Application of lower-bound stress fields to stability assessment of soil backfilled masonry arch bridges

Limit analysis is a convenient approach for the estimation of the ultimate collapse state of geotechnical constructions, including pipes, tunnels and retaining walls. A soil-filled masonry arch bridge is a combined geotechnical/masonry structure where rapid limit analysis can play a valuable role in assessing the ultimate load-carrying capacity for multiple load cases. However, currently available rapid analysis techniques for masonry arches only model masonry elements directly, with the soil backfill indirectly modelled, leading to reduced clarity in the predictions of the bridge load-carrying capacity. To address this, a soil backfill model based on lower-bound stress field theory is proposed in this paper. The results, compared with upper-bound solutions obtained using the discontinuity layout optimisation (DLO) numerical limit analysis procedure, show good matches of upper and lower bounds typically to within 10%. The proposed methodology has applications beyond that of arch bridges, such as to tunnels and buried pipes.