The Trenchless Trend

Pipeline shore crossings are often one of the most complex and technically challenging elements of any subsea development. Challenges are compounded by shallow waters, which are typically subject to breaking waves, storm surge, and tidal movements. The presence of complex geological features, as well as difficult site accessibility can also complicate matters. Close to shore, an emphasis is placed on environmental values and social sensitivity as the development of infrastructure in the coastal environment is often subject to strong public opinion and specific code requirements.

Increasingly, trenchless methods are being incorporated into shore crossing designs as an alternative to traditional open cut and cover methods. These can be used to help minimise impact on the coastal environment. Two trenchless shore crossing methods being used with an increased frequency are horizontal directional drilling (HDD) and microtunnelling.

Design challenges for a trenchless pipeline shore crossing extend beyond considering pipeline mechanical, stability and cathodic protection (CP) design. Engineers must also tackle the challenges associated with the trenchless methods of HDD or microtunnelling at a coastline and ensure they are suitably integrated with the pipeline design. Every pipeline shore crossing is different and no method is universally suitable. Costs and risks involved will change with every site, and every project.

Traditionally, pipeline shore rossings have integrated the open cut and cover method into the design. In this method, the pipeline traverses the shoreline within a pre-excavated trench which, after pipeline installation, is backfilled with an engineered material. While proven and reliable, the method can have a high physical impact and is often not compatible with environmentally sensitive coastlines.

Where the shoreline is made up of cliffs, is difficult to access, or when difficult weather patterns and metocean environments are present, the implementation of a trenchless shore crossing can reduce not only the environmental footprint, but also the overall risk, schedule and cost for a project.

The Trenchless Trend September-2012-page-0

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