## 1 Introduction
In 2018, [PERSON] et al. [13] presented their research results on the potential use of raw TBM muck obtained from European TBM projects as concrete aggregates. They also showed test results on TBM muck extracted from two more recent Norwegian projects. By studying the Particle Size Distribution (PSD) of TBM muck from different sites and by measuring the effect of PSD of fine particles on the flow of fresh cement paste, they concluded that the utilization of raw TBM muck from eight different European projects varied from 0% to 100%. They also showed that the TBM fines (0-0.125 microns) from the two Norwegian projects had a very similar effect as natural limestone filler on the flow of the fresh cement paste. Generally, TBM muck may have a limited usage in worldwide construction applications as there are no universal specific standards, which permit/control the use of this material in road and building construction. This is because sustainability of TBM muck is not yet well demonstrated. The properties of TBM muck are highly dependent on the geology of the area from which it has been extracted as well as the TBM technology used for excavation (cutter size, chemicals used, etc.). Hence, the excavated material from each TBM project should be studied separately to determine its suitability as a construction material and to decide on the processing requirements. If only raw TBM spoil is used, it may result in a water demanding concrete and the potential loss of mechanical properties due to the flaky-shape particles and the presence of impurities [5]. One of the breakthroughs in TBM tunneling is Doha's Metro project. Under the capital of Qatar, a 111 km of brand-new and extra-modern metro tunnels have been created in just over two years using TBMs managed by Qatar Rail Company. The construction of such a huge tunneling system could be considered to be one action taken for the preparation of the country to host the FIFA World Cup in 2022 and to achieve the vision of connecting every part of the country by an efficient public transport system. The rapid construction of Doha's Metro project with the highest standards of safety and quality made it gain an entry to the Guinness Book of Records [3]. The construction of Doha's metro tunnels has been divided into two phases. Phase-1, which was fully operational in 2020, consists of three main lines namely, Red Line, Green Line and Gold Line. Phase-2 of the project consists of the excavation and construction of the Blue Line, which is expected to be operational in 2026. It should be noted that the routes for all the metro lines runs under congested and highly populated areas as well as under tourist centers and health facilities. A settlement-free tunneling was consequently required during construction. Twenty-one TBMs were designed and operated to tunnel their way forward and to achieve the successful construction of this mega project. As per the information provided by Qatar Rail Company, the TBM muck generated from Phase-1 tunnel lines was piled at four different logistical areas in Doha with an approximate total quantity of five million tons. Those areas were designated as MLPA South, MLPA West, MLPA North and MLPA Al-Rifaa. It should be emphasized that the properties of TBM muck is highly dependent on the geological properties of the tunneled area as well as the chemicals that are used in the TBMs to facilitate the excavation process. Accordingly, the properties of TBM muck generated from Doha's Metro project should be evaluated for every route separately in order to investigate the variations in the properties, if any. In order to have accurate information and quantitative data on the muck generated from Doha's Metro project and to guarantee an access to the different logistical areas to collect muck samples, collaboration was established with Qatar Rail Company to carry out this research study.