the study of the micro-mechanical behavior of soil deformation.In the discrete element software that has been developed,PFC can quantitatively determine the relationship between soil macroscopic parameters and mesoscopic parameters by simulating biaxial tests.Thus,the macroscopic mechanical behavior and deformation and destruction of the soil are revealed from the perspective.The main contents of this paper are as follows:(1)A biaxial test model of PFC2D sand is established,and the influence of fine parameter friction coefficient,particle stiffness,and surrounding pressure on sample strength is studied by controlling variable method.By comparing with the indoor experiment,the relationship between the microscopic parameters of sand and the macro parameters such as friction angle is analyzed.The mesoscopic parameters of sand soil are calibrated.(2)Generate 10cm and 15cm bar foundation models,respectively,and apply loads from 100kpa to 400kpa to the foundation to obtain settlement curves of different base pressure P and foundation settlement S,compared with indoor tests.(3)Extract the initial position coordinates of the particles and the particle displacement vector that has applied the last primary load,and write a program through Matlab to generate a displacement cloud map of the soil particles.The movement of soil particles was analyzed from a microscopic point of view.(4)Establish a reinforced foundation model,apply a load of 100 KPA to 400 KPA to the foundation,observe the deformation of the bar,and obtain a settlement curve diagram of the different base pressure P and the foundation settlement S,and compare with the unreinforced foundation settlement curve and indoor test results.To verify the reliability of PFC program simulation.(5)The model of one layer of reinforced foundation and two layers of reinforced bar foundation are established,and the position of the first layer of reinforced foundation is changed.The effects of the number of different reinforced layers and the depth of the first layer of reinforced foundation on the bearing capacity of the foundation are studied.Through the laboratory test and numerical simulation analysis,the main conclusions are as follows:(1)The microscopic parameters of the sample have a certain quantitative and qualitative relationship with the macroscopic parameters.The strength of the sample is greatly affected by the friction coefficient and the contact stiffness of the particles.As the friction coefficient and stiffness increase,the strength of the sample increases.Therefore,the greatest influence on the settlement of the foundation is the friction coefficient and the particle stiffness.When the friction coefficient is small,the friction angle is sensitive to the friction coefficient parameter.When the friction coefficient exceeds a certain value,the strength of the sample will tend to be stable;there is a certain quantitative relationship between the friction coefficient of the meso-parameter and the friction angle of the macro-parameter.As the coefficient of friction increases,the friction angle of the sample increases,but does not exceed 45 degrees.(2)When it is about 1B under the substrate,the contact force between the particles is larger and more concentrated.When the distance exceeds 1B,the stress spreads faster,and the farther away from the substrate,the more uniform the contact force distribution between the particles;(3)The laying of the ribs can effectively improve the bearing capacity of the foundation and reduce the settlement of the foundation.Within a certain range,the smaller the reinforced depth of the first layer,the greater the deformation of the reinforced materials,and the better the reinforced effect;(4)When the first layer has a reinforcement depth of 0.3B,the reinforcement effect is the best.As the first layer reinforcement depth increases,the foundation bearing capacity decreases.The settlement of the foundation under the same load is increased.The reinforcement effect of the first layer is more than 1.5B.(5)Two layers of reinforcement work better than one.With the increase of the number of layers,the contact force between the particles is more evenly distributed,the soil is more force-bearing,the bearing capacity of the foundation is enhanced,and the deformation is reduced.