HS2: Undertaking the UK’s largest ever ground investigation

The UK’s largest ever ground investigation for the new High Speed 2 (HS2) rail link between London Euston and Birmingham Curzon Street is now in its fourth year. RPS has successfully delivered thirteen of the original ground investigation work packages working directly for HS2 Ltd, the most of any company on the framework with the value of works completed so far totalling circa £5 million.

The appointed main works and enabling works contractors are now undertaking supplementary ground investigation to support scheme and detailed design, including value engineering and RPS is currently delivering an additional three packages of works.

Sharing their experience, Mike Barker (Project Director) and Lloyd Williams (Project Manager) from RPS discuss how the team have overcome a complex mix of varied ground and weather conditions as well as stakeholder and logistical challenges to successfully deliver the scheme.

MB - “Not only the UK’s largest ever ground investigation, HS2 Phase One is arguably also one of the most varied ground investigations ever undertaken; requiring a unique and complex mix of techniques.

The nature and scale of the scheme, divided into packages of works across the 140 mile long HS2 route, means continuously working across land where numerous stakeholders are involved as well as responding to diverse ground conditions and vast quantities of varied geological data.”

LW – “Over the last four years RPS has undertaken 726 (and counting) exploratory locations with some 6450 metres of boreholes drilled to date and over 7000 geotechnical laboratory tests. However these numbers only scratch the surface of the logistical, access and data management challenges of delivering this project.”

MB – “At the peak of work we have had a team of 40 people on site working within two teams in different areas along the route, with a full team out in the northern section of the Phase One route (Warwickshire) currently.”

LW – “It has been a uniquely complex ground investigation due to the variety and scale of techniques used to deliver it. On site, we have utilised conventional and wireline rotary, cable percussive drilling, high pressure dilatometer tests and self-boring pressuremeter testing, sonic drilling and Cone Penetrometer Testing. We have also undertaken gamma, televiewer downhole and surface and downhole seismic testing as well as trial pitting and window sampling.

To deliver the data required, we developed a framework of specialist and local sub-contractors, with all works managed and supervised by our team. Additionally, our work has supported the local economy as non-technical contractors including access plant vehicles have been sourced locally to the individual work packages through local farmers and businesses, supporting their workforce with the necessary HSE certifications.”

MB – “One of the main challenges encountered on a project of this scale is how to manage and most effectively distribute the data generated. In response we have developed a robust data management plan and quality management systems. Developing and enhancing the processes throughout the works we have: liaised closely with the logging software company; provided AGS4 and GI data management (HoleBASE) training to all project and site staff; resourced a large team of dedicated personnel to data management and data quality control; and provided training, guidance and workshops to some specialist contractors and laboratories that were not set up for reporting AGS4 data.

HS2 Ltd presented our data management plan / processes and systems to the other GI Framework Contractors, exemplifying our best practice and to implement consistency in standards and approach to data across the whole of the project.”

LW – “Specialist geotechnical laboratory testing has been a core element of the scheme including complex and lengthy testing on over-consolidated clays, only able to be undertaken by a handful of UK laboratories.”

MB – “From navigating the complexities of one of the busiest urban environments in the UK to working in rural locations in difficult conditions, the project necessitated a responsive and flexible approach.

While working in Central London for the redevelopment of London Euston Station to accommodate the new HS2 platforms, we faced strict limitations on access, traffic management and control of construction noise. As well as the other HS2 enabling and main work contractors, we liaised closely with HS2 Ltd, Transport for London (TfL), London Underground, Camden Council and London Buses (including attending and inputting into Camden Traffic Liaison Group Consultations) to ensure maximum collaboration and keep the works on schedule.”

LW – “Attaining drill rig access for some locations involved entry through the main TfL bus station at Euston. To ensure minimal disruption to the bus service, access was arranged during overnight operations.

Other positions at Euston involved drilling several boreholes in locations at critical design points within extremely busy sections of the station. This required positioning the boreholes in precise areas between the tube tunnels of the Northern, Victoria and Circle lines. Meanwhile at ground level dealing with the logistics of working on the highway and within metres of the main pedestrian entrance of Euston Station."

MB – “It was crucial to minimise the disturbance to the 120,000 people that pass through the station gates daily.”

LW – “In contrast, at the other end of the scale and the other end of the route in Warwickshire and Northamptonshire, the rural environments presented their own unique challenges. With drilling works being undertaken all year round, we faced winter conditions and very soft ground. We required widespread use of bog mats to get access and on occasion bespoke methods were required. On several occasions dedicated haul roads were constructed (a rarity for a typical ground investigation) and during the severe wet and snowy weather conditions in March 2018 a specialist sledge was used to transport the cable percussion drilling rigs.”

MB – “Adding to the challenge was the fact that some of the areas were not relatively well known in terms of drilling conditions. Notably the Tamworth area where the Hopwas Breccia and underlying Kidderminster Formation were particularly challenging. The initial scope of work called for wireline geobore rotary drilling to progress these holes, however early on in the programme it became apparent that this wouldn’t work.”

LW – “The matrix material of the Breccia was heavily weathered while the casts and cobbles contained in the weak matrix retained a lot of strength. The result meant it was a challenge even to progress the boreholes let alone carry out suitable sampling and testing. Immediate identification of the issue allowed us to quickly mobilise a sonic rig to progress the hole with minimal delay.”

MB – “The experience of delivering a project of this scale has been massively beneficial for our team and the opportunities we have been able to provide for staff at all levels to develop capability. The scheme has exposed our team to a wide variety of geological conditions and allowed excellent development opportunity with chance to rotate into different roles from technical, logistical and data management.”

The HS2 project is one of several large-scale ground investigations RPS has undertaken during the last three years on linear infrastructure including the M4 corridor around Newport, South Wales and A701 in Scotland.