关键词: 无黏性土, 管涌, 黏土层, 渗透系数, 涌砂量, 流量

Abstract: Piping effect has serious hazards to river embankment engineering. The understanding of piping is gradually deeper and deeper to people. Nowadays, people know more about the beginning conditions of piping occurred and the consequences of piping channel completely penetrated the levee. However, because of the failure and development mechanism of piping is very complex, the study of the emission of sand and the flux after the piping effect is not deep enough. Three groups of cohesionless soils, in the same soil features, are used to make a series of tests by changing the thickness of overlying clay layer, using a self-designed equipment. A comparative analysis is made from the aspects such as piezometric head, scope of piping channel, sand production and flux. Furthermore the changing laws of the porosity, coefficient of permeability and flux are studied. It is found by the tests that cumulative amount of sand changing with time satisfies the Boltzmann model, a kind of nonlinear model. By using the relationship between permeability and porosity and the relationship between the porosity and cumulative amount of sand, a theoretical formula, from the changing flux over time, can be deduced and verified. The formula has a very important significance for the understanding of piping, the effective controlling of piping development, and the reducing or avoiding disasters of embankment collapsing.

Key words: cohesionless soils, piping, clay layer, coefficient of permeability, sand production, flux