Professor Charles W. W. Ng is a Vice-President of the Hong Kong University of Science and Technology (HKUST). He is also the Dean of HKUST Fok Ying Tung Graduate School, CLP Holdings Professor of Su-stainability and Chair Professor in the Department of Civil and Environmental Engineering at HKUST. Professor Ng is a Fellow of the Royal Academy of Engineering and the immediate Past President of the ISSMGE (2017–2022). Prof. Ng earned his PhD degree from the University of Bristol in 1993. After carrying out postdoctoral research at the University of Cambridge between 1993 and 1995, he returned to Hong Kong and joined HKUST as Assistant Professor in 1995, where he rose through the ranks to become Chair Professor in 2011. A world authority on unsaturated soil mechanics, landslides, debris flows, eco-geotechnical engineering, Professor Ng is Changjiang Scholar (Chair Professorship in Geotechnical Engineering), Fellow of the Hong Kong Aca-demy of Engineering Sciences and Overseas Fellow of Churchill College, the University of Cambridge. He is also Fellow of the Institution of Civil Engineers, ASCE and the Hong Kong Institution of Engineers. Currently, he is an Editor-in-Chief of Canadian Geotechnical Journal and an Editor of Landslides. Professor Ng has published some 400 SCI journal articles with over 20,000 citations and H-index of 76. He has also delivered more than 100 keynotes and state-of-the-art reports across the six continents. He is the main author of three reference books: “A Short Course in Soil-structure Engineering of Deep Foundations, Excavations and Tunnels” published by Thomas Telford in 2004, and “Advanced Unsaturated Soil Mechanics and Engineering” and “Plant-Soil Slope Interaction” by CRC: Taylor & Francis in 2007 and 2019, respectively.

Plenary Lecture

Effects of thermal cycles on soil behaviour: theoretical and experimental studies

Fundamental understanding and proper modelling of soil behaviour under thermal cycles are important and essential for the analysis and design of many emerging infrastructures, such as geothermal structures and embankment-atmosphere interactions under a changing climate. Previous studies of the thermo-mechanical behaviour of soil mainly focus on monotonic loading. This lecture will focus on the cyclic thermo-mechanical behaviour of saturated and unsaturated soils. A new bounding surface constitutive model developed in terms of Bishop’s stress and suction will be introduced. Apart from the loading and bounding surfaces, a memory surface is incorporated in the model to simulate cyclic behaviour of soils. Moreover, a new design equation is proposed to model the state-dependent shear moduli. To verify the new model, suction and temperature-controlled triaxial apparatus equipped with a double-cell total volume measuring system and local strain devices will be introduced. By using the newly developed apparatus, a number of series of tests were conducted, including cyclic heating-cooling tests on saturated and unsaturated soils, and shearing tests at different temperatures and suctions. The measured and predicted results by the new constitutive model will be compared and analysed. The comparisons will focus on the accumulation of cyclic thermal strains and degradation of shear stiffness at various suctions and temperatures. Based on the theoretical and experimental studies, two engineering applications (i.e., floating energy pile foundations and deep excavation in the unsaturated ground) are analysed. Key deformation mechanisms will be revealed and explained and design recommendations will be provided.