Abstract
Submarine slope instabilities are considered one of the major threats for offshore buried pipelines. This paper presents a novel method to evaluate the ultimate pressure acting on a buried pipeline during the liquefaction of an inclined seabed. Small-scale model tests with pipes buried at three different embedment ratios have been conducted at an enhanced centrifugal acceleration condition. A high-speed, high-resolution imaging system was developed to quantify the soil displacement field of the soil body and to visualize the development of the liquefied zone. The measured lateral pressures were compared with the hybrid approach proposed for the landslide–pipeline interaction in clay-rich material by Randolph and White (2012) and Sahdi et al. (2014). The hybrid approach is proved to be able to predict later pressures induced by the movement of (partially) liquefied sand on buried pipelines. It is found that the fluid inertia (fluid dynamics) component plays an important role when the non-Newtonian Reynolds number >~2 or the shear strain rate > 4.5 × 10−2 sec−1.
Highlights
Offshore pipelines are often buried in the seabed for protection against hydrodynamic forces caused by strong currents/waves or fishing gear (Fredsøe 2016)
If a segment of a buried pipeline is subjected to seabed movement, the pipeline will deform due to the landslideinduced pressures as schematically shown in Fig. 1
Knowing the ultimate lateral pressure acting on a buried pipeline due to a marine landslide is crucial in offshore pipeline design
Summary
Offshore pipelines are often buried in the seabed for protection against hydrodynamic forces caused by strong currents/waves or fishing gear (Fredsøe 2016). At the onset of a subaqueous sandy slope failure triggered by either external dynamic or static loads, soil material may undergo partial liquefaction. Sassa and Sekiguchi (2010, 2012) presented an analytical framework that is capable of consistently simulating the dynamics of submarine liquefied/fluidized sediment flows involving flow stratification and deceleration leading to redisposition on the basis of two-phase physics They stated that for a rational understanding of the processes of subaqueous sediment gravity flows, the integration of fluid dynamics and soil mechanics approaches is necessary. Regarding the velocity of seabed movement, the soil–pipeline interaction mechanism of submarineburied pipelines has been commonly investigated from two perspectives, namely the geotechnical approach and the fluid dynamics approach These two approaches consider two extreme offshore landslides in terms of the slide velocity. Based on the fluid dynamics and rheology principles (Pazwash and Robertson 1975), the ultimate lateral pressure can be estimated from Eq 2
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