Uneven Settlement Control Of Subgrade Based On Bending Fatigue Strength Of Slab In High-speed Railway

Uneven settlement of subgrade is the key factor in subgrade design of railway, and it has a direct effect on training running safety and comfort. Besides, the uneven settlement will intensify vibration of train, and then reduce the fatigue life. In basically, uneven settlement control of subgrade in high-speed railway is based on train running safety and comfort rather than the service performance of slab. The effect of long-wave uneven settlement on slab vibration and slab force has become grater and grater as the speed of train increases. A control method of uneven settlement of subgrade based on slab fatigue strength is badly needed as the effect of uneven settlement on track structure is becoming serious day by day.The dynamic effect induced by train load is becoming more and more obvious as train speeds up, as a result, the determination of dynamic load has become a key problem in study of track—subgrade system. There are lots of factors that affect the dynamic load produced by high-speed train, and the speed of train is one of the key factors. It is rather difficult to determine the effect of train speed on dynamic load by theoretical method due to the complexity of vehicle-track-subgrade system. At present large-scale model test has become on the most popular means for studying the dynamic characteristic of ballastless track structure of high-speed railway. A full-scale model of subgrade is constructed based on the design and construction standard for Shanghai-Nanjing section of high-speed railway line. The dynamic strain of slab and subgrade soil pressure are obtained by carrying out single wheel axel exciting test, on basis of which the relationship between train load and train speed is presented. In the end, the determination method of dynamic load magnification factor for track subgrade system is proposed based on the calculation formula of dynamic load magnification factor in German railway.The determination of dynamic load magnification factor for track-subgrade system lays a foundation for analysis on influence of subgrade uneven settlement on track structure force. Uneven settlement model of cosine type with different settlement chord and amplitude is established to analysis the distribution of slab moment, and section moment between the start of settlement curve and the end of settlement curve are compared. In the end, considering the effect of uneven settlement and temperature load, the medium-long wave uneven settlement of subgrade is controlled based on fatigue strength of slab with the help of the Smith design drawing of concrete fatigue strength.