土の強度について

土のレオロジ的構造 (IV)

抄録

Coulomb-Mohr's yield condition (IV-theory) had been abandoned in former days, but in the field of soil mechanics it has been considered to be valied up to the present. To-day's yield condition is based on Mises-Hencky's theory (V-theory). This theory was generalized by Schleicher-Mises et al, as the equation σ_oct= f (σ_oct) which can be applied to the plain twodimensional case, where σ2= σ8, to get the same result as shown by Rendulic (1937). From these points the authors obtained the yield condition poet (σ1, σ2, σ3) = f (σ_oct).
On the basis of IV-theory the yield condition is determine only by the principal shear stress σf. However, from the view point of V-theory, it is to be put that σf is proportional to τ_oct, and τ(= (τ1+ τ3)/ 2) is nearly equal to the diagonal sum of the stress tensor (=τ1+τ2+τ3=τ_oct). In this way coulomb-Mohr's yield condition can be approximately reduced to Mises-Hencky's condition.
In the state of the stress tensor, r_oct is lowered according to the decrease of the chemical potential μ of the soil water that is due to σ_oct. On the other hand, σ_oct is made higher by the compacting action of τ_oct. If the soil structure is massive and saturated with water, the yield value τf can be determined only the pF value of the soil water. Here, log τf is nearly equal to pF. Dilatancy in the case of over-consolidated soil is due to the closest parking of the soil colloid in the gel-state, where micelle water is thinner than that of normal consolidated soil-gel and comes to have the higher pF value.