The use of precast Reinforced Concrete has been the norm for the construction of tunnel linings for decades. However, the use of Steel Fiber Reinforced Concrete is gaining popularity due to its beneficial mechanical properties, improved sustainability, improved durability, and lowered costs compared to traditional Reinforced Concrete (RC). The amount of reinforcing steel can be reduced significantly, lowering the costs and carbon footprint of a project making it an appealing alternative. One application of SFRC is found in tunnels making use of precasted concrete segments, typically built with a Tunnel Boring Machine (TBM). This type of tunnel is found in Amsterdam, namely the
Noord/Zuidlijn: a metro line linking the north and south of the city. This project is used as a reference to perform a feasibility study on the use of SFRC and investigate its benefits.

The research involves a structural analysis of an SFRC design considering the loads and boundary conditions of the original Noord/Zuidlijn. The loads occur at different phases in the realization of the tunnel: transient, construction, and service phase. These loads can lead to various failure mechanisms, with the primary concern being tensile splitting of the concrete. Each phase is defined by a dominant component that governs its behaviour. During the transient stage, involving demoulding, stacking, and handling of the segments, the bending stresses inside the segment need to be checked. During the construction stage, the ring joints of the segments presents a weakness and need to be checked for
spalling and/or splitting of the concrete. During the service stage, the longitudinal joint needs to be checked for splitting of the concrete and the global cross sectional stresses of the lining need to be examined.

Numerical models are created to assess SFRC’s performance in the governing parts of the tunnel during the three phases, with the addition of identical RC models as a basis for comparison. The general bending and shear stresses, as well as localised splitting and spalling stresses, are investigated in both the Serviceability Limit State and Ultimate Limit State. The structural behaviour of SFRC corresponded with the characteristics found in literature, with a higher initial cracking load than RC and a more stable crack propagation due to its residual tensile strength. The peak strength of SFRC is found to be lower, but still passes all the checks. The results show that an SFRC design with the
minimum fiber content of 30 kg/m3 is sufficient for the transient and construction phases, but 40 kg/m3 is needed for the service phase. The benefits of implementing SFRC in the Noord/Zuidlijn can be quantified in a steel reduction of 60%, which would mean a decrease in steel consumption of 3050
tons. The CO2 emissions would decrease with 5500 tons, equivalent to the amount absorbed by 220.000 trees over the course of one year.

The concluding results can be used as guidance when opting for SFRC in a new bored tunnel project. The performed design checks show a governing load situation in both the construction phase and the service phase. The sufficiency of SFRC for the ring joint check during construction is governed by the
splitting force between the loading shoes of the TBM. The magnitude of this splitting force depends on the size of the TBM, the characteristics of the soil, and the depth of the tunnel. A large diameter tunnel, high-friction soil, or deep tunnel will decrease the likelihood of a design with solely fibers. The same unfavorable conditions cause large internal bending moments which could pose problems for the longitudinal joint and global cross section check. A small diameter tunnel and a tunnel constructed in stiffer soil will increase the feasibility of a design making use of solely fibers

The geographical features in the Southern part of Limburg forces precipitation from upstream located areas to flow through a bottleneck, which is exactly located at the city centre of Valkenburg. This makes increasing the safety level more complicated than in other areas. The safety level of Valkenburg has a lower standard in comparison to the rest of the country, namely 1 in 25 years. The combination of those two characteristics is not desirable. Official documents
state that this lower standard is based on detailed (societal) Cost-Benefit Analyses. In reality however, the safety standard is based on simple back of the envelope calculations. The Limburg Waterboard has indeed developed a Cost-Benefit tool which they could use to find out whether the implementation of safety measures are cost effective, however they have not been able to
implement it until now. Additional safety measures to increase the safety level are assumed too costly based on the same brief calculations. It is doubtful whether individual risk laws are met, since the Limburg Waterboard assumes no casualties in the Geul area. The 2021 flood however showed that this might be false for future floods which get more severe over time due to climate change.

The citizens and entrepreneurs in Valkenburg were not completely aware of the risks they were exposed to and their sense of safety related to flooding decreased after the flood. Most of the people questioned in a survey demanded a higher safety level than the current standard. They would even be open for an increase in tax to realise this improvement. Raising the quay walls would be a cost-effective solution according to some of the citizens. However, the entrepreneurs who rely on tourist based income, do not prefer this option due to loss in aesthetic value.

Hydraulic, structural, and non-technical solutions which are investigated in this report, have the aim to increase the safety level or make the safety level more acceptable for citizens. The hydraulic, and structural solutions focus on four main aspects. The first aspect is related to the redesign of bridges in the city centre. This is mainly done by applying a flat bridges design, which is further elaborated with a case study for the collapsed Emmalaan bridge, and a liftable bridge design. The second aspect is related to closing the gaps in the quay walls, and increasing the height of the quay walls. The third aspect is related to the implementation of water tunnel concepts with six different design concepts. The fourth aspect is related to implementing parts of Meerssen’s 4-step approach. The first three aspects of the hydraulic and structural solutions are focused on increasing the discharge capacity of the Geul, while the latter aspect focuses on retaining, delaying, and storing the precipitation. Non- technical solution are also proposed
that focus on making people more aware of the risk they are exposed to. This could eventually lead to more acceptance and thus more pleased citizens.

The first order estimations for investment costs and safety level for the hydraulic, and structural solutions are graphically displayed in order to provide an overview of possible interventions to the municipality of Valkenburg and the Limburg waterboard. Although preliminary, and based on limited available data, these results should encourage both stakeholders, and other relevant parties, to reconsider safety standards and search for measures that could increase the safety level of Valkenburg when desired.