Volume 9: Offshore Geotechnics最新文献

{"title":"Geohazard Study of Mudslide Event at a Subsea Escarpment and Structural Response of Crossing Flowlines: Part II – CFD and FSI Analysis","authors":"Hyunchul Jang, L. Lai, K. Hayes, Anthony Musto","doi":"10.1115/omae2022-80539","DOIUrl":"https://doi.org/10.1115/omae2022-80539","url":null,"abstract":"\u0000 Mudslides can occur on the seafloor due to subsea earthquakes. These extreme events have a significant impact on the structural integrity of subsea flowlines and equipment. A numerical geohazard study was performed on a subsea mudslide event occurring at an escarpment. The study objective was to determine the structural response of two flowlines and one umbilical crossing an escarpment area subject to the extreme mudslide event and to assess requirement for additional stabilization ancillaries.\u0000 The study utilized several numerical methodologies such as Computational-Fluid-Dynamics (CFD), Finite-Element-Analysis (FEA), and Fluid-Structure-Interaction (FSI). Different levels of CFD models were first considered (without flowlines) to show the effect of including additional physics with the final CFD model considering a viscous seawater column, viscoplastic multi-layered soil and high-mobility mud phases. The mudslide velocity field from this CFD simulation is extracted at every 1 s and applied to the Abaqus FEA simulation approach. This is presented in a separate paper [1].\u0000 The current paper utilized a FSI simulation approach where the evolution of mudflow debris is directly coupled with the FEA flowline model. This allows the FEA model to continuously update loading created by the mudslide motion. The flowline structural responses were monitored and assessed in terms of displaced shapes and structural loading. This methodology reduces conservatism over conventional approaches by considering viscous effects of the seawater, multi-layer soil and mud layers.\u0000 Key findings from the study is that the mudslide event did not significantly displace flowlines over the escarpment. The two flowline responses were within structural design limits. It was also found anchoring did not significantly affect structural responses. The umbilical line, however, exceeded compression limits by four times the design limit. This is due to the high velocity mud-front interacting with an initially stationary umbilical and pushing it into compression during the initial stages of the mudslide event. The solution proposed was line rerouting which helped reduce compression levels to within design limits. This analysis assisted the project in CAPEX and installation cost reduction with no requirement of further umbilical compression mitigation components, and the omission of the pre-planned anchors.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126506565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decline in Slope Stability as a Consequence of Gassy Soil in Submarine Slopes on the Balearic Promontory","authors":"P. Kaminski, J. Grabe, T. Sager, M. Urlaub","doi":"10.1115/omae2022-81151","DOIUrl":"https://doi.org/10.1115/omae2022-81151","url":null,"abstract":"\u0000 Submarine landslides can entail a substantial hazard for offshore infrastructure as they are capable of triggering tsunamis and may develop into highly mobile turbidity currents capable of breaking seabed cables. Despite considerable research activity, the trigger mechanisms for such landslide events cannot be clearly defined. Recently, marine gas occurrence has been investigated as a possible trigger mechanism. The behaviour of a fine-grained gassy soil is influenced by a variety of micromechanical processes; amongst destructuring due to fracture formation or gas bubble expansion, and bubble flooding with subsequent cavity collapse. Capturing and modeling these processes in order to assess the destructive potential of enclosed gas bubbles in submarine slopes is to date a considerable scientific challenge. With the help of a large number of Finite Element Limit Analyses (FELA), which are based on laboratory tests on a gravity core from the western Mediterranean Sea, submarine slope stability in the respective region was evaluated. Based on these analyses, gassy soil can be defined as a preconditioning factor but not as a capable trigger mechanism for submarine landsliding.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130278882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the Validity of Miner’s Rule and Its Application in Offshore Pile Design Practice","authors":"A. Stark, Sebastian Breidenstein, J. Grabe","doi":"10.1115/omae2022-81150","DOIUrl":"https://doi.org/10.1115/omae2022-81150","url":null,"abstract":"\u0000 Current design practice simplifies complex loading scenarios, i.e. highly cyclic loads from varying direction offshore, using classification methods by combining different cycle packages with constant frequency, mean load level and amplitude. This procedure assumes the resulting accumulated deformation in the soil to be independent of the ordering of the cycle packages, i.e. the validity of miner’s rule. This paper presents an experimental study on the validity of Miner’s rule in non-cohesive soils based on high cyclic direct simple shear tests. The test program comprises monotonic and high cyclic direct simple shear tests in fine silica sand, which is routinely used at Centre of Offshore Foundation Systems. The paper investigates the effect of ordering of the cycle packages on the resulting cyclic deformation accumulation for different loading scenarios with varying mean and cyclic load level. The results are evaluated in terms of the accumulated volumetric and the resulting shear strain. Based on the literature, Miner’s rule is assumed to be valid for a deviation of the relevant variables of < 20 %. Conclusions with respect to the influence of cyclic preloading are drawn and related to current design practices.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130332623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calibration for Interpretation Parameter Nkt of CPTU in Offshore Wind Farm at Coast Area of the Mekong River Delta","authors":"Kuan-jun Wang, Gang Liu, K. Shen, Shan Gao","doi":"10.1115/omae2022-79090","DOIUrl":"https://doi.org/10.1115/omae2022-79090","url":null,"abstract":"\u0000 Sample disturbances during drilling work in offshore wind farms are inevitable due to the marine environment, and much higher than those in onshore projects, which would lead to an underestimate of soil strength, especially for soft clay. Piezocone penetration test (CPTU) is now widely used in the geotechnical investigation in offshore wind farms, which has slight the disturbance on soil. But the soil parameters cannot be directly obtained by CPTU, and the interpretation process should be carried out, while the parameters for interpretation are site-specific. Based on an offshore wind farm at the coast area of the Mekong River Delta in Vietnam, laboratory tests and CPTU results are analyzed to calibrate the cone factor Nkt, which is used for CPTU interpretation of undrained shear strength su. The calibrated Nkt from the triaxial UU test, which ranges from 10.82 to 57.89, is much higher than the calibrated Nkt values from DSq and triaxial CU test. A possible reason is that the soil samples for triaxial tests were disturbed during drilling and transportation, the triaxial UU tests might underestimate the strength of in-situ clay. The cone factor Nkt calibrated from the DSq test and triaxial CU test respectively range from 15.65 to 25.86 and 12.51 to 30.50, with the total average value of 22.29 and 20.44, which are more accurate compared to the Nkt values calibrated from the triaxial UU test. Finally, a negative correlation between pore pressure ratio Bq and Nkt is established based on triaxial CU test results, which can be used to choose the appropriate Nkt value for interpretation. The CPTU interpretation by Bq-Nkt correlation and the total average value 20.44 of Nkt both show good agreement with the measured soil strength. For simplicity, the total average value of Nkt calibrated from triaxial CU test results is recommended to be used for the CPTU interpretation in engineering projects, which is more convenient.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"119 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122915158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Effect of the Height of the Regular Wave on Seabed Liquefaction","authors":"K. Kazimierowicz-Frankowska, M. Kulczykowski, D. Majewski, J. Mierczyński, Marcin Smyczyński","doi":"10.1115/omae2022-78537","DOIUrl":"https://doi.org/10.1115/omae2022-78537","url":null,"abstract":"\u0000 This paper presents the results of an experimental study of seabed liquefaction under progressive waves. Firstly, during preliminary tests, the physical and mechanical parameters of the soil selected as the subgrade material were determined. A series of monotonic triaxial shear tests were carried out at different initial void ratios and mean effective stresses. The susceptibility of soil samples to liquefaction was estimated. The results were used to design experiments in a wave flume. Their main purpose was to study the effect of wave height on wave-induced liquefaction. The experiments were carried out in a wave flume that is 64.1 m long, 0.6 m wide, and 1.4 m high, in a specially built experimental stand located 5.0 m from the wave generator below the flume bottom. Wave propagation was conducted over constant water depth which was equal h = 0.5 m. The wave surface elevation was measured by resistance type wave gauges. The pore-water pressure was measured by transducers located in the middle of the sediment pit, at four different soil depths. Parametric studies were carried out to investigate the influence of wave height on the liquefaction process. The results of experiments shown that pressure buildup is a strong function of the wave height and increases with increasing its value.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133030180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Potential and Consequences of Earthquake Induced Liquefaction Under a Gravity Based Structure","authors":"B. Carlton, Patrick Lee, F. Belloni, A. Kaynia","doi":"10.1115/omae2022-80169","DOIUrl":"https://doi.org/10.1115/omae2022-80169","url":null,"abstract":"\u0000 This study focused on the potential liquefaction due to earthquake shaking of a gravity based structure (GBS) located off the northeast coast of Italy in the Adriatic Sea. The reinforced concrete GBS is 88 m wide by 180 m long and is underlain by a sand unit with variable thickness that could cause differential settlement and sliding. We first estimated settlements using cone penetration test (CPT) based liquefaction triggering methods and simplified settlement calculations with adjustments to account for the influence of the GBS. We then performed the same calculations but with the earthquake demand estimated from 1D site response analyses. Finally, we performed 2D finite element analyses of the soil-structure system using the advanced constitutive model PM4Sand to model the liquefiable sand layers. The results show that the total amount of displacement is small (1.5–7.5 cm), and no significant differential settlement or sliding is expected for the design earthquake scenarios. A practical observation from the study is that the more detailed and integrated analyses resulted in lower estimates of settlements and a more accurate representation of the soil-structure response.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116341621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geohazard Study of Mudslide Event at a Subsea Escarpment and Structural Response of Crossing Flowlines: Part I – FEA Analysis","authors":"K. Hayes, Hyunchul Jang, L. Lai, Anthony Musto","doi":"10.1115/omae2022-81036","DOIUrl":"https://doi.org/10.1115/omae2022-81036","url":null,"abstract":"\u0000 Subsea earthquakes have the potential to cause mudslides on the seafloor. These extreme events can have a significant impact on the structural integrity of subsea flowlines and umbilicals. A numerical geohazard study is performed on a subsea mudslide event occurring at an escarpment. The study objective is to determine the structural response of flexible lines crossing the escarpment area when subjected to an extreme mudslide event and to determine both the survivability of the lines and the need for proposed anchoring devices.\u0000 The study utilizes several numerical methodologies of increased complexity, precision, and cost, such as Finite-Element-Analysis (FEA), Computational-Fluid-Dynamics (CFD), and Fluid-Structure-Interaction (FSI).\u0000 This paper focuses on the FEA analysis, with the CFD and FSI analyses presented in a separate paper [1]. The FEA methodology reduces conservatism over conventional approaches by applying the mud debris flow effects on the flexible lines with a one-way CFD to FEA coupling and a morphing escarpment bathymetry. A CFD simulation is performed on a rigid seabed bathymetry to extract the mudslide velocity field at every second. This velocity field is applied to the Abaqus FEA simulation using Abaqus/Aqua with a one-way coupling approach, thereby allowing the FEA model loading on the flexible flowlines to be updated from the load created by the mudslide motion.\u0000 A key finding from the FEA study is that although the mudslide event creates large displacements in the flexible lines, it does not significantly pull the flexible flowlines over the escarpment, thereby eliminating the need for planned anchors and saving significant capital expenditure and installation costs.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"61 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132148993","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical Modelling of Liquefaction Around Marine Structures - Progress and Recent Developments","authors":"C. Windt, N. Goseberg, S. Schimmels, M. Kudella, R. Shanmugasundaram, H. Rusche, B. Sumer, V. Kirca, V. Vanjakula, F. Adam, D. Majewski, K. Kazimierowicz-Frankowska, Grzegorz Hrycyna","doi":"10.1115/omae2022-79821","DOIUrl":"https://doi.org/10.1115/omae2022-79821","url":null,"abstract":"\u0000 The liquefaction around marine structures can lead to severe structural failure and the susceptibility of seabed soil to liquefaction at a specific installation site of, e.g., floating offshore wind turbines should be included within the design process and site evaluation. To that end, advanced prediction tools based on numerical modelling can provide valuable insight into the hydro-geotechnical processes. However, due to the complex interaction of the underlying physics, developing a holistic modelling framework for seabed liquefaction is a challenging task. The NuLIMAS research project (Numerical modelling of seabed liquefaction around marine structures) aims at the development of such a numerical model of seabed liquefaction implemented in the OpenFOAM® framework. This paper provides an overview of the NuLIMAS project, laying out the current state of the art of experimental and numerical modelling approaches for seabed liquefaction and presenting some initial results.","PeriodicalId":427776,"journal":{"name":"Volume 9: Offshore Geotechnics","volume":"1939 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128850978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}