چكيده به لاتين
The significant role of local construction effects in amplifying ground tremors has been well-established for a considerable period of time. The local conditions of the building affect all the essential properties of the strong ground motion, including the amplitude, frequency content, and duration of the earthquake. The local effects of a building depend on factors such as the properties of the materials in the underground layers, the building's topography, and the characteristics of incoming movement. As the importance of these factors have been determined, they have been turned into regulations. The aim of this research is to study the impact of twin tunnel's underground structures on the seismic response of the ground surface. It is based on validated numerical modeling and test results from a shaking table. In the experiments conducted, the effect of a twin subway tunnel with a circular cross-section on the acceleration response of the ground surface was investigated. The main objective of this thesis was to investigate the impact of twin subway tunnels on ground surface acceleration for different soil types based on the 2800 standard, using 2D numerical modeling with Abaqus finite element software. Based on numerical modeling, it was concluded that the amount and pattern of acceleration amplification or reduction on the earth's surface, as compared to the free field, are dependent on various dimensionless parameters. These parameters include dimensionless period (𝝀/D), dimensionless depth (h/a), and dimensionless distance of two tunnels (Sr=Space ratio), where 𝝀 represents the wavelength and D represents the diameter of the tunnel. Additionally, h stands for the height of the center of the tunnel from the ground, and a represents the radius of the tunnels. In the dimensionless period range of 6 to 8 and the dimensionless distance of -10 ≤ X/a ≤ 10, the surface of the ground amplifies the response compared to the free field. This results in up to a 60% increase in acceleration on the surface of the tunnels compared to the free field. In the dimensionless period range between 2 and 4, and dimensionless distances ranging from -10 ≤ X/a ≤ 10, there is a reduction in earth's surface response due to the presence of tunnels. This reduction is most significant in the middle ridge line, as compared to the free field. The space has two tunnels and is 60% smaller than the free field. It can be observed that surface tunnels always cause a 10% greater acceleration response on the surface in dimensionless distances and varying dimensionless periods, as h/a increases from 1.68 to 3.3. Based on the findings of the research, it can be concluded that twin underground tunnels with a diameter of 9.6 meters, constructed in soil with a shear wave speed ranging from 625 meters/second to 750 meters/second, for a frequency between 5 and 10 Hz, and a center-to-center distance of 2.5 times the radius of the tunnel, would be a practical solution. There is an increase in distance between the two tunnels, which affects low-height structures with short period and high frequency in between.
