Numerical assesment of the effect of adjacent backfilling activities on the overall stability of an old masonary barrage

The Ministry of Irrigation in Egypt has made the decision to replace an aging large barrage situated across the Nile River with a new barrage and a hydropower plant. In the process of replacing the old barrage, backfilling is required on the raft foundation of the existing structure, both from the upstream and downstream sides, to create the new east bank. Originally, the foundation of the old barrage comprised of a masonry raft on a plain concrete raft, with piers and an arch bridge constructed using rubble masonry. In 1936, the masonry raft was extended with a plain concrete raft, and the piers and arch bridge were similarly extended using plain concrete. This paper focuses on conducting advanced three-dimensional finite element analyses to investigate the impact of backfilling activities on the stability of the current barrage during the formation of the permanent east Nile bank. The numerical model simulates the construction activities of the new barrage and hydropower plant preceding the backfilling works, including the construction of the existing old barrage, the cofferdam, and the dewatering process inside the cofferdam. The investigation also delves into crack propagation in the masonry and concrete elements of the old barrage. The analysis results encompass anticipated ground deformation, stresses, and the projected zones of cracking within the masonry and concrete elements of the old barrage due to the proposed backfilling operations. These findings have played a crucial role in reorganizing the construction sequence to maintain the operation of the old barrage until the completion and activation of the new barrage.