## 4 Results and Discussion  
### Deformation Behaviour of Single Tunnels  
After conducting the test on both lined and unlined tunnels, the results are analyzed. It has been noted that deformation is more in unlined samples as compared to lined samples. This is due to the absence of liner material in the unlined tunnel, as the liner material offers resistance against the developed stresses. It is also reported that the strength properties of the rock and cover depth also play an important role in the deformation behaviour of tunnels. GM-1 and GM-2 models experience more deformation as compared to POP models; this is due to their weak strength characteristics. From the results, it can also be concluded that the maximum deformation is experienced at the centre of the tunnel, i.e., L/2, as compared to the LVDTJs fixed at L/3 and 7L/12. It is also observed that as the distance from the centre of the tunnel increases towards the end faces of the tunnel, the effect of deformation decreases. No deformation is experienced at the end of the tunnel in all cases. Firstly, the single tunnel models prepared from 100% POP material are tested with a compression testing machine. As the load is applied to the top surface of the tunnel sample, it begins to deform. Then, the deformation is observed at various selected points along the tunnel length. For the sample prepared from 100% Plaster of Paris material, the deformation graph is shown in Figure 8. The deformation value obtained from the graph shows that maximum deformation is experienced in unlined samples having less cover depth, i.e., in the case of a 3 cm unlined tunnel which is quite obvious because liner material is absent in unlined samples. The centre location of the tunnel, i.e., L/2,experienced the maximum deformation in the case of 3 cm cover depth. Less deformation is computed at L/3 and 7L/12 distances. In the case of 3 cm cover depth unlined samples, the maximum crown deformation experienced at L/2 distance is 0.19 mm, whereas the deformation noticed at points L/3 and 7L/12 is 0.03 mm and 0.13 mm. In the case of 5 cm unlined tunnels, the crown deformation at L/2 distance is 0.16 mm. The minimum deformation is noticed in the case of a 5 cm lined sample. This is due to the presence of liner material. In the case of 5 cm lined samples, the deformation experienced at L/3, L/2,and 7L/12 is 0.01 mm, 0.08 mm,0.03 mm, respectively. Figure 8: Deformation Profile of Lined and Unlined Tunnel for 100% POP material. Secondly, the tunnel samples of GM-1 material (50% POP, 40% Sand, and 10% Clay) are tested with a compression testing machine, and the deformation graph is obtained, which is shown in Figure 9. GM-1 is a weak material in terms of its strength properties as compared to POP material. Therefore, the extent of deformation will be more in GM-1 material. From the graph results, it has been analyzed that the deformation in the case of the unlined tunnel is more as compared to lined tunnel samples. Maximum deformation is experienced in the case of a 3 cm unlined tunnel sample at L/2 distance, and its value is 0.25 mm, whereas the deformation experienced at L/3 and 7L/12 distance is 0.04 mm and 0.17 mm, respectively. In the case of 5 cm cover depth unlined samples, the maximum crown deformation is noticed at L/2 distance and its value is 0.19 mm, whereas the deformation experienced at L/3 and 7L/12 distance is 0.03 mm and 0.14 mm, respectively. It is noticed that as the cover depth increases, the deformation decreases. In GM1 tunnel models, the minimum deformation is noticed in the case of 5 cm lined tunnels.In lined tunnels with a 5 cm cover depth, the deformation value obtained at L/2 distance is 0.10 mm, whereas the crown deformation value experienced in 3 cm lined tunnels is 0.12 mm at distance L/2.