عنوان مقاله [English]
Ground-borne vibrations due to passing trains are a complex dynamic problem. Different types of vibrations can be produced due to passing trains on the track and existing irregularity of wheel and rail surface. Due to the
construction of subway and railway lines in the most urban areas in the world, they have been encountered with adjacency problem of railroads lines to some sensitive areas such as buildings, laboratories, hospitals, research centers with the precise instruments or monuments. Four major steps exist for transferring train induced vibrations to infrastructures that follow: (A) Generation of vibrations due to repeated train loads (B) Transmission of vibrations in the surrounding medium (C) the effects of vibrations on adjacent reception structures (D) Interception of vibrations. Waves transfer through structure of track including rail, traverse, ballast, sub ballast and soil so with arriving to the buildings, their effects cause discomfort of residents.
Studies of Researchers indicate that the various methods are presented for controlling the train induced vibrations in the path of wave propagation (e.g. rench and wave obstacle), source of vibration (e.g. Rail grinding, resilient wheels and Floating slabs) and reception structure of the vibrations (e.g. elastic support systems). Among proposed methods for reduction of train induced vibrations, the use of open and in-filled trenches can be pointed out. In all presented researches for reduction of train induced vibrations with using trenches, the rectangular shape of trenches is considered. Because of the shape effect of trenches hasnt been investigated in reduction of train induced ations, therefore firstly the numerical model of present study has been verified with accomplished work by Ni et al (1994) with using two techniques for simulating boundary elements(infinite elements and dashpot elements) for common rectangular shaped trench. Finally the three shape effects of
rectangular, triangular and step shaped trenches for both open and in-filled concrete ones have been investigated. In this regard, the effect of train induced vibration has been investigated with finite/infinite element method (or energy-absorbing damper elements). Amplitude reduction ratio (Ar) has been used for estimating and comparing the efficiency of the rectangular, triangular and step shaped trenches. The obtained results for three shapes of rectangular, triangular and step trenches indicate that Triangular and step shaped trenches
have better efficiency than the common rectangular trench with considering equal areas and harmonic train load applied for both open and in-filled trenches.