In July 2001, a power transmission line tower located in a high class residential area in the southern part of Sao Paulo city, Brazil, suffered a substantial tilting due to failure of an adjacent retaining structure under construction. He retaining structure was 9,0m high and consisted of a tieback wall with two anchor levels. The soil under exctivation belongs to the Sedimentary Basin of Sao Paulo city (tertiary sediments). The main material consists in stiff to hard clay with high compressive strength under confinement, but with possibility of severe loss of strength with no confinement and under water table. This behavior, combined with other factors, led to failure of the retaining structure. An adjacent tower has remained in place and a retaining wall of root piles was constructed surrounding the tower to provide adequate protection in case the failure surface progressed This paper presents a description of the peculiar geologic and geotechnical conditions at the site, the original tieback retaining wall, the construction procedures, the mechanisms that led to failure, as well as the emergency remediation solution for the remaming tower.
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