UNDRAINED SHEAR STRENGTH OF K0 CONSOLIDATED SOFT CLAYS UNDER TRIAXIAL AND PLANE STRAIN CONDITIONS

2014 ◽  
Vol 06 (03) ◽  
pp. 1450032 ◽  
Author(s):  
QIUSHENG WANG ◽  
XIULI DU ◽  
QIUMING GONG
Keyword(s):  
Shear Strength ◽  
Plane Strain ◽  
Yield Surface ◽  
Critical State ◽  
Volumetric Strain ◽  
Stress Path ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Soft Clays ◽  
Undrained Shear

Theoretical formulas for predicting the undrained shear strength of K0 consolidated soft clays under the stress path related to triaxial and plane strain tests are presented within the framework of critical state soil mechanics. An inclined elliptical yield surface is adopted to take account of the initial anisotropic stress state. The undrained strength is determined by combining the undrained stress path in the volumetric stress–strain space and the initial yield surface in the deviator-mean stress space. The derived mathematical expressions are functions of the critical state frictional angle, the plastic volumetric strain ratio and the overconsolidation ratio, which can be simplified into the solutions for isotropically consolidated clays under triaxial tests or under plane strain tests. The results calculated by using the theoretical formulas obtained in this paper are in good agreement with the available collected test results. It indicates that these new formulas are applicable to triaxial and plane strain tests on normally and lightly to moderately overconsolidated soft clays.

A Characteristic and a Precisely Constitutive Model for Undrained Clay

2020 ◽  
Vol 975 ◽  
pp. 203-207
Author(s):  
Shih Tsung Hsu ◽  
Wen Chi Hu ◽  
Yu Heng Lin ◽  
Zhuo Ling
Keyword(s):  
Shear Strength ◽  
Plastic Strain ◽  
Constitutive Model ◽  
Strain Hardening ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Stress Strain ◽  
Proposed Model ◽  
Taipei Basin ◽  
Undrained Shear

Constitutive models for soils are usually adopted in numerical method to analyze the behavior of geotechnical structures. This study performs a series of consolidated-undrained triaxial tests to establish the stress-strain curve of clay. A constitutive model that considers continuous strain hardening-softening is proposed based on the results of triaxial tests. Triaxial test results reveal that undrained shear strength linearly increases with an increase in consolidated pressure , the normalized undrained shear strength is about 0.52 not only for this study but also for the other two cases around Taipei Basin. Due to undrained condition, an associated flow rule between plastic strain increment and stress tensor is adopted. As accumulative plastic strain or/and consolidated pressure change, the mobilized undrained shear strength also changes. All parameters needed for the proposed model can be expressed as a function of undrained shear strength Su, The mobilized undrained shear strength for the proposed model during strain hardening-softening can be in term of accumulative plastic strain. This model can calculate the stress-strain curves of clayed soils accurately.

Structure characteristics and mechanical properties of kaolinite soils. II. Effects of structure on mechanical properties

2006 ◽  
Vol 43 (6) ◽  
pp. 601-617 ◽  
Author(s):  
Y -H Wang ◽  
W -K Siu
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Shear Modulus ◽  
Critical State ◽  
Soil Structure ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Undrained Shear Strength ◽  
Interparticle Forces ◽  
Undrained Shear

This paper reports the effects of structure on the mechanical responses of kaolinite with known and controlled fabric associations. The dynamic properties and strength were assessed by resonant column tests and undrained triaxial compression tests, respectively. The experimental results demonstrate that interparticle forces and associated fabric arrangements influence the volumetric change under isotropic compression. Soils with different structures have individual consolidation lines, and the merging trend is not readily seen under an isotropic confinement up to 250 kPa. The dynamic properties of kaolinite were found to be intimately related to the soil structure. Stronger interparticle forces or higher degrees of flocculated structure lead to a greater small-strain shear modulus, Gmax, and a lower associated damping ratio, Dmin. The soil structure has no apparent influence on the critical-state friction angle (ϕ′c = 27.5°), which suggests that the critical stress ratio does not depend on interparticle forces. The undrained shear strength of kaolinite is controlled by its initial packing density rather than by any interparticle attractive forces, and yet the influence of the structure on the effective stress path is obvious.Key words: interparticle forces, shear modulus, damping ratio, stress–strain behavior, undrained shear strength, critical state.

Reply to the discussion by Mesri and Wang on “Correlations for undrained shear strength of Finnish soft clays”

2017 ◽  
Vol 54 (5) ◽  
pp. 749-753 ◽  
Author(s):  
Marco D’Ignazio ◽  
Kok-Kwang Phoon ◽  
Siew Ann Tan ◽  
Tim Länsivaara ◽  
Suzanne Lacasse
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Soft Clays ◽  
Undrained Shear

Triaxial tests on model sand columns in clay

2004 ◽  
Vol 41 (2) ◽  
pp. 299-312 ◽  
Author(s):  
V Sivakumar ◽  
D McKelvey ◽  
J Graham ◽  
D Hughes
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Stone Columns ◽  
Triaxial Tests ◽  
Column Length ◽  
Uniform Loading ◽  
Moist Sand ◽  
Triaxial Cell ◽  
Foundation Type ◽  
Undrained Shear

Vibro-stone columns can improve the bearing capacity and reduce the settlement of foundations. Their performance depends on the strength of the column material, reinforcement method of column installation, type of in situ soil, area replacement ratio, and column length. This paper examines the behaviour of small laboratory specimens of soft clay (undrained shear strength ≈ 30 kPa) reinforced with sand columns when tested under known boundary stress conditions. Two series of tests were carried out on kaolin specimens (diameter 100 mm, height 200 mm) in a triaxial cell. In the first series, specimens were reinforced with a 32 mm diameter column of sand, 80, 120, 160, or 200 mm long. Columns were installed by (i) compacting moist sand into a prebored hole or (ii) freezing a column of moist sand before inserting it into a prebored hole. In the second series, columns were reinforced with geo-grids before installation. The specimens were subjected to (i) uniform loading in which the load was applied over the entire surface area of the specimen or (ii) foundation-type loading in which only a small area in the centre of the specimen was loaded. Under uniform loading, the specimens containing a full-depth column were significantly stronger than specimens without columns. Specimens with single, partially penetrating columns installed by wet compaction were weaker than specimens without columns. When frozen columns were installed, strengths increased progressively. Under foundation-type loading, bearing capacities increased with an increase in column length. Geo-grid reinforcement produced significant increases in load-carrying capacity.Key words: ground improvement, undrained shear strength, consolidation, stress path.

scholarly journals UNDRAINED SHEAR STRENGTH PARAMETERS OF SAPROCK FROM A WEATHERING PROFILE OVER PORPHYRITIC BIOTITE GRANITE AT KM 31 OF THE KUALA LUMPUR - KARAK HIGHWAY, PENINSULAR MALAYSIA

2021 ◽  
Vol 33 (2) ◽  
Author(s):  
John Kuna Raj
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Regression Analyses ◽  
Shear Strength Parameters ◽  
Weathering Profile ◽  
Strength Parameters ◽  
Zone Ii ◽  
Undrained Shear

Three broad zones can be differentiated at the weathering profile; an upper, 9.4 m thick, pedological soil (zone I), an intermediate, 31.7 m thick, saprock (zone II) and the bottom bedrock (zone III). The saprock (zone II) comprises gravelly silty sands that distinctly preserve the minerals, textures and structures of the original granite and can be separated into sub-zones II A, II B, II C, and II D, based on differences in preservation of relict structures and content of litho-relicts (core-boulders). To characterize the undrained strength of saprock, samples were collected from sub-zones II A, II B, II C and II D and their physical and soil index properties determined before unconsolidated undrained triaxial tests were carried out on remolded samples. Three to four individual samples from each sub-zone were compressed under confining pressures of 138 kPa, 207 kPa, 276 kPa and/or 345 kPa. Plots of pf = [(σ1 + σ3)/2] versus qf = [(σ1 - σ3)/2] were then used to calculate apparent cohesions of 41.9 kPa, 100.3 kPa, 76.1 kPa and 73.9 kPa, and friction angles of 32.2o, 28.1o, 26.6o and 27.8o, for the samples from sub-zones II A, II B, II C, and II D, respectively. Regression analyses show apparent cohesions to decrease with increasing clay contents, and degrees of saturation; features indicating the influence of negative pore water (or suction) pressures. Regression analyses also show apparent friction angle to increase with increasing sand contents; a feature attributed to greater inter-locking and resistance to displacement of these particles. It is concluded that the undrained shear strength parameters of saprock are characterized by an average apparent cohesion of 54.6 kPa, and friction angle of 30.5o; the parameters influenced by the degree of saturation as well as clay and sand contents.

scholarly journals A Random Forest Model for the Prediction of Spudcan Penetration Resistance in Stiff-Over-Soft Clays

2020 ◽  
Vol 27 (4) ◽  
pp. 130-138
Author(s):  
Pan Gao ◽  
Zhihui Liu ◽  
Ji Zeng ◽  
Yiting Zhan ◽  
Fei Wang
Keyword(s):  
Shear Strength ◽  
Random Forest ◽  
Penetration Resistance ◽  
Undrained Shear Strength ◽  
Soil Parameters ◽  
Good Prediction ◽  
Resistance Profile ◽  
Soft Clays ◽  
Centrifuge Tests ◽  
Undrained Shear

AbstractPunch-through is a major threat to the jack-up unit, especially at well sites with layered stiff-over-soft clays. A model is proposed to predict the spudcan penetration resistance in stiff-over-soft clays, based on the random forest (RF) method. The RF model was trained and tested with numerical simulation results obtained through the Finite Element model, implemented with the Coupled Eulerian Lagrangian (CEL) approach. With the proposed CEL model, the effects of the stiff layer thickness, undrained shear strength ratio, and the undrained shear strength of the soft layer on the bearing characteristics, as well as the soil failure mechanism, were numerically studied. A simplified resistance profile model of penetration in stiff-over-soft clays is proposed, divided into three sections by the peak point and the transition point. The importance of soil parameters to the penetration resistance was analysed. Then, the trained RF model was tested against the test set, showing a good prediction of the numerical cases. Finally, the trained RF was validated against centrifuge tests. The RF model successfully captured the punch-through potential, and was verified using data recorded in the field, showing advantages over the SNAME guideline. It is supposed that the trained RF model should give a good prediction of the spudcan penetration resistance profile, especially if trained with more field data.

scholarly journals Critical undrained shear strength of sand-silt mixtures under monotonic loading

2015 ◽  
Vol 18 (2) ◽  
pp. 149-156 ◽  
Author(s):  
Mohamed Bensoula ◽  
Hanifi Missoum ◽  
Karim Bendani
Keyword(s):  
Shear Strength ◽  
Void Ratio ◽  
Undrained Shear Strength ◽  
Monotonic Loading ◽  
Triaxial Tests ◽  
Empirical Relationships ◽  
Fine Content ◽  
Fines Content ◽  
Chain Force ◽  
Undrained Shear

<p>This study uses experimental triaxial tests with monotonic loading to develop empirical relationships to estimate undrained critical shear strength. The effect of the fines content on undrained shear strength is analyzed for different density states. The parametric analysis indicates that, based on the soil void ratio and fine content properties, the undrained critical shear strength first increases and then decreases as the proportion of fines increases, which demonstrates the influence of fine content on a soil’s vulnerability to liquefaction. A series of monotonic undrained triaxial tests were performed on reconstituted saturated sand-silt mixtures. Beyond 30% fines content, a fraction of the silt participates in the soil’s skeleton chain force. In this context, the concept of the equivalent intergranular void ratio may be an appropriate parameter to express the critical shear strength of the studied soil. This parameter is able to control the undrained shear strength of non-plastic silt and sand mixtures with different densities.</p><p> </p><p><strong>Resumen</strong></p><p>Este estudio utiliza evaluaciones experimentales triaxiales con cargas repetitivas para desarrollar relaciones empíricas y estimar la tensión crítica de corte bajo condiciones no drenadas. El efecto de contenido de finos en la tensión de corte sin drenar se analizó en diferentes estados de densidad. El análisis paramétrico indica que, basado en la porosidad del suelo y las propiedades del material de finos, la tensión de corte sin drenar primero se incrementa y luego decrece mientras la proporción de finos aumenta, lo que demuestra la influencia de contenido de finos en la vulnerabilidad del suelo a la licuación. Una serie de las evaluaciones se realizó en  mezclas rehidratadas y saturadas de arena y cieno. Más allá del 30 % de los contenidos finos, una fracción del cieno hace parte principal de la cadena de fuerza del suelo. En este contexto, el concepto de porosidad equivalente intergranular puede ser un parámetro apropiado para expresar la tensión crítica de corte del suelo estudiado. Este parámetro nos permite controlar la tensión de corte sin drenar de cieno no plástico y mezclas de arena de densidades diferentes.</p>

Geotechnical properties of soft clays from the Witch Ground Basin, central North Sea

1991 ◽  
Vol 7 (1) ◽  
pp. 151-156 ◽  
Author(s):  
M. A. Paul ◽  
L. M. Jobson
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Geotechnical Properties ◽  
Seismic Surveys ◽  
Soft Clays ◽  
Fine Grained ◽  
Acoustic Signatures ◽  
The Witch ◽  
Central North Sea ◽  
Undrained Shear

AbstractThe Witch Ground Basin to the northeast of Peterhead is occupied by Late to Postglacial clays which reach a maximum thickness of over forty metres. High resolution seismic surveys have shown that the Sediments can be divided into two stratigraphic units on the basis of their acoustic signatures: the upper Witch Ground Formation shows in its lower part a finely detailed pattern of laterally continuous multiple reflectors, whereas the lower Swatchway and Coal Pit Formations present a disorganised signature in which few reflectors are continuous.Profiles of bulk density, water content and undrained shear strength have been obtained from two continuously sampled, adjacent boreholes which penetrated the sediments to a depth of forty metres. These show that the deposits of the Witch Ground Basin comprise a single geotechnical unit with the properties expected of a fine grained sediment of glaciomarine origin. The principal geotechnical properties change gradationally as a result of changes in composition and from selfweight compression. The different seismic signatures on which the basin stratigraphy is based are not reflected by major geotechnical changes within the sediment, but may well result from secondary features of the geotechnical profile.

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