## 2 Research Methodology
### Pipes Used  
One of the objectives of this study was to assess the factors that may affect the ability of the NDTs for leak detection. Therefore, the pipe material and types of leaks were two of the three factors that were varied during experimentation. The diameter of all the pipes was 3.8 cm. First, the three pipe materials used were: Polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PPR). Polymeric pipes are increasingly being employed in WDS [45]. Hence, polymeric pipes were employed in the present research study. Three wooden boxes were constructed, with each box containing four pipes of the same material as shown in Figure 3.  
Figure 2: Detailed drawing of experimental setup. Second, different types of leaks were induced to evaluate the ability of the NDTs on wide-ranging pipe conditions. The first pipe was undamaged, the second contained a vertical crack, the third had a hole, and last pipe consisted of a faulty joint as illustrated in Figure 4. To prevent water leaking from one pipe to seep to the adjacent pipes, the three simulated leaks were induced in different ends of the pipes. Thus, the vertical crack was induced on the left end of the second pipe (Figure 4a), the hole was drilled at the right end of the third pipe (Figure 4b), and the joint was installed at the center of the last pipe (Figure 4c). Figure 4: Leaks and their locations: (**a**) crack; (**b**) hole; (**c**) faulty joint; and (**d**) top view with leak position marked green. Figure 3: Setups with different types of pipe material: (**a**) PVC; (**b**) PE; and (**c**) PPR. The pipes in the three boxes were buried in dune sand to replicate the common conditions of underground pipes in the water distribution infrastructure in the UAE. The two soil properties of interest are soil particle size distribution, which was obtained by performing sieve analysis on the dune sand, and the maximum dry density of the sand (1689.41 kg/m\({}^{3}\)), which was obtained by performing the standard proctor test. All the soil procedures and tests were performed by following the ASTM standard. After determining the maximum dry density of the dune sand, it was compacted by using a custom-made vibrating plate compactor. Figure 5 shows the compaction of three layers to replicate the standard procedure of the proctor test. The total weight of dune sand could not be divided into three equal layers because the thickness of the first 1/3 rd layer was less than the level of the pipe and the installation of the wooden partitions along with the large size of the compactor restricted the use of the compactor below the pipe level. The compactor was used along the width of the box. Figure 5 also presents the number of times (cycles) the compactor was passed over the sand to reach the desired compaction level. The degree of compaction of the dune sand for each box was calculated to be 90%. Figure 6 illustrates the final view of the experimental setup after compaction. Even though the standard procedure should represent the actual soil conditions, a certain variability would exist in the field applications with actual site conditions. The levels of MC of the dune sand were the last factor that was varied to determine its effect on the ability of the NDTs to detect leakage. The experimental study was conducted at the following three approximate moisture content levels of dune sand: 2%, 5%, and 10%. The first round of experiments was performed on air-dried dune sand (tested at 2% moisture content). Next, a calculated amount of water was sprinkled on the top surface of the boxes to achieve a 5% moisture content in dune sand. Similarly, additional water was added to achieve the final 10% moisture content in dune sand. However, small variations  
Figure 5: Compaction pattern. Figure 6: Setups compacted with dune sand: (**a**) PPR, (**b**) PE, and (**c**) PVC. in the soil moisture content were expected as some water may be lost via evaporation, the sand may absorb water from the air on humid days, etc.