含盐量对上海人工冻融软黏土特性的影响

Effects of Salt Content on the Characteristics of Artificial Freeze-thaw Soft Clay in Shanghai

研究目的:在河口三角洲地区使用人工地层冻结法修建越江、跨海隧道等大型工程的联络通道时,常常会遇到孔隙水含盐量高软黏土地层,这不同于以往的小型淡水冻结工程。通过配置不同孔隙水含盐量的重塑软黏土,经过冻融处理后,采用直剪、渗透、压缩、压汞试验的方法探究孔隙水含盐量对冻融软黏土强度、渗透、压缩的特性和孔隙结构的影响,并测定探究冻融时孔隙水中离子浓度变化规律,从而为三角洲地区软黏土孔隙水盐分过渡带的融沉注浆、沉降预测等提供参考依据。研究结论:(1)盐分能增大冻融软黏土的不排水抗剪强度、减小渗透系数、增大压缩模量,且浓度越高,影响程度越大;(2)冻融能使软黏土孔隙水中的Cl^-、Na^+浓度轻微降低;(3)盐分能使得冻融软黏土整体孔径和峰值孔径不同程度地减小;(4)本研究结果有助于沿海越江、跨海等大型冻结工程的施工控制,以及周围工程环境的治理。

Research purposes:In estuarine delta areas,when the artificial ground freezing(AGF)is used to build the cross passage of large-scale projects such as cross-river or cross-sea tunnels,soft clay layers with high salt content in pore water are often encountered,which is different from previous small projects of AGF in fresh water.Reconstituting soft clay with different pore water salt content,after artificial freeze-thaw,the tests of direct shear,penetration,compression,mercury intrusion were conducted to explore the effects of pore water salt content on the characteristics of strength,permeability,compression and relevant pore structure of freeze-thaw soft clay.Finally,the change law of ion concentration in pore water during freeze-thaw was measured and analyzed as well,to provide a reference for the thaw settlement grouting and settlement prediction of the soft clay pore water-salt transition zone in the delta area.Research conclusions:(1)The salt content can increase the undrained shear strength,reduce the permeability coefficient,and increase the compression modulus;the higher the salt content,the greater the degree of influence.(2)Freeze-thaw can slightly reduce the concentration of Cl^-and Na^+in the pore water of soft clay.(3)The salt content can reduce the overall pore size and peak pore size of the freeze-thaw soft clay to varying degrees.(4)The research results are helpful for the construction control of large frozen projects in coastal areas,such as river crossing and sea crossing,as well as the treatment of the surrounding environment.