When 70km of Teréga’s gas transmission network needs to be replaced, trenchless crossings are inevitable. This project has over 50 of them !!! – some short, some long, some relatively straightforward, others highly complex. But each one needed careful analysis and geotechnical expertise. That’s where OPTIMUM came in.
Engineering teams were set to work to assess the feasibility and design the profile for every single one. Recognising the potential risks in some of the crossing sites, OPTIMUM also commissioned a reinterpretation of the geophysical data – from Donie – to ensure the trenchless design engineering was based on the most precise soil models possible.
Since then, dedicated engineers from OPTIMUM Southwest have been monitoring construction on the 16 most complex crossings. Completed works now include :
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- A curved 418-metre-long microtunnel beneath the fast-flowing River Tarn, the AVN 1600 angled at 9° on entry from a 9m x 9m secant pile shaft. The 6 weeks tunnelling through the underlying molasse substratum, 8m under the riverbed, ran smoothly thanks to excellent preparation and careful monitoring. Microtunnel by Denys, shaft construction by Spie Batignolles.
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- A 642-metre-long HDD under the A68 motorway, the Albi – Toulouse railway as well as an industrial estate. With OPTIMUM onsite, a steel casing on entry, a crossing profile passing 11m under the tracks, and careful monitoring of the annular pressure throughout the drilling operations, no breakouts occurred. HDD construction by Gendry.
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- A 270-metre-long DN165 HDD passing under a road and garden, with midi rigs either side to complete an intersect with a straight section of just 40m, one of the shortest ever ! HDD construction by Gendry, assisted by Prime Horizontal.
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- 13 additional HDDs and auger bores under the region’s roads and waterways : 350-metre-long crossing under the Agout, 300-metre-long crossing under the Parisot, ….
Success has hinged on OPTIMUM’s precise geotechnical knowledge of the region, the proximity of its teams, a deep understanding of the project history, and strong collaboration with Teréga. Attention now turns to the remaining crossings.
