Permanent deformation characteristics of expandable foam grout under cyclic loading

Expandable foam grout (EFG) is a novel flowable cementitious material for filling underground cavities. This study evaluates the permanent deformation behavior of EFGs under cyclic loading. EFG consists of cement, water, and admixture. EFG samples are mixed at a water–cement ratio of 100% and an admixture content of 5.6% to prepare cylindrical specimens cured at four different times. Sinusoidal loads with different maximum axial stresses are vertically applied. The permanent deformation of EFG increases with the number of load cycles but at a decreasing rate. A power function model is used to represent the relation between the permanent deformation and number of load cycles. The model generally matches the measured values but can overestimate the deformation at specific strain levels and curing times. The accumulated permanent deformation increases with the applied axial stress and decreases with longer curing times. The final permanent deformation decreases with the increase in the curing time, and the rate of final permanent deformation also decreases. A linear relationship is found between the final permanent deformation and unconfined compressive strength. These findings can help estimate the damage and durability of underground structures backfilled with highly flowable and expandable cementitious materials under cyclic loads.