The Hong Kong Government’s Construction 2.0 recognises the importance of Building Information Modelling (BIM) to the future development of the construction industry. The Buildings Department (BD) of the HKSAR Government also encourages authorised persons, registered structural engineers and registered geotechnical engineers to consider adopting BIM in their building projects.
Many project owners in Hong Kong, including the Airport Authority Hong Kong (AAHK) and government bodies, already mandate the use of BIM in their contractual requirements. These requirements usually relate to modelling the Employer’s Design to a specified level of detail (LOD), coordination and clash analysis, and sometimes the provision of programme simulations known as 4D.
For Leighton Asia, the Terminal 2 (T2) Foundation and Substructure Works at the Hong Kong International Airport (HKIA) project is no exception. It is a flagship project which has raised the implementation of digital engineering to the next level.
In addition to the employer’s foundational BIM requirements, the Leighton Asia T2 team (“the T2 team”) has adopted digital engineering throughout the planning and execution phase of the T2 extension project, showcasing how enduring value can be created for the client.
As part of the AAHK strategic Three-Runway System project, the T2 contract includes construction of the South Annex Building foundations and basement for the T2 expansion, together with various associated civil and external works.
Figure 1: Photomontage of excavation and lateral support works
To prevent potential disruptions to the operation of the world-class international airport and to minimise dust and noise impacts to surrounding HKIA stakeholders, the T2 team decided to retain the roof and façade of the building for as long as possible. This meant adopting an innovative “inside out” sequence in which the retained structural framing is critical to maintaining the structural stability of the building.
After developing the initial work sequence in plan and section, the T2 team decided that the process would be much better planned, understood and communicated using digital engineering tools. Accordingly, the T2 team leveraged the capabilities within its broader group and commissioned a BIM model of the existing building to LOD300 following the AAHK BIM Standards.
Figure 2: Sequence of works
A custom parameter was also added to assign structural elements to different stages and sub-stages of the works. The sequence was modelled according to the first plan. Immediately the model showed its value in highlighting the complex interaction between the different levels of the structure that was not apparent from the 2D drawings.
The single source of truth
Existing standard practice in Hong Kong is for designs to be developed using 2D tools and then modelled to form 3D illustrations. Unfortunately, these cannot be described as true “digital twins” and might give rise to many discrepancies and errors between the two sources of information. In fact, 2D drawings can be produced directly from the authoring software, consistent with the 3D model. The great advantage of using a model to develop drawings is that when new information is added, the drawings update themselves.
A simple example is to compare the plan and section of a beam when the beam size changes. With traditional drawing tools, both the plan and section, and all the annotations on those sheets need to be updated. With drawings produced from the model, changing the model element will update both the geometry and the annotations without any further input from the draftsman other than perhaps checking the visual appearance.
This concept may be expanded when the model becomes ”the single source of truth”. Every new piece of information received about the structure, including the architecture, the mechanical and electrical equipment can be added to the model. That information is immediately available on every affected drawing, including point cloud surveys, used extensively on the project. This naturally introduces a different design management challenge, in that the sudden appearance of new information on a nearly completed drawing is disruptive to the process of finalising and issuing it. However, in the case of an existing structure with incomplete records and the gradual receipt of information, the 3D informed approach is far preferable. This approach is superior to relying on a frozen set of as-built drawings, since the method and sequence finally adopted must suit the site condition to be useful.
Meanwhile, the BD recognises that for alterations and additions plans, applications of BIM include the final stage of partially demolished structures, the sequence and phasing of works, method statements and temporary precautionary measures. The T2 team therefore decided to use the model to develop the detailed method, sequence, phasing and precautionary measures for the works in the model and produce the submission drawings from the model. This included presenting the sequence and methodology with 3D illustrations as far as practicable for better understanding by reviewers and the site staff using the drawings.
The submission by the T2 team is somewhat uncommon among the statutory submissions to be made to the BD, in that some parts more closely resemble a method statement than a design for approval. The submission as approved contained a mix of 2D drawings to convey design information and 3D graphics to convey the method and sequence, but all of them were produced from the model.
Figure 3: Approved drawing produced from the model
4D simulation of construction works
The value of the model to the T2 team continued from the planning stage into the construction stage. Since the method and sequence had previously been planned in detail, method statements and rendered simulations of the works could be prepared for efficiently briefing the site workers.
A forward looking 4D simulation of the works was prepared by matching the construction stage parameter to programme task identifiers. Meanwhile, the progress of works was tracked in the model with another custom parameter. This not only enabled the rapid quantification and tracking of progress but also enabled live updating of progress drawings and backward looking 4D simulation of works. Additional information learned during site work was then fed back into the model as “the single source of truth”. This input was used in the development of design amendments to ensure they were up to date and consistent with the reality onsite.
Digital engineering is reaching the next level of maturity in the construction industry. Full innovative implementation of BIM has brought many benefits throughout this project from design and planning to the execution stage.
Figure 4: Design drawing updated to show work progress from the model
About the author: Ir William Hopkin is the Senior Design Manager of Leighton Asia.