Tianjin Economic-Technological Development Area

Abstract As a natural telluric current interference, tidal interference severely compromises the corrosion protection effectiveness of coastal oil and gas pipelines, posing a serious threat to their safe operation. To study the regularity of tidal interference on coastal pipelines, the monitoring data of pipe-to-soil potentials (PSP) from 3 pipelines in the coastal region of Shandong and Liaoning, China were analyzed systematically. The fluctuation characteristics of PSP under tidal interference and tidal interference frequency were obtained by spectrum analysis and waveform comparison techniques. The results show that the tidal interference is a localized phenomenon whose intensity progressively decays from the coastal towards the inland of the pipeline. The range of tidal interference exceeds 30 kilometers, causing the ON potential to shift positively to +3.28V and the instant-OFF potential to shift positively to -0.4V. The intensity of tidal interference between different pipelines is obviously different, but the variation trend of the ON potential and instant-OFF potential is basically consistent with the tidal fluctuation curve. Additionally, tidal interference has a typical feature of "double peaks and double valleys" and 12-hour interference period. The established pattern of PSP fluctuations in coastal pipelines under tidal interference provides a critical foundation for corrosion protection strategies in coastal regions.

Ground deformation resulting from strong earthquake fault ruptures can cause significant damage, including the collapse of building structures, garnering considerable research attention. (1) In this study, a large-scale physical model test device was implemented to simulate the loading mode of bedrock dislocation under constant gravity. Based on seismic damage analysis, tests were designed to explore key influencing parameters—bedrock fault dip angle, soil properties, and overburden thickness—on a system comprising strong earthquake normal fault rupture, overburden soil, and independent foundation.(2) The progressive failure of the overburden soil was found to be a dynamic evolution process of the internal rupture zone (IRZ) formed by the tension rupture zone (TRZ) and shear rupture zone (SRZ); this failure process could be divided qualitatively into three stages: the rupture incubation stage (Stage I), development stage (Stage II), and completion stage (Stage III). The failure severity of the independent foundation was reasonably assessed. (3) The setback distance was further refined. This research provides a scientific basis for understanding the failure mechanism and determining the setback distance for buildings in bedrock dislocation sites.