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Ground investigation: Delivering High Speed GI

rps hs2 ground investigation

Construction plans for the High Speed 2 rail link between London and Birmingham has called the UK’s largest ever ground investigation. GE takes a look at the challenges of delivering the work over the last four years.

The scale of construction needed to deliver the UK’s new rail line between London and Birmingham is greater than anything the country has seen before. But the ground investigation work needed for High Speed 2 (HS2) also on magnitude beyond what has been previously delivered – and it hasn’t been without its challenges.

The ground investigation on the route was split into 92 packages – split into two lots of up to £0.5M and £0.5M to £5M – with nine contractors appointed to the framework and invited to bid for the work. The framework was set up in 2015 to run for four years with the option to extend it by a year twice to add flexibility to meet the demands of the project as Royal Assent had not been achieved when ground investigation started.

Four years on and work is still underway with supplementary ground investigation now being carried out.

RPS has delivered 13 of the ground investigation packages and has had to have overcome a complex mix of varied ground and weather conditions as well as stakeholder and logistical challenges to successfully deliver the schemes.

RPS project director Mike Barker said: “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.

rps hs2 ground investigation snow

rps hs2 ground investigation snow

RPS faced winter conditions and very soft ground on some sites

“The nature and scale of the scheme, which is divided into packages of works across the 224km long 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.”

RPS project manager Lloyd Williams adds: “Over the last four years RPS has undertaken 726 – and counting – exploratory locations with some 6,450m of boreholes drilled to date and over 7,000 geotechnical laboratory tests. However, these numbers only scratch the surface of the logistical, access and data management challenges of delivering this project.”

Barker says: “At the peak of work we have had a team of 40 people on site working in two teams in different areas along the route and we currently have a full team out in the northern section of the Phase One route in Warwickshire.”

According to Williams, it has been a complex ground investigation due to the variety and scale of techniques used to deliver it. “On site, we have used conventional and wireline rotary, cable percussive drilling, high pressure dilatometer tests and self-boring pressuremeter testing, sonic drilling and cone penetrometer testing,” he explains. “We have also undertaken gamma, televiewer downhole and surface and downhole seismic testing as well as trial pitting and window sampling.”

The scale of the work also meant that RPS had to call on external support, as Williams details: “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.”

However, just collecting the data was not the only hurdle. Barker says: “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 involved liaising closely with the logging software company; providing AGS4 and GI data management through Keynetix’s Holebase software; providing training to all project and site staff; resourcing a large team of dedicated personnel to data management and data quality control; and providing training, guidance and workshops to some specialist contractors and laboratories that were not set up for reporting AGS4 data.”

HS2 used the data management plans, processes and systems developed by RPS as best practice and worked with other framework contractors to roll out similar standards and approaches to data management across all the work packages to ensure consistency.

Testing capacity also needed to be considered as Williams explains: “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.”

rps hs2 ground investigation euston station

rps hs2 ground investigation euston station

Careful planning was needed for sites in busy urban locations

According to Barker the varied locations of the work from busy urban environments through to remote rural locations called for a flexible and responsive approach to the work.

“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,” he says. “As well as the other HS2 enabling and main work contractors, we liaised closely with HS2, 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.”

Williams adds: “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.”

With 120,000 people passing through Euston each day, Barker describes the need to minimise disturbance as “crucial”.

Williams says: “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.”

The rural locations also brought new ground conditions. Barker says: “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.”

Williams adds: “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.”

While the challenges encountered have been on a scale not seen before, Barker says that the work has benefitted RPS, as well as HS2. “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,” he says. “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.”

 

 

 

 

 

 

 

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