Engineers planning the route for a new sewer in south London discovered one very big surprise during their initial surveys. NCE reports.
Stratascan Sumo has recently completed a ground penetrating radar (GPR) survey over a major obstruction beneath the streets of Lewisham, south London.
Civil and structural engineering consultant Tully De’Ath’s Andrew Picton commissioned Stratascan Sumo to determine the extent of a former railway bridge, suspected to still exist beneath the junction of Lewisham Road and Sparta Street in south east London.
During some earlier work on a gas main, steel beams were found beneath the street. The site gave no indication of what lay beneath but a historic map search revealed that the now redundant South Eastern and Chatham Railway once passed under the junction.
As part of the development of the Heathside and Lethbridge Estate the consultants were looking to upgrade the sewerage system in Lewisham Road for client Family Mosaic. The purpose of the GPR survey was to establish the extremities of the bridge and determine how much of the structure remained beneath the road. This would enable the new sewer to be positioned away from any remaining structures.
The radar survey revealed that much of the structure still remained, with clear evidence that the steel girders supporting the bridge
The results of the radar survey revealed that much of the structure still remained, with clear evidence that the
steel girders supporting the bridge deck were left in situ when the railway was abandoned.
The bridge is rather complex, with different angles of skew at each end, and the section under Lewisham Road is to a different design to the triangular section beneath Sparta Street.
The former section is thought to be made up of large girders running parallel with Lewisham Road; the latter consists of smaller, closer centred steel members of reducing length.
In addition, sleepers of the former Lewisham Road tramway are seen presenting yet another obstruction to be addressed by the sewer designers.
Picton says his firm is reviewing the results and is working with its contractor to develop the optimum drainage route following the survey, which has enabled it to have a better understanding of what lies directly beneath the road surface.