Research On The Isolation Efficiency Of Multi-rows New Cross-sectional Trenches

With the rapid development of urban rail transit technology in China,rail transit has entered a period of large-scale,high-speed,and ultra-conventional development.The environmental vibrations produced by trains with higher loads and speeds and an increasingly dense subway network are more sensitive to the effects in densely populated urban areas.With the improvement of environmental requirements for vibration isolation,the traditional trench barrier gradually cannot meet the needs of actual vibration isolation engineering.In order to improve the efficiency of mitigating ground vibration caused by traffic,optimized design of the trench barrier vibration isolation measures was made.In this paper,combining basic wave theory and finite element numerical analysis,the following researches have been done on the isolation efficiency of multiple-rows new trench barriers:(1)The basic equations of wave theory are introduced,and the vibration isolation principles of traditional trenches and new trench barriers are explained.On this basis,a series of model parameters,such as the section of the open trench,the size of the finite element model,boundary conditions are introduced,the rationality of the proposed model is verified by comparing with previous reports.(2)Six new types of open trenches with different cross-sectional shapes are proposed,the PLAXIS finite element program is used to establish vibration isolation models for the six new open trenches under different cross-sectional shapes,different cross-sectional areas,and different numbers of trenches,the isolation efficiency of new open trench under homogeneous and isotropic elastic half space on steady state vertical harmonic excitation is studied.The results show: increasing the cross-sectional area does not effectively improve the isolation efficiency,and it is more beneficial to improve the isolation efficiency when the cross-sectional hypotenuse is set near the vibration source side,compared with the traditional rectangular open trench,the isolation efficiency of the cross-section 6 open trench can be improved by 10.2%,moreover,the inclination of the sidewall should be 60°,and the number of open trenches should not exceed 3 rows.On the premise of meeting the requirements of vibration isolation,compared with 1 row of new open trenches,the number of new open trenches is increased to 2 and 3 rows,and the depth is reduced by 38.8% and 50.9%,respectively,multi-rows shallow trenches are used instead of single-row deep trenches,it is a new idea for the optimal design of trench barriers.(3)The finite element model of multi-row new open trenches under different geological conditions is established by selecting specific soil parameters,and analyze in detail the conditions of upper stiff and lower soft,upper soft and lower stiff soil layers and the isolation efficiency of multiple-rows new trench barriers under different groundwater levels.Secondly,the isolation efficiency of multiple-rows new open trenches on ground vibration caused by traffic loads is discussed.The results show: the vibration isolation performance of the new open trench on the surface of soft soil is better than that on the surface of stiff soil,the existence of underground water level usually has a negative effect on the isolation efficiency of open trench,when the local water level is 2m,the isolation efficiency of the 1 row,the 2rows and 3 rows of open trench are weakened by 35.9%,42.3% and 45.6%,respectively.In addition,the installation of multiple-rows new open trenches can significantly reduce the vibration of the foundation caused by the traffic load.(4)A three-dimensional finite element model under the action of moving point load and moving surface load was established,and then the isolation efficiency of different numbers of new open trenches under different moving speeds were analyzed.The results show:Increasing the number of new open trenches can significantly improve the isolation efficiency.When the load moving speed is increased,the isolation efficiency of multiple-rows new open trenches will be slightly improved,but this improvement is not obvious.