Retroerosion in a TBG Gas Pipeline Crossing and its Rehabilitation

This Paper presents a case study of the Jardim Novo Maracanã stream situated in Campinas, São Paulo, in which recent streambed modifications were characterized, aiming to define the rates and the potential erosions along the channel alignment of which have Bolivia-Brazil Gas Pipeline crossing. Its presents the erosion process analysis and mitigation concepts aimed at the pipeline and fiber optic cables facilities integrity, as well as to indicate the design issues, considering the streambed deepening in this watershed. For this, satellite images and aerial photographs were collected in different periods, soil and subsoil surveys were performed, information on rainfall and watershed characteristics was analyzed, as well as hydrological and hydrotechnical studies were developed. These studies included geotechnical channel and banks analyzes, the spatial and temporal trends of the fluvial geomorphology evolution and the infrastructures safety conditions analysis. It was concluded that a new channel erosion process occurred after the streambed was filled by recent sediments. This process is associated with an increase floods magnitude, the slopes occupation intensification with the county urbanization and the streambed conditions changes, from an alignment sinuous to rectilinear and from a shallow to deeper channel. Once initiated, the channel erosion process maintained its retroerosion, i.e. its “headcutting” trend, deepening its equilibrium profile to its stratigraphic base level, located about 5.0 m below the 2014 stream bottom, in the pipeline cross section. Alternative concepts for the infrastructure integrity rehabilitation in these new morphological-fluvial conditions were also developed and dimensioned. Among these, the rectangular culverts alternative was adopted. They support a landfill at the crossing with the buried pipe and have to 100-year return period peak flows capacity.