Research On The Liquefaction Resistance And Characteristics Of Saturated Loess Improved By Fly Ash

For the purpose of economic and environmental improvement of the seismic liquefaction damage on saturated loess foundation,the dynamic constitutive relation of saturated fly ash improved loess is discussed,and the variation characteristics of its dynamic stress,dynamic strain,dynamic pore water pressure with vibration times are analyzed through dynamic triaxial tests on the improved loess with different fly ash dosages.The relationship among the initial dynamic elastic modulus,maximum dynamic stress amplitude,and damping ratio of the saturated modified loess with different fly ash dosages were compared.Then the influence law of fly ash dosage on the liquefaction stress ratio,dynamic residual deformation,and dynamic pore water pressure of the improved loess is analyzed.Combined with the micro structural test and XRD test results,the physical-chemical anti-liquefaction mechanism of saturated loess improved by fly ash is also discussed in this study.The results show that the dynamic constitutive relation of the saturated modified loess with different fly ash dosages obeys the hyperbolic model.The maximum initial dynamic elastic modulus appears when the dosage of fly ash is 20%.With the increase of fly ash dosage,the maximum dynamic stress amplitude increases,but the damping ratio decreases correspondingly.When the fly ash content is more than 25%,the change of dynamic elastic modulus and damping ratio of saturated modified loess with the increase of dynamic strain becomes very slow.The dosage of fly ash has significant influence on the liquefaction stress ratio,dynamic strain,and dynamic pore water pressure of the improved loess.With the increase in the dosages of fly ash,the liquefaction stress ratio of the improved loess continues to grow;when the dosage reaches to 15%,the liquefaction stress ratio will obviously increase if the dosage continues to increase.The dynamic strain and dynamic pore water pressure of the improved loess increase with the decrease of fly ash dosage;after the dosage reaches to 25%,the saturated improved loess will not be liquefied.The microscopic test results by using scanning electron microscope(SEM)indicate that the physical-chemical anti-liquefaction mechanism of saturated loess improved by fly ash mainly includes the hydration process of fly ash,filling effect of colloid product and particles,and adsorption of free water by fly ash.