Newcastle Chapter

41st Karl Terzaghi Lecture: Unsaturated Soil Mechanics in Engineering Practice

Professor Del Fredlund

Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows:

  1. The need to understand the fundamental, theoretical behaviour of an unsaturated soil;
  2. the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships;
  3. the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods;
  4. the determination of indirect techniques for the estimation of unsaturated soil property functions, and
  5. in situ and laboratory devices for the measurement of a wide range of soil suctions.

This presentation outlines the nature of each of the previous challenges and describes the solutions that have emerged from research studies. breakthroughs in the in situ and laboratory measurement of soil suction are allowing unsaturated soil theories and formulations to be verified through use of the ‘observational method’.

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