The interaction of reverse faults with flexible continuous pipelines

Abstract

Permanent ground displacements due to earthquake faulting may induce large deformation and loading of a buried pipeline. In particular, a pipeline crossing a fault rupture emerging at the soil surface will be subject to a combination of bending and/or axial compression or tension depending on the form of the fault displacement, the dip angle and the direction of the pipe with respect to the fault. This complex combination of loadings may be sufficient to cause disruption to the pipeline supply or leakage of product and so has potential for large financial and/or environmental impact. In this paper, the response of buried flexible pipelines crossing reverse fault ruptures has been examined using centrifuge modelling. A reverse fault is actuated in the 20th-scale model at an initial fixed dip angle in the bedrock and the fault rupture is seen to propagate upwards through a layer of sand towards the soil surface. Pipelines were buried in the sand layer to typical embedment ratios and their response was monitored as the fault displacement increased monotonically. Primary data capture was by the use of image analysis: semi-cylindrical modelm pipelines were placed at the front-face of the model and digital images were captured during the loading event. This allowed pipeline deformation patterns and thereby bending moment distributions to be calculated throughout the fault rupture event. Results are presented to show the effect of pipeline diameter, stiffness and embedment depth on the performance of buried pipelines during reverse and normal faults. In particular, it is shown that additional embedment of the pipeline is detrimental to its performance due to the additional confining effect of the soil which changes the relative pipe­soil stiffness.

Acoustic Emission Sensing of Pipe–Soil Interaction: Full-Scale Pipelines Subjected to Differential Ground Movements

“…On the moving (hanging wall) side, the pipe experiences a sagging deflection and resistance here is controlled by the soil's uplift capacity. Peak bending moments develop in the hogging zone because the soil's bearing capacity is significantly greater than its uplift capacity (Bransby et al 2007;Anastasopoulos et al 2007;Saiyar et al 2016;Ni et al 2018). A critical value that may be used in design is ipipe, which is the distance between the position of peak curvature to the point of contraflexure along the pipe's deflection profile.…”

“…Relative pipe/soil stiffness influences ipipe and it has been observed to increase with displacement as postpeak soil shear strength (i.e. reduced stiffness) is gradually mobilised along the length of the pipe (Bransby et al 2007;Ni et al 2018). High stiffness pipes (e.g.…”

“…A flow-around mechanism is formed accompanied by a reduction in the uplift resistance due to post-peak shear band formation. The failure mechanism resembles an inverted trapezoidal block (Bransby et al 2007;Cheuk et al 2008).…”

“…The free pipe ends introduce boundary conditions that are not representative of the real in situ case. The subgrade reaction method (Bransby et al 2007;Ni et al 2017) (Equations 2 to 5) was used to calculate the critical pipe length, lc, beyond which the pipe behaves as if it is infinitely long (fully flexible). lc was used to select a pipe length (6.5 m as shown in Figure 1) that minimised pipe end boundary effects.…”

Thirty-Sixth Canadian Geotechnical Colloquium: Advances in visualization of geotechnical processes through digital image correlation

“…To overcome these issues, Saiyar et al (2011) adopted a strategy pioneered by Bransby et al (2007) to track the deformation of a half-model pipe at the plane of the transparent window. A comparison of the curvature measured in the full section of the model pipeline in the middle of the plane strain model using strain gauges with that calculated from the filtered deflected shape of the half-model pipeline section measured at the plane of the Fig.…”