When energy and utility networks have to be moved ahead of the construction of an urban metro line, finding space underground is definitely not easy. This was the scenario OPTIMUM engineers were faced with in 2023 when BIR commissioned the trenchless specialists to carry out feasibility studies and find potential drill paths for 2 cable installations southwest of Paris.
OPTIMUM established and analysed a detailed programme of geotechnical investigations, given the challenging geology in the area (millstone clays, very hard and abrasive sands and sandstones), before overseeing the crucial and meticulous network detection and topographical investigations. With the myriad of information in hand and the numerous project constraints in mind, OPTIMUM engineers then set about designing the crossing routes, one for ENEDIS / RTE, one for Orange, optimising the construction works between the 2 project owners wherever possible.
The result ?
- Crossing n°1 : Using the same entry point but different exit points, one 90-metre-long HDD and one 252-metre-long HDD drilling under a dual-carriageway and a pedestrian underpass.
- Crossing n°2 : Parallel HDD crossings of 140 metres and 156 metres, drilling down 14+ metres under a roundabout to pass underneath the future metro line construction.
Designing a trenchless engineering project in this already saturated underground environment, was always going to be a challenge; only by knowing precisely where all the existing networks lay was it possible to avoid them and ensure the construction works ran smoothly. The HDD works are now complete.
