Collaborative analysis of principal strain-azimuth of buried pipeline under lateral landslide: insights from centrifugal simulation

Buried pipelines in mountainous regions are highly vulnerable to lateral landslides, which generate complex soil–pipe interactions and multi-axial deformation. This study develops a principal strain–azimuth coupling method and applies it to 1:75 centrifuge model tests to quantify pipeline responses under controlled landslide loading. High-resolution strain rosettes were used to monitor both principal strain magnitudes and their orientations. Before sliding, only minor settlement-induced deformation and stable azimuth patterns were observed. Once landsliding initiated, the pipeline exhibited rapid azimuth rotations of 20–40° and clear asymmetry between tensile and compressive strains. Soil density and moisture strongly affected the response: higher dry density increased maximum tensile strain by approximately 2.7%, whereas high-moisture soil produced larger shear–torsional effects and frequent azimuth fluctuations. At 75 g, maximum tensile strain reached 0.53–0.64% and maximum compressive strain reached 0.71–0.84%, exceeding ASCE allowable limits. In the high-moisture test, deformation resulted from a combination of settlement-induced bending and landslide-driven lateral displacement. Importantly, azimuth rotation consistently preceded strain accumulation, demonstrating its potential as a leading indicator of soil–pipe interaction changes. These findings provide quantitative evidence supporting early-warning monitoring strategies and offer design guidance for improving the resilience of pipelines in landslide-prone regions.