双层堤基管涌通道扩展机制和计算方法研究

RESEARCH ON MECHANISM AND COMPUTATIONAL METHOD OF PIPING CHANNEL EXPANSION OF DOUBLE-LAYER DIKE FOUNDATION

双层堤基管涌通道是否扩展,取决于砂层颗粒条件、通道内冲刷水流和边壁渗流力等因素。通过分析通道边壁颗粒的受力平衡条件,引用河流动力学的相关公式,考虑砂粒相对暴露度、脉动流速、起动标准和管涌通道水流特性等因素提出通道扩展的判定条件。用2个砂槽模型试验研究冲刷水流和边壁渗流力的不同组合对通道扩展的影响,并用一维渗透试验证实渗流溢出面附近实际坡降远小于平均坡降的现象,说明提出渗流力有效比参数的合理性。在上述研究的基础上,用通道边壁稳定条件控制,建立有限元计算迭代流程,对管涌通道的扩展进行了数值模拟,并与试验结果进行对比,验证该方法的可行性。

The piping channel expansion in double-layer dike foundation is determined by the characteristics of particles in sand layer, water flow in the channel and the seepage force in the surface of the channel. By analyzing the mechanical balance of the particles in the surface of the channel and introducing some formulae of river dynamics as well as considering the relative exposure degree of the particles, fluctuating velocity, criteria of the particles＇ incipient motion and flow characteristics, the critical condition of piping channel expansion is proposed. Two sand box model experiments were done to study the combination impacts of the flow and seepage force on channel expansion. And the one-dimensional seepage experiment has proved that the hydraulic gradient near the overflow surface is much less than average gradient. It shows the rationality of the effective ratio between the actual and calculated seepage forces. Based on the experiments, a finite element method which is controlled by the critical condition of the stability of channel＇s surface is built. It was used to simulate the expansion of piping channel. By comparing the calculated results and the experimental results, it is shown the proposed methods are reasonable.