Accumulated plastic deformation behavior of granite residual soil under cyclic loading considering the influence of initial unloading

Abstract

In engineering practice, excavation near existing transport infrastructures is inevitable due to space limitations. The effect of excavation-induced unloading on soil response to subsequent traffic loads is well worth studying, yet previous studies mainly focused on the effect of initial loading (rather than unloading). Undrained cyclic triaxial tests on undisturbed granite residual soil were conducted to study the effect of initial unloading on accumulated plastic deformation behavior. The unloading effect was achieved by reducing cell pressure before cyclic loading. The influences of amplitude of cyclic stress (σd) and degree of initial unloading (Di) on accumulated plastic deformation behavior were investigated. The results indicate that accumulating mode of axial plastic strain changes gradually from “stabilization” to “failure” as σd increases. Initial unloading has a significant promoting effect on the development of accumulated axial strain, and the promoting effect heightens with the increase in Di. Besides, a comparative study was conducted by employing another two stress paths, and it is found that initial shearing stress path makes a considerable difference to accumulated plastic deformation behavior. Under the same Di and σd, soil specimen experiencing initial unloading shows a poorer capacity for resisting cyclic deformation, compared to the other initial shearing stress paths. An empirical model was developed for predicting accumulated axial strain under the condition that initial unloading occurs prior to cyclic loading, considering the effects of amplitude of cyclic stress and degree of initial unloading.