Abstract:

The shield tunneling underneath existing railway subgrade will inevitably cause a series of adverse effects on the railway subgrade. The overlarge bending and distortion would occur to railway track when the shield tunnelinginduced railway subgrade displacement exceeds limit; as a result, the smoothness and the safety of the running train can not be guaranteed. The displacement rules of railway track, subgrade slope toe and railway shoulder induced by shield tunneling in a section on Hangzhou Metro Line No. 2 are analyzed. The monitoring results show that: 1) The deformation of the monitoring point is closely related to relative position of the shield. The relative position of the shield can be divided into 3 phases, i.e. before shield arrival, shield passing through and after shield arrival. 2) Before shield arrival, ground heave would occur when shield soil pressure is larger than lateral soil pressure; and ground settlement would occur when shield soil pressure is smaller than lateral soil pressure. 3) During shield passing through, distinct ground heave can be measured. 4) However, after shield arrival, ground displacement settles continuously. Due to the adjustment of the filled gravel in the subgrade, the heave values measured at the railway shoulder are much smaller than that measured at the subgrade slope toe. The measured displacements of the railway tracks are generally smaller than that of the railway shoulder due to the resistibility of railway track with bending stiffness against soil displacement.

Key words: shield tunneling, underneath crossing, railway subgrade, metro, soft ground, site monitoring