Experiment and analysis of seepage failure process of multi-layer sand

FAN Yunyun; WU Xiujie; ZHANG Fang

doi:10.7688/j.issn.1000-1646.2025.03.16

Abstract：[Objective]Seepage failure seriously threatens engineering safety,and research on the process of multi-layer sand seepage failure is of practical significance for disaster prediction and optimization of prevention and control engineering,which is,however,still not deep enough currently.This study employed experimental methods to analyze the seepage failure process of multi-layer sand,aiming to obtain the influence of sand layer arrangements on the occurrence conditions,failure modes,and water-sand transport process of seepage failure,and further analyzed the formation mechanism of multi-layer sand seepage failure and the transport characteristics of water-sand two-phase flow.[Methods]The independently developed high-speed seepage test equipment for water-sand two-phase flow was used to conduct indoor experimental research on the process of multi-layer sand seepage failure,and an experimental method of seepage failure for water sand separation was proposed in the study.By conducting seepage failure experiments with different sand layer arrangements,the occurrence conditions and failure modes of multi-layer sand seepage failure were determined,and water-sand transport characteristics were revealed during the process of water-sand two-phase flow.[Results]The distribution of multi-layer sand has an impact on the mode and occurrence conditions of seepage failure.Sand layers with small particle sizes bear large local hydraulic gradients,and when they differ significantly from particle sizes in downstream areas,the critical hydraulic gradient is small.When the sand layers are arranged in the order of particle size from fine to coarse,the sample has filtration characteristics,and the critical hydraulic gradient is relatively large at this time.The distribution of multi-layer sand has an impact on the flux of water-sand transport caused by seepage failure.In the absence of downstream sand layer protection,fine sand layers may experience soil flow failure,which leads to the rapid formation of a large amount of sand inrush during seepage development.While there is a protective sand layer at the downstream area of the fine sand layer,the amount of sand inrush will be significantly reduced.The distribution of multi-layer sand has an impact on the water-sand transport flux.During the process of multi-layer sand piping,the sand structure gradually deteriorates,and the flux increases accordingly.The water-sand flux curve shows regular fluctuations due to the alternating compression and expansion of the sand layer.[Conclusion]The experiment results indicate that multi-layer sand can withstand a large hydraulic gradient under reasonable inverted filter settings.Fine sand layers bear a greater hydraulic gradient than other sand layers and are prone to soil flow failure in the absence of downstream sand-layer protection.When the downstream protective sand layer has a large grain size,the piping failure is more likely to occur.When soil flow occurs,a large amount of sand inrush occurs rapidly,and the water-sand two-phase flow process shows a regular fluctuation when piping occurs.The obtained critical conditions for seepage failure and data of water-sand transport process in this study can serve as reference for further experimental research and the correctness verification of numerical simulation.