Fugro boosts efficiency of super sewer site characterisation

Fugro’s leading expertise in over-water geotechnical characterisation has saved time, cost and congestion during riverbed assessment for London’s major sewer upgrade, the Thames Tideway Tunnel.

The global geoscience leader recently completed two site investigation campaigns for Ferrovial Agroman and Laing O'Rourke, the consortium undertaking construction of the project’s central section for client, Tideway. Over a seven-month period work has included drilling, downhole geophysics and testing to depths of 80 metres to provide ground risk and engineering data along a 10-kilometre stretch of the river.

Efficiency in cycle-time and river transit was crucial in delivering information from over 40 borehole and Cone Penetration Test (CPT) locations in tidal waters to suit the phasing of planning and design. The programme involved 55 bridge manoeuvres negotiating 12 of the Thames’ most famous, but also structurally diverse bridges, between Blackfriars and Wandsworth.

Fugro designed, manufactured and installed adaptations to the Skate 2D jack-up barge allowing leg handling and leg storage to be carried out by a single, self-equipped vessel, in addition to carrying a full suite of geotechnical drilling, sampling and testing equipment capable of being mechanically folded.

Using engineering proven on global marine projects, Fugro technicians reconfigured the platform deck to accommodate a centrally located, high capacity crane. This provided the capability to self-lift the jack-up legs between a storage cradle on the stern of the vessel and positions at the platform jacking corners to allow execution of height restricted bridge manoeuvres. The solution eliminated the need for a support barge and crane to install, remove and transport the legs when passing under bridges.

Having used the self-removing leg system to reduce jack-up height and enable bridge manoeuvres on previous Thames projects, Fugro believes that the addition of the onboard storage cradle is a first for a modular jack-up undertaking geotechnical work on the river.

Matt Chappell, a specialist in nearshore site investigation at Fugro, said: “Our uniquely designed, self-contained platform simplified logistical and health and safety management risks for the complex transits and bridge manoeuvres, improving efficiency and reducing supply chain risk. It also reduced the cost to the client by eliminating the need for a support barge, together with associated standing time incurred from tidal delays.” Disruption to river traffic was also minimised.

Shawn Sismondi, senior geotechnical engineer for Ferrovial Agroman, said: “The Skate 2 proved well suited to dealing with London’s various challenges. As well as bridge transits, its ability to safely undertake ground investigation in close proximity to tunnels, river walls and heliports was extremely useful. ”

Working in challenging intertidal waters, Fugro barge masters drew on their substantial experience to achieve problem-free jack-up and preloading operations in the highly variable geology, avoiding leg penetration and punch-through risks in the challenging riverbed formations.

A total of 25 boreholes were drilled using a combination of cable percussive, rotary and directional methods to depths ranging between 25 and 79 metres. A programme of downhole geophysics and in situ testing provided further, high resolution geological and geotechnical data. Cone penetration testing was carried out at 19 locations, many of which used the seismic piezocone to deliver key information on geotechnical parameters.

The complex work demanded high levels of competence from Fugro’s team, including geotechnical engineers trained and experienced in London Basin logging. Team members also completed Tideway’s progressive health and safety induction, EPIC, which is championing a rigorous safety culture for workers on the project.

One of the UK’s biggest civil engineering projects, the £4.2 billion Thames Tideway will incorporate 25 kilometres of tunnelling to update London’s ageing sewer system for modern needs.

Fugro’s comprehensive expertise in nearshore and inter-tidal site investigation has made it a long-trusted partner on numerous Thames projects. They include: Garden Bridge, London Gateway, Putney-Becton Sewage Tunnel, the London Array, Canary Wharf, Royal Terrace Pier, and other current contracts at Tilbury Power Station, Tilbury Docks, and the Oikos Jetty (Canvey Island).