High speed trains are planed with a maximum of 250–300 km/h speed and a maximum of 22.5 ton force axle loads. Railway platform which is vibrated with higher frequency dynamic loads induced by high speed train cars transfer these vibrations energies to surrounding ground and close by structures are effected by them. Strong ground motion not only can give damage to the nearby buildings and their footings but also effect the human comfort by undesired vibrations. Thus for an effective protection of railway platforms, nearby buildings, and mitigation of strong vibrations optimum in-situ isolation material needs to be determined by well understanding the wave propagation problems depending on soils conditions. Extensive in-situ research are still required for both recent ongoing construction projects in soft soil deposits (Eskişehir-Adapazarı-Izmit) and for planned construction projects on highly populated areas (Edirne-Istanbul-Ankara-Kars). Since high speed train transportation is newly initiated in our country and existing researchers only being focused on platform vibrations and reduction of noise contamination, there is a gap in the research of dynamic behavior of structures considering soil-structure interaction effect and wave propagation in soft soil. With this study this gap is planned to be fullfilled. Most of the vibration energy is transferred by Rayleigh Surface waves. Railway traffic on soft soil condition for which measured shear velocity value is as low as 200 km/h can create damage to the surrounding buildings and railway itself. Dynamic stresses and deflections will be amplified with Resonance when the critical velocity which can cause maximum deflection railway sub-structure is equal to the velocity of Rayleigh waves. In this situation, a precaution as constructing the sub-structure of railway as rigid slab without ballast instead of constructing the substructure using ballast in alluvial soil conditions can be taken to reduce such affects due to resonance. Moreover, a civil engineering solution for existing buildings can be offered as constructing elastic, elasto-plastic or rigid isolation structures perpendicular to the wavefront direction, underneath with an optimum depth or around the building to be protected for overcoming vibration problems. Thus, wave propagations of vibrations produced by dynamic sources in the soil is prevented to reach structures by the reduction affect created by saturating reflecting or refracting waves. Active isolation is defined when wave barrier is constructed near to vibration source while passive isolation is defined when it is constructed near to the structure to be protected. The most important factors effecting the performance of the isolation barriers are location, dimension and the material density of the barrier that defines the impedance contrast for this type of isolation barrier constructed in soil.
The aim of the study can be summarized as to determine comfort disturbance and devastating structural vibration created by high speed trains on near structures and to reduce these vibrations depending on the design parameters defining the performance of reflecting and absorbing the approaching energy in passive wave isolation model for in-situ conditions.
For this purpose the targets of the project are summarized as below:
I. Evaluation of environmental vibrations: Strong ground and structural vibrations induced by high speed train will be measured and recorded at the inspection points selected at the site close to high speed train line passing through highly populated regions. Environmental effects of these vibration data then will be compared and evaluated with those given in international norms.
II.Preliminary studies of the national nom: In order to avoid vibration affects causing discomfort in human daily life, structural damages to buildings as well as delays and quality problems in production lines of industrial structures when new development constructional projects and industrial structures are to be planned close to high speed railway lines, preliminary studies to create a national code compatible with universal codes and based on velocity response spectrum obtained for various soil conditions will be prepared.
III.Mitigiation of vibration in propagation area: Investigating of in situ performance of wave barrier model which will be constructed between dynamic source and structure to be protected to mitigate vibration energy will be conducted to reduce the vibration affects of strong environmental vibrations in soft soils which can decrease the serviceability life of structure and structural elements to the acceptable limits defined by universal codes.
Isolation performance of wave barrier based on construction location, geometrical dimensions, filling material and various train speed will be investigated parametrically both conducting numerical and experimental studies.
