2.2.1 Dependency of soil behaviour on stress level and stress history

As mentioned in the previous section, behaviours of soil materials are largely governed by confining pressure which is mainly generated by self-weight of a soil mass.

• Stress-strain relationship

  Generally, soils show non-linearity over the wide range of strain in its stress-strain relationship. Especially, a variation of volumetric strain, which is caused by a dilatancy during shearing, highly depends on stress level. A soil contracting during the shear in prototype might expand in a low stress level, such as a test with a small model under Earth's gravity.

  

• Compressibility

  A compressibility of clay varies beyond the maximum previous stress. On the normal consolidation line, void ratio is thought to be almost proportional to logarithm of its confining stress. Assuming self-weight consolidation in a 1/n scale model with saturated clay layer under n G field, water content at the depth, which corresponds to the prototype, of the model ground is the same as that of the prototype. However if it is done under Earth's gravity field, it could simulate only the 1/n upper part of the prototype.

  

• Strength

  A Strength of a confined undrained/drained saturated clay is conspicuously affected by its stress history. Even if strength of a cohesion-less material is not always proportional to its confining stress, especially a crushable material shows remarkable non-linearity under high stress level.

  
  Fig.3 Effect of stress history on strength (Takada and Kusakababe 1987)

Fukushima, S. and Tatsuoka, F. (1984) : Strength and deformation characteristics of saturated sand at extremely low pressures, Soils and Foundations, Vol. 24, No. 4, pp. 30-48.

Takada, N. and Kusakabe, O. (1987) : Centrifuge model tests, 3. Principle, Tsuchi-to-kiso,Vol. 35, No. 12, pp. 89-94 (in Japanese).