Experimental Study On The Steady-State Behavior Of Flyash

The steady state of deformation for any mass of particles is that state in which the mass is continuously deforming at constant volume, constant normal effective stress, constant shear stress, and constant velocity. The steady state of deformation is achieved only after all particle orientation has reached a statistically steady-state condition and after all particle breakage. The steady state strength and the steady state line which are abtained by steady state deformation are the important parameters for estimating the stability of saturated cohesionless soils. Now the behavior of steady state deformation for saturated cohesionless soils is not well known to us yet. Many qustions have no conclusion.Based on some normal behavior tests, such as grain composition, specific gravity and relative density, the large strain static triaxial shear tests were made. The relations bwtween the streas and strains under the different experimental condition were analysised. The steady state strength and the steady state line of flyash and Fujian standard sands were given. The influence of confining pressure and drainage shear condition and initial relative density for flyash in steady-state deformation characteristic were discussed. The steady state of flyash with different paticles was compared. The effect of average grain diameter on the behavior of steady state of flyash was studied. The diference of steady state between flyash and Fujian standard sand under same initial relative density was compared.The strain-controlled static triaxial shear apparatus was used. The initial relative density of the samples for flyash varied from 20%, 30%, 45% to 60%, and the consolidation confining pressure varied with 40, 70, 100, 150, 200, 300, 400, 500kPa alternatively for flyash. The initial relative density of the samples for Fujian standard sand was 20% and 30%, and for confected flyash was 20%. The consolidation confining pressure varied with 30, 40, 50, 70, 100, 150, 200, 300kPa alternatively for Fujian standard sand, and 40, 70, 100, 150kPa for confected flyash. The samples were prepared by dry method. The saturation procedure was that the air was replaced by CO₂ firstly, then was fulfilled by pure water. The rate of shear strain controlled was 0.4mm/min in the CU tests and 0.166mm/min in the CD tests. The lagest axial strain of samples was 35-50%.It was found that the shape and the place of steady state line was not effected by the drainkage conditions, but was effected with the initial relative density. The location of steady state line in the e-kgσ′₃ plane was lower in larger initial relative density. With the samedegree of homogeneity of flyash, the average grain diameter had clearly influence on steady state line. The lower the place of steady state line was, the smaller the average grain diameter.For undrained condition, after the axial strain was developed to some level, if the pore water pressure of a sample was no changed, the effective confined pressure was remained constant during the shear process. The only steady state line in the e-lgcr'^ plane was abtained easilyno matter what the deformation of steady state could be observed in the tests. The steady deformation state for flyash could appear clearly in the CD tests normally.