## 2 Muck Sampling and Collection  
The required information and quantitative data on the muck generated in Qatar were provided by Qatar Rail Company. Qatar Rail staff made all arrangements and granted access for the research team to collect samples of TBM muck from the site. As the TBM properties may vary depending on the location where they were extracted from, this study was limited to the TBM muck generated from Doha's Metro Gold Line and piled at MLPA Al-Rifa site (Figure 1). The Gold Line (also called the Historic Line) links Qatar's industrial area in the north with the Doha international airport. The geology of the area through which the Gold Line runs could be considered consistent. In order to obtain an exact picture of the geological properties, an adequate number of boreholes with depths up to 70 m was drilled and investigated in the whole project area. It was found that the soil strata comprise fill material (or man-made soil with minor thickness), Simsima Limestone, Midra Shale and Rus Formation. The tunnels are completely located in the Simsima Limestone. This layer consists of crystalline limestone and contains dolomite rock and with a number of cavities and irregular fissures filled with soft siltstone. However, no joints or parallel discontinuities were encountered within this layer, and hence, it is considered homogeneous and isotropic in terms of its strength and deformability. The subsequent Midra Shale layer is encountered beneath the tunnel structure. It consists of crystalline limestones and siltstones with pronounced discontinuities and steeply inclined joints. Accordingly, this layer could be considered heterogeneous, and hence, the anisotropic behavior of the rock mass model should be assumed. The Rus Formation, encountered below Midra Shale, comprises dolomite limestone with various extensive layers of saline residues, mainly consisting of gypsum [15]. Planning and formulating all aspects of TBM muck sampling and obtaining representative samples were carried out according to ASTM D4687 [16] and ASTM D6009 [17] standards. Such standards state that sampling scheme/strategy and frequency (number of samples) for a waste pile should be based on several factors, including the study objectives, properties of wastes in the pile, degree of confidence required, access to sampling points, and budgetary constraints. Because of the site and financial constraints and because the research's main goal is merely to establish whether the muck meets some certain criteria, a judgment sampling scheme was employed in this study as recommended by ASTM D4687 standards [16]. Such a sampling scheme or strategy normally calls for collecting a composite of surface samples and samples taken from a specified depth. The composite sample is a well-mixed blend of those subsamples taken from different points, and locations are normally decided by visual observations and the collector's judgment. Such a sample could be considered a representative sample that reflects the whole composition of the TBM muck in a cost and resource efficient way, and it is commonly effective in determining an average measure of a parameter [16; 17]. As per the information provided by Qatar Rail Company, 576,926 m\({}^{3}\) of TBM muck were generated from Doha's Metro Gold Line and piled in the MLPA Al-Riffa area, as  
Figure 1: Gold Line TBM muck piled at MLPA Al-Riffa area. shown in Figure 1. Fifteen tons of TBM muck were collected by taking 10 random samples of the same size (about 1.5 tons) from five different locations at the muck pile surface, and another five locations deeper than 50 cm below the surface of the muck pile. Samples from the surface were directly collected using a wheel loader. Other samples were collected by removing about 50 cm of the muck pile face and moving it to another site location using a front-end loader bucket to expose the inaccessible inner portions of the muck at approximately equal increments. The discrete samples were then loaded to a single truck for mixing in order to form a homogeneous representative sample.