# Digital Twin for Supply Chain Coordination in Modular Construction
## 2 Literature Review  
### Supply Chain in Modular Construction  
The supply chain of modular construction involves many interdependent parties (e.g., manufacturer, retailer, and assembler) thus supply chain coordination is essential for a successful modular project [3]. Such coordination requires efficient information sharing among project participants to achieve a project goal (e.g., schedule reduction). Over the last decades, BIM has been widely applied in construction supply chain management. [PERSON] et al. [17] suggested a BIM-based information flow process model for a reinforced concrete supply chain. [PERSON] et al. [18] suggested a 4D BIM-based supply chain model to optimize logistics and on-site production. They stated that 4D BIM, which includes 3D BIM geometry and project schedule information, can help communication among stakeholders with better visualization. [PERSON] et al. [19] provided a BIM- and discrete event simulation-based supply chain management model for effective team coordination. [PERSON] et al. [20] and [PERSON] et al. [21] suggested a cloud-based BIM data sharing service to exchange project schedule and status information among project participants. [PERSON] et al. [22] argued that BIM helps supply chain integration and may enable 'just-in-time' delivery that reduces cost and waste in modular construction. [PERSON] et al. [23] suggested an integrated blockchain technology and BIM for more traceable and immutable data communication in supply chain process. These studies show that BIM facilitates information (e.g., schedule and cost) sharing for design, fabrication, transportation, and onsite work; thus it has good potential to improve overall supply chain coordination in modular construction.  
However, BIM-based supply chain management is limited in the logistics stage. BIM barely supports the logistics process because it does not have geospatial data. For example,to find logistics risks (e.g., road accessibility, accident zone, and curfew) or to find the optimal module delivery route, external geographic information is needed together with BIM. Recent studies have thus tried to combine BIM and GIS for more accurate and effective logistics monitoring and management. [PERSON] et al. used BIM and GIS to select optimal suppliers considering their transportation distance and material unit price. [PERSON] et al. [24] and [PERSON] et al. [25] integrated BIM and GIS to visually track logistic statuses together with spatial data for material delivery time estimation. Despite the potential of integrated BIM and GIS for logistics management, existing approaches do not often take into account dynamic transportation conditions (e.g., traffic and regulations), which makes it hard to estimate accurate module delivery time. Furthermore, modules leaving the factory are often large and heavy which are more vulnerable to real-time transportation conditions. For example, when an accident occurs on a highway and an alternative route needs to be taken, a more elaborate plan is required because the routes a modular truck can enter are limited in terms of size. Also, there is often not enough space to store a large module on site, so 'just-in-time' delivery is particularly important in modular construction. [PERSON] et al. [26] have noted that module delivery delay is still one of the most critical risk factors that derails the benefits of modular construction in practice. Therefore, modular construction logistics require more sophisticated schedule management than previous stick-built construction methods; more accurate and reliable logistics monitoring and simulation techniques are thus necessary for more effective supply chain coordination.