With all the upheavals of 2022 such as the passing of the late Queen, having the third Prime Minister in a single year at the time of writing and the deeply disturbing ongoing multi crisis it is easy to overlook that we celebrate a successful 25 years of the BTS/ICE Specification for Tunnelling in 2022. An internationally well recognized flagship publication of the BTS, it has stood the test of time very well and is still highly relevant to the global tunneling industry more than ten years after its last revision was released. The major projects conducted since have benefitted from the document but in turn have indicated the need to review and update some elements of the specification to capture emerging Best Practice as well as to allow for the increased maturity of sprayed concrete and fiber reinforcement technology, in particular.
The engineering landscape has changed significantly since 2009. As recently highlighted in COP26 hosted in Glasgow, adaption to combat climate change is required. Since then, the war in the Ukraine and the corresponding disruptions of the supply chain, combined with significant inflation have further changed the priorities of our customer base. Selecting “Underground solutions for a world in change” as topic for the World Tunnelling Conference (WTC) 2022, in Copenhagen, demonstrates that awareness of change and the need to engage with it are firmly on the agenda of our industry.
Here in the UK we benefit from the collaboration and learning opportunities provided through the sequence of mega infrastructure projects Crossrail, Tideway and HS2 which facilitated a cross industry and cross stakeholder exchange of ideas, leading to considerable communality of what is considered Best Practice in tunneling.
As the BTS, our role is to link between major projects, standard-developing bodies and the UK tunneling industry. We monitor guidance and evaluate best practice, which we in turn consolidate into our BTS/ ICE specification for use on projects large and small, world wide. Within the global tunneling community, the BTS/ICE Specification for Tunnelling enjoys considerable popularity. One important aspect of the BTS Specification is its comprehensiveness, capturing the majority of aspects of tunneling. It is unique in this aspect, and the “one stop shop” approach is contributing to a large extent to this popularity.
The BTS as a body represents the whole of the UK tunneling industry and thus facilitates collaboration. Industry initiatives such as the Transforming Tunnelling Safety Group (TTSG) as well as representation in British Standards Institution (BSI) and European Committee for Standardisation (CEN) drafting committees, together with our strong representation in the working groups of the International Tunnelling Association (ITA) allow the promotion of Best Practice through the various publications of these organs, in particular through the BTS/ICE Specification for Tunnelling.
The technical sub committee (TSC) of the BTS decided in 2020 to produce an update and revision of this Specification, organized and facilitated through the BTS with the inclusion of relevant stakeholders and subject matter experts within the UK tunneling industry. Our stakeholders include key client organizations, the supply chain and partner organizations both domestic and abroad.
We decided to approach this update with a strong focus on sustainability. A task force drawn from sustainability specialists reviewed the 3rd Edition of the Specification to identify “sustainability inhibitors”, i.e. specification aspects with the potential to prevent application of sustainable methods and materials. The task force identified prescriptive clauses (such as minimum cement content, or specific types of material) as problematic.
Having set this overarching principle, we facilitated workshops on specific evolving and potentially contentious topics, namely sprayed concrete, fiber reinforcement, segment accessories, and segment tolerances. The workshop results were used by the subject matter experts (SME) assigned to each section to review and evaluate existing content, and to develop new content where appropriate.
Every sub clause in the BTS Specification was reviewed. More than 60% were changed, and three new sub clauses were introduced to the Specification. The following paragraphs illustrate key changes to the Specification.
INTRODUCTION OF COMPETENCE MANAGEMENT AND UPDATING SAFETY RELEVANT CONTENT
The TTSG has collaborated to produce the SKATE competence matrix for tunneling which consolidates best practice and benchmarks the role levels and Skills, Knowledge, Attitude, Training and Experience criteria for most occupations involved in shaft and tunnel construction.
Recognizing the importance of competence assessment and competence management the 4th Edition of the Specification newly contains the new Clause 109 which captures the establishment and management of a competence framework, and specific training requirements. The reader is pointed towards the SKATE matrix, whose current version is hosted on the BTS website.
This new content is one facet of a full review of our specification for compliance with revised Best Practice and H&S relevant regulation in tunneling, mainly consolidated in the reviewed and updated Section 107 which in turn refers mainly to BS 6164:2019.
SUSTAINABILITY FOCUS
A new Clause 101.2 – Carbon management introduces the management hierarchy of PAS 2080 into the Specification for Tunnelling and jointly assigns the responsibility for identifying carbon reduction opportunities to the Designer and the Contractor. The carbon management process is to be part of the project’s quality management system and can therefore be used for performance monitoring.
Carbon footprint can be significantly reduced with the use of alternatives to Portland cement, such as alkali activated binders, or glass fiber reinforced plastic as replacement for conventional rebar. However, such materials are typically not standardized or might still undergo the standardization process which complicates their use in structural design, where compliance to codes needs to be demonstrated. Similarly, the durability of novel materials needs to be demonstrated.
The Specification refers in these cases to a “design assisted by testing” approach, as standardized in e.g. BS EN 1990, and has removed specific requirements for cement type in concrete from the Specification.
While these additions facilitate the use of the BTS Specification in a more carbon conscious construction environment they do not constitute a universal baseline specification for carbon-aware design, as the regulation and standardization required to consistently address carbon management is still evolving
The interested reader is referred to Allen, C. (2021). Low carbon concrete for shaft and tunnel linings, T&T Nov 2021 and de Rivaz, B. (2022). Moving to low carbon linings, T&T March 2022 for a tunnel specific perspective on low carbon liners as well as the Low Carbon Concrete Routemap currently drafted by the ICE.
SPRAYED CONCRETE AND SPRAYED MEMBRANES
The relevant sections of our Specification have been comprehensively reviewed through a series of workshops where a panel of industry experts assessed the relevant clauses 210 and 305 line by line. Using the experience gained by the scale and complexity of sprayed concrete use on Crossrail and follow up projects allowed significant streamlining of the corresponding sections, resulting in a more flexible, open text conductive to use of cement replacement materials as these emerge.
To the author’s knowledge, Crossrail was so far the largest use of sprayed water proofing in sprayed concrete tunneling.
The BTS specification clauses linked to sprayed water proofing predated the Crossrail project, and while the original Crossrail sprayed waterproofing membrane specifications were based on the BTS clauses considerable changes emerged from practical experience.
These are captured in the updated sections 212 and 313, and together with the reviewed and updated clauses on sprayed concrete allow the implementation of water proofed sprayed concrete with a high degree of confidence.
PRECAST CONCRETE LININGS
Our BTS Specification is a global reference document for specifying tunnel segments and their production. Many of the BTS authors have strong links to the design, production and construction of segmentally lined tunnels, which provided a strong link to the industry and allowed us to identify areas benefitting from improvement.
Therefore, we undertook a comprehensive review of segment tolerances.
While the existing production tolerances were largely not modified we have recognized the increasing popularity of new products such as dowels and cast-in gaskets by providing specific tolerance values.
Illustrations to avoid ambiguity in tolerance interpretation have likewise been provided, as have been clauses on measuring segments to demonstrated compliance with the specified tolerances.
While we recognize the trend towards contactless survey of segments and the aspiration of production control through virtual rings, the Specification still allows to check segments entirely through traditional means such as calipers, templates and feeler gauges as these might be either the appropriate or the available tools, or both.
DOWELS, PACKERS, BICONES
In addition to tolerances associated with dowels and bicones, the Specification now also contains specific requirements on performance declaration and associated testing which we have developed in a workshop with the supply chain. These new requirements recognize the increasing use of these elements in shear where interface effects between the connector and the surrounding concrete can have a significant influence on the short-term and long-term performance of the elements.
Similar performance declarations have been introduced for packing material, again recognizing the trend towards ever more detailed analysis considering material properties explicitly.
PRIMARY GROUT FOR SEGMENTAL LINING
The last decade has seen considerable advances in the design of primary grout used for TBM drives and a significant increase of the use of bi-component grouts. The characterization solely by compressive strength over time has been found inadequate both for cement-based grout and for bi-component grout, in consequence additional tests have been adopted based on the proposals of DB (2022). Ringspaltverfuellung bei Eisenbahntunneln, RIL 853.4006: Eisenbahntunnel planen, bauen und instand halten.
The basis for the publication referenced above is referenced in Gehwolf et al (2022) in Tunnelbau 2022, DGGT. We have consolidated the proposed test in a series of parameter-test standard combinations applicable both for design and for preconstruction testing. In production control it is typically not feasible to undertake any testing beyond strength and strain tests on hardened grout specimen. The results of these will indicate compliance of the product installed on site with the product tested in pre-production
SUMMARY
Updating of the BTS/ICE Specification for Tunnelling is a far reaching effort open to all tunneling practitioners organized within the BTS. The examples above can only provide snippets of the review and update work which has been undertaken by the tunneling industry, leading to what we believe to be a enduringly relevant and helpful document. This is our UK tunneling business card, and a prime reference how to do things right first time, safely, and professionally.
The relevance of the Specification is assured through the peer review process, where the first round is now complete and the comments are reviewed and incorporated into a second complete draft.
