Experimental Investigation of Water-Retaining and Mechanical Behaviors of Unbound Granular Materials under Infiltration

Abstract

Unbound granular materials (UGM) in permeable pavement will experience large numbers of infiltration during their service-life. The frequently changed moisture not only affects the cooling effect of permeable pavement, but also influences the mechanical behaviors of UGM. However, evidence is lacking to state the influence of infiltration on the behaviors of UGM, which is commonly in fully permeable pavement. Considering the influence of infiltration, this study conducted experimental tests to investigate the effect on the water-retaining and bearing capacity of UGM. With the water-retaining tests, the water-retaining rate in the whole structure and at different depths was analyzed under different infiltration numbers and duration. The results showed that the water-retaining rate increased with the extension of the infiltration duration. The infiltration duration had a significant influence on the water-retaining capacity of UGM, while the infiltration number had little. The difference in the water-retaining rate between the top and bottom layers was up to 2.56%. The water-retaining capacity of the integrated structure was hardly affected due to the dissimilarity of the water-retaining rate at different depths. With infiltrations, the fine aggregate in the upside structure migrated downward to the lower structure, resulting in a reduction in water-retaining rate in the upper structure and an increase at the bottom. In addition, the mechanical behaviors were evaluated by the traditional California Bearing Ratio (CBR) and repeated CBR tests under five infiltrations. The first and second infiltration had a significant influence on the CBR of UGM. With two infiltrations, the plastic strain increased by 57.8% via the repeated CBR tests. The resilient strain had an increase by 36.52% and the equivalent modulus decreased by 28.7% with the first infiltration. The first infiltration presented a critical influence on the bearing capacity of UGM and the effect decreased with the increase in the infiltration number. These findings will enrich the behaviors investigation of UGM and promote its application in the fully permeable pavement.