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.

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.

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.

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>

Stability threshold for cyclic loading of saturated clay

1989 ◽  
Vol 26 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Guy Lefebvre ◽  
Denis LeBoeuf ◽  
Benoît Demers
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Strain Rate ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Repeated Loading ◽  
Loading Test ◽  
Stability Threshold ◽  
The Stability ◽  
Undrained Shear

This paper presents the results of an experimental investigation performed to study the stability threshold under cyclic (repeated) loading, and the postcyclic static strength of a sensitive clay from the Hudson Bay region. The strain rate and structure effects were also studied by carrying out monotonic and cyclic triaxial tests at both slow and rapid strain rates or frequencies, and at confining pressures above and below the apparent preconsolidation pressure. The stability threshold for both structured and normally consolidated Grande Baleine clay is about 60–65% of the original undrained shear strength measured at the same strain rate as that used in the repeated loading test. The undrained shear strength and the failure envelope remain essentially unchanged if the repeated preloading is kept below the threshold. The clay structure remains unaltered by this preloading. Key words: clay, stability threshold, cyclic loading, earthquake, postcyclic strength.

Interpretation of field vane strength of an anisotropic soil

1992 ◽  
Vol 29 (4) ◽  
pp. 627-637
Author(s):  
Vinod K. Garga ◽  
Mahbubul A. Khan
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Strength Anisotropy ◽  
Shear Tests ◽  
Direct Shear Tests ◽  
State Of Stress ◽  
Anisotropic Soil ◽  
Undrained Shear

Determination of the undrained shear strength (Su) of overconsolidated soils such as the weathered clay crust overlying Leda clay is important for the design of shallow foundations and embankments. In situ vane shear tests and isotropically consolidated undrained triaxial tests have been conventionally used for this purpose. Contrasting test results from these two methods, low Su obtained from triaxial tests and high Su obtained from in situ vane shear tests, motivated further research into this problem. Strength anisotropy, due to in situ anisotropic state of stress and orientation of soil fabric during deposition, is believed to be the reason for these contrasting results. Improved testing and interpretation techniques for this type of anisotropic soil have been proposed. Weathered crusts are generally heavily over-consolidated, with K0 values greater than unity. Undrained triaxial shear tests conducted to date by various researchers are either isotropically consolidated or are anisotropically consolidated assuming K0 smaller than unity. Neither of these two methods represents the in situ state of stress of a clay crust. Therefore, in this investigation, the undisturbed samples were reconsolidated anisotropically to the in situ state of stress (K0 > 1) before shearing undrained in the triaxial test. Direct shear tests on horizontal and vertical specimens consolidated to normal stresses equal to σvo′ and σho′, respectively, were also conducted to investigate the strength anisotropy. Field vane tests have been reinterpreted in terms of this strength anisotropy. The undrained shear strength on top and bottom horizontal planes (Suh) obtained from these field vane tests within the crust provided comparable results with those from laboratory triaxial and direct shear tests which were reconsolidated to in situ stresses. Key words : in situ vane test, undrained shear strength, strength anisotropy, rate effect, anisotropic in situ state, weathered clay crust, overconsolidation.

Disturbance effects in pressuremeter tests in clay

2004 ◽  
Vol 41 (4) ◽  
pp. 738-759 ◽  
Author(s):  
Vincenzo Silvestri
Keyword(s):  
Shear Strength ◽  
Strain Curve ◽  
Undrained Shear Strength ◽  
Case Histories ◽  
Stress Strain ◽  
Test Analysis ◽  
Hardening Material ◽  
Expansion Test ◽  
Undrained Shear

This paper analyzes the effect of borehole disturbance, caused by installation of pressuremeter probes in clays, on the derived stress–strain curves. Both overpushing- and overcutting-induced disturbances are considered. It is shown that overpushing results in underestimation of the undrained shear resistance. In general, the degree of underestimation cannot be determined. As for overcutting, the derived stress–strain curves are characterized by high peak strengths. The degree of overestimation of the undrained shear strength may reach 100% for the case of a strain-hardening material. Determination of the strain that corresponds to the peak shear strength allows determination of the true stress–strain curve from the expansion test. Analysis of four well-documented case histories serves to illustrate the proposed approach.Key words: pressuremeter, borehole disturbance, clay, stress-strain curves, case histories, undrained shear strength.

Behavior of a Cemented Plastic Clay as an Embankment Foundation

1974 ◽  
Vol 11 (1) ◽  
pp. 46-58
Author(s):  
Guy Lefebvre ◽  
Liguori M. Lefebvre ◽  
Peter Rosenberg
Keyword(s):  
Shear Strength ◽  
Pore Pressure ◽  
Applied Pressure ◽  
Undrained Shear Strength ◽  
Glacial Lake ◽  
Triaxial Tests ◽  
High Plasticity ◽  
Degree Of Consolidation ◽  
Undrained Shear ◽  
Varved Clay

A 32 ft (10 m) high embankment has been built at Matagami, Quebec, on a varved clay deposit of the glacial lake Barlow–Ojibway. This paper reports on some aspects considered in the design, mainly the cementation and the high plasticity of the clay. The variation of settlements and pore pressure is presented and indicates that, 8 months after construction, the pore pressure dissipation is very small while the measured settlements reach 18 in. (45 cm).Triaxial tests, with various consolidation times, were carried out on specimens cut from undisturbed block samples obtained in the same area, in order to study the effect of consolidation on the shear strength of these cemented clays. Results indicate that the undrained shear strength decreases during consolidation until the degree of consolidation reaches 50%. This phenomenon together with the non-dissipation of pore pressure in the field is attributed to the collapse of the cemented structure when the applied pressure exceeds Pc.Similar behavior reported for two other cases of embankments built on deposits of the same origin, leads to the conclusion that the stage construction method is not suitable for embankment on cemented clays, at least those from the glacial lake Barlow–Ojibway, because no gain in shear strength is recorded over a normal consolidation period.

scholarly journals Parameter variability of undrained shear strength and strain using a database of reconstituted soil tests

2020 ◽  
Vol 57 (8) ◽  
pp. 1247-1255 ◽  
Author(s):  
Mair E.W. Beesley ◽  
Paul J. Vardanega
Keyword(s):  
Shear Strength ◽  
Shear Strain ◽  
Triaxial Compression ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Shear Mode ◽  
Soil Failure ◽  
Ground Investigation ◽  
Reconstituted Soil ◽  
Undrained Shear

During construction, the mobilization of undrained shear strength must be limited to avoid soil failure. Soil strains must be controlled to avoid compromising structural serviceability. To assess foundation performance by strength mobilization, an understanding of soil strains at various levels of strength mobilization is required. In practice, ground investigation data are often limited, and assessment of the expected variation of stress–strain and undrained shear strength is improved with empirical correlations calibrated with a database. The new database RFG/TXCU-278 contains data of 278 consolidated–undrained triaxial tests on reconstituted fine-grained soil samples compiled from the literature. Analysis of the database to evaluate the variability of undrained strength ratio (cu/[Formula: see text]) and a reference shear strain with shear mode is undertaken in this paper. The new database provides evidence that shear strain (like undrained shear strength) is sensitive to the consolidation (isotropic or K0) and shear mode (triaxial compression or extension) applied in the test. For the materials included in the database, the strength mobilization parameters obtained from a triaxial compression test can be used to predict the corresponding triaxial extension parameters to a reasonable accuracy.

Effect of the Time on the Undrained Shear Strength and Permeability of Clay-Wooden Sawdust Mixtures Used to Improve Landfills Liner

2020 ◽  
Vol 857 ◽  
pp. 311-318
Author(s):  
Omar Hamdi Jasim ◽  
Doğan Çetin
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Unconfined Compression Test ◽  
Remarkable Effect ◽  
The Impact ◽  
Undrained Shear

This study aims to assess the impact of time on sawdust usage to enhance the behavior of the clay used in landfills. The soil used in this paper was brought from Büyükçekmece region / Istanbul. Four proportions (1, 2, 3 and 5) of the sawdust were added as a percentage of the dry weight of the soil. Soil-sawdust mixtures were compacted with the optimum water content corresponding to each percentage and samples were extracted. The extracted samples were divided into two groups, the immediate tests were performed on the first group while the second group was kept in special containers for long-term tests after 90 days. A series of undrained unconsolidated triaxial tests (UU) and unconfined compression tests (UCS) were performed on the specimens and compared with the row soil, in the immediate tests, the results from the UU triaxial test showed that the undrained shear strength was increased as the sawdust content increased and then decreased, it was conducted that the optimum sawdust content was 3%, it was increased the undrained shear strength by (39.5%) and (41.44%) for UU triaxial and Unconfined compression tests respectively. After 90 days of the curing period, it found that 2% is the optimum sawdust content, it was increased the undrained shear strength by (202.51%) and (176.64%) for UU triaxial and unconfined compression test respectively. In the immediate and long-term tests, the coefficient of permeability increased by (66.66) and (94.44%) as the sawdust increased from 0 to 5 % respectively. Sawdust increases the hydraulic conductivity of the clay. It can be concluded that the sawdust usage has a remarkable effect on the shear strength of the clay for both immediate and long-term tests.

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