The growth of projects has elicited much interest in the last decades, both in academia and amongst practitioners. The increase in scale and complexity has further brought attention to the particulars of interorganisational collaboration: as projects grow, the relevance and impact of interdependencies between participating organisations rise to the surface. No organisation is an island and so a project becomes an archipelago of interconnected networks.  Current literature on interorganisational collaboration focuses on contract and procurement, both important aspects of project management. There is, however, less research pertaining to project realisation and how these changes in interorganisational collaboration shape the project process.   A field where this change has been especially noticeable is the infrastructure construction industry, where collaborative project management models have been introduced to reduce adversity and improve project outcomes. These new models necessitate a study of changes these new models bring with them to the conventional ways of work within the field, as they call for new processes and roles in the projects, thus changing how the actors engage with the project network. As such models are based on collaboration, the role of social ties within the project become an especially  interesting question. In this work, I expand on the theory pertaining to project networks in the empirical setting of infrastructure projects applying a collaborative project management model, with the aim of examining and gaining a deeper understanding of the collaboration between interorganisational project actors in a collaborative project delivery model. The methods used in this thesis are based in the qualitative research tradition and emphasise interviewing and observation. During this work, 44 interviews were completed in a pre-study and two case projects and observation of both project’s shared office space was carried out. I also analysed project documents and analysed the social network between respondents in the case projects.   My results show the importance of social relations as enablers of the realisation of expected benefits of collaborative models. They moreover illustrate the changes necessary for the models to be effective, as well as study how the use of such project models affect the actors’ engagement in the project network.