Influence of Pipe Wall Thickness on the Response of Buried Pipelines Subjected to Earthquake Faulting

Permanent ground deformation induced by seismic faulting is a severe hazard for buried transmission pipelines. Over the years, many studies have attempted to investigate the factors that influence the performance of buried pipelines subjected to earthquake faulting. Some of the influential factors are normalized pipe thickness with pipe diameter (t/D), normalized burial depth with pipe diameter (H/D), fault offset rate, soil density, and soil moisture content. A better understanding of the effect of these factors or discovering new influential factors can lead to a more appropriate design of buried pipelines in the future. This study presents results from a series of experimental tests designed to investigate the influence of pipe thickness on pipe behavior while the outer pipe diameter remains constant. In contrast to previous studies that investigated the t/D factor by changing both pipe diameter and pipe thickness, this experimental research explores the independent effect of pipe thickness on soil-pipe interaction. The experimental tests were carried out in a split-box apparatus modeling the reverse faulting under 1 g conditions. Two copper pipes with thicknesses of 0.7 and 1.0 mm and the same outer diameter of 15 mm were used as the model pipes. A scaling factor n = 25 was used for the model pipes to represent a 600 mm diameter API 5L prototype steel pipe with wall thicknesses of 6.35 mm and 9.53 mm, respectively. The model pipes were buried in a medium dense sandy layer and subjected to 180 mm reverse fault offset. The results show that the thickness of the pipe has a significant effect on the maximum bending strain generated along the pipe. For the thinner pipe, it was shown that the required fault offset for buckling the pipe is about 30% less than the thicker pipe, indicating a safer response for pipes with a larger thickness value.