Study On Loess Seismic Subsidence And Dynamic Settlement Of Roadbed Of Zhengzhou-Xi'an Passenger Express Railway

Zhengzhou-Xi'an passenger express railway is the first high-speed (350 km/h at best ) railway construction in loess area in China. Compared with common railway of ballast track,it is required to paved by ballastless track on the whole line and has stricter control of roadbed deformation. As the railway pass through high earthquake intensity region with huge thick loess, loess seismic subsidence should be considered in roadbed seismic design, in addition dynamic loess additional settlement caused by the long term vibration of the train should also be considered. Based on the present research situation about seismic subsidence and dynamic additional settlement of soil at home and abroad, in addition to comprehensive analysis of characteristics of environmental geology and loess property along the line, the research project on loess seismic subsidence and dynamic loess additional settlement caused by the long term vibration of the train are carried out, which is supported by China-MOR(Ministry Of Railway).Based on the analysis of environmental geology and geological condition along the railway line, loess dynamic and static experiments are carried out. Through field investigation as well as field and lab test, semiquantitative and quantitative method, linear and nonlinear analysis, simulation and computation loess seismic subsidence, dynamic loess additional settlement caused by the long term vibration of the train as well as their correlations are studied. The research work has accomplished with the following achievements: 1.By collecting environmental and engineering geological materials along the passenger express railway line and field investigation; engineering geological characteristics of the passenger express railway have been comprehensively understood. And by means of routine physics and mechanics tests, a series of loess physical and static parameters have been obtained.2.Field shear wave velocity test of loess along the passenger express railway line have been carried out. The test results shows that as depth rises, shear wave velocity increases in exponential trend. According to result of shear wave velocity and lab seismic subsidence experiment of loess, the regression model has been established through which seismic subsidence of loess can be predicted by shear wave velocity.3.By imposing long time-sustained sinusoid loading on natural loess specimens in dynamic triaxial test, characteristic of loess residual strain(dynamic subsidence) has been studied. Based on the results, the settlement of the embankment in different height under long time-sustained vibration of train has been computed. The result shows that dynamic loess additional settlement has negative relationship with the height of embankment and positive relationship with frequency of vibration. At the same time, predicting model of dynamic additional settlement of loess has been proposed.4.Based on seismic hazard analysis results, seismic wave has been artificially synthesized in typical loess field (Huayin Tongguan Lingbao Yanshi). By imposing synthesized seismic wave on natural loess specimens along the passenger express railway line in dynamic triaxial test, seismic subsidence is studied. According to test results, seismic settlement quantity of loess in four research area has been evaluated. Which indicates that severe seismic subsidence may appear in Huayin as well as Tongguan and slim seismic subsidence takes place in Lingbao under seism exceedance probability of 2%; slim seismic subsidence may appear in Huayin Tongguan and Lingbao under seism exceedance probability of 10%; under both probability above, there is no seismic subsidence in Yanshi. 5. A fuzzy neural network model is proposed through the combination of fuzzy information optimization technology and neural network, with which loess seismic subsidence can be predicted. The method overcomes the shortage in data processing of neural network and disadvantage of computation of information diffusion. By examples, this method is superiorer to multiple regression analysis in prediction of loess seismic subsidence.6.By SEM GIS and Fractal Theory, Loess micro-structure of pre-and-post seismic subsidence have been studied, the study shows that subsidence is mainly induced by the changes of weakly cemented void and space void. Therefore, change principle of the loess porosity of pre-and-post seismic can be described better by Fractal Theory.7.Factors influencing loess seismic subsidence have been analyzed; through simplifying loess structure to micro-elastic model, loess dynamic subsidence mechanism has been deeply discussed.8.Loess dynamic elastic-plastic models of Tongguan and Huayin area etc are established by FLAC software, and through inputting artificial seismic wave data, loess roadbed settlement have been dynamically analyzed. Through numerical simulation loess seismic subsidence quantity under different seismic loading are obtained. At the same time, the model for roadbed in different height is established through which static subsidence settlement as well as dynamic subsidence settlement under the train vibration can be calculated.9. A new method combining finite element analysis with artificial neural networks is proposed, which is used for calculating dynamic subsidence settlement induced by long term vibration of train.10. According to characteristics of loess seismic subsidence along the railway, measures of dynamic tamping, chemical grouting, compaction pile etc are proposed to improve the roadbed properties.