Abstract: The bearing capacity and dynamic characteristics of railway subgrade are bound to change in the presence of large-diameter pipe jacking passing underneath. The increment of vertical dynamic displacement above the pipe jacking should be within 5 mm, according to railway administrations. The process of train passing on the pipe jacking is numerically simulated. The instantaneous vertical displacement of subgrade and the additional dynamic stress of pipes are given. Newmark dynamic analysis method in association with Seed's equivalent linear method is employed to simulate the vibrational softening of subgrade. The simulation scenario is designed as a pipe jacking group composing six pipes of 4.7 m diameter passing underneath the Beijing-Shanghai railway, with the velocity of train reaching 100 km/h and 200 km/h respectively. When the pipes are buried at a depth of 12 m, the maximum vertical dynamic displacement of subgrade is 1.3 mm, and the additional tensile/compressive stress of pipes are around 0.14 MPa, within in allowable range.

Key words: railway ground motion, pipe jacking, equivalent linear method, finite element method, time history analysis