neering (SE). Nowadays, this approach is more and more instructed by clients in the Netherlands. The switch to Systems Engineering was necessary because of the development of integrated contracts (UAV-GC; Uniform Administrative Conditions for Integrated Contracts) such as Design-Build-Finance-Maintain (DBFM) and Design & Construct (D&C). Before the introduction of integrated contracts, mainly RAW contracts (Rationalization and automation Soil, Water and Road Construction) were used in the Netherlands for public procurement in infrastructure projects. In RAW contracts, the to be built system is described in detail and the segregation of responsibilities between client and contractor is distinctly defined. In integrated contracts, this distinctly defined segregation of responsibilities is missing. As a result of the integrated contracts, the projects became more complex and multidisciplinary, which asked for a more structured approach (Emes et al., 2012). Another difficulty of integrated contracts is the communication between client and contractor because more information has to be transferred. An important element of SE are the verification and validation processes. This validation process is considered complicated in the civil engineering industry. Four subproblems are determined by means of literature and practical knowledge. First, the interaction between client and contractor. Findings of a questionnaire performed by the CROW (2017) about the relationship between client and contractor are:56.9% of the contractors’ employees do not feel equally treated by the client, 43.6% of the clients’ employees and 69.7% of the contractors’ employees agree on the statement that the other party is mainly defensive instead of cooperative, another issue during the interaction between client and contractor is trust. 23.3% of the clients’ employees and 17.7% of the contractors’ employees say that the other party cannot be trusted, 73.6% of the clients’ employees and 73.5% of the contractors’ employees disagree on the fact that the other party puts the common interests of the project above their own interests. The second subproblem is the confusion between verification and validation. Verification is the process of determining if the system meets the specified requirements (Alsem et al., 2013). Nevertheless, the purpose of the validation process according to ISO (2015) is "to provide objective evidence that the system, when in use, fulfils its business or mission objectives and stakeholder requirements, achieving its intended use in its intended operational environment" (ISO, 2015, p. 74). The third subproblem is executing sufficient validation. The difficulty is to represent the client and stakeholders needs in requirements. Therefore, the validation is often conducted last-minute in the construction phase of the project. The fourth subproblem is that the effects of the use of 3D visualisation during design validation on project performances are unknown. These problems result in the following research objective and question. The aim of this research is to gain insight in the effects of 3D visualisation during the design validation on the project performances, namely time, costs and quality. What are possible effects of 3D visualisation on design validation within the civil engineering sector in the Netherlands? The methodology for this research consists of three phases: (1) context, which includes literature and project evaluations, (2) experiment, which contains baseline and follow-up measurements and (3) the results and conclusion. Phase two, experiment, is a gaming simulation called the ontwikkelstraat. In this research, the following definition is used for gaming simulation: "a special type of model that uses gaming techniques to model and simulate a system. A gaming simulation is an operating model of a real-life system in which actors in roles partially recreate the behaviour of the system (Meijer, 2009)". The Ontwikkelstraat is a two-day case imitating a project from tender till exploitation and includes design, construction and maintenance of a hydrogen factory. During this gaming simulation, three types of measurements are conducted: questionnaires, recordings of the interaction between client and contractor, and observations. According to the literature, sufficient design validation has to fulfil several conditions. The aim is to acquire proof that the system in its ability to achieve its intended use (ISO, 2015). Rijkswaterstaat (2017) prescribes three conditions the design validation should meet, namely design validation is an integral element of the design process, confirmation by client and stakeholders, and determine the validation process in cooperation with the client. There are multiple ways of conducting design validation. Several design activities are of importance for design validation. During the system design phase, these activities are analysing contract documents, as well as document functionalities, requirements and systems. In the preliminary design phase, these activities are based on the variants and validation of the design products. It is concluded from the three cases studied that alignment of the design products with client and stakeholders is a key validation step in all cases. Bryde et al. (2014), Sebastian and Van Berlo (2011), and Azhar (2012) described the capabilities of 3D visualisation. Three-dimensional visualisation can be static or dynamic. With a static image of the 3D model of the design, the communication and coordination between actors and disciplines are more detailed. By decomposition in subsystems and objects, the technical details of the design can be sufficiently discussed during the validation sessions with the client and stakeholders. Another capability of the 3D visualisation is expectation management between contractor, client and stakeholders. 3D visualisation can also be used for dynamic images for moving systems, such as locks and movable bridges, which can be used for showing the functionalities of the design. Dynamic images can confirm that the design meets the intended functionalities and use of the system that is going to be built. Currently, 3D visualisation is used within the civil engineering sector in the Netherlands is by means of BIM. Within the civil engineering sector in the Netherlands companies deviate in the BIM maturity level, as well as the multiple subsidiaries within the contractor firm VolkerWessels. According to the BIM wedge that is developed by Bew and Richards (2008), level 1 of the BIM maturity is implemented. Therefore, the use of 3D visualisation is implemented in all integral projects within the infrastructure branch of VolkerWessels. The 3D models are used for clash detection, reinforcement in concrete, immediate vicinity and quantities. Conclusion According the results of the gaming simulation, visualisation does not have an effect on the project performances time, costs and quality. A possible explanation that no effect of visualisation on the project performances has been found is that the physical model of the hydrogen factory in the ontwikkelstraat was only used during one of the follow-up measurements. During the other two follow-up measurement, the physical model was not used by the participants. The follow-up measurement where the physical model was used, it was used by one participant, who built the model. However, the participant did not communicate his findings from the physical model to the other project team members. Therefore, there are not enough results to conclude that there are no effects of visualised validation on the project performances. From observations during the gaming simulation, it can be concluded that not the availability of the 3D model, but the standard practice of project teams is the issue. This research aimed to fill the theoretical gap on the effects of 3D visualisation on design validation. Although this aim is achieved, every research has to make compromises to stay within scope. The main limitations are presented in the itemisation below. • Lack of proper literature regarding the conditions for sufficient design validation; • Small sample size of the gaming simulation, which makes it harder to generalise the findings; • Time constraints during the gaming simulation, the participants are under a lot of time pressure during particularly the design phases. Therefore it is possible they overlooked the physical scale model. Soms suggestions for further research are: • It is found that not the availability of the 3D visualisation is the problem, but the standard practice of project teams play a role. Therefore, research on the problems of implementation of 3D models during design validation and how to solve these problems would b relevant for the whole construction industry; • During the project evaluations, it has been found that the way of handling changes in the contract after procurement is challenging. It turns out that validation of the design is often obstructed because the results of the validation process can result in uncertainties for all actors in a construction project. Research on the politics behind the changes in construction projects is relevant, because of the uncertainties these politics bring in the development of projects and the relationship between all actors that are involved; • Lastly, further research on the interaction between client and contractor is needed. Research on the development of achievable strategies to manage the counterbalance between collaboration and competition between client and contractor would be significant. Recommendations for practice Based on the literature and project evaluations, a proposed approach, called visualised validation approach (VVA) is developed. The VVA is a combination of two different project management methodologies, which are the V-model and the scrum. During the System design phase, three activities are essential: determining V&V management plan, requirement validation, and interaction with the client about the intended use of the system. The preliminary design phase is an iterative process, with scrum design sprints and validation sessions with the client and stakeholders. The biggest challenge in the construction industry is the implementation of the visualised validation approach. According to an internal investigation, the accessibility of the process and in particular the 3D mod- els have impact on the implementation of the VVA. Several employees indicated that they are reserved to use new approaches because of the lack of skills or manpower.