Collecting ground engineering data along an extremely busy tidal river for the construction of Europe’s biggest super sewer presented challenges of logistics and scale.
The riverbed was geologically complex, so we were tasked with gathering and interpreting additional data to inform design. We also completed a ‘driveability’ assessment to optimise foundation choices.
At 25 kilometres long and more than seven metres in diameter, London’s Thames Tideway Tunnel is the biggest infrastructure project ever undertaken by the UK water industry. The project’s Central Section, undertaken by Ferrovial Laing O’Rourke Joint Venture (FLO) for Tideway, has the greatest variation in geology. This poses particular challenges for the tunnel design and site characterisation.
Complex programme requirements
Our site characterisation programme involved:
- Characterising the ground and its engineering properties, including potential hazards in locations for connecting structures to the live sewer network
- Helping to evaluate the types of foundation construction that could be supported by the ground conditions along the route
- Helping to determine ground risk, to support the planning and implementation of a safe process for tunnelling operations
- Flexibly delivering hydrogeoloigcal data to help resolve design and construction detail in relation to dewatering, groundwater levels and aquifer stratigraphy
We were awarded the site characterisation project because of:
- Our previous Thames experience
- Our expertise in managing large, complex marine investigations
- Our established relationships with River Thames and City authorities, which helped us run logistically challenging work in an efficient way
- Our proven ability to provide a full spectrum of overwater geotechnical and downhole geophysical techniques in response to evolving programme needs
Efficient and innovative delivery
To provide the required ground risk and engineering data along a 10-kilometre stretch of the river, we completed drilling, downhole geophysics and testing to depths of 80 metres. Based on the quality of our site investigation data and interpretation, our geophysicists were later asked to carry out a ‘driveability’ assessment, to help inform the selection and planning of appropriate piling systems for specific sewer substructures.
The work involved 55 bridge manoeuvres: we had to negotiate 12 of the most famous, structurally diverse bridges on the River Thames, located between Blackfriars and Wandsworth. To ensure we delivered this complex programme in a flexible and efficient way, we designed, manufactured and installed multiple adaptations to the Skate 2D jack-up barge.
These innovations enabled leg handling and leg storage to be carried out by a single, self-equipped vessel, which also had on board a full suite of geotechnical drilling, sampling and testing equipment capable of being mechanically folded. Our solution eliminated the need for a support barge and crane to install, remove and transport the legs when passing under bridges. This resulted in significant time and cost savings.
Shawn Sismondi, Senior Geotechnical Engineer at FLO, said: “The Skate 2 proved well suited to dealing with London’s various challenges. As well as bridge transits, its ability to undertake ground investigation safely, in close proximity to tunnels, river walls and heliports, was extremely useful.”
Using the Skate 2D, we also resolved access issues for the structural assessment of an historic wall, to guide the construction of a connection culvert to the existing sewer at Blackfriars.
Fugro had the required resources, experience and expertise to implement and coordinate a busy site investigation programme, working with other river operatives such as the Port of London Authority. Faced with a challenging programme, the team offered the flexibility and scope to collect supplementary data when needed, without the complication of bringing in other subcontractors.
Our progressive approach to site characterisation and our innovative equipment design enabled us to achieve significant time and cost savings, relieve river congestion and resolve our client’s foundation assessment and constructability challenges.