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Alan Willoner: Geotechnical design and reporting - is there a better way?

A more integrated approach to design on a major flood defence project has led me to question whether the conventional approach to geotechnical design and reporting in the UK is the best way or whether this alternative could be more beneficial.

The Hull River Defence (HRD) is a £50M design and build project with several large combi-piled retaining walls to support the dilapidated riverside and provide defences to a 1 in 200-year fluvial event.

On this project, design was led by a geotechnical team with some specialist input provided by others in structures, maritime, materials and hydraulics teams. Therefore, it seemed logical to produce a multi-disciplinary basis of design report, rather than an interpretative ground investigation report. The basis of design approach allowed demonstration of the optioneering which had been done and agree principles and conceptual designs with stakeholders at the earliest opportunity.

As detailed design calculations progressed, a design report was produced which included the requirements on Eurocode 7 though BS EN 1997-1 cl.2.8 but also covered relevant parts of BS EN 1990, 1991, 1992, 1993, BS 6349 and cathodic protection requirements, so that the design behind the drawings, was explained. This approach enabled an appropriate amount of effort – and words – to be assigned to the most significant aspects of the design, addressed interfaces between disciplines and kept design information in a single location.

However, the Design Manual for Roads and Bridge (DMRB) section on managing geotechnical risk on earthworks (HD22) requires focuses on BS EN 1997 and a specific geotechnical design report. This may be a convenient way to manage geotechnical risk, or certify geotechnical design, on major highway projects but because the DMRB is such a good client design manual, it’s approach is often adopted outside the highways sector and has influenced the way that large UK consultancies operate, with a growing number of geotechnical designers (outside tunnelling departments) focusing on the requirements of BS EN 1997 rather than to the full suite of Eurocodes.

Should civil engineers, who design structures that interact with the ground practice both geotechnical and structural design, demonstrate understanding of how the imposed actions have been derived? Or, at least, understand what actions are reversible, which must co-exist, and which partial factors have or have not already been applied via BS EN 1990 and 1991 before a particular geotechnical limit state is checked? This issue resides within the UK and countries that are influenced by British engineers.

In large global multidisciplinary organisations with operations in Italy, Czech Republic, Hungary and other European countries, engineers regularly practice both geotechnical and structural design using the full suite of relevant Eurocodes and routinely “own” an entire sub structure design.

UK piling contractors with in-house designer and small specialist geotechnical consultancies who are more agile in their design approach also see the value in combining geotechnical and structural skills to reduce interfaces that can create misunderstandings, mistakes or re-work.

For a new graduate with an interest in ground engineering, initial professional development with a year of geotechnical design, a year of structural design and a year on site (ideally seconded to a contractor or design and build joint venture) would be well placed to take their chartered professional review. pay as y network licencing agreements reduces the cost of individuals having access the full range of multi-disciplinary software.

Look ahead 10 years and, using this more united approach in the UK, we could be well harmonised with Europe, assuming the Brexit business doesn’t turn sour.

  • Alan Willoner is technical principal with Mott MacDonald

 

 

 

Talking PointAlan Willoner: Geotechnical design and reporting - is there a better way than current UK practice? 

A more integrated approach to design on a major flood defence project has led me to question whether the conventional approach to geotechnical design and reporting is the best way or whether this alternative could be more beneficial.

The Hull River Defence (HRD) is a £50M design and build project with several large combi-piled retaining walls to support the dilapidated riverside and provide defences to a 1 in 200-year fluvial event.

On this project, design was led by a geotechnical team with some specialist input provided by others in structures, maritime, materials and hydraulics teams. Therefore, it seemed logical to produce a multi-disciplinary basis of design report, rather than an interpretative ground investigation report. The basis of design approach allowed demonstration of the optioneering which had been done and agree principales and conceptual designs with stakeholders at the earliest opportunity.

As detailed design calculations progressed, a design report was produced which included the requirements on Eurocode 7 though BS EN 1997-1 cl.2.8 but also covered relevant parts of BS EN 1990, 1991, 1992, 1993, BS 6349 and cathodic protection requirements, so that the design behind the drawings, was explained. This approach enabled an appropriate amount of effort – and words – to be assigned to the most significant aspects of the design, addressed interfaces between disciplines and kept design information in a single location.

However, the Design Manual for Roads and Bridge (DMRB) section on managing geotechnical risk on earthworks (HD22) requires focuses on BS EN 1997 and a specific geotechnical design report. This may be a convenient way to manage geotechnical risk, or certify geotechnical design, on major highway projects but because the DMRB is the best UKsuch a good client design manual, it’s approach is often adopted outside the highways sector and has influenced the way that large UK consultancies operate, with a growing number of geotechnical designers (outside tunnelling departments) focusing on the requirements of BS EN 1997 rather than to the full suite of eurocodesEurocodes.

Should civil engineers, who design structures that interact with the ground practicce both geotechnical and structural design, demonstrate understanding of how the imposed actions have been derived? Or, at least, understand what actions are reversible, which must co-exist, and which partial factors have or have not already been applied via BS EN 1990 and 1991 before a particular geotechnical limit state is checked? This issue resides within the UK and countries that are influenced by British engineers.

In large global multidisciplinary organisations with operations in Italy, Czech Republic, Hungary and other European countries, engineers regularly practice both geotechnical and structural design using the full suite of relevant eEurocodes and routinely “own” an entire sub structure design.

UK piling contractors with in-house designer and small specialist geotechnical consultancies who are more agile in their design approach also see the value in combining geotechnical and structural skills as there are lessto reduce interfaces that can create misunderstandings, mistakes or re-work.

For a new civil engineering graduate with an interest in the ground engineering, Initial Professional Developmentintegrated project delivery with a year of geotechnical design, a year of structural design and a year on site (ideally seconded to a contractor or design and build joint venture) would be well placed to take their chartered professional review. An agile desk policy is a good way to enable bridge and geotechnical engineers to sit next to each other when working on the same structure and pay as you go network licencing agreements reduces the cost of individuals having access the full range of multi-disciplinary software.

Look ahead 10 years and, using this more united approach in the UK, we could be well harmonised with Europe, assuming the Brexit business doesn’t cause too many problemsturn sour.

Alan Willoner is technical principal with Mott MacDonald

 

 

 

 

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