As the train passes through the metro station, dynamic load is applied to the station floor, tunnel and the surrounding soil. This dynamic loading can cause adversely impacts on adjacent buildings or disturb the occupants of nearby buildings. This issue becomes more important in cases where the station has crossed a city's historical region. The aim of this study is to investigate the effect of train transit from the inside of the metro station on the ground surface points through dynamic analysis. Parameters such as train passage speed, train weight, distance to the station center, geometrical position of station, characteristics of soil layers and groundwater level are the most important factors affecting the vibration of the soil around the metro station. This study has been carried out by finite difference method and implemented through FLAC3D software modeling. The train wheels applied load was modeled with respect to the speed and weight of the wagons using the Fourier transform, firstly. Finally, the level of ground surface vibration is presented in terms of displacement, velocity and acceleration maps. Numerical modeling results show that when the train passes at 80 km/h from the studied station and the weight of each wagon is 50 tons, the maximum vertical displacement, the maximum vertical component of the velocity, and the maximum vertical component of the acceleration at the ground surface is 6.55*10−4 m, 4.8*10−6 m/s, and 1.8*10−3 m/s2, respectively.
The loads that size, direction and their impact point change during the time are called dynamic loads and are expressed by F(T=P). Static loads are special case of dynamic loads, defined by constant function. In other words, the variable accelerations in a dynamic system provide forces proportional with their size, which apply the loading set with varying intensities on the structure. The average load intensity can be obtained from the differential equation and integration at each section. In general, the dynamic loads are divided into two periodic and non-periodic groups (Clough et al., 2003).