Plenary Lecture

Plenary Lecture

Design of Foundation Structures using the
Mechanics of Unsaturated Soils

Professor Sai K. Vanapalli
Co-author: Won T. Oh
Civil Engineering Department
University of Ottawa, ON

Abstract: Bearing capacity and settlement behavior are two key properties required in the design of foundations. In conventional geotechnical engineering practice, the bearing capacity of saturated soils are typically analyzed using two different approaches; effective and total stress approach using Terzaghi (1943) and Skempton (1948) bearing capacity theory, respectively. In most cases, the bearing capacity of unsaturated soils is also interpreted using the effective stress approach regardless of the type of soil (i.e., coarse- and fine-grained soils), which is not rational. In addition, the conventional theory for the estimation of immediate settlement using the modulus of elasticity, E of saturated soils cannot be extended for unsaturated soils or compacted soils as they do not attain saturated condition during their service period.
The mechanics of saturated soils are however employed in practice due to the following two reasons: (i) extending the approach used for saturated soils to soils that are in a state of unsaturated condition provides conservative analysis and (ii) there is no simple framework to design geotechnical structures using the mechanics of unsaturated soils.
In this paper, simple models are proposed for predicting both the bearing capacity and the modulus of elasticity of unsaturated soils for different types of soils. These models use the Soil-Water Characteristic Curve (i.e. SWCC), which is defined as the relationship between the water content and soil suction, as a tool along with saturated soil properties (i.e., bearing capacity and modulus of elasticity under saturated condition). Details of how the proposed models can be implemented into geotechnical engineering practice and differences associated with the proposed methods and conventional methods are also discussed with practical examples. Lastly, a method to estimate matric suction of as-compacted soils using a pocket penetrometer is described.
The simple techniques proposed in this paper should encourage the geotechnical engineers to implement the mechanics of unsaturated soils in practice.

Brief Biography of the Speaker:
Dr. Vanapalli is a Professor and Graduate Program Coordinator of the Civil Engineering Department, University of Ottawa. Dr. Vanapalli received his PhD from the University of Saskatchewan in 1994. Since then, he has been actively involved with research activities related to mechanics of unsaturated soils including expansive soils. The focus of his research was primarily extended towards studying the mechanical behavior of unsaturated soils and proposing simple techniques for the estimation of the soil-water characteristic curve, bearing capacity and settlement behavior of unsaturated soils.
Dr. Vanapalli has authored or co-authored over 120 research publications in peer reviewed journals and conference proceedings, a book chapter and three state-of-the-art reports. He has also delivered three Keynote addresses at the International Soil Mechanics Conferences on topics related to the mechanics of unsaturated soils.
Dr. Vanapalli has been a Co-Chair for the Diamond Jubilee Canadian Geotechnical Conference held in Ottawa, Canada in 2007, Co-Chair of the 12 IACMAG, Goa, India in 2008 and advisor for the 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering Conference to be held in Toronto, Canada in 2011. He has served as Technical or Scientific Committee Member for several national and international conferences. He has reviewed publications for several technical journals that include Geotechnique, Canadian Geotechnical Journal, Journal of Geotechnical and Geo-environmental Engineering, American Society of Testing Materials, Soil Science Society of America and Transportation Research Board.
Dr. Vanapalli has been nominated by the Civil Engineering Department and the Faculty of Engineering, University of Ottawa for the OCUFA Teaching Excellence Award (2007); University of Ottawa Award for Excellence in Teaching (2006); Civil Engineering Department for the John V. Marsh Teaching Excellence Award (2006). In addition, fifteen students of Dr. Vanapalli over the last 8 years have received national honors by the Canadian Geotechnical Society and other organizations for submitting best undergraduate (individual and group thesis) and graduate student papers.
Dr. Vanapalli is a volunteer for several activities of Canadian Geotechnical Society, Professional Engineers of Ontario and TC6 of the International Society of Soil Mechanics and Geotechnical Engineering which is responsible for promoting cooperation and exchange of knowledge in the area of mechanics of unsaturated Soils.

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