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Geotechnical: Parsons Brinckerhoff – team players

Parsons Brinckerhoff’s award winning solution for a collapsed slope in Dorset is evidence of its high level of technical expertise.

Beaminster portal: Bespoke solution

Beaminster portal: Bespoke solution

In association with:

In association with:

Last month, the prizes were handed out at NCE sister magazine Ground Engineering’s annual awards event. The award for the best UK project with a geotechnical value of between £1M and £3M went to consultant Parsons Brinckerhoff for its work at Beaminster Tunnel in Dorset.

The award reflects the company’s approach to the job after it was called in to design and manage the stabilisation of the slopes above the tunnel portals, following a landslide in July 2012.

The project, which was completed in July 2013, was carried out in a glare of publicity, as closure of Beaminster tunnel - the oldest on the UK road network - caused considerable disruption to traffic in the area.

It also put the spotlight on Parsons Brinckerhoff and the capabilities of its geotechnical engineering team.

When Beaminster came along, we could see that the process needed a lot of careful and sensitive management

The consultant initially became involved in discussions about repairing the collapsed slopes above the tunnel portals through its on-going technical services framework contract with Somerset County Council.

Under the terms of that framework, adjacent Dorset County Council can also call on Parsons Brinckerhoff’s services, which in this instance saved a great deal of time, and meant that work could begin almost immediately after the collapse.

Among the issues the consultant had to consider were the level of public scrutiny, engaging local landowners and stakeholders, and the sensitivity of the listed tunnel structure itself. In addition, very few parts of the existing slope were accessible for ground investigation.

European resilience project

Parsons Brinckerhoff’s geotechnical team has been involved for the last four years on a European Commission-funded project strengthening the resilience, prevention, preparedness, and response to man-made and natural disasters of countries adjacent to the EU.

These include Armenia, Azerbaijan, Belarus, Georgia, Moldova and Ukraine. The firm’s primary role has been to assist in developing a web-based electronic regional risk atlas, which includes hazards like landslides, earthquakes, flooding, forest fires and chemical and biological incidents.


Typically, in designing a slope stabilisation solution, engineers will analyse the slope in sections, and in a linear slope the cross section may not change very much. Here, the “bowl” shaped geometry of the slopes above each of the tunnel portals changes considerably, and so it was important to make sure enough sections were analysed to take account of these geometric changes.

“When you are trying to solve a 3D problem like this, you look at various sections. But because of the unusual geometry over the two tunnel portals, there were numerous sections,” explains Parsons Brinckerhoff technical director and head of discipline for geotechnical engineering Ian King.

Slope stabilisation

The consultant used existing information, together with the results of the ground investigation, to create a model of the existing ground, and also carried out a back analysis of the slip event to establish exactly what had happened. The resulting solution was to stabilise the slopes above the tunnel using soil nails and tensile mesh.

“I don’t think there was any real doubt about the solution,” says King, adding that any attempt to cut out the slope would have been very expensive and time consuming, and would have had a devastating impact on the landscape.

One of the aspects of the project that made it so successful was the early involvement of main contractor Raymond Brown and specialist subcontractor Can to resolve practical issues on the access and equipment required to get the soil nails in. As a result, ramps were used to enable the majority of the nails to be installed using a long reach excavator instead of rope access A-frame rigs, speeding up the installation.

King says that previous experience of high profile projects gave Parsons Brinckerhoff an understanding of the sensitive public and stakeholder issues surrounding the Beaminster Tunnel remediation. Among those previous jobs is the stabilisation of former limestone mines at Combe Down near Bath. These shallow mines - just 2m to 6m below the surface - were worked extensively in the 18th and 19th centuries as a primary source of the honey coloured stone used to build the city of Bath.

The focus for us is on providing expert leadership and high level technical advice

They remained largely unnoticed until 1989, when a utilities contractor accidentally broke through into the abandoned mine complex, and it became evident that the village sitting directly on top - complete with over 700 homes, schools, businesses and roads - was at risk of collapse.

Parsons Brinckerhoff was the “architect” for the remediation solution, which involved filling the voids with lightweight concrete that incorporated quarry waste.

“Combe Down involved very intense stakeholder engagement, so when Beaminster came along, we could see that the process needed a lot of careful and sensitive management,” explains Parsons Brinckerhoff director and head of ground engineering Adrian Dolecki.

Both projects highlight the firm’s approach to geotechnical projects - focusing on what director of civils, structures and ground engineering David Gullick describes as “added value, technically challenging services”, rather than “commodity design”. “The focus for us is on providing expert leadership and high level technical advice,” he adds.

In fact, the entire company was founded on complex geotechnical projects, including the first segment of the New York City subway, designed by William Barclay Parsons in 1904. And Gullick believes the spirit behind that innovative project still pervades the company’s culture today.

Parsons Brinckerhoff currently employs around 2,500 people in Europe, of which around 125 are geotechnical specialists. Gullick and Dolecki have plans to grow that number to around 200 in the next two years by increasing market share and moving into new markets, such as offshore wind and specialist advisory roles. But they insist that this level of growth will only be achieved by retaining the culture of high level expertise.

Forensic focus

The company is often called in for what Dolecki calls “forensic” investigations - looking at how geotechnical failures have happened, as well as what can be done to solve the problems. An example of this is the Bridge Valley Road in Bristol, where the company carried out an investigation into a complex landslip that was threatening to affect a disused railway tunnel and the main A4 road at the toe.

Again the solution involved soil nails and drainage measures, as well as other repairs to the gorge face.

Parsons Brinckerhoff’s reputation for high level technical advice and forensic expertise relies on staff being at the forefront of academic research and technical developments, and the firm has many initiatives to ensure this happens.

Among them is a technical route to promotion within the firm, with the expectation that people choosing this route (as opposed to project management or business management) will write academic papers and present their work at conferences.

Worldwide there is also the William Barclay Parsons Fellowship - open to anyone within the company. Parsons Brinckerhoff invests time and money over a period of approximately 12 months for the winning Fellow to research his/her topic, write a monograph, and promote and disseminate the research globally. The company also encourages links with universities - something the geotechnical team is currently making use of as it investigates three landslips in south Wales.

“These are three of the largest landslips ever to happen in Wales, and they have happened in strata that was not previously seen as likely to fail,” explains Gullick.

“We have two MSc students working with the British Geological Survey and Cardiff University to investigate what is happening, so we’re bringing together industry-wide expertise and students to do the research.”

Istanbul Strait road tube crossing project

Challenging: Istanbul Strait tunnel

Istanbul Strait tunnel

Parsons Brinckerhoff is lead designer on a 14.6km scheme that includes constructing a twin deck, four lane road tunnel beneath the Bosphorus Strait, connecting the European and Asian shores of Istanbul.

The company was appointed to lead an international joint venture of consultants, and developed the initial design concept and later oversaw the development of the detailed design.

The most challenging section is 5.4km in length and includes 3.4km of bored tunnel - using the world’s largest diameter slurry shield tunnel boring machine - and 1km of twin tunnels constructed using observational methods, as well as approach roads, toll plazas, ventilation facilities, tunnel control facilities, portal structures, and cut and cover tunnels.

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