土の力学的転移点

土のレオロジ的構造 (III)

抄録

The soil-water systems were classified on the basis of the pF value by SUDO et al (1, 2) and a few transition points for mechanical properties were determined.
In this paper we studied on these transition points from the viewpoint of the behavior of soil as the Burgers model (13, 6) and considered on the significance of liquid limit and on the mechanism of softening or hardening of soil.
On the basis of the pF scale, transition points are determined as follows:
(1) At pF=-1.5 (State of sediment in water) stands second-order transition point in relation to yield value θ. viscosity η and elasticity G.
(2) At pF=1.5 (state of liquid limit) stands the first-order transition point in relation to θ, η, G.
On the L. L. test in case of ω>ωL, Bingham flow occurs. In case of ω<ωL, flow according to ηM-element on the Burgers model occurs, then hardening (Fig. 5) is observed.
Softening is caused by the mobilization of pore water due to the breakdown of the structure of kinetic units in case of ω>ωL, and the plastic viscosity η_ρl is lowered. In case of ω<ωL, softening occurs in the only process in which the stress progressively increased.
The process of hardening is concerned with non-equilibrium i. e. rate process in the soil-water system. If pF_s of water inside kinetic units is higher than pF_ω of pore water or bulk water, pore (or bulk) water will be immobilized with the increase of hydration, and hardening occurs.
The thixotropy (softening) and hardening of soils were, for the first time, explained theoretically in this paper, according to both the classification of the states of the soil-water system and the introduction of the concept of transition points.