Study of Soils Liquefaction Effect on Double Tunnels under Harmonic Loads

Liquefaction is one of the destructive phenomena that every year causes a lot of damages to engineering structures. Tunnels are a type of engineering structure and they are considered as one of the most important and essential requirements of modern urbanization. Depending on their rigidity, these structures are affected by various deformations based on their surrounding soil. In saturated sand soils by applying dynamic load in untrained condition, pore water pressure increases, effective stress between particles decreases and shear strength is removed and consequently it results in consistency of soil , and imposed internal forces on tunnel lining, deformations and surface settlements have increased compared to static state. In this study, by using FLAC-2D software the single and twin tunnel has been modeled and the effect of changes in soil parameters (friction angle, adhesion, elastic modulus and Poisson coefficient), geometric characteristics of the tunnel (diameter, embedded depth and distance of tunnels) and harmonic load characteristics (frequency, load range) on surface settlement and internal forces of tunnel lining have been investigated through static and dynamic analysis. This study showed that in soils that are susceptible to liquefaction, these parameters will have a significant effect on surface settlement and internal forces of the tunnel lining. One of the findings is the reduction of liquefaction potential, surface settlement and increase of internal forces by increasing the adhesion and embedded depth. In this study the results are presented in detail using charts and tables.