The development of deformation and excess pore water pressure of clay under intermittent cyclic loading

During the passage of a train, the underlying soil experiences both a cyclic and an intermittent loading phase. During the cyclic loading period, both deviator stress and confining pressure varies periodically. The variation in soil response with loading frequency is observed. During the intermittent period, the drainage conditions affect the mechanical behaviours of the soil. Cyclic triaxial tests with intermittent cyclic loading are performed. The impacts of cyclic confining pressure, loading frequency and drainage conditions during the intermittent period are investigated. Results show that the accumulated axial strains during cyclic loading periods are greater and decrease as both cyclic confining pressure and loading frequency increase in the first loading stage, while lower strains are obtained in subsequent loading stages. The attenuation of strain increments varies with cyclic confining pressure. However, the attenuation of strain increments is similar across different loading frequencies. Moreover, the strain increment attenuates as a power function, with the attenuation under undrained conditions reaching up to 93.51%, higher than that under partially drainage conditions. Meanwhile, the excess pore water pressure decreases with increasing cyclic confining pressure and loading frequency, remaining below 25 kPa after the first loading stage. An empirical model is proposed for predicting accumulated axial strain under intermittent cyclic loading.