## 1 Introduction  
The world is witnessing an unexpected population growth and urbanization and, hence, there is an increasing demand for new and efficient infrastructure systems. In order to adapt to such trends, many construction activities are already taking place in different countries such as building underground highway networks and rail tunnels. Conventionally, drill and blast methods were used for tunneling. However, Tunnel Boring Machines (TBMs) have been used over the last 20 years in many countries to excavate tunnels in hard rock [1, 2, 3, 4]. This technology leap has shown a leverage exceeding the conventional methods. TBM provides a gentle tunneling with smooth cross-sections and at the same time avoids any existing underground construction. It also overcomes the depth and underground flow limitations that were experienced earlier. The resulting TBMmuch is much finer and has a flaky-shape material that could potentially be used as an alternative to rock aggregates or sand [5]. Several million tons of muck are generated each year by TBMs. This excavated rock material is mostly competent and strong. However, it is normally treated as a waste, ending up in landfills or stockpiled as deposits with no beneficial use [6; 7]. The extensive transport of muck for long distances may be required throughout the project, which results in the emission of polluting gases. Treatment and disposal are also required sometimes for such TBM spoil, which increase the cost of the project. Accordingly, researchers started to investigate the potential use of TBM muck as a construction material for roads, parking lots and buildings. Utilizing TBM muck as concrete aggregates, roadway fill and subgrade and/or backfilling under structures would be more beneficial economically and environmentally compared to landfilling [8; 9; 10; 11; 12; 13]. To be utilized as a construction material, TBM muck must meet certain physical and chemical properties and have economic benefits for using it in lieu of disposal. Relatively few research studies have been conducted or published on the use of TBM muck in construction applications. Such studies have concluded that TBM muck could be utilized in many construction and specialty applications and could be increasingly used as an aggregate substitute in the future with minimum processing [8; 14]. [PERSON] et al. [10] investigated the stability of muck produced by a laboratory TBM operating in a welded tuff in different construction applications. They have described various tunneling projects that have utilized, or tried to utilize, TBM muck in construction purposes. They concluded that TBM muck from hard rock is a well-graded material containing flaky chips with little fines, and hence, it could be used successfully for many purposes with a little modification (if needed) by conventional aggregate-processing methods. [PERSON] et al. [11] described a method for the evaluation of muck extracted from the pilot gallery of the Mismove tunnel (northern Slovakia). This method included different laboratory tests such as short frost resistance and adsorption tests. Although they could not demonstrate a definitive conclusion on the use of muck in construction applications, they indicated that in order to make the decision on the possibilities of utilizing the muck as a construction material, it should be evaluated separately each time depending on the driving method and the geology of the area from which it has been extracted. In 2011, [PERSON] and [PERSON] [7] investigated the effects of different treatments on rock excavated using TBM or traditional drill and blast excavation methods. They conducted laboratory tests on raw muck as well as muck treated in mobile and fixed plants. They reported that raw TBM muck is not suitable as concrete aggregates due to its flaky-shape particles. However, they observed that the treatment of TBM muck in a fixed plant using a two-hammer crusher and a secondary jaw crusher could reduce the flakiness index and, hence, make the muck comply with the concrete aggregate requirements.