Long-term behavior of clay-fouled unbound granular materials subjected to cyclic loadings with different frequencies

Experimental studies were conducted to investigate the engineering geological characteristics of clay-fouled unbound granular materials (UGMs) under different-frequency cyclic loadings. The computed tomography (CT) scan was firstly conducted to examine the inner structure of UGMs with various fines contents; then a series of drained large-scale tri-axial tests were conducted on the clay-fouled UGMs under cyclic loadings with various frequencies (f = 0.2 Hz, 1 Hz and 3 Hz). The combined effects of the fines content and the cyclic loading frequency on the excess pore water pressure, accumulated strain and resilient modulus were analyzed. Test results showed that the dominant effects of fines on the UGMs transited from the lubrication, densification to suffocation as the fines content increased. The lubrication effect led to the increase of the accumulated axial and volumetric strain; the densification effects reduced the accumulated strain; and the suffocation effects resulted in the accumulation of excess pore water pressure and thus rapid deterioration of UGMs. The transition point of these effects were closely related to the loading frequency and loading amplitude. The drainage conditions of clay-fouled UGMs transited from full drainage to partially drainage as the fines content, loading amplitude and frequency increased.