TECHNICAL | LININGS - SCL
BTS DESIGN GUIDE FOR SPRAYED CONCRETE LININGS
The BTS has published its best practice design guide on ‘Sprayed Concrete Linings
in Soft Ground’. Background to the guide is shared and description of its contents provided by the Technical Subcommittee’s Chair, Bethan Haig
projects; the A3 Hindhead tunnels; and, the ongoing HS2 works. For the task, the BTS first established a Working
Group to share best practice from all aspects of SCL back in 2011, when the Crossrail project was in full swing. Some delays due to the global pandemic and the authoring team being particularly busy meant that the document was finally completed at the close of 2025. These delays meant that developments in design
and materials have been able to be incorporated over the years, including: lessons learnt from the transition to using fibres to provide flexural capacity in primary linings (avoiding the need for lattice girder and rebar reinforcement in many circumstances); and. methods to reduce the workforce needing to enter the face. The guide can be used as a checklist for designers,
SCL works on Crossrail project, London. PHOTO CREDIT: TFL/ CROSSRAIL
The British Tunnelling Society (BTS) is pleased to share that the latest free-to-download guidance produced by the Technical Subcommittee - ‘Sprayed Concrete Linings in Soft Ground: A Best Practice Design Guide’ - is now available to read. It has been published and made available by Emerald Publishing. The guide aims to provides comprehensive guidance
on the design of sprayed concrete linings (SCL) in soft ground, particularly in London Clay. It is intended for designers, project managers, contractors, and clients involved in SCL infrastructure projects. Published at the end of 2025, the guide covers
industry standards, excavation sequencing, material parameters, sustainability, fire safety, and monitoring. While the HSE guidance produced in the wake of
the collapse of the tunnels at Heathrow (Safety of the New Austrian Tunnelling Method (NATM) tunnels), established many of the tunnel management practices employed by the industry in the years since, subsequent lessons learnt, from successful projects, had not been gathered together and shared. The document seeks to build on the ‘Tunnel Lining
Guide’ produced by the BTS in 2004, folding in the knowledge gained from a number of projects, including: the Elizabeth Line (nee Crossrail); London Underground’s series of station upgrades; utility
30 | March 2026
contractors and clients to ensure they are using the most up-to-date methodologies and maximising the efficiency of their sprayed concrete linings. While the guide is written based on projects in the
UK, and undertaken in London in particular, the lessons will be relevant to any projects using sprayed concrete linings (also known as the Sequential Excavation Method (SEM), or Conventional Tunnelling Method in other countries) around the world. By making the guidance free to access, the BTS
aims to fulfil its role in promoting best practices and encouraging tunnel projects to be as sustainable and safe as possible. It emphasises collaboration, risk management, and continuous improvement in design and construction practices. The document also guides those needing further
information with a detailed list of standards, codes, and references for further reading and guidance. Comprehensive knowledge of the relevant geotechnical
and structural standards will not be replaceable for those with design responsibilities, but the guide can help ensure they have considered practicable permutations, while also leading those less involved in the design details and analysis to ask the right questions. Key chapters include:
● Design Process: the guide emphasises a risk-based approach, progressive design development, and
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