渗流作用下粉土质砂潜蚀演化特征与预测模型

Evolution characteristics and prediction model on suffusion of silty-sand subjected to seepage

长期渗流作用下,土体发生内部潜蚀常会诱发结构变形甚至破坏。利用自主研发的渗流装置开展砂土潜蚀试验,研究渗流作用下不同初始孔隙比粉土质砂的颗粒流失过程及潜蚀演变特征,并阐明各影响因素的作用机制,建立颗粒流失量随水力梯度和时间增长的预测模型,继而基于颗粒级配试验和三相关系推演,揭示粒度分布与孔隙比的变化规律。结果表明:渗流作用易导致砂土内部细颗粒和砂粒流失并逐渐形成优势渗流通道,诱发砂土局部坍塌并在持续潜蚀后呈整体不均匀沉降变形,直至水压主要沿优势通道消散时,达到潜蚀稳定;初始孔隙比或密实度是影响土体潜蚀程度的主要内部因素,直接改变了颗粒移动的起动水力梯度、流失速率、累积总质量及土样沉降变形量,水力梯度增大会加快颗粒流失、通道形成和潜蚀稳定;建立的预测模型拟合度高,能较好地反映上述演化特征以及初始孔隙比和水力梯度对颗粒流失发展规律及稳定时间的影响;潜蚀对粉土质砂物理状态的影响主要表现在孔隙比总体增大而颗粒粒径的不均匀性降低。

Soil suffusion induced by long-term seepage generally lead to deformation or damage of soil structure.The suffusion experiments of silty sand had been accomplished by the independently developed seepage instrument,to study the particle loss process and suffusion evolution characteristics of silty sand with different void ratios induced by seepage of different hydraulic gradients,and the influential mechanism of factors is understood on the sand suffusion,then a model is established to predict the increase of particle loss with seepage duration and hydraulic gradient.Furthermore,the development patterns are revealed of particles size distribution and void ratio during suffusion based on the particle grading test and three phases relationship.The results show that:firstly,fine and sandy particles are both washed away by the long-term seepage and some dominant seepage channels will form subsequently in the samples,and then the internal local collapse and the overall differential settlement will be induced by continuous suffusion,until the water pressure mainly dissipates along the dominant channel to achieve the suffusion stability.Secondly,the initial void ratio or compactness is the main internal factor affecting the degree of the seepage suffusion of the soil,which directly changes the hydraulic gradient threshold,loss rate,cumulative total mass of particle movement and settlement deformation of sandy samples.The increase of the hydraulic gradient will also accelerate the particles loss,channel formation and suffusion stability.Thirdly,the prediction model fits the experiment result well,which can reflect evolution characteristics above and the influence on particles loss process of initial void ratio as well as the hydraulic gradient.Finally,the void ratio of samples will increase and the uniformity of particle size will decrease during sand suffusion.