Due to the transition towards a circular economy, sustainable design strategies are growing in importance. An example of such a strategy is IFD: Industrial, Flexible and Demountable design. This design strategy has been developed recently and focuses on modular designs that can be changed in shape and whose components can be demounted and reused. This thesis aims to investigate how the principles of IFD can be applied in the design of a sustainable superstructure for an overpass. The goal is to assess which structural system is best for use in a sustainable IFD overpass and to determine how the overpass can be converted into a modular overpass by focusing on connections and module dimensions. To demonstrate the potential of the IFD design, the sustainability benefits of the overpass are evaluated.

Through a review of literature on IFD and similar design strategies, guidelines were formulated that are relevant for overpasses. Based on the guidelines, designs for three structural systems were developed using a preliminary design approach. These designs were assessed on their environmental impact and compliance with IFD principles, using an Environmental Cost Indicator and Multi-Criteria Assessment respectively. Due to its good behaviour on both aspects, the Composite alternative was found to be the best.
Then, a literature study on the connections was performed to investigate the different options. The number of relevant shear connectors was reduced to four by considering the tolerances for assembly and the protrusion of connectors from the main elements of the structure. A finite-element model was made to evaluate the effects of the four different shear connectors on the structural behaviour. To be able to use the connectors in the model, an elastic limit was imposed to ensure demountability and reusability; small adjustments were made on the reported behaviour of the connectors using a parametric study. From the four remaining connectors, the Embedded Coupler Device connection without injected resin was found to be the most favourable, due to it requiring the lowest number of connectors in the serviceability limit state. For the steel girder connection, a shear-loaded bolted connection was proposed; shear keys were found to be a good solution for the deck connection. Moreover, module dimensions were determined based on sustainability considerations and IFD principles, leading to the final design.

The proposed design shows that IFD principles can successfully be applied to come to a design for an overpass. The use of a small selection of modular elements and demountable connections creates a flexible design, which complies with all the IFD principles. By application of a structural system with a low environmental impact, sustainability of the design is also accounted for.

The IFD design is competitive in situations where the overpass is extended or when it is disassembled and reassembled, since for these scenarios it ends up with the lowest overall environmental impact. This leads to the recommendation to use IFD design in situations where flexibility and reusability are advantageous.

Soil is an important part of a railway track structure. It provides the foundation for the structure and distributes the imposed loads. Consequently, soil has an influence on the condition of a track structure and a low quality soil can ultimately cause failure of the track structure. To be able to include the condition of a soil in the assessment on track quality, the following research question is posed:
“What is the quantitative influence of soil on the track condition for the railway tracks between Utrecht and Den Bosch?”

To be able to answer the research question, first the influence of soil on track condition is distinguished. The most important failure types, progressive shear failure and excessive plastic deformation, are best characterised by the strength of the soil and the deformation of the tracks respectively. For these characteristics a method is developed, which assesses the track condition. For strength a bearing capacity approach is used and for deformations a beam-on-an-elastic-foundation model is used. The process of the method is illustrated by executing it for a specific trajectory, being the Utrecht-Den Bosch line in the Netherlands. To take into account the variability of different soils, the soil type and some specific soil parameters derived from Cone Penetration Tests are determined and applied in the calculations for the assessment.

From the results can be concluded that for the Utrecht-Den Bosch line, the track quality considering passenger trains will either deteriorate limitedly or not at all. This is the case for quality related to both strength and deformation. For cargo trains, the quality related to deformation is such that limited deterioration can be expected. For strength, however, a large number of sections has a condition varying between the failure level and the desired level, which means that significant deterioration is possible, though, there are sections with higher quality as well.