The "Benefit" of construction excavation accidents

The authors examine a failure of a reinforcement structure located in the city of Sofia, resulting in a soil slide and the collapse of an existing retaining wall with a length of about 30 m. Neighboring properties were affected, where cracking of pavements and damage to garage cells were found, fortunately without any injuries. The excavation has an average depth of 10 – 12 m, reinforced with driven steel piles made of IPE270, between which there is a lining of wooden planks (“Berliner Wall” reinforcement type). The static scheme is a single-row, in some places, double-row, supported structure. The failure occurred suddenly, under relatively favorable weather conditions, without significant precipitation or sudden changes in air temperature. Before the failure, no deformations, cracks or other warning signs were observed. The paper examines the causes of the collapse, presents the results of subsequent studies and analyses, as well as recommendations for eliminating the consequences. Comparisons are made with other excavations, and the authors present the conclusions and lessons learned from similar events that could be considered as “benefits” for construction science and for preventing similar accidents.