Geotechnics View - Choosing the Right Solution

Jul 25, 2016

Remediating 180 year old railway earthworks provides countless challenges to the practicing engineer. During a recent inspection of a section of cutting along the Liverpool to Manchester railway I was reminded that this was the world’s first inter-city passenger line, opening in 1830. It struck me that providing earthwork solutions for Britain’s rail network is unique in terms of the age of the asset and the various constraints on construction. Unlike other linear assets, there is generally no opportunity for a rebuild
and works must be carefully planned to limit impact on rail operations. Combined with tight working clearances, extensive electrification and trackside equipment and the remote nature of certain sites, you have an extremely challenging but rewarding environment. Understandably, given budgetary constraints and growing pressures on the railway, the asset management process is now underpinned by risk assessment. With around 185,000 earthwork assets within Network Rail’s control, it is invariably a case of picking your battles to ensure that critical assets are identified through inspection and monitoring.

The process of choosing the right solution for a failing earthwork is always a balancing
act between technical aspects, buildability and budget. Network Rail’s most recent earthworks asset policy provides useful clarification of the earthwork solutions available, classifying them as renew, refurbish or maintain. Renewal implies significant works to a cutting or embankment to reduce the risk of instability.

The expectation is that these works will be designed to Eurocodes and achieve a design
life of 60 or 120 years. Refurbishment works are less extensive and often limited to resolving a local earthwork defect. The maintain classification indicates nominal works which maintain the asset at a steady state. This classification scheme has proved useful in defining the expectation of Network Rail and what interventions can be considered.

Inevitably the transition between intervention types is not entirely clear cut. The
case of heavy cess support provides a good example. The presence of steel piles will help resist deep seated slope movement, but won’t necessarily protect against shallow instability of the embankment flanks. For this, and other scenarios, the project team must weigh up the benefits in terms of buildability and cost against employing more robust, but expensive options. To ensure a successful project outcome client, contractor and designer must collaborate to identify risks and constraints. As new technology becomes available, the engineer must also embrace innovation to provide robust, value-engineered solutions. Of course this won’t be possible without adequate funding. Given the age of the infrastructure, I feel future earthwork budgets will need to increase significantly with additional focus on monitoring and proactive interventions. Provided this investment is there, I see no reason why our railways won’t be around for another 100 years or until the next great innovation in public transport arrives.

Written by David Jowett, Associate Director at ByrneLooby.
This article featured in the August 2016 NCE edition.