Load‐deformation behavior of locally corroded reinforced concrete retaining wall segments: Experimental results
Authors: Haefliger Severin , Kaufmann Walter 
Published: December 2022

Local reinforcement corrosion damage reduces the load‐bearing capacity of reinforced concrete structures and, even more severely, their deformation capacity. This problem is of particular concern for cantilever retaining walls, whose loading is dominated by earth pressure and hence, depends on the wall deformations. With a limited deformation capacity at the ultimate limit state due to the locally corroded reinforcement, the earth pressure may not drop to its reduced value typically assumed in design, and simultaneously, the structural resistance may be severely impaired by the cross‐section loss. Load redistributions are impeded since retaining walls are statically determined vertically and typically segmented longitudinally. This increases the risk that affected structures collapse, exhibiting a brittle failure. The situation is aggravated by the fact that the wall deformations prior to failure are too small to be detected by conventional monitoring, as indicated by a previous study.

To improve the basis for quantifying the related risks and the magnitude of prefailure deflections, this study investigates the load‐deformation behavior of cantilever retaining walls affected by local pitting corrosion, focusing on (i) the influence of the corrosion pit distribution among different reinforcing bars on the load‐bearing and deformation capacity and (ii) the interdependence of corrosion, reduced deformation capacity and deformation‐dependent loading. To this end, eight large‐scale experiments on retaining wall segments were conducted in the Large Universal Shell Element Tester (LUSET), simulating the lower part of a 4.65‐m‐tall cantilever retaining wall. Five specimens contained initial damage (pitting corrosion simulated by a spherical mill). In the remaining three specimens, artificial corrosion damage was induced during the experiments. For two of the latter specimens, the loading was adapted in real‐time control depending on their deformation to simulate the decreasing earth pressure. These are the first large‐scale hybrid tests in the field of corrosion research to our knowledge.

The experiments confirmed that the ultimate load and the corresponding deformation strongly differ depending on the corrosion pit distribution, even among specimens with equal mean cross‐section loss. Furthermore, it was found that the deformation increase due to corrosion damage depends on the loading and, hence, on the compaction of the backfill. The observed deformation increase ranged between 0.8 and 1.4 mm per meter height at 40% cross‐section loss, with loose soil causing a larger deformation increase. The load transfer between the damaged and undamaged reinforcing bars was found to take place in the first two crack elements above the construction joint. Local bending moments occurred in the reinforcing bars in the vicinity of the corrosion pits due to the shift of the center of gravity of the bar at the pit. Fiber optic strain sensing allowed visualizing the bending moment decrease in the embedded part of the damaged bars as a consequence of a lateral bearing pressure.