© 2022, Southeast Asian Geotechnical Society. All rights reserved.The design and construction of tunnels is among the most specialized fields in underground engineering. There are various uncertainties during tunnel excavation. Predictable and unpredictable uncertainties are important sources of risk in tunnel engineering. The effect of uncertainty on risk assessment and decision-making is therefore provided priority, particularly for tunnel projects where predictable uncertainty is often the primary cause of risk. First phase of the Kabatas-Mahmutbey tunnel excavation, some collapses occurred due to uncertainties in different parts of the tunnel route. Regardless, Kabatas-Mahmutbey metro line, which is 24.5 km long and consists of 19 stations, was planned to be operational in the first quarter of 2020. For this purpose, electrical and mechanical tests were successfully continuing within the scope of the project. In addition, the signalling works of the metro line were near to the end. All technical uncertainties and risks were thought to be circumvented. In the last phase of the project, Coronavirus Disease 2019 (COVID-19) was encountered as unpredictable uncertainty. Unfortunately, due to COVID-19, the work in the project has been postponed to a later date. With the commissioning of the metro project, which will breathe the traffic of Istanbul upon commissioning, it is foreseen to carry 500 thousand passengers a day.