Coupling effect of water immersion and dynamic loading on accumulative strain and pore structure of foamed concrete

As a new type of high-speed railway subgrade filler, the deformation performance of foamed concrete under longterm traffic loading requires further research. In addition, the potential adverse effects caused by water immersion in actual environments cannot be overlooked. In this paper, a series of dynamic triaxial tests were performed to study the deformation behavior of foamed concrete samples under dry and water immersion conditions, considering the effect of dynamic stress amplitudes and confining pressures. Moreover, scanning electron microscopy was used to capture the microstructure characteristics of the foamed concrete. The pore shape coefficient and fractal dimension were introduced to explain the macroscopic deformation properties. For the dry sample subjected to dynamic loading, its resistance to deformation increases with increasing buried depth. However, the previous water immersion treatment led to the pore structure of the foamed concrete being more vulnerable to damage under subsequent dynamic loading. At this time, the accumulative deformation of the wet samples was greater than that of the dry samples, especially at the top and bottom layers. Notably, as the dynamic stress amplitude exceeded 20 kPa, a rapid growth of the accumulative deformation was observed for the samples. In addition, the pore structure characteristics of the foamed concrete under the excitation of dynamic loading experience significant variation, with the large pores splitting into small pores and the pore diameter decreasing. The pore walls of the large pores ruptured and connected with others, accompanied by an increase in the number of narrow pores. The findings in this paper contribute to a better understanding of the design and maintenance of the foamed concrete subgrade.