无黏性土管涌出砂及流量研究

管涌对堤防工程的危害极为严重,人类对管涌的认识也逐渐加深。目前,对管涌破坏开始的条件及其破坏后通道贯通的后果了解较多,然而,因其破坏及发展机制的复杂性,对于管涌发生后涌砂及流量的研究并不深入。通过自行设计的室内模型,改变上覆黏土的厚度对3组土性相同的无黏性土试样进行试验。对测压管水头、通道范围、涌砂量和流量等进行对比分析,研究孔隙率、渗透系数以及流量的变化规律,发现涌砂随时间变化满足非线性关系——Boltzmann模型。最后,利用渗透系数与孔隙率以及孔隙率与累计涌砂量的关系,推导并验证了流量随时间变化的理论公式。这对于认识管涌和有效控制管涌发展以及减灾避难有着非常重要的意义。

Analysis of piping sanding and flux of cohesionless soils

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.