With digitalisation and building information modelling (BIM) gaining ever increasing importance in all sectors of infrastructure asset development and operations, the latest guidance on the field for the global tunnelling community was published last month at the World Tunnel Congress (WTC), in Copenhagen.
The International Tunnelling and Underground Space Association (ITA) published its BIM guide to have a focus on segmentally lined bored tunnel projects. ITA’s guide has been produced by the organisation’s Working Group 22 (WG22), which considers information modelling for underground infrastructure.
A 32-page guide, the ITA report is called BIM in Tunnelling: Guideline for Bored Tunnels (Vol 1) and has 16 sections. After developing a briefing on what BIM is for underground space, and discussing information management, definitions, classifications, data formats, ground modelling, sustainability and geographical information systems (GIS), the guide concludes with two extensive appendices that contain checked tables that cover BIM use cases and those levels of definition, respectively.
ITA said WG22 developed the guide to support implementation of BIM in the tunnelling industry, doing so by providing recommendations that should be considered and adapted to developing and available best practices in project supply chains. Its audience is both tunnellers and asset owners.
However, the guide is not meant to compete with or claim superiority to local best practice or project owner’s systems, such as Employer’s Information Requirements (EIR). The aim is to have the guide provide more detail and clarification, to “alleviate ambiguity” due to generalised definitions.
With its focus on bored tunnels, the guide does not cover all underground construction and it has more BIM guides in development, such as for conventional tunnelling. Non-heavy civil engineering aspects of assets creation are not featured, such as mechanical and electrical, control systems, internal structures, ventilations, etc.
ITA points elsewhere for more general information of the use of BIM for underground construction, such as those published by The German Tunnelling Committee (DAUB). There is also the Norwegian Tunnelling Society’s (NFF) publication No28, out in 2019, called Digitalisation in Norwegian Tunnelling.
Meanwhile, the BIM for bored tunnels guide, albeit new – and like others to follow on other aspects of tunnelling, will have updates as the rapidly moving field develops still further.
BUT WHAT IS BIM
BIM is often used as an umbrella term, says the ITA guide, for it covers much including generation and management of asset information, ideally through their lives from concept to creation and operation and maintenance.
But various digital tools and methods for holding this information as well as encompassing legal and contractual rules and agreements surrounding the activities, and ways owners and supply chain parties might wish to use the systems, also fall under the purview of the catch-all term of BIM.
Taken all together, BIM can end up being confusing and seen to be open to wide interpretation. ITA’s working group took the view to describe BIM more of a process approach, a methodology.
Particular software, programs, models or data structures therefore are not vital to understanding BIM while they fit within its operations; neither are the varied ways the supply chains may wish to utilise the systems, such as computational design, visualisation systems, clash detection, 3D spatial and 4D/5D approaches (i.e., adding time and cost dimensions to models) to be equated to specifically and exclusively being BIM.
It is about the process approach, overall.
As such, it should fit well with what engineers, tunnellers and all project development and asset owning professionals should appreciate, no matter if they deal in digital or other systems. It is about getting and managing the data and details to make or operate an object, and that can be done in many ways, including increasingly the use of digital tools, and held in many way – and the strategic aim in many BIM-related discussions is to move toward centralised digital environments, or Digital Twins.
So much, then, could be looked at in underground infrastructure. But a start needed to be made for the global industry and so, with such an understanding of BIM, and ITA’s WG22 decided to look first at segmental lined bored tunnel projects.
While such projects and other tunnelling approaches and structures may have a common approach to using BIM, it was noted that each area has its own variations, its aspects to be addressed as part of the data gathering and management process. For bored tunnel this arises with tunnel boring machines (TBMs), such as logging or tracking process data as well as that of geotechnical, geological or ground characteristics.
USES, LEVELS AND CLASSIFICATION
To effectively align the BIM process, goals need to be set – purpose chosen. These tasks or objectives get known to be BIM Use Cases, when properly aligned to EIRs and terminology employed in do so matches or has alignment with that of buildingSMART systems.
They also help to clarify what to use, how and when. As such, the information load and demands varies greatly between Use Cases.
A list of BIM Use Cases is provided in the guide’s appendices, and categories can include: design variants investigation; design production environment; sustainability; surveying; 3D ground modelling; GIS; bill of quantities; procurement; scheduling; logistics; compliance management; progress control; invoicing; monitoring; and digital twins.
Then, the information management vision determines how these Uses are brought together for the BIM process to work effectively, and the nominate or required levels of definition/information required – and recommendations vary on those in general, and in suitability for different types of projects, such as tunnels.
In that regard, a bored tunnel is defined as an extruded tube in 3D space and also has generic information for the tunnel as a whole, the guide explains. It also includes a Tunnel Model on this in the appendices.
Another layer of information arises from the BIM approach not holding details as simple data entries but as digital objects with data associated, and as such a rigorous approach to naming and classification is needed.
Again, not a new task in project development for engineers and tunnellers but one that is fully digitised and requires an integrated, hierarchical whole for the objects to work together which is the intention. And that is without even looking at formats needed for software systems to talk and share but this aspect, too, is addressed by the new ITA guide.
With all of these decisions to be made it is clear that the ultimate information holder in terms of the asset – the project owner – needs to set the vision and rules for using BIM processes.
GROUND MODELLING
Interestingly, the guide begins its section on ground modelling by noting that ground information, although vital and fundamental to underground construction, is not always specified in a BIM model.
The guide therefore not only encourages but gives recommendations on how to do so for information such as data from pre-construction boreholes and geophysical and geochemical surveys, and geological models. Data can also come during the tunnelling stage from face mapping and probing ahead.
It adds the importance of data from instrumentation and monitoring for inclusion, too, for during the creation of the structure as well as its operational life.
The different formats that ground information and data can be held is discussed.
But unlike for materials used for surface structures, ground information is sampled data and therefore never complete and so is updated as projects progress. In addition, the guide notes, in BIM the data structures also often differ.
There is discussion, too, on factual versus interpretive data (and contractual versus noncontractual).
The point is made that, especially in a data-information environment, shared and used widely across a project, uncertainties in interpretation not only be quantified but classified, and reported, within the system – even as approaches vary internationally.
The overall advice, therefore, is that “added value” is sought and not heaped complexity in this area that already requires some “specialist interpretation”.
