Experimental investigation on the shear behaviour of the brickwork-backfill interface in masonry arch bridges

This paper presents the results from an experimental campaign to characterise the shear behaviour of the brickwork-backfill interaction in masonry arch bridges. Two representative backfill materials found in real masonry arch bridges (compacted crushed limestone and clay) were sheared against brickwork masonry specimens with two different bond patterns (a soldier course bond and an English bond). The results demonstrated that the interface shear behaviour between masonry and backfill was different from the internal shear behaviour of backfill materials. When compacted crushed limestone was adopted as the backfill material, the ratio between the masonry-limestone interface friction angle (φi) and the internal friction angle (φ) of limestone was determined to lie within the range from 0.70 to 0.75. However, when clay was used as backfill material, the φi/φ ratio was much lower, and of the order of 0.51 to 0.52 under the assumption of zero-cohesion at the interface, or 0.35 to 0.39 if interface cohesion was considered. Moreover, the properties of the backfill material had a significant influence on the interface shear behaviour, whereas the effects of brickwork bonding pattern were marginal. This study provides valuable insight into the identification of brickwork-backfill interface parameters for the numerical analysis of masonry arch bridges.