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undrained shear strength evaluation for hydrate-bearing sediment overlying strata in the Shenhu area, northern South China Sea

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Acta Oceanologica Sinica 2019年第3期38卷 114-123页

作者： Yanlong Li Gaowei Hu Nengyou Wu Changling Liu Qiang Chen Chen'an Li Key Laboratory of Gas Hydrate Ministry of Natural Resources Laboratory for Marine Mineral Resource Pilot National Laboratory for Marine Science and Technology (Qingdao) Qingdao Institute of Marine Geology China Geological Survey College of Information and Control Engineering China University of Petroleum

The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water *** situ piezocone penetration tests(CPTU) and laboratory experiments are performed at Site W18-19 in the Shenhu area, northern South China Sea, where China's first marine hydrate exploitation operation is due to be located. The validation of the undrained shear strength prediction model based on CPTU parameters. Different laboratory tests, including pocket penetrometer, torvane, miniature vane and unconsolidated undrained triaxial tests, are employed to solve empirical cone coefficients by statistical and mathematical methods. Finally, an optimized model is proposed to describe the longitudinal distribution of undrained shear strength in calcareous clay strata in the Shenhu area. Research results reveal that average empirical cone coefficients based on total cone resistance, effective resistance, and excess-pore pressure are 13.8, 4.2 and 14.4, respectively. The undrained shear strength prediction model shows a good fit with the laboratory results only within specific intervals based on their compaction degree and gas-bearing conditions. The optimized prediction model in piecewise function format can be used to describe the longitudinal distribution of the undrained shear strength for calcareous clay within all depth intervals from the mud-line to the upper boundary of hydrate-bearing sediments(HBS). The optimized prediction result indicates that the effective cone resistance model is suitable for very soft to firm calcareous clays,the excess-pore pressure model can depict the undrained shear strength for firm to very stiff but gas-free clays,while the total cone resistance model is advantageous for evaluating the undrained shear strength for very stiff and gassy clays. The optimized model in piecewise function format can considerably improve the adaptability of empirical models for calcareous clay in the Shenhu area. These results are significant for sa

关键词： piezocone penetration test hydrate exploitation test undrained shear strength calcareous clay Shenhu area South China Sea

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undrained stability of a spherical cavity in cohesive soils using finite element limit analysis

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第6期11卷 1274-1285页

作者： Suraparb Keawsawasvong Boonchai Ukritchon Centre of Excellence in Geotechnical and Geoenvironmental Engineering Department of Civil EngineeringFaculty of EngineeringChulalongkorn University

A parametric study of undrained stability of a spherical cavity in clays is investigated by finite elementlimit analysis with an axisymmetric condition. Influences of cover depth ratio of cavity and dimensionlessoverburden factor on predicted failure mechanisms and dimensionless load factor are *** is found that a previously recommended and up-to-date lower bound solution to the problem wassignificantly inaccurate for practice use. Thus, an accurate approximate solution to the problem is proposedfrom nonlinear regression analysis of the computed average bound solutions. New cavity stabilityfactors for the soil cohesion and soil unit weight are proposed. New findings are revealed for the threedimensionaleffect of the cavity shape on these factors between the axisymmetric and plane strainconditions, and their applications to the undrained stability evaluation of cavity problems in practice aredescribed.

关键词： Limit analysis undrained stability Spherical cavity Sinkhole Axisymmetry

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SPT based determination of undrained shear strength:Regression models and machine learning

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Frontiers of Structural and Civil Engineering 2020年第1期14卷 185-198页

作者： Walid Khalid MBARAK Esma Nur CINICIOGLU Ozer CINICIOGLU Department of Civil Engigeering Bogazici UniversityIstanbul 34342Turkey School of Business Quantitative Methods DivisionIstanbul UniversityIstanbul 34320Turkey

The purpose of this study is the accurate prediction of undrained shear strength using Standard Penetration Test results and soil consistency indices,such as water content and Atterberg *** this study,along with the conventional methods of simple and multiple linear regression models,three machine learning algorithms,random forest,gradient boosting and stacked models,are developed for prediction of undrained shear *** models are employed on a relatively large data set from different projects around Turkey covering 230 *** an improvement over the available studies in literature,this study utilizes correct statistical analyses techniques on a relatively large database,such as using a train/test split on the data set to avoid overfitting of the developed ***,the validity and consistency of the prediction results are ensured with the correct use of statistical measures like p-value and cross-validation which were missing in previous *** compare the performances of the models developed in this study with the prior ones existing in literature,all models were applied on the test data set and their performances are evaluated in terms of the resulting root mean squared error(RMSE)values and coefficient of determination(R^2).Accordingly,the models developed in this study demonstrate superior prediction capabilities compared to all of the prior ***,to facilitate the use of machine learning algorithms for prediction purposes,entire source code prepared for this study and the collected data set are provided as supplements of this study.

关键词： undrained shear strength linear regression random forest gradient boosting machine learning standard penetration test

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Using Piezocone Dissipation Test to Estimate the undrained Shear Strength (su), Nktand NΔuFactors in Cohesive Soils

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Journal of Geoscience and Environment Protection 2019年第8期7卷 96-104页

作者： Dante René Bosch Rubén Rafael Sotelo Fernando María Mántaras Center of Applied Geosciences Faculty of Engineering UNNE (National University of Northeast) Resistencia Chaco Argentina Geoforma Engenharia Ltda Joinville Brazil

The current practice of geotechnical engineering commonly uses a combination of theoretical and empirical correlations to estimate the soil undrained shear strength in clays from the piezocone test. In order to complement the use of such correlations, the application of a method to estimate the soil undrained shear strength, using measures of the excess pore pressure in dissipation tests of piezocone is presented. In cohesive soils, excess pore pressure and undrained shear strength are dependent on the same variables (stress state, stress history, soil stiffness), which allows them to be related by the theoretical cavity expansion-critical state framework. This paper mentions the mathematical formulation that supports the theoretical framework used, its relationship with the Nkt and NΔu factors and their estimation in a case studied. The results obtained are consistent within the dispersion found in the international literature and encourage the use of the method in engineering practice.

关键词： CPTu Piezocone Overconsolidation Ratio undrained Shear Strength Dissipation Test

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DEM Simulations of Granular Soils under undrained Triaxial Compression and Plane Strain

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Journal of Applied Mathematics and Physics 2015年第8期3卷 1003-1009页

作者： Guobin Gong Department of Civil Engineering Xi’an Jiaotong-Liverpool University (XJTLU) Suzhou China

The paper presents 3D DEM simulation results of undrained tests for loose assemblies with varied porosities under both triaxial compression and plane strain conditions, using a periodic cell. The undrained tests were modelled by deforming the samples under constant volume conditions, which corresponds to saturated soil samples. The undrained stress paths are shown to be qualitatively similar to physical experimental results. The triggering of liquefaction and temporary liquefaction is identified by a microscopic parameter with redundancy factor (RF) equal to unity, which defines the transition from “solid-like” to “liquid-like” behaviour. The undrained behaviour of granular soils is found to be mainly governed by the evolution of redundancy factor, and a reversal of deviatoric stress in stress path (temporary liquefaction) is found to be due to temporary loss of contacts forming a structural mechanism in the system where RF is smaller than unity during the evolution.

关键词： DEM Periodic Cell Saturated undrained Liquefaction Coordination Number Redundancy Factor

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Tapered Suction Caissons:A Numerical Investigation into Their Pull-out Performance

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China Ocean Engineering 2009年第4期23卷 695-707页

作者： M.Zeinoddini J.Keyvani M.Nabipour Faculty of Civil Engineering KNToosi University of Technology Faculty of Engineering Tarbiat Moallem University

Suction caissons have been widely used as anchors and foundations for floating and fixed offshore platforms. The pull-out performance of conventional suction caissons （with upright walls） has been investigated by a number of researchers. However, no attention has been paid to tapered suction caissons. This paper deals with the performance of tapered suction caissons under vertical pull-out loads. A numerical approach is used for this purpose. The numerical model is first verified against test data available for common upright caissons. The verified model is then used to study the pullout performance of tapered suction caissons. It is noticed that the pull-out capacities exhibited by tapered suction caissons are in general considerably higher than those from their corresponding traditional upright caissons. To obtain an insight into this superior behaviour, effects from certain soil/caisson/drainage parameters on the pull-out capacity of tapered suction caissons are studied. Soil cohesion is noticed to have a linear improving effect on the capacity of both upright and ta- pered suction caissons. The soil internal friction angle is noticed to have an exponential increasing effect on the pull-out capacity. With a constant caisson diameter, an increase in the aspect ratio is seen to particularly influence the pull-out capacity. With a constant caisson length, an increase in the aspect ratio is discovered to result in non-linear decrease in the pull-out capacity. Under undrained conditions, tapered models generally show less sensitivity to above mentioned soil/caisson parameters as compared with those under drained conditions.

关键词： suction caisson pull-out capacity numerical study upright caisson tapered caisson offshore structure sand clay drained undrained

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A multi-stage triaxial testing procedure for low permeable geomaterials applied to Opalinus Clay

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 137-148页

作者： Katrin M. Wild Marco Barla Giovanni Turinetti Florian Amann Engineering Geology Group Geological Institute ETH Zürich Sonneggstrasse 5 Zürich 8092 Switzerland Department of Structural Building and Geotechnical Engineering Politecnico di Torino Corso Duca degli Abruzzi 24 Torino 10129 Italy Swiss Competence Center of Energy Research Supply of Electricity (SCCER-SoE) Geological Institute ETH Zürich Sonneggstrasse 5 Zürich 8092Switzerland

In many engineering applications,it is important to determine both effective rock properties and the rock behavior which are representative for the problem’s in situ *** this purpose,rock samples are usually extracted from the ground and brought to the laboratory to perform laboratory experiments such as consolidated undrained(CU)triaxial *** low permeable geomaterials such as clay shales,core extraction,handling,storage,and specimen preparation can lead to a reduction in the degree of saturation and the effective stress state in the specimen prior to testing remains *** changes in structure and the effect of capillary pressure can alter the properties of the specimen and affect the reliability of the test results.A careful testing procedure including back-saturation,consolidation and adequate shearing of the specimen,however,can overcome these *** substantial effort has been devoted during the past decades to the establishment of a testing procedure for low permeable geomaterials,no consistent protocol can be *** a special focus on CU tests on Opalinus Clay,this study gives a review of the theoretical concepts necessary for planning and validating the results during the individual testing stages(saturation,consolidation,and shearing).The discussed tests protocol is further applied to a series of specimens of Opalinus Clay to illustrate its applicability and highlight the key aspects.

关键词： Triaxial test Saturation Consolidation undrained Opalinus Clay Clay shale

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Effects of Moisture Content and Plasticity Index on Duncan-Chang Model Parameters of Hydraulic Fill Soft Soil

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World Journal of Engineering and Technology 2019年第3期7卷 408-417页

作者： Erzhong Chen Meng Yan Jihui Ding Cen Gao Yu Gan Institute of Civil Engineering University of Hebei Baoding China

In order to explore the effects of moisture content and plasticity index on Duncan-Chang model parameters?K,n,?C?and?Rf,?we selected 8 groups of soft soil with water content of 69.1%?-?94.3% and plasticity index of 32.2?-?54.1 for triaxial unconsolidated undrained shear test. The results show that?Cuu,?K?and?n?values all showed a downward trend, and?Rf?variation was not obvious with the increase of moisture content. The variation rule of each parameter is not obvious with the increase of plasticity index. When moisture content is constant,?Cuu?and?n?values do not change much,?K?increases with the increase of plasticity index within the range of 70%?-?80% moisture content, and does not change much with the increase of plasticity index when moisture content is greater than 80%,?Rf?has no obvious rule.?When the plasticity index is constant,?Cuu,?Kand?n?decrease with the increase of moisture content,?Rf?has no obvious rule. The maximum value of?Cuu?is 20.18?kPa, the minimum is 3.72?kPa, and the maximum to minimum ratio is 5.42. The maximum value of?K?is 0.517, the minimum is 0.022, and the maximum to minimum ratio is 23.5. The maximum value of?n?is 1.198, the minimum is 0.150, and the maximum to minimum ratio is 7.99. The maximum value of?Rf?is 0.872, the minimum is 0.679, and the maximum to minimum ratio is 1.28.

关键词： Moisture Content Plasticity Index Duncan-Chang Model Unconsolidated undrained Test

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