Study On Techniques And Theories Of Excitation Test On Pile-Board Structure Of Low Embankment In Beijing-Shanghai High-Speed Railway

Pile-board structure of low embankment is mainly composed of four parts:reinforced piles, soil around piles, platform plate and fill subgrade, making it a kind of excellent structure style both in structure treatment and in adjusting the uneven settlement and controlling the post-construction settlement. Large-scale excitation equipment is limited to testing dynamic displacement, velocity and acceleration of dynamic response in high-speed railway subgrade before laying track, to which minor theoretical research is related. Since 1970s in China, discussions about the mass-spring-damper system and elastic half-space theory have already existed in the basic vibration subjects of dynamic machine;how to modify the vibration parameters by analyzing and testing and establish equivalent mass-spring-damper model based on elastic half space theory have been the urgent issue in the kinetic studies of basic dynamics.Therefore, according to current dynamic analysis theories and calculating method of large-scale excitation equipment, a set of calculating method based on the interaction of the vibration exciter and the subgrade was put forward, combined with field excitation test of pile-board structure of Zhengzhou-Xi'an high-speed railway, the correctness of this calculation was verified. Thus great significance engendered to guide further field excitation of pile-board subgrade of Beijing-Shanghai high-speed railway.Firstly, according to the current theory, calculation and testing technology of large-scale excitation equipment, Visual Basic 6.0 was adapted to programming calculation, including six forms and a general module:DTS-1 main form, excitation parameters form, natural foundation form, pile form, dynamic response form and field test form. Dynamic machine foundation design specification, anti-force substitution, analogy and reciprocity law equation were included in natural foundation form; Dynamic machine foundation design specification and group pile foundation design were included in pile form; dynamic response form included fixed and variable parameter system of natural ground and piles, from which dynamic response could be calculated; field test form was inverse dynamic parameter method of field vibration test, including point-peak method and low frequency peak demanding stiffness method. A set of practical calculation method referring to natural, pile and other kinds of foundation was proposed.Secondly, three-dimensional dynamic simulation model of vibration exciter-pile-board structure of low embankment was established to study dynamic performance of the Pile-board structure of low embankment under excitation load and the effects to dynamic response peaks for different vibration frequency and load position, dynamic stress increased linearly with increasing frequency, acceleration was approximately four times polynomial relations with frequency, the speed was approximately three times polynomial relations with frequency while dynamic displacement was approximately two times polynomial relations with frequency, which was consistent with mechanical vibration relationship; therefore, the effect of different load position to the dynamic response were slightly different, so load position was thought having no impact to the dynamic response.Finally, analytical calculation and numerical computation were comparatively analyzed, the dynamic displacement of the two methods remained essentially the same level, in which numerical computation results were relatively larger; the dynamic tress growth trends of the two methods were almost the same when the dynamic frequency was less than 20Hz, but when the dynamic frequency was greater than 20Hz, the result of analytical calculation was obviously bigger than numerical computation, so the dynamic stress should be multiplied by a certain reduction factor in the case of vibration frequency less than 20Hz in the field test.