Behaviour of buried pipes in unstable sandy slopes

Abstract

Significant forces can be applied to embedded pipelines in sloping grounds due to soil instabilities, which potentially might lead to leakage of hazardous fluids into the environment. The soil-pipeline interaction in sandy slopes has been investigated experimentally using small-scale physical models tested in geotechnical centrifuge. A novel method is developed in this paper to estimate the ultimate external forces, induced by slope failures, acting on buried pipes at various locations inside the slope. Instabilities were triggered by surcharge loading on the slope crest in the centrifuge tests. Six dense coarse sandy slopes were tested with different pipe locations with respect to the slope crest. Moreover, two medium dense fine sand slopes were tested in the same manner to study the effect of the grain size distribution on the soil-pipe interaction. The external forces on the pipe induced by the surrounding soil movements were calculated based on the measurements of four strain gauges installed on the pipe. The shape of failure surface and pipe movements were monitored with the aid of advanced image analysis techniques. The results indicate that a buried pipeline has the potential to affect the slope failure mechanism. Normalised force-pipe displacement relationships were derived and compared to the estimation methods suggested in previous studies, which were mainly done on pipes installed in flat grounds. A new prediction method is introduced in this study, which considers the pipe burial distance to the slope crest. Moreover, the slope angle effect on the ultimate force applied to the pipe is also investigated, and a generalised formula is developed. Finally, two examples of the application of the new method are presented for pipelines installed at the toe of two large-scale subarial and submarine slopes.