Lateral and Uplift Capacity of Pipeline Buried in Seabed of Homogeneous Clay

Abstract

Buried offshore pipes are prone to upheaval and lateral buckling because of the high temperature and pressure of the materials being transported. An attempt has been made in the present study to evaluate uplift and lateral capacity of buried offshore pipes in a soft clay seabed using finite-element software. The numerical model used in the present study has been validated against results available in the literature. Finite-element analyses are carried out to study the upheaval and lateral buckling behavior of pipes for both the no-tension (NT) condition, i.e., when separation occurs between the pipe and soil, and the full-tension (FT) condition, i.e., when the soil beneath the pipe remains attached to the pipe. The variation of both uplift and lateral normalized capacity factors with soil cover depth ratio is presented for different combinations of soil strength and effective weight. Both uplift and lateral capacity factors have been found to increase and reach a constant peak value with increasing depth of soil cover. A transition from global and local failure mechanisms of a pipe is observed when the capacity factors attain their peak values at a limiting soil cover depth. The critical cases for the design of buried offshore pipe in homogeneous clay are established for both NT and FT conditions.

Uplift Behavior of Pipelines Buried at Various Depths in Spatially Varying Clayey Seabed

“…However, when H/D was greater than or equal to 2, a localized circumferential soil flow surrounding the pipeline occurred. This is consistent with the conclusions obtained by Kumar et al [4], which suggested that critical soil cover depth ratios for both the global and local failure modes was 2 for rough pipelines under full tension in uniform soils. Figures 4 and 5 depict the displacement contours and the corresponding soil's undrained strength distribution in the random soil with pipeline soil cover depth ratios of 0.5 and 1, respectively.…”

“…Furthermore, when the soil cover depth ratio H/D was less than 2, N u increased with the increase of H/D and reached a maximum value when H/D equaled 2 and remained constant as H/D increased, indicating a critical depth ratio for H/D = 2. According to the study of Kumar et al [4], in the case of a full tension condition, H/D = 2 is the critical depth ratio for a failure mechanism to transition from a global failure to a local failure. The results of this study also indicate this trend.…”

“…Generally, the pipelines are buried into the seabed to diminish external forces acting on them, which are caused by waves or human activities (see Figure 1). The transportation of fluids through the pipeline under very high temperatures and pressure conditions leads to thermal expansion, thus making it susceptible to buckling [4,5]. For buried pipes, upheaval buckling is a major current focus for oil and gas projects and, in this scenario, its resistance is affected by the shear strength and the submerged unit weight of the soil cover.…”

Buckling Mechanism of Offshore Pipelines: A State of the Art

“…Further, it is observed by the other researchers that the behaviour of the piles under lateral displacement is similar to the behaviour of the pipelines under vertical displacement [54,56]. It is also found by the researchers that, for ideal cases (weightless soil and unlimited pipe-soil interface tension), the penetration resistance and uplift resistance [54,56,58,59] of the pipeline reached a peak value of 9.14 for smooth pipes and 11.94 for rough pipes. Several authors observed that soil strength is one of the crucial factors to influence the uplift resistance.…”

“…For a buried pipeline, the uplift resistance of the pipeline is usually lesser than the lateral resistance and downward penetration resistance. Thus, the global uplift buckling is the predominant buckling criteria for a buried pipeline [49][50][51][52][53][54][55][56][57][58][59]. However, global lateral buckling was also analysed in some cases as they were believed to be crucial for the pipeline design.…”