Application of particle image velocimetry (PIV) in the study of uplift mechanisms of pipe buried in medium dense sand

Abstract

Geotechnical centrifuge modeling, which can effectively simulate the stress field of soil in the prototype, was adopted to help investigate the effects of the uplifting of pipes buried at different depths within a medium dense sand under (1) a static state and (2) a dynamic state. To acquire the displacement vector fields and strain contours in the soil around pipes, particle image velocimetry technology was applied. The study focused on the deformation mechanisms of soil surrounding the pipes and ground surface. Two different deformation triggers, external forces and soil liquefaction, were considered. When uplifting was caused by an external force, the relationship between the soil deformation and uplift resistance was similar to the typical ground load-deformation characteristic relationships. There was little displacement of soil during the elastic stage. Along with the uplifting of the pipe, a plastic zone within the range of one pipe diameter (1D) above the pipe appeared in the soil at peak resistance. During the post-peak period, a shear failure plane extended upwards to the ground surface, at an inclined angle forming a trumpetlike shape. The ground surface deformation range expanded according to the buried depth of the pipe. Meanwhile, in a liquefied field, the soil flowed within a heart-shaped region around the pipe. The soil deformation region surrounding a shallow buried pipe, with a width of 5D-6D, was far larger than that found for a pipe buried at the same depth in a static field. Both heave and settlement could be observed on the ground surface.

Upward Pipe–Soil Interaction for Shallowly Buried Pipelines in Dense Sand

“…3(b)-3(e) were also observed in model tests (Stone and Newson 2006;Cheuk et al 2008;Huang et al 2015). The formation of complete slip planes after ṽp can be attributed from noticeable vertical displacement of the ground surface after Nvp in model tests (Dickin 1994;Bransby et al 2002;Huang et al 2015).…”

“…It is worth noting that, although it is a different type of loading, because of progressive development of shear bands, the attainment of peak load before the formation of a complete failure mechanism was also found in model tests and numerical modelling for footing in dense sand (Tatsuoka et al 1991;Aiban and Znidarčić 1995;Loukidis and Salgado 2011). Note, however, that in the simplified limit equilibrium method (LEM), a complete slip mechanism is assumed to calculate the peak load irrespective of burial depth; for example, White et al (2008) (Bransby et al 2002;Stone and Newson 2006;Chin et al 2006;Cheuk et al 2008;Saboya et al 2012;Eiksund et al 2013;Huang et al 2015). However, it does not happen at shallow burial depths.…”

“…The vertical inclination of slip planes decrease with ̃, and they become almost vertical at large ̃. A model test conducted by Huang et al (2015) shows that  gradually increases in the prepeak, reaches ~p at the peak Nv and then decreases in the post-peak zone.…”

“…Experimental studies show that the vertical slip plane model is primarily applicable to loose sand at medium ̃(White et al 2001;Wang et al 2010). For dense sand, two symmetrical inclined slip planes form from the springline of the pipe at  ~ (White et al 2008;Huang et al 2015).…”

Static and Seismic Performance of Buried Pipelines: A review

“…Many studies were performed on large and small scale buried pipelines using many physical modeling techniques like geotechnical centrifuge under N-g level [2,4], under 1-g level using shaking table tests [5] and using finite element method [6,7]. Experimental tests have been performed using the dynamic centrifuge model to estimate the uplift behaviors of shallow-constructed pipe in liquefied zones and susceptible to seismic shaking [4]. Through the response of the earth surface and pore pressures near the pipe, the uplifting mechanism was discussed.…”