无粘性土中管涌的临界水头梯度研究

将管涌型无粘性土中的颗粒分为骨架颗粒、阻塞颗粒和可动颗粒三组，在分析骨架孔隙中可动颗粒受力的基础上，将总压力降分为骨架孔隙壁引起的压力降、骨架孔隙中静止颗粒引起的压力降及正在运动的颗粒引起的压力降三部分，从而得到了可动颗粒起动的临界水头梯度公式，对管涌试验的校验证实了该公式的有效性，计算结果表明：当有细颗粒流失后，级配不连续的管涌型土比级配连续的管涌型土更易发展成管涌破坏，同时还证实：随着可动颗粒的流失，管涌破坏可以转化为流土破坏。

Critical Hydraulic Gradient for Piping in Noncohesive Soils

In this paper, the grains of piping-typed noncohesive soils are classified into three groups: skeleton, movable and clogging. Based on the analysis of the forces acting on movable grains, the pressure drop is ascribed to the wall of skeleton pores, the at-rest grains and moving ones in skeleton pores, and therefore a formula of critical hydraulic gradient for movable grains' incipient motion is obtained.Its application to some examples of piping tests gives reasonable results in comparison to the experimental observations. The calculated results show that, after some fines is washed out, piping failure more easily takes place in the piping-typed soil with a bimodal grain-size-distribution than in the soil with the unimodal grain-size-distribution. In addition, it also proves that the piping failure can turn into soil-flow failure with the washout of movable grains.