HS2 Ltd’s civils team has revealed the lessons learnt from its Phase 1 work on bridges and viaducts, along with how this will inform the next phase of the scheme as it extends north.
HS2 Ltd head of civil structures Tomas Garcia reflected on the procurement, design and delivery of the project’s bridges during NCE’s Future of Bridges conference this week.
Garcia said that with 61 viaducts and 150 overbridges on Phase 1 it “makes sense” to have a “certain level of standardisation” to achieve “some efficiency in the delivery” of the structures.
However he added: “There is a tension between that aim of standardisation and offsite construction and the HS2 design vision which seeks design for a sense of place. Therefore careful design exploration is needed to find the appropriate balance between overall systematic repetition and local variation.”
As such, HS2 Ltd has produced design approaches, requirements and developed specimen designs.
This has a number of benefits. The team can test the specification and prove feasibility, create a quality benchmark, respond to stakeholder requirements and create families of structures to promote some level of standardisation.
Finally, it allows HS2 Ltd to prove that all of the above can be delivered with design for manufacture and assembly (DfMA) solutions. Examples of the DfMA approach on Phase 1 include the Colne Valley Viaduct, Wendover Dean Viaduct and Small Dean Viaduct.
Garcia said the team is “satisfied in general” with the Phase 1 outcomes but added that “obviously things can always be improved”.
Considering different ideas from different contractors could enable a more precise definition of the balance between the project’s various requirements.
“In Phase 1, there are some differences in design between contracts depending not only on the particularities of each location but also on the preferences of the designers and contractors,” Garcia explained.
“This is not necessarily a bad thing. The design is a compromise between competing requirements and the balance point could have some level of flexibility and judgement. However having the benefit of seeing different ideas, approaches and designs from the different contractors we can probably define the best aspects of each one and define more precisely that balance point.”
Garcia also sees scope to “refine and clarify some of the design requirement” for Phase 2, and use the available time before contract award to develop some of the solutions further.
“We could maximise the design time and engage with lower tiers within the supply chain. Tier 2 and 3 are typically where the experience is however their time to contribute is normally left to the end of the process where there are fewer opportunities to influence the outcome,” he said.
“As we would have typical solutions developed we could also engage with third party stakeholders and work together to achieve better outcomes.
“This could de-risk the programme but should be done with plenty of time in order to discuss and agree the best solution. This approach doesn’t mean solutions will be set in stone. They will be the default solutions that we expect to be challenged and improved further once the main designer and contractor are on board.”
Overall, Garcia said the ideal outcome of a standard bridge specimen design is “a system of limited but coherent, versatile and high quality viaducts that define HS2 identity and at the same time are compatible with a variety of contexts with different landscapes and local particularities”.
“The aim is to deliver a project that everyone can be proud of, a project that speaks a national language yet respects regional dialects,” he said.
Department of Civil Engineering https://www.ibu.edu.ba/department-of-civil-engineering/