This paper presents a method to determine the safety threshold of bridge pier settlement in high-speed railways.An analytical expression of the mapping relationship between the pier settlement and the rail deformation is derived theoretically for the double block ballastless track-bridge system.By adopting the superposition of the track random irregularity and the rail deformation caused by the pier settlement as the excitation inputs,the variations of vehicle dynamics indices with pier settlement are comparatively analyzed.Then,the safety threshold of the bridge pier settlement is obtained according to the limit of vehicle running safety and ride comfort indices of the high-speed trains.Results show that the dynamics indices of different trains have different sensitivities to the pier settlement,and the train CRH2C is the most sensitive one among all the types of Chinese high-speed trains.When passing through the bridges in common span with pier settlement at the speed of 250–350 km/h,the trains suffer the low-frequency excitations,and the vertical acceleration of car body is most sensitive to the pier settlement of all the dynamics indices.When the car body vertical acceleration just exceeds the allowable limit,the critical settlement value is 23.4 mm,which is much bigger than the pier differential settlement limit in the current code for Chinese high-speed railways.
A precondition for correctly analyzing the stability of a slope and designing its bracing structure is to study and determine the influence of excavation blasting on the properties of weak intercalation in the layered rock slope. On the basis of in-situ stratification-cracking blasting tests,the properties of weak intercalation were investigated using the LS-DYNA3D program. The displacement distribution and compactness of weak intercalation at different positions away from the charge center and their various laws are discussed. The critical displacement of stratification-cracking(0.1 mm) was obtained,and an approximate expression of compactness were deduced. Furthermore,through the simulation of a layered rock blasting under the same geological conditions,the stratification-cracking effect of deep-hole blasting on the properties of weak intercalation was compared with that of short-hole blasting,and the influencing differences,in addition to their causes,were analyzed. The results indicated that the blasting cavity of weak intercalation in short-hole blasting with a radius of 40 mm was nearly a circle,whose radius was about 28.7 cm;whereas in deep-hole blasting with a radius of 150 mm,the shape of the blasting cavity was different from that in short-hole blasting,the radius of the cavity behind the charge(89.1 cm) was further smaller than those of the other three(138.7 cm) ,and there were sharp crinkles on the surface of weak intercalation. When the distance from the charge center(DCC) was less than 40 and 150 cm in short-hole and deep-hole blasting,respectively,the displacement of weak intercalation was reduced remarkably with the increase in DCC.
