| Summary: | As commonly used canal system structures, masonry arch aqueducts constitute a significant proportion of Chinese old irrigation infrastructures. Most of these existing aqueducts are well over 50 years old, the deterioration of their constituent materials over time, as well as the development of other defects, significantly affects the mechanical responses of these structures. A deep understanding on the dominant factors that influence the structural safety behaviour of masonry arch aqueducts is essential for determining maintenance and strengthening strategies. Taken the Zhaimen masonry aqueduct in the famous Red Flag Canal as a case study, sensitivity analyses of the influences of mortar aging and loss on the structural performance were carried out. The aqueduct, with unknown geometric dimensions and uncertain physical and mechanical parameters, has defects such as the arch ring detaching from the upper structure and the continuous loss and falling of mortar. The discrete element method (DEM) was employed to analyse the structural behaviour. The results show that the upper structure and the supporting structure are stable under the no bond strength condition. When the mortar is lost locally, the vault position is the most dangerous, followed by the arch shoulder, and then the arch foot part. The mortar loss, manifested as denseness reduction, greatly affects the aqueduct stability. Conversely, the deterioration of the mechanical properties of the mortar, caused by weathering and Calcium ion dissolution due to ambient environment and aqueduct leakage, has relatively little impact on the structural safety. Supplementary grouting of the mortar between the stone masonry should be timely carried out to maintain the structural integrity to ensure the overall stability of the structure. The proposed approach can provide a reference to structural diagnosis and performance assessment for similar structures.
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