Study On The Engineering Properties Of Cement Loess Filling Materials And Dynamic Settlement Of Subgrade Of Datong-Xi'an Passenger Dedicated Line

Datong-Xi'an passenger dedicated line is a 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 subgrade deformation. As the railway pass through high earthquake intensity region with huge thick loess and complex geological conditions, the situation that the lack of optimum filling materials should be considered in subgrade design. One of the effective solutions to this situation is to change the nature of ordinary filling materials for enhancing the engineering properties through adding other ingredients. This method has an important meaning for the railway construction as it can be used to expand the scope of filling materials.Based on the review of studies on filling materials, the loess, remolded loess and cement loess along the Datong-Xi'an passenger dedicated line in Shanxi were selected as research objects and the common experiments and dynamic triaxial test were carried out with simulation in order to master the engineering properties of them. And the dynamic characteristics of cement loess which caused by the long term vibration of the train were mainly studied. The research work has accomplished with the following achievements:1. The physical and mechanical experiments of undisturbed loess and remolded loess were carried out in order to master the engineering properties of loess. The results show that the common loess, as one of the ordinary filling materials, could not be used in subgrade construction because of its poor engineering properties.2. The results of physical and mechanical experiments of different cement maxture ratio (4%,5%,6%,7%) loess show that compared with the remolded loess, the engineering properties of cement loess has been improved greatly, and all of the mechanical control indices of cement loess could meet the high requirements of railway subgrade when the cement maxture ratio more than 6%. Therefore, the optimum cement maxture ratio is 6%.3. It is the first time to use the dynamic triaxial test to study the dynamic additional settlement of cement loess which caused by the long term vibration of the train. According to the results we obtained the variation of dynamic additional settlement with cement maxture ratio, depth and vibration frequency. Then the prediction model of dynamic additional settlement was created and the dynamic additional settlement mechanism of cement loess was revealed. According to relationship between dynamic elastic modulus, damping ratio and dynamic strain, the hyperbolic model of dynamic elastic modulus and dynamic response of different cement maxture ratio loess was created, in which the test parameters have specific physical meaning.4. Finally, the subgrade settlement of different cement maxture ratio loess which caused by different loads was calculated using of finite element method. The results show that with the cement maxture ratio increases, subgrade settlement which caused by static or vibration loads both significantly reduce. The effect of cement loess has been verified and the scientific basis of high speed railway design has been obtained.