美国科罗拉多矿业大学Ning Lu(卢宁)教授将于11月19日来我院作学术报告。
报告题目：A unified effective stress for variably saturated soils
时间：2012年12月19日（周三）下午2:30-4:30
地点:土木建筑工程学院力学楼四楼报告厅
1. Ning Lu教授简介
Ning Lu 1991年毕业于美国约翰霍普金斯大学获土木工程博士学位，现任美国科罗拉多矿业大学土木与环境工程学院教授，美国科罗拉多矿业大学与美国地质调查局联合岩土工程实验室主任，国际著名的非饱和土力学和水力学专家，研究方向为非饱和土力学，渗流-应力耦合作用浅层滑坡的监测、分析与预测。
他首次提出了非饱和土的“吸应力”、“吸应力曲线”概念;他提出的“统一有效应力原理”，将非饱和土与传统的饱和土力学有机地结合在一起，是非饱和土力学领域的标志性成果。他主持研制的“土壤水分特征曲线与渗透系数实验室快速测量仪器(TRIM系统)”，使得非饱和细粒土脱湿、吸湿参数的测量时间大大缩短，促进了非饱和土力学的发展。他将非饱和土力学理论运用于浅层滑坡的监测与预测中，取得了非常好的效果。
他是多个国际岩土顶尖学术期刊如Jornal of Geotechnical and Geoenvironmental Engineering、Jornal of Georisk等编委，美国土木工程师学会(ASCE)资深会员、美国岩土学会会员、美国地球物理学会永久会员，美国交通研究委员会会员、粘土矿物学会会员。
他于2007年获得获美国ASCE 历史最悠久、级别最高的科技类奖励-诺曼奖章(Normal Medal)，2010年获得美国著名的J. James Croes Medal奖。
2.报告内容简介
A unified effective stress concept based on the suction stress characteristic curve (SSCC) for variably-saturated soil is discussed. Particle-scale equilibrium analyses are employed to distinguish three types of interparticle forces: (1) active forces transmitted through the soil grains (Terzaghi’s); (2) active forces at or near interparticle contacts (physicochemical); and (3) passive, or counterbalancing, forces at or near interparticle contacts (Born’s and steric). It is proposed that the second type of forces, which includes physicochemical forces, cementation forces, surface tension, and the force arising from negative pore-water pressure, can be conceptually combined into a macroscopic stress called suction stress. Suction stress is an internal stress that is completely balanced by Born’s repulsion and is independent of the external or total stress. Suction stress characteristically depends on degree of saturation, or soil suction, thus paralleling well-established concept of the soil–water characteristic curve in soil physics. The existence and behavior of the SSCC are experimentally validated by considering unsaturated shear strength and volumetric behavior data for a variety of soil types in the literature. The characteristics and practical determination of the SSCC are demonstrated. A closed form equation for predicting the suction stress for all soils is found. A case study of shallow landslide initiation induced by heavy rainfalls in Seattle area illustrates that variation in suction stress can well reconcile the spatial and temporal characteristics of the event. Suction stress provides a potentially simple and practical means to describe the state of stress in unsaturated soil.
