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Unsaturated Soil Mechanics

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About This Course

This course is based on notes presented in the book “Unsaturated Soil Mechanics in Engineering practice” published in 2012 by prof. Delwyn G. Fredlund. The objective of the course is to introduce unsaturated soil mechanics within the framework of classical soil mechanics by incorporating soil suction. It includes 6 Chapters, with titles and summaries as follows:

Chapter 1 - Introduction to Unsaturated Soil Mechanics (41 min). The first lecture introduces unsaturated soils by illustrated practical problems. The link between field and laboratory conditions is established by the “Soil-Water Characterization Curve” (SWCC) also called the soil retention curve.

Chapter 2 - State Variables and their Measurement (34 min). The second lecture presents the state variables by which the transition from the saturated soil condition to the unsaturated soil condition can be described, in particular the matric suction as the difference between pore-air and pore-water pressures. The measurement of soil suction helps in linking the state of stresses in field and laboratory conditions.

Chapter 3 - The Soil-Water Characteristic Curve, SWCC (50 min). The third lecture details the determination of SWCC in providing information about the amount of water and the energy state in water phase. The experimental measurement of the SWCC is explained and inherent parameters depending on the type of soil are introduced.

Chapter 4 - Seepage through Unsaturated Soils (51 min). The fourth lecture is dedicated to the theory and solution dealing with water flow problems in unsaturated soil. Focus is made on the measurement of unsaturated coefficient of permeability function for design purposes. Steady state and unsteady (transient) state methodologies are explained for the calculation of unsaturated coefficients of permeability. Selected water flow case studies are shown.

Chapter 5 - Shear Strength of Unsaturated Soils (45 min). Lecture five addresses the determination of shear strength of unsaturated soils. The latter is described by two independent state variables among which soil suction contributes to the cohesive component of soil. Measurement of shear strength of unsaturated soils is conducted by the conventional shear box and triaxial equipment needing modifications to allow air-entry in tested specimens. Using the shear strength parameters of unsaturated soil, current soil mechanics applications: e.g. earth pressures, bearing capacity and slope stability of foundations are formulated.

Chapter 6 - Volume Change & Deformation of Unsaturated Soils (39 min). In the sixth lecture, the theory with related solution of stress deformation problems is investigated. The main objective is to establish the relation between stress state variables and deformation strain state variables for unsaturated soils. In this process, the use of SWCC enables the assessment of the behaviour of unsaturated soil.


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Delwyn G. Fredlund

Dr. Delwyn G. Fredlund, O.C., P. Eng.

Delwyn G. Fredlund has spent over 40 years conducting research into the behavior of unsaturated and expansive soils. Most of his career was spent at the University of Saskatchewan, Saskatoon, where he organized the Unsaturated Soils Group for research into all aspects of unsaturated soils behavior. Presently Del heads the Golder Unsaturated Soils Group linking the worldwide offices of Golder Associates. His research studies have involved all areas of unsaturated soil behavior; ranging from the flow of water and air through unsaturated soils to the shear strength and volume change of unsaturated soils.

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  1. Subjects

    Soil Mechanics, Groundwater Flow & Seepage, Shear Strength of Ground Materials, Settlements
  2. Course Number

  3. Course Launched

  4. Estimated Effort

    04 hours 20 minutes


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