三层堤基中细砂层厚度对管涌影响的试验研究

Effect of thickness of fine sand layer on piping development in three-stratum dike foundation

对由弱透水黏土层、细砂层和强透水砂砾层组成的三层堤基进行了管涌发展的砂槽模型试验,为了便于观察分析,细砂层由各种颜色的细彩砂依次排列在砂砾石层上表面,通过改变彩砂层的厚度分析研究了不同细砂层厚度对管涌发生、发展机制及过程的影响。试验结果表明,三层堤基细砂层厚度的不同使管涌发生的临界水力梯度、涌砂量和通道发展的速度不同,与双层堤基有很大区别。临界水力梯度是由多种元素决定的,包括破坏土体的性质及其整体性等;细砂层的存在使流量在渗透变形初期对涌砂不敏感;在试验中发生的相同水位下多次间歇性涌砂,其原因一方面是颗粒在运动过程中发生堵塞,另一方面是通道边界的土体失去支撑发生应力释放,抵抗力随着时间逐渐减小。

A series of flume model tests was conducted to study the process and mechanism of piping in a three-stratum dike foundation, which was composed of weak permeable clay layer, sand layer and strong permeable sand gravel layer. To observe the process clearly, fine sand layers of different colors were laid on the gravel layer according to the color sequence. The thickness of colored sand was changed to investigate the effect of thickness on the process and mechanism of piping. The experimental results indicate that the different thicknesses of color sand results in the different critical hydraulic gradients, eroded masses and developing speeds of piping channel, which are quite different from those in two-stratum dike foundation. The critical hydraulic gradient depends on a number of factors including the properties and integrity of the damaged soil. The sand layer makes the flux insensitive to the erosion at the early stage of seepage deformation. Furthermore, it is also found that several times of intermittent erosion occur at the same upstream hydraulic head. One of the reasons for this is that the particles are dogged in the process of movement, and the other reason is that the stress release of the soil near the boundary of piping channel after the erosion of soil at the frontend, resulting in a decrease in the soil resistance over time.