Analysis And Evaluation Of Building Vibration Induced By Ground Urban Rail Transit And Study On Vibration Reduction Measures In Pit Extension

With the acceleration of urbanization and the progress of rail transit technology,the construction and operation of public rail transit in China has reached a new level of blowout development.At the same time,the building indoor vibrations near the rail transit are becoming more and more serious,which has a huge negative impact on the daily life and work of the urban residents.In this paper,we will use the finite element method and the full-scale experiment to study the influence of the urban rail transit on the indoor environment vibration,and try to design a new type of vibration reduction measure in foundation pit.The main research contents are as follows:First,comparative study of environmental vibration standards and specifications is carried out.We analyzed the similarities and differences of standard dependency,applicable condition,vibration assessment value,limit of vibration and vibration measurement condition.Then we study the advantages and disadvantages of those standards and specifications based on numerical examples.Some reasonable suggestions are put forward for the measurement and evaluation of indoor environment vibration,and some pertinent recommendations are suggested for the improvement of the specifications and standards.Then,based on the dynamic finite element method,the propagation law of rail transit vibration in the soil and the law of building environmental vibration is studied.The study includes the relationship between vibration response and source distance,soil parameters,vibration direction and source frequency in the soil.The results show that the vertical acceleration in the soil presents wave-like or step-like reduction with the increase of the vibration source distance,and the soil modulus can significantly affect the resonant frequency.In addition,based on the existing vibration evaluation method and the response of multiple points,the formula of artificial load is deduced.We also established the wheel-rail incentive-soil-structure finite element model to explore the vibration of the indoor environment.The study includes the influence of the scope of rail transit vibration,the structure volume and floor frequency on the indoor vibration level.The results show that the vertical vibration level in the structure is much higher than the horizontal total vibration level,and both of them decrease with the increase of source distance.What's more,the natural frequency of the floor can significantly affect the vertical vibration level,but cannot affect the horizontal vibration level.The influence quantity of the structural volume on the indoor vibration level is up to 5dB,so the vibration assessment of small building should not be overlooked.Finally,the vibration reduction scheme of foundation pit is designed,and the feasibility is verified by comparing the measured data of experimental structure with the theoretical calculation.Base on the finite element method,the vibration transmission condition of the basement wall and the basement floor,and the vibration transmission condition of the basement wall to the vertical and horizontal vibration under the load of ground rail trainsit is discussed.The results show that the vertical vibration in the soil around the outer wall of the basement greatly affects the vibration level of the upper structure.With the guarantee of engineering feasibility and structural safety,the vibration reduction scheme of foundation pit is designed.The results of field experiment and finite element calculation about two experimental structures at a metro depot in Beijing are compared and analyzed.It is proved that the vibration reduction measure has good performance and can be used in various construction projects along the ground urban rail transit.