Performance of buried natural gas distribution pipes in a landslide area: Observations from nine years of pipe strain monitoring

ABSTRACT: The long-term performance of buried natural gas pipes in an ongoing landslide area was monitored as a part of a collaborative research program. In 2013, a research site was established within a slow-moving landslide in the Marble Hill area of Chilliwack, BC by installing five Medium Density Polyethylene piping. Four pipes were installed such that their alignments are mostly parallel to the direction of the ground movement, while the remaining pipe length was placed approximately perpendicular to the ground movement. A total of 187 strain gauges were installed to obtain an accurate estimation of axial and bending strain distributions induced due to ground movement. In addition, 11 GPS survey hubs were utilized to monitor the ground displacement. Since the installation (with 77% of gauges functioning after nine years), the largest ground displacement of 460 mm was recorded at a hub located in the upslope area, while this displacement reduced to about 250 mm in the downslope area. This differential ground displacement has resulted in a peak compressive strain of 1% in pipes parallel to landslide, which were in concurrence with the ground failure/movement features that were identified from LiDAR images, aerial photographs and on-site observations. The measured pipe strains are compared against those estimated using the analytical model proposed by Weerasekara (2011) to validate the model applicability and identify any limitations thereof. While the model was able to estimate the strain distribution, the most difficult task was the identification of the slide geometry and differential displacements especially when two soil masses converge. Other limitations in estimating pipe strains using analytical or numerical models are also discussed.