**5. Use-case scenarios**

In the context of BIM workflows, the use of augmented reality is usually associated with three basic use-case scenarios [21]: (1) design phase - review of proposed solution, (2) construction phase - monitoring of construction progress [22] and (3) operation phase – building maintenance [4]. But as identified by C. Woodward and M. Hakkarainen [23] many other relevant use-case scenarios should be considered, including layout optimization, excavation, positioning, inspection, coordination, supervision, commenting, etc.

In the following subsections, three different representative use cases are described. Two of them are based on infrastructure projects (railway/tunnel, bridge) and the last one is based on an office building. In all presented use cases, a BIM specific mobile application [6] has been used to access BIM models as well as to use the integrated AR solution. The mobile apps use a BIM shared data environment solution that provides a central hub for all person-to-person communication, data sharing, etc.

#### **5.1 Use-case 1: infrastructure (design and planning phase)**

The project used for this use-case is a construction of the second railway line from Divača to Koper that includes construction of more than 17.4 km of access roads with various structures serving as service lines for the construction of tunnels, retaining walls and a bridge approximately 35 m long. It is one of the largest infrastructure project in Slovenia.

The first use-case clearly falls into the design and planning phase of the full life cycle using AR for visualization of the construction site organization as well as visualization of the completed structure in real environment. One of the main goals for the use-case was also to examine how AR technology and its implementation in the selected mobile application can be used for an infrastructure projects that are defined primarily with long distances.

We used a tablet computer with augmented reality application to test the usecase in two different locations that are a few kilometers apart. However, both are georeferenced in a 2D model on the tablet (**Figure 4**) and correctly link the required information in the 3D model.

Its integration through AR technology to visualize interactive 3D models on site [24, 25] (**Figure 5**). As seen in the images bellow, it was possible, for example, to check the tunnel portal and MEP installations, railway track to be build, as well as to get the general scale and complexity of the construction site.

Key takeaways: (1) it is absolutely essential that all BIM models are correctly georeferenced for use by AR system, (2) use of tablets/phones can be challenging in bright environments, (3) difficult to orient yourself in the field and correctly position and scale BIM model, (4) can be used for general understanding of future construction site, and (5) determining geolocation can be challenging and it is depended on geographical characteristics of the construction area.
