Study On The Mechanism Of Pipe Bursting In Self-adaptive Stress

Seepage failure is the main reason for the instability and destruction of a large number of water conservancy projects.The main form of seepage failure is pipe failure.The essence of pipe failure is the loss of fine particles inside the soil,which is caused by the seepage field,stress field and strain field of the soil.Under the action of field coupling,in order to study the influence of the loss of fine particles,stress and the development of piping during the occurrence of piping,a piping test of upward seepage and cohesionless soil was carried out using a homemade piping test device system.The influence of the change of stress during the development of piping on the development law of piping.The PFC3D numerical simulation software was used to generate four sets of particle models with different fine particle content.Under the same confining pressure conditions,different confining pressure conditions,and different fine particle content deletions,the stress and strain simulations were performed on the four sets of particle models.(1)The pipe erosion test system was developed,and the pressure and volume control system was improved.The previous test system needed to use weights to load the pressure,and the surrounding pressure needed to be completed with a water and gas exchange tank.This test system only needs to input the target confining pressure and the target axial pressure in the software on the computer,the pressure controller can automatically load to reach the target pressure,and the sample volume change only needs to read the record in the computer software.It is more convenient and can observe the progress of the internal piping in soil samples in real time.(2)Using the self-made pipe erosion test system,the pipe erosion test of granular soil was carried out.Based on the results obtained,the variation law of seepage flow velocity with hydraulic gradient and the variation law of seepage flow with time were analyzed.It further reveals the relationship between the erosion rate of the pipe and the stress state of the soil sample during the pipe surge.The change of the stress state has a greater impact on the occurrence and development of the pipe surge.(3)Based on the PFC3D numerical reconstruction technology,the generated particle model is sliced,and the distribution of fine particles is studied from within the particle model.It reveals the arrangement of fine particles in the particle model and the contact of fine particles with surrounding particles under different porosity and different fine particle content.(4)Based on the PFC3D numerical simulation technology,the particle model with the same initial conditions was subjected to triaxial shear simulation under different confining pressure conditions,which revealed the influence of the confining pressure on the internal stability of the particle model.(5)Based on the PFC3D numerical simulation technology,before and after loading,the particle model suddenly undergoes a certain amount of fine particle removal,the strength of the particle model changes,and the effect of fine particle loss on the strength of the particle model is explored.And compared with the results obtained by Yang Yongmei’s indoor experiments.