Damping ratio evolution of saturated Ningbo clays under cyclic confining pressure

The mechanical behaviours of soft clays under cyclic loading are not only related to loading parameters, but also the physical indices of soft clay. One-way cyclic triaxial tests with constant confining pressure were adopted, however, the stress field induced by traffic loads includes cyclic confining pressure and cyclic deviator stress. So far, the damping ratio evolution of soft clays under traffic loading has rarely been studied. To establish an empirical formula for the damping ratio, a series of cyclic triaxial tests with variable confining pressure were conducted on saturated Ningbo clay. The effects of some factors, such as cyclic stress ratio (CSR), effective consolidated confining pressure, loading frequency, and cyclic confining pressure were investigated. The trend of the relationship between the normalised damping ratio and accumulated axial strain is similar under different conditions, in which the normalised damping ratio degrades with the increase of accumulated axial strain. Be -sides, the damping ratio increases with an increase of CSR and effective consolidated confining pressure, while decreases with increasing loading frequency and cyclic confining pressure. Based on that, an empirical formula relating to CSR, effective consolidated effective confining pressure, loading frequency, and cyclic confining pressure is established to predict damping ratio under cyclic loading. A comparison between predicted results and measured data shows that the empirical formula cannot only characterise the trend of the damping ratio versus accumulated axial strain curve, but also provides a good prediction of the damping ratio.

Automated summary

This study investigated the damping ratio evolution of soft clays under traffic loading through a series of cyclic triaxial tests. It was found that the normalized damping ratio decreases with the increase of accumulated axial strain, while increases with an increase of cyclic stress ratio and effective consolidated confining pressure. Loading frequency and cyclic confining pressure were found to decrease the damping ratio. An empirical formula considering CSR, effective consolidated effective confining pressure, loading frequency, and cyclic confining pressure was established to predict damping ratio under cyclic loading.