Field Test Research With Vibration Exciter Of Pile-Board Structure In Zhengzhou-Xi'an Passenger Dedicated Line

Pile-board structure is a new structure used in high-speed railway,which is composed by cap plate,joists,piles and foundation soil.Compared with soil subgrade,Pile-board structure has the advantages of smaller post-construction settlement and higher integral rigidity.The accumulated dynamics information of pile-board structure is lacked at present,and its dynamic response parameters under the dynamic load of train has not been acquainted a lot in engineering field and the dynamic property under repeated load is not very clear.This paper is closely combined with key subject for science research and development plan of China Railway Ministry "Research Test of Subgrade Pile-board Structure in Zhengzhou-Xi'an Passenger Dedicated Railway Line",which carriy out field vibration exciting test,verify through theoretical analysis,numerical simulation and other technical means centering on test results,and systematically study the dynamic response and dynamic response of long-term of pile-board structure under the dynamic load of train,then come to the following conclusions:(1) Fully investigate current applying and researching situation of pile-board subgrade at home and abroad,systematically analyse pile-board structure's performance and characteristics,give out pile-board subgrade's definition and application scope.(2) Establish single degree of freedom vibration model of inertial-type vibration exciter,systematically analyse the exciter's dynamic response,testing methods and processing means of results.(3) Establish continuous beam of three degrees of freedom vibration model of pile analyse structure,systematically analyse two cases:free vibration and harmonic forced vibration,deduce that the calculation formula for natural frequency of pile analyse structure is f= 1.1αEI/ml^31/2,which correction factorαcan be 0.1～0.3.(4) Establish three-dimensional finite element model of vibration exciter-pile-board structure,the calculation shows that pile-board structure's natural frequency is 0.4～1.5Hz,the three major factors that effect pile-board structure's natural frequency are:the length of pile,span and pile lateral soil modulus.Also the calculations show:under the same dynamic load amplitude,when the frequency increases,the dynamic stress and the dynamic displacement of pile-board structure decrease linearly,while the speed and acceleration increase linearly;under the same dynamic load frequency,when the amplitude increases,the dynamic stress,dynamic displacement,speed and acceleration of pile-board structure increases linearly;the axle load of train influence the dynamic response of pile-board structure most.(5) Use large scale inertia-type exciter to simulate uniaxial train load,conduct swept excitation and 100 million times of repeated load test on pile-board structure.The test's result shows that pile-board structure's response frequency equals to its loading frequency,dynamic stress attenuated along the pile,at the bottom of a 50m long pile,the attenuation coefficient is 0.4. The test measured that the natural vibration frequency of pile-board structure is less than 5Hz.(6) The measured maximum dynamic displacement of pile-board structure is 0.133mm,acceleration is 0.105g,pile-board structure has good bracing stiffness of subgrade surface to meet the comfort and stability requirement of high-speed passenger train.(7) In the 100 million times of repeated load excitation,the dynamic stress amplitude of the structure is always less than the material's allowable fatigue stress,and fluctuate very small,so pile-board structure has large fatigue strength to meet the durability requirements of high-speed railway.