The Strength and Deformational Behaviour of a Cohesionless Soil Under Generalised Stress Conditions

  • S Dyson

Student thesis: Doctoral ThesisDoctor of Philosophy


Predictions of the stresses and displacements induced within a soil
mass by interaction with an engineering structure are made, at present, with
only a limited knowledge of the deformational behaviour of soils under generalised stress conditions, The majority of routine testing and laboratory
research investigations are performed on cylindrical soil specimens in the
conventional triaxial apparatus, which is limited to imposing axially-symmetrical
stress conditions. In very few field problems are such conditions
strictly relevant. Many problems approximate more closely to plane strain,
and recent progress has been made in investigating the behaviour of cuboidal
specimens constrained from deformation in one of the principal directions.
However, the experimental difficulties are increased, and controversies
remain regarding the influence exerted by the apparatus on the soil behaviour.

The general field condition is one in which the stresses and strains
are different in each of their three principal directions at a point. Very
few satisfactory attempts have been made to overcome the complex problem of
testing elements of soil under similar conditions.

The design and development of a new apparatus described which allows
generalised stress or strain conditions to be applied to cuboidal specimens.
The methods used to apply the three boundary principal stresses ensure a
high degree of stress, uniformity, and suitable lubrication encourages uniform
strains, Comparisons between the results of tests carried out under
simple stress conditions, on specimens of the same sand, in this and in more
conventional apparatus, indicate negligible apparatus interference. A
further series of tests in plane strain shows that the deformational behaviour
of loose specimens is similar to that observed in triaxial compression,
For dense specimens, however, considerable strength increases result
from the restriction imposed on strains. The results of generalised stress
tests suggest that the intermediate principal stress is of most significance
when its magnitude is less than that observed at failure in plane strain.
Date of Award1970
Original languageEnglish


  • strength
  • cohesionless
  • stress
  • conditions

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