Dynamic Response of Buried Gas Pipeline with Partially Bottom Empty under Tunneling Blasting Vibration

Based on Xiannüyan tunnel blasting engineering of the high-speed railway from Xi’an to Chengdu passing through a buried gas pipeline, the 3-D dynamic finite element model for tunnel blasting including the empty zone of the pipeline was established. Under the action of blasting seismic waves, the dynamic response law of buried gas pipeline with different lengths of empty caused was studied thoroughly and comprehensively. The results show that when there is clearance between the lower part of the buried pipeline and the surrounding soil, the peaks of vibration velocity and displacement at the bottom of the pipeline are greater than that of the top of the pipeline and these two parameter values are gradually decreasing along the axis of the pipeline with the center point of the empty zone as the point of symmetry. With the increase of the length of empty zone, the maximum vibration velocity of the pipeline decreases slowly, but the maximum vibration displacement shows a rapid increase. Under the blasting vibration, the peaks of the effective stress and the maximum principal stress occur at the bottom of the pipeline near the center of the empty zone and both of them increase almost linearly with the increase of the length of the longitudinal empty zone of pipeline. Under the condition of the operating internal pressure 6 MPa and the tunnel depth 40 m as well as the maximum charge per delay interval 17 kg, when the length of the empty zone is 5 m, the blasting vibration does not affect the operation safety of the pipeline. When the long-distance gas pipeline is operated at a high pressure of 10~12 MPa, the blasting vibration will reduce the safety reserve of the pipeline.