Search Results (4)

The buckling tendency of an offshore pipeline buried in a liquefiable soil aggravates under earthquake situations. Moreover, to understand the upheaval displacement behavior of an offshore pipeline under dynamic loading, it is crucial to understand the variation of liquefaction potential within the soil bed. Thus, in the present study, the variation of the liquefaction potential within the soil body and its effect on the pipeline upheaval displacement (u) and post-shake uplift resistance (V_up) is investigated using a finite element package called PLAXIS 2D. The study was performed for different seismic and soil conditions. To define the soil, two advanced constitutive models are used. The static stages are modelled with the ‘Hardening Soil Model with small strain’ (HSS model), while the dynamic stage is modelled with the PM4Sand model. Moreover, the problem is defined as a 2d plane strain problem. The pipe is considered to be covered with Nevada sand. Several parameters such as a sand-density index (D_r), pipe embedment depth (H), seismic frequency (f) and amplitude are varied to study the variation of the soil liquefaction potential, the pipe upheaval buckling and the post-shake uplift resistance. The model is validated with past studies and a considerable match is obtained. The liquefaction potential is shown using the shadings of a user-defined parameter called a pore water pressure ratio (r_u). Moreover, the variation of pipe upheaval displacement (u) and pipe uplift resistance (V_up) are shown using various plots. Thus, it is observed that the liquefaction potential is reduced with an increase in the frequency and the amplitude of the seismic signal. Moreover, the peak upheaval buckling, and the duration of earthquake loading to reach the peak upheaval buckling, decreased with an increase in the earthquake signal frequency. Again, the variation of post-peak uplift resistance of the buried pipeline with the pipe embedment depth is observed to be independent of the signal parameters. However, the variation of uplift resistance of the pipeline with the soil relative density is influenced by the signal parameters. Full article

The behavior of buried offshore pipelines subjected to upheaval buckling has attracted much attention in recent years. Numerous researchers have made great efforts to investigate the influence of different soil cover depth ratios, soil strengths and pipe-soil interfaces on failure mechanisms and bearing capacities during pipeline uplift. However, attention to soil spatial variability has been relatively limited. To address this gap, a random small-strain finite element analysis has been conducted and reported in this paper to evaluate the influence of the random distribution of soil strength on pipe uplift response. The validity of the numerical model was verified by comparison with the results presented in the previous literature. The spatial variation of soil strength was simulated by a random field. The effect of soil variability on the failure mechanism was determined by comparing the displacement contours of each random realization. Probabilistic analyses were performed on the random uplift capacity obtained by a series of Monte Carlo simulations, and the relationship between the failure probability and the safety factor was also determined. The findings of the present work might serve as a reference for the safety designs of pipelines. Full article

The buckling analysis of an offshore pipeline refers to the analysis of temperature-induced uplift and lateral buckling of pipelines by analytical, numerical, and experimental means. Thus, the current study discusses different research performed on thermal pipe-buckling and the different factors affecting the pipeline’s buckling behaviour. The current study consists of the dependency of the pipe-buckling direction on the seabed features and burial condition; the pre-buckling and post-buckling load-displacement behaviour of the pipeline; the effect of soil weight, burial depth, axial resistance, imperfection amplitude, temperature difference, interface tensile capacity, and diameter-to-thickness ratio on the uplift and lateral resistance; and the failure mechanism of the pipeline. Moreover, the effect of external hydrostatic pressure, bending moment, initial imperfection, sectional rigidity, and diameter-to-thickness ratio of the pipeline on collapse load of the pipeline during buckling were also included in the study. This work highlights the existing knowledge on the topic along with the main findings performed up to recent research. In addition, the reference literature on the topic is given and analysed to contribute to a broad perspective on buckling analysis of offshore pipelines. This work provides a starting point to identify further innovation and development guidelines for professionals and researchers dealing with offshore pipelines, which are key infrastructures for numerous maritime applications. Full article

The monitoring of the effects of geohazards on pipelines can be addressed by optical fiber Bragg gratings (FBGs). They are sensitive to strain and bending, and are installed on the external surface of pipelines at discrete locations. A joint approach of theoretical analysis and laboratory experiments is useful to check the reliability of the performance of this technology. We focus on the theoretical analysis of pipeline buckling and investigate the reliability of FBG monitoring both by examining the analytical model available and by performing a laboratory-scale experiment. The novelty lies in the analysis of models and methods originally developed for the detection of pipeline upheaval buckling caused by externally imposed forces in the context of service loads (temperature). Although thermal strain is very relevant in view of its potentially disruptive effects on both pipelines and the FBG response, it has not been yet fully investigated. We point out the merits of the approach, such as the functionality and simplicity of design, the accessibility and inexpensiveness of materials, the controllability and repeatability of processes, the drawbacks are also described, such as temperature effects, the problem of slipping of gages and the challenge of performing quasi-distributed strain measurements. Full article