OPTIMUM engineers were onsite with project owner RTE last week for the successful completion of a 243-metre-long S-shaped HDD under the River Marne, just east of Paris, enabling RTE – Réseau de Transport d’Électricité – to proceed with network extension works and connect key electricity substations around the capital.
The 225kV three-phase underground connection now passes 16 metres below the riverbed. Using a Brownline gyroscopic guidance system, drilling contractor BIR was able to ensure that the pilot hole was drilled with pinpoint accuracy, avoiding underground structures – bridge foundations, a pedestrian access ramp, as well as 11-metre-deep sheet pile walls on both sides of the river – which could otherwise have jeopardised operations.
OPTIMUM engineers proposed the S-shaped crossing after the initial drill path was deemed unfeasible during preliminary studies, given the abundance of existing underground networks in the area. A dedicated team then assisted RTE at every stage of the project, from design engineering to contractor selection, risk analysis and mitigation, and finally daily monitoring of the HDD operations. Particular attention was paid to the drilling fluid, which was constantly monitored and adapted to neutralise the potential clogging action of the underlying clayey soils on the drilling equipment and tools, and so maintain borehole integrity.
Despite the relatively short crossing length, the site’s complexity, both above and below ground, demanded geotechnical precision and expertise.
Thanks to great teamwork with RTE and BIR, operations ran smoothly, and the HDD was completed on schedule, after just a 11 days drilling.
