循环往复水流对反滤系统的作用机理研究

通过自行研制的循环往复水流试验装置，研究了不同频率的正弦循环水流对反滤系统的作用机制，建立了与试验模型相一致的定解条件，并求得孔压微分方程的解析解。理论分析表明，土的固结系数与循环往复水流的频率的比值越小，靠近边界处土体的水力梯度就越大，土体内部的水力梯度就越小。试验中，当周期为0.5 min时，边界处水力梯度振幅接近系统平均水力梯度振幅的2倍；当周期为62.5 min时，则基本没有边界水力梯度集中现象。实测结果与理论分析结果较为一致。这种水力梯度边界集中现象，容易加剧渗透边界层的冲刷，降低反滤系统的渗透稳定性，应当在试验研究和工程实践中引起注意。

Research on effect mechanism of cyclic flow on filtration system

A cyclic flow device is developed to study the effect mechanism of sine flow with different frequency on filtration system. A differential equation of pore water pressure accordant with the test model is built; and its analytic solution is achieved. Theoretical analyses show that the smaller ratio between the consolidation coefficient of soil and the frequency of cyclic flow leads to the higher hydraulic gradient on the border of soil and the lower hydraulic gradient inside the soil. Test results show that when the period of the cyclic flow is 0.5min, the amplitude of hydraulic gradient near to the border of the soil is nearly double of the average amplitude of the filtration system. When the period of the cyclic flow is 62.5 min, the phenomenon of hydraulic gradient focusing is neglectable. Test results show good accordance with the analytical results. The phenomenon of hydraulic gradient focusing will lead to more filtration border erosion and it will diminish the stability of the filtration system. Proper attention shall be paid to this phenomenon in the filtration engineering.