Details of a study by HS2 project promoter HS2 Ltd into cutting the cost of phase 1 of the rail line between London and Birmingham have been revealed.
The pilot study, which was independently chaired by Aecom engineering director Mark Raiss, examined ways to streamline the designs of bridges, viaducts, tunnel portals and retaining walls to reduce construction costs.
HS2 Ltd commissioned the report to ensure the project designs were the best value for money.
Raiss said around 12 main conclusions had been drawn from the study, which started in November last year.
One was that design specifications for some of the structures had been incorrectly applied or misunderstood.
The study also concluded that not enough design time had been spent on smaller structures, and this had resulted in higher costs.
In addition, the study said that cheaper alternatives to the use of barriers on viaducts contain train derailments should be considered.
Last year HS2 Ltd chief executive Mark Thurston told New Civil Engineer that the project has been facing increasing cost pressures ahead of the notice to proceed. This is the point at which the costs are agreed and construction can start. The deadline for this was pushed back three months from February to June this year.
According to one source, contractors had been told to “go away and sharpen their pencils” to cut costs.
Raiss said that in some cases bridge column spacing specifications had been misunderstood.
“This has unfortunately not been well understood, such that that central span on one bridge was 20m and another was 33m for exactly the same purpose,” said Raiss.
“The difference between those is a significant increase in cost for the bridge, probably about 50% extra, multiply that by several hundred bridges and that’s a lot of money.”
He said that sometimes a requirement had been applied correctly in one situation and then “extrapolated” to apply to another, with expensive consequences.
“The specification for water tightness for retaining walls, this is good for tunnels [to make the concrete walls watertight], but when there’s rain on the other side of the retaining wall, why do you not want to make the ground water come through,” he said. “It’s just an example of one area where it’s a specification used on one area and has been extrapolated to another and added £20M to one structure.”
But he said that collaboration between contractors, designers and HS2 Ltd had brought many benefits to the project.
Raiss said a lot of time had been spent designing the big ticket items, but not enough has gone into designing the smaller structures. He said more effort should be spent on smaller structures as they would be repeated many times.
Designers had not included much fat or contingency in their work, limiting scope for some cost savings, said Raiss.
Foundation designs were the exception as a lack of detailed geotechnical investigationhad limited scope for designing out risk. Raiss said this had been inevitable because of the lack of land access when designs were being worked on.
Use of large barriers to prevent the trains from detrailing on viaducts is also under review, said Raiss. He said other cheaper derailment prevention options are available, and they are now being considered.
The study is one of a number examining different aspects of HS2’s phase 1 design. Lessons will also be used on phase 2 of the line to improve the design.
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