June 22 - 25, 2025
Delta Hotel and Conference Centre
Ottawa, Ontario, Canada
Biography
Ning Lu has been working on fundamental concepts of effective stress (suction stress) and soil water potential (matric suction) in the past two decades. He has unified soil’s effective stress under both saturated and unsaturated conditions, moving beyond the classical Terzaghi’s and Bishop’s effective stress representations. For his work on unification of effective stress, he received American Society of Civil Engineers (ASCE) Norman Medal twice; first in 2007 for conceptualization of suction stress, and second in 2021 for formulation of a practical closed form effective stress equation. He further defines a general thermodynamics-based pore water potential in soil under both saturated and unsaturated conditions. In the past two decades, he has formulated a new paradigm for slope stability under variably saturated conditions, which has been bestowed by ASCE for its 2017 R. B. Peck Award, and M. A. Biot Medal. He is the recipient of 2023 ASCE Karl Terzaghi Award. He is a distinguished member of ASCE, a fellow of Geological Society of America, and Engineering Mechanics Institute. He has published two widely used textbooks: Unsaturated Soil Mechanics (Lu and Likos, 2004, John Wiley and Sons), and Hillslope Hydrology and Stability (Lu and Godt, 2013, Cambridge University Press).
Abstract
This study explores the behavior of pavements built on expansive soils in extreme climates. Our main objective is to understand the intricate interplay among extreme weather events prompted by climate change, pavement structures, and soil characteristics. Pavements are susceptible to damage due to the differential settlement caused by expansive soils. Climate change significantly influences the settlement dynamics of these expansive soils, which are highly responsive to moisture content fluctuations, resulting in swelling and shrinkage. Alterations in precipitation patterns intensify this sensitivity, coupled with unprecedented occurrences of extreme weather phenomena like droughts and heavy rainfall. Consequently, such climatic shifts amplify crack initiation and development, impacting infiltration patterns within pavements. Considering that pavements are typically designed with a finite lifespan, overlooking the complexities of their interaction with expansive soil and climate change can trigger serviceability failures. To address this concern, we conducted 3D finite element modeling of pavements using ABAQUS, incorporating the behavior of expansive soils in both saturated and unsaturated conditions. We developed a subroutine to define the constitutive relationship of these soils and conducted a coupled hydro-mechanical analysis, also considering the effect of temperature on deformation. Historical weather data, including rainfall, temperature, and humidity, were collected from federal agencies over the past two decades. Time series analysis was employed to forecast future weather patterns, which were then integrated into the model through the definition of flux boundary conditions. Our findings underscore the vulnerability of pavements built on expansive soils to climate change-induced events. Neglecting these factors may lead to an overestimation of the life cycle of such structures, particularly critical in coastal regions abundant in expansive soils susceptible to frequent coastal flooding. This research aids in anticipating the long-term performance of pavements on expansive soils, providing valuable guidance for engineering methodologies and pavement design amid a swiftly evolving environment.