Cα/Cc Concept Applied to Compression of Peat

Eight long-term multiple-stage-loading oedometer tests were performed on a fibrous peat from Middleton, Wisconsin. Both conventional-size and large specimens were treated with pore-pressure measurement. Load-increment duration and load-increment ratio were additional variables of the testing program. Time-settlement curves show that the coefficient of secondary compression ($C_{\alpha }$) is not constant but increases in time under constant effective stress. Plots of $C_{\alpha }$ versus compression index ($C_c$) indicate that, for this peat, a poor linear relationship exists between $C_{\alpha }$ and $C_c$, and this relationship worsens if tertiary compression points are included. Plots of $C_{\alpha }/C_c$ versus void ratio show significant scatter but indicate that, in general, the $C_{\alpha }/C_c$ ratio increases with decreasing void ratio. Load-increment ratio and sample disturbance are significant factors affecting the $C_{\alpha }$ versus $C_c$ relationship. The fact that inorganic soils do not exhibit exaggerated creep effects or tertiary compression may explain, in part, the success of the $C_{\alpha }/C_c$ concept for clays.