Rigidity, Yield Value and pF in Soil Engineering

Relation between Engineering Properties of sil and pF (I)

Abstract

I. Many of the engineering properties of soil are affected by its wetness. The consistency is not necessarily dependent on water content, but on a state of water in soil. If the free energy of water in soil particle is known, the consistency of soil would have a more useful sence in engineering.
Yield value and rigidity are discussed in this paper by corelating them with pF as one of the energy component interacting between water and particle in soil water system.
II. Samples (subsoil): Volcanic ash soil, the Kita-kanto Loam and the Minami-kanto Loam. Non-volcanic ash soil, Gyoda (clay, alluvial), etc.
III. Measurement: i) In case the moisture content is larger than Liquid Limit (LL), the yield value θ of soil paste is measured by a co-axial cylindrical viscometer and rigidity modulus G by a forced oscillation viscometer. ii) In case the moisture content is less than LL, θ and G are obtained by the torsion method. iii) pF is measured by different methods in accordance with range of pF.
pF 1-2.5: Saction method pF 2.5-4.2: Centrifugal method
pF 4.2: Vapour pressure method
IV. The results is summarrized as follows.
1) The rigidity of soil is greater than the yield value in wide range of pF. At low pF, G is nearly equal θ, but at high pF, G≥θ. This relation is reverse when the soil is dilatant (G is smaller than θ).
2) The relation between rigidity and water content larger than LL is as follows:
G=G_3t exp A(φ-φ₀)
Where A is a constant in a range of Bingham and plasticity.φ is the volume concentration of soil, φ0 is that of sedimentation volume. G=G_st when φ=φ0
3) log θ is approximately equal to pF if thixotropy constant is taken into consideration. a·logφ+logk =pF
α≅ 1 at plastic soil, and k is a thixotropy constant.
4) The following relation is obtained in case of a massive structure soil such as Gyoda clay and sub-soil of volcanic ash soil.That is, logθ=1.5 at LL and logθ=3.0 at PL (Plastic Limit), where θ is expressed as water head pressure in cm.