Researches On Meso-scale Mechanism Of Piping Failure By Means Of Model Test And PFC Numerical Simulation

This article does deep research on the formation and development mechanism of piping from the angle of meso-scale mechanism. Advanced digital photographic video tracing and image processing technology is introduced into the indoor model test of piping to record the motive orbit of soil grains, determine critical parameters in piping-formation, identify and analyze tunnel-forming mechanism during piping. On the basis of model test and the meso-scale mechanism means such as the particle flow code of discrete mediums theory and its analytic method, this article analyses the collective influence of seepage and soil medium, and researches further meso-mechanics mechanism of piping-formation. The software of PFC2D and PFC3D are used and developed in meso-analog simulation of soil particles' motion rules in the process of piping formation and development. Combined with the case analysis and research of embankment piping, this article provides theoretic support for forecasting and handling piping failure conditions.Four technical problems are solved: 1. to determine critical parameters in piping-formation through model test; 2. to determine the relation between water head pressure and grain motion by precisely setting the change of sample loss amount in model test; 3. to analog simulate meso-numeric model in piping formation and development and optimize numeric model so as to solve the problem resulted from the long-time computing; 4. to combine the PFC analytic technology, advanced model test measurement technology with computer analog simulation technology.In model test, piping process is recorded and meso-parameters beneficial to numeric simulation are acquired through advanced digital image test analytic method. In numeric simulation, discarding the natural limitation of finite element method simulation's deformation and failure while adopting the PFC theory which can simulate failure phenomenon, and utilizing and developing PFC software to simulate piping, breakthrough is made in using meso-parameters to quantitatively determine macro-parameters. Attention should be paid to the researches in this article as blow:1. Aimed at soil samples of different graded and fine particles content, using digital camera and advanced digital image deformation measurement technology to analyze and research macro critical parameters in piping failure, this article acquires the critical hydraulic gradient in piping, the relation between velocity of flow and hydraulic gradient, variety rule of the loss amount, the macro the particles' movement and formation process of tunnels.2. Using high-resolution microscope to record the whole meso-scale process of piping, makes it possible to record the creation and development process of particle loss and the interaction between particles in piping in the view of meso-scale. With this as the basis, adopting advanced digital photographic soil body meso-structural measurement technology to research variety rules of meso-porosity and interaction between meso-particles, and thus the meso-mechanical mechanism in piping is revealed.