## 4 Conclusions  
This study has shown that soil and fault properties have a major impact on tunnel displacements. Four important soil properties were focused on: water content, soil particle size, soil cohesion, and soil friction angle, which have been proven in this study to have major effects on tunnels. Fault angle and tunnel depth also showed influences on tunnel displacements. * The results showed that the major difference in displacements (almost 34%) was between the water contents of 2% and 12%. An increase in soil water content causes less displacements in wet soil compared to dry soil because there is more shear stress in wet soil. * Results also showed a significant effect of soil particle size on displacements. It was indicated that fine soil has less strength in faulting and has a major impact on tunnels. For instance, at the fault angle of 60\({}^{\circ}\), the curves showed an almost 39% difference between the finest (0.2 mm) and the largest (0.6 mm) soil particle size. Furthermore, the findings of [PERSON] et al. showed that fine soil has less strength in sudden movements, and faults are one of the sudden movements that happen in a short period of time [43]. * The results on cohesionless soil at the angle of 60\({}^{\circ}\) under a reverse fault condition showed that cohesionless soil deformed very easily when the vertical component changed by more than 10 mm. Even with the increasing soil density, fractures appeared due to no cohesion in the soil. Hence, sand is very sensitive to displacements, and tunnels become deformed very easily. For instance, the results showed that when soil cohesion was changed from 20 kPa to cohesionless soil at a fault angle of 30\({}^{\circ}\) for a reverse fault, displacements increased by 64%. Moreover, higher cohesion increased the shear strength and the stability of the soil, leading to less displacement in soil. * It was also shown that friction angles play a crucial role in tunnel displacement. Increasing the friction angle decreased the settlements and also increased the shear strength in soil. The results showed that dense soil transfers more forces compared to soft soil. Also, the density of the soil helped to protect the tunnels from damages. On the contrary, in soft soil, all the forces were focused on the tunnels. Hence, displacements were more likely to be sharper. * Fault angles were also proven to play an important role in tunnel damages, and the current findings added to our understanding of fault angles and showed how they could have a major impact on tunnels. According to the results, the major changes were reported when the three fault angles of 30\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\) were tested. Sharp changes such as those at the fault angle of 90\({}^{\circ}\) caused more damages on tunnels because the forces were focused directly to the tunnels. However, at the fault angle of 30\({}^{\circ}\), the damages to tunnels could be less and the tunnel could have less damages from the displacements because the distribution of forces on the tunnels does not focus on any specific point (unlike at the fault angle of 90\({}^{\circ}\)). The existence of tunnels has a major impact on the direction of the forces caused by fault angles. Tunnels change the direction of forces to vertical and more energy is pointed toward the middle part of the tunnels. However, when the fault angle is 30\({}^{\circ}\), more tunnel parts are involved in tolerating the forces and the results showed 25% and two times less displacement compared to at the fault angles of 60\({}^{\circ}\) and 90\({}^{\circ}\). * It was also shown that the displacements of the tunnel are different when the tunnel is located at a different depth. The findings can be concluded in three steps when a tunnel is added in a different depth. First, when the tunnel was located in 250 mm from the ground surface, the tunnel tolerated more forces induced by faults because soil absorbed some displacements and protected the tunnel from severe damages. Hence, the tunnel displacements decreased.