富水砂层基坑止水缺陷高宽比对漏水漏砂的影响

在富水砂层地质条件下，基坑支护常因止水缺陷导致水土大量流失，进而引发地表沉降。目前有关止水缺陷导致基坑漏水漏砂灾害方面的研究还有待深入。本文以江西省南昌市临近赣江某地铁基坑砂土为研究对象，考虑基坑止水缺陷高宽比因素，通过可视化室内实验装置研究基坑缺陷漏水漏砂灾害的演化过程，并利用PFC3D软件进行模拟对比分析，探究几何形态和微观变化过程。结果表明：止水缺陷高宽比越大，漏水漏砂发展速度越快，颗粒流失速率越大，砂土颗粒受侵蚀范围越大；缺陷高宽比由1:1增加至2:1时，颗粒损失个数由2673扩大至40127，土拱形成时间从60万步发展至无法形成土拱，存在出现土拱时的临界缺陷高宽值。数值模拟过程中的配位数波动表明，漏水漏砂过程中细颗粒与粗颗粒骨架之间一直产生着剧烈碰撞，水土的流失导致孔隙率与渗透系数的增加，进而又加剧漏水漏砂现象。

Influence of height-width ratio of water stop defect on water and sand leakage in foundation pit of water-rich sandy layer

In water-rich sand layer, the support of foundation pits often suffers from water and soil loss due to the water stop defect, which will lead to surface settlement. At present, further research is needed to be focused on the disaster of water and sand leakage of foundation pit caused by water stop defect. Taking the sand of a subway foundation pit near Ganjiang River in Nanchang City, Jiangxi Province as an example, this work considered the height-width ratio of water stop defect in the foundation pit, and investigated the evolution process of water and sand leakage disaster through visual indoor experimental device. The PFC3D software was adopted for simulation and comparative analysis to explore the change process of geometric morphology and microscopic parameters. Results show that the larger the height-width ratio of water stop defect is, the faster the water and sand leakage develops. The greater the particle loss rate is, the larger the erosion range of sand particles is. With the height-width ratio increasing from 1:1 to 2:1, the number of particle loss increases from 2673 to 40127, and the formation time of soil arch develops from 600000 steps to failure to form soil arch, with the presence of critical height and width value when soil arch occurs. The fluctuation of coordination number in the process of numerical simulation shows that during the process of water and sand leakage, a fierce collision occurred between fine particles and coarse particle skeleton. The water and soil loss leads to the increase of porosity and permeability coefficient, which further aggravates the phenomenon of water and sand leakage.