Numerical Simulations Of Dynamic Characteristics For Saturated Compacted Clayey Sands Based On PFC3D With The Elexible Boundary Conditions

Based on the Nanchang underground saturated dense mud-sandy soil and the three-shear unified elastoplastic boundary surface model,a number of indoor geotechnical tests have been performed and the conventional triaxial and dynamic three-axis flexible boundary surface has been established in the PFC3D particle flow program.The numerical and experimental models of axial and dynamic triaxial and the engineering numerical models of single and double tunnels.At the same time,the laboratory test results of conventional triaxial and dynamic triaxial,PFC3D simulation results and theoretical calculations are compared.The dynamic triaxial PFC3D simulation results are compared with the theoretical calculation results,and the mechanical properties of sand and the dynamic response of the tunnel and soil during single and double tunnel driving are analyzed.The main research contents and conclusions are as follows:(1)The static and dynamic method of establishing a flexible boundary numerical model for triaxial tests and the calibration process of the model's mesoscopic parameters.The calibration of the meso-parameters of the numerical model of the PFC3D test needs to be based on the results of laboratory tests.The soil samples of the static and dynamic triaxial test models can be generated by the radius exclusion method,and the confining pressure is achieved by a flexible rubber film composed of small particle units.Control the speed of the upper and lower walls.(2)Comparison of PFC3D numerical simulation results,laboratory test results,and theoretical calculation results of sand with 0%,5%,and 10%mud content at 100kPa and 400kPa confining pressure in conventional triaxial tests shows that Under conventional triaxial drainage conditions,the body strain state and stress-strain relationship of the three results are in good agreement,and the numerical model can also generate a corresponding meso-response from the particle displacement and the force chain.(3)Stresses of saturated sand samples with different mud contents during different confining pressures,different amplitudes,and different vibration frequencies during the first 20 cycles of conventional dynamic triaxial theoretical calculations,laboratory tests,and PFC3D numerical simulations.The strain relationship and the pore water pressure state are in good agreement;the stress-strain relationship and the pore water pressure state of the dynamic true triaxial in theoretical calculation and PFC3D numerical simulation are also in good agreement when the principal stress influence coefficient b=0.5.It shows that PFC3D has a better applicability in the study of the early liquefaction of saturated sand,and it can also respond to the micromechanical performance with the change of coordination number.(4)Based on numerical experiments and Nanchang Metro Line 2 established a single tunnel PFC3D model with 0%and 5%sand content and a dual tunnel PFC3D model with 0%sand and soil content indicates that:When a single tunnel is operating,as the train passes through the tunnel,it will cause a downward and gradually stable wave displacement of the tunnel,and at the same time,it will cause a downward displacement of the soil around the tunnel,vortex speed and stable stress fluctuations;the soil on the tunnel vault The downward displacement of the soil converges downward,the displacement of the soil below the arch bottom diffuses downward,the vortex of velocity diffuses with the tunnel as the center,and the dynamic response decreases as the distance from the tunnel increases.Soil mud content is positively related to tunnel displacement and soil dynamic response.During the operation of the dual tunnel model,the vibration,displacement,velocity and dynamic response of the tunnel are approximately the same as those of the single tunnel operation,except that the dynamic response and displacement of the soil in the lower part of the tunnel are superimposed by the two vibration sources.Effect,the soil in the middle of the two tunnels will produce mutually restrictive effects.