关于举行澳大利亚新南威尔士大学卢锡璋学术报告会的通知

发布时间： 2012-05-31

题目：软粘土地基堤防长期特性研究：数值预测与长系列现场监测数据对比分析

Long term behaviour of an embankment on soft clay: Prediction versus years of field monitoring

报告人：卢锡璋教授

时间：2012年6月4日下午3：30-4:30

地点：交通大楼604会议室

欢迎广大师生参加

土木与交通学院

二〇一二年五月三十一日

报告人简介：

卢锡璋教授在香港大学获得本科学位，在新南威尔士大学获得博士学位。在投身学术界之前，卢教授在工业界工作多年，曾参与多项大型基建项目。卢教授科研领域广泛，从土基本特性到加筋土结构均有丰富科研经验。卢教授曾以一篇有关非线性土-结构共同作用的文章获得Thomas Telford 奖。卢教授是国际土力学与岩土工程协会TC9（加筋土分会）成员、TC39（海岸防灾减灾分会）核心成员以及国际防灾联合小组的常务理事。在作为一个活跃的科研工作者的同时，卢教授还与工业界保持紧密联系，在澳大利亚与香港地区参与多项高水平建设项目，致力于将学术研究与专业工程紧密结合。

S.R. Lo got his Bachelor degree from HKU and his PhD from UNSW. He spent many years with industry, working on a number milestone projects, before taking up an academic career. Dr Lo’s research interest spans from basic soil behaviour to reinforced soil structures. He was awarded the Thomas Telford Price for his paper on non-linear ground structure interaction. Dr Lo was a member of TC-9 (reinforced soil), a core member of TC-39 (coastal disaster mitigation) and an executive member of JWG. In addition to being an active researcher, he maintains closed linkages with industry and has contributed to a number of high profile projects in Australia and Hong Kong. What is particularly closed to his heart is bridging academic research and professional engineering.

报告内容摘要：

进行现场监测试验的堤防高约5.5米，修建于软粘土地基上，地基含水率介于72%~99%之间。该地基采用预制垂直排水板（PVD）进行固结处理，同时堤防采用轻质填料修建。设计研究贯穿于施工前与施工过程中。一系列监测设备安装于堤防（以及地基）上，并进行了长期的监测。其中，超孔隙水压监测、土压力监测以及基底土工格栅拉力监测持续了约400天，测斜监测持续了数年，沉降监测则长达9年。

单元分析建立在改良剑桥模型与水动力学模型耦合的基础上，并配合一系列保守假定。分析中涉及的一切力学参数均由室内试验确定。值得注意的是，虽然本次分析采用了保守假定，但是堤防中轴沉降量的计算值，在三年后开始逐渐低于实测值。对此，唯一似乎合理的解释是地基产生了显著的次固结沉降（SC）。根据室内试验研究，次固结沉降在对数时间轴上为非线性，且与应力状态相关。为了在耦合有限元模型中考虑次固结沉降的影响，须将其作为徐变量在弹粘塑性模型（EVP）中加以模拟。徐变系数方程则根据室内长期固结试验结果而建立。在考虑次固结影响的新模型上对堤防进行重新分析。结果显示，新模型预测沉降值与9年长系列沉降观测值相比，要么接近，要么略大。其余现场观测结果，包括水平位移，孔隙水压（pwp）以及土工格栅拉力亦同时与模型预测值作出比较。

Abstract:

A wide embankment of ~5.5m height was constructed over soft clay with water content in the range of 72 to 99 %. The foundation soil was improved with Prefabricated Vertical Drains (PVD) and light weight fill was used. A series of design studies was conducted before and during construction. The embankment (and foundation soil) were instrumented and monitored over a long period, ~400 days for excess pore water pressure, earth pressure and basal geogrid tension, several years for inclinometers and 9 years for settlement profiles.

A series of unit cell analyses based on the modified Cam-Clay model and hydro-mechanical coupling were conducted with conservative assumptions. All mechanical soil parameters used in the analytical studies were determined by laboratory testing. It is noted that the analysis was conducted with conservative idealizations but the computed settlement, after 3 years, is less than that observed settlement in the central zone of the embankment. The only plausible explanation was attributed to the significant secondary consolidation (SC), which was found to be, in lab studies, non-linear with log-time and stress state dependent. To enable SC to be embedded into a coupled FEA, SC was modelled as creep with an EVP model. A new creep coefficient function was developed to capture the long duration oedometer test results. The complete embankment was then re-analysed. The predicted settlement profile over the 9 years period was either close to or slightly higher than observed. Comparisons were also made for the lateral displacement profile, pore water pressure (pwp) and geogrid tension.