The effect of radial fins on the uplift resistance of buried pipelines

Abstract

This paper investigates the potential for increasing the uplift resistance of buried pipelines through the addition of radial fins on the pipe circumference. Experiments conducted in loose sand showed that fins extending by 20% of the pipe diameter increase the vertical peak uplift resistance by up to 25%, depending on embedment depth and fin configuration. A limit equilibrium solution -based on known values of peak friction and dilation angles -predicts the uplift resistance within 13% of the measurements. The trends of peak uplift resistance with embedment and fin configuration were also replicated in numerical analyses conducted using a non-associated Mohr-Coulomb soil model. The numerically predicted peak uplift resistances were within 10 and 21% of the experimental values for rough and smooth interfaces, respectively. Soil failure mechanisms from the numerical analyses were broadly consistent with that assumed in the limit equilibrium solution. However, the experimentally observed mechanisms differed subtly, with a limited extent of lifted soil above the pipe and circulatory flow occurring from above to beneath the pipe. This mechanism was approached in the numerical analyses for a smooth interface by specifying a small negative dilation angle, which had minimal effect on the predicted peak uplift resistance.

Nonlinear soil–structure behavior of a deployable and compliant anchor system

“…Although there is some variation at small deployment angle, the failure mechanisms for both sand and clay are associated with shearing through the soil to the surfacei.e., a shallow wedge type mechanism. This is consistent with both experimental and numerical D r a f t observations for uplift of buried plates (Merifield et al 2001;Roy et al 2020) and pipelines (Cheuk et al 2008), including pipelines with external fins similar to the awns considered here (Tom et al 2017). The capacity for shallow failure is associated with (a) the work done against gravity lifting the volume of soil within the failure mechanism, and (b) work done via soil-soil shearing along the shear planes (Tom et al 2017;White et al 2008).…”

“…Limit analysis is appropriate for undrained analysis of clays, but the full finite element analysis mode was selected for sand analyses to allow for non-associated flow soil behaviour to be incorporated. Geotechnical capacity over-estimation for associated flow sands is well known and particularly onerous for problems related to vertical uplift of buried structures (Krabbenhoft et al 2012;Tom et al 2017).…”

Drained Bearing Capacity of Shallowly Embedded Pipelines

“…Validation of analysis methodology Figure 6 compares elastoplastic analysis in OptumG2 for vertically loaded, rough strip footings with previous numerical results for both associated (Martin 2003;Lyamin et al 2007) and non-associated soils (Loukidis et al 2008). the appropriateness of the current approach for drained resistance can be found in Tom et al (2017), where a similar approach is used with good success for back-calculating the uplift resistance of buried pipelines in relatively loose sand of known friction and dilation angles.…”

Consolidation effects on uplift capacity of shallow horizontal plate anchors in dilating sand

“…This section derives an analytical expression for the undrained capacity (𝑁 𝛾,𝑢𝑛 ) of a horizontal strip anchor 423 in cavitating sand. The approach follows the limit equilibrium approach for drained capacity (𝑁 𝛾,𝑑𝑟 ) assuming an 424 inclined slip model (White et al 2008, Tom et al 2017), but with modifications to account for the additional…”