Study on Dynamic Response Characteristics of Tunnels and Overhead Pipelines Traversing Soft and Hard Rock in Strong Earthquake Zones

Rugged mountainous areas in western China are featured with complex geology and high seismicity, which endangers the safe operation of oil and gas pipeline tunnels. Taking a pipeline tunnel in a high-seismic region as the background, this study adopts numerical simulation and large-scale shaking table tests to investigate the dynamic responses of tunnels and overhead pipelines crossing soft-hard rock interfaces under different peak ground accelerations (PGA). The stress-strain behavior and failure modes of the structures at rock interfaces are analyzed. The results demonstrate that dynamic responses of the tunnel mainly occur near soft-hard rock interfaces. The peak maximum and minimum principal stresses at the tunnel crown and springline rise by 15%-63% with increased seismic intensity, and the lining is subjected to adverse tension-compression stress. For overhead pipelines, obvious dynamic responses appear at interface-side supports and mid-spans, and axial stress presents a wave-shaped distribution around the interface. At PGA = 0.6 g, the pipeline peak axial stress reaches 40-45 MPa, larger than that of pipeline sections away from the interface. Longitudinal cracks commonly develop at the lining shoulders and springlines near the interface. Segment C of the interface lining suffers the most severe damage, with penetrating longitudinal cracks up to 60 cm in length. The overhead pipeline experiences remarkable longitudinal stress concentration with a peak strain of 150.85 με and an overall torsional deformation of about 15° during earthquakes. The findings can serve as a reference for the seismic design and safe operation of oil and gas pipeline tunnels crossing soft-hard rock strata in high-seismic areas.