饱和黏性土试样底部孔压时间滞后机理探讨  

Mechanism of pore pressure time lag for saturated clays

作　　者：欧颜雨馨 牟聪 翁佳兴 洪振舜[1] OU Yanyuxin;MOU Cong;WENG Jiaxing;HONG Zhenshun(School of Transportation,Southeast University,Nanjing 211189,China;Jiangsu Water Source Company Ltd.of the Eastern Route of the South-to-North Water Diversion Project,Nanjing 210000,China)

机构地区：[1]东南大学交通学院,江苏南京211189 [2]南水北调东线江苏水源有限责任公司,江苏南京210000

出　　处：《岩土工程学报》2024年第4期864-870,共7页Chinese Journal of Geotechnical Engineering

基　　金：国家自然科学基金项目(41977243,52278334);江苏“卓博计划”项目(2022ZB815);江苏省南水北调科技研发项目(JSNSBD202205)。

摘　　要：采用一维固结仪进行饱和黏性土固结试验时,测量的试样底部孔压普遍存在“时间滞后”现象,荷载施加后,孔压随固结时间先增大至最大值,然后开始消散。以往研究发现,测压管式孔压计的刚度不足,导致孔压计腔体体积在施加荷载后发生变化,从而得出孔压滞后可以归结于孔压测量系统刚度的结论。基于已有理论,分析了不同孔压测试系统刚度对孔压滞后性状的影响,发现隔膜式孔压测量系统刚度足够大,固结试验中施加荷载所引起的孔压计腔体体积变形可以忽略不计,测量系统刚度不是隔膜式测量系统孔压滞后的主要影响因素。对比分析三轴固结试验和一维固结试验不同边界排水条件诱发不同的孔压滞后性状,发现一维固结试验中施加荷载时,试样顶部处于自由排水条件,外加荷载引起的水力梯度均匀地分布于试样之前试样顶部便产生排水固结是诱发底部孔压时间滞后的关键因素。基于一维固结试验数据,分析了孔压滞后时间与土体试样固结参数的关系,可以得出:底部孔压峰值滞后时间随着试样渗透系数的减小和压缩指数的增大而增大;渗透系数的影响比压缩指数更为显著。Time lag of pore pressure often occurs during oedometer consolidation of saturated clays.After applying loading,the pore pressure measured at the base of specimens increases up to the maximum and then decreases with the increase in consolidation time.The previous studies have concluded that the stiffness of the standpipe piezometers is not enough to resist the applied loading,resulting in a non-negligible deformation of pore pressure gauge chamber.Accordingly,the time lag of pore pressure is attributed to the effects of stiffness on the pore pressure measurement system.In this study,the role of stiffness of pore pressure measurement system in pore pressure time lag behaviour is investigated,based on the existing theories.It is found that the diaphragm piezometer currently used for measuring pore pressure has a large stiffness enough to resist the applied loading.Consequently,the deformation of pore pressure gauge chamber induced by the applied loading can be negligible.The test results available on the pore pressure behaviour under undrained conditions using the triaxial testing apparatus indicate that the pore pressure reaches the order of the applied loading within a very short consolidation time of a few minutes.Such a result is consistent with that from the theoretical analysis.On the other hand,when the oedometer consolidation apparatus is adopted,the top boundary condition of the specimen is freely drained during applying loadings.That is,consolidation occurs at the top layer of the specimen before the hydraulic gradient induced by the applied loadings is uniformly distributed on the specimen.The difference in the measurements of pore pressure between the triaxial and the oedometer consolidation tests is most probably attributed to the difference in the boundary drainage conditions when applying loadings.The time lag of pore pressure at the base of the specimen during oedometer consolidation is caused by the dissipation of pore pressure from the top boundary.The consolidation time responsible for the maximu

关 键 词：饱和黏土 一维固结试验 孔压滞后 渗透系数 压缩指数 

分 类 号：TU43[建筑科学—岩土工程]