Failure, instability, and the second work increment in loose silty sand

2011 ◽  
Vol 48 (6) ◽  
pp. 943-955 ◽  
Author(s):  
Mehmet Murat Monkul ◽  
Jerry A. Yamamuro ◽  
Poul V. Lade
Keyword(s):  
Triaxial Compression ◽  
Failure Surface ◽  
Stress Path ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Stability Conditions ◽  
Stability And Instability ◽  
Constant Shear Stress ◽  
The Mean ◽  
Undrained Conditions

Triaxial tests have been performed to demonstrate the conditions for stability and instability in loose silty sand. Drucker (1951) and Hill (1958) stability conditions in terms of the sign of the second work increment were employed in the design of the stress paths used in the triaxial compression and extension tests performed with quasi-constant shear stress while the mean normal stress was reduced until failure occurred. It is shown that the sand is completely stable under drained conditions for any stress path and irrespective of the sign of the second work increment. This is demonstrated by completely stopping the change in stresses and observing the stable behavior in the range of stresses where the sand contracts and where it dilates. Once the effective stress failure surface is passed, the sand becomes unstable, and the sign of the second work increment is always negative. Run-away instability can occur inside the failure surface for loose silty sand under undrained conditions for which the sand tends to contract, pore pressures continue to develop, and the second work increment is negative. Liquefaction may follow if the loose silty sand is sufficiently loose.

Experimental behaviour and modelling of an unsaturated compacted soil

2000 ◽  
Vol 37 (4) ◽  
pp. 748-763 ◽  
Author(s):  
Celestino Rampino ◽  
Claudio Mancuso ◽  
Filippo Vinale
Keyword(s):  
Unsaturated Soils ◽  
Mechanical Response ◽  
Stress Path ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Experimental Program ◽  
State Variables ◽  
Soil Response ◽  
Optimum Water Content ◽  
Triaxial Cell

This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.

Anisotropic three-dimensional behavior of a normally consolidated clay

1993 ◽  
Vol 30 (5) ◽  
pp. 848-858 ◽  
Author(s):  
M.M. Kirkgard ◽  
P.V. Lade
Keyword(s):  
Pore Pressure ◽  
San Francisco ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Failure Surface ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Principal Stresses ◽  
Stress Strain ◽  
Strain Behavior

An experimental study is presented of the influence of the intermediate principal stress on the stress–strain, pore-pressure, and strength characteristics of a normally consolidated, natural anisotropic clay, San Francisco Bay Mud, under undrained conditions. Consolidated undrained triaxial compression tests and triaxial tests with independent control of all three principal stresses on cubical specimens were performed. The stress–strain behavior and the pore-pressure characteristics as well as the effective stress failure surface can be described as being cross-anisotropic. Key words : anisotropic soils, clays, deformation, shear strength, triaxial tests.

Simplified analyses of stress induced anisotropy in remolded soft clay under undrained conditions

2020 ◽  
Vol 2 (105) ◽  
pp. 56-64
Author(s):  
P. Lin ◽  
Z.-x. Li ◽  
A. Garg ◽  
J.S. Yadav
Keyword(s):  
Soft Clay ◽  
Constitutive Models ◽  
Stress Path ◽  
Complex Stress ◽  
Triaxial Tests ◽  
Induced Anisotropy ◽  
Stress Induced Anisotropy ◽  
Undrained Conditions ◽  
Plain Strain ◽  
Properties Of Soil

Purpose: The soil’s anisotropy induced by stress (i.e. stress induced anisotropy) has an important effect on the behavior of soil. This paper focuses on analyzing the anisotropy of remolded Shantou soft clay under compression stress path. Design/methodology/approach: Experiments were executed by using three axle experimental instruments. The data obtained from the plain strain tests were analyzed and the relationship between stress and strain was calculated by using the modified Duncan- Chang and Lade-Duncan models. The models were modified under the condition of plain strain and cohesion. Findings: It was concluded that in complex stress path conditions, the conventional triaxial tests may not fully reflect the actual stress of soil and its response in the Duncan-Chang and Lade-Duncan models. Research limitations/implications: The formulation of Mohr-Coulomb failure criterion in the plasticity framework is quite diffcult. As a result, dilatancy cannot be described. The properties of soil in unload or drained conditions remain to be part of further investigated. Practical implications: Based upon the two stiffness parameters, the modified Duncan- Chang model has captured the soil behaviour in a very conformable way and is recommened for practical modeling. These constitutive models of soil are widely used in the numerical analyses of soil structure such as embankments. Originality/value: Duncan-Chang and Lade-Duncan models widely used in engineering practices are modes based on conventional triaxial cases. Both models have have some inherent limitations to represent the stress-strain characteristics of soils, such as shear-induced dilatancy and stress path dependency and required corrections. In this investigation, the tests are carried out in undrained conditions. It is related to the properties of soil in load conditions.

Initiation of static instability in the submarine Nerlerk berm

1993 ◽  
Vol 30 (6) ◽  
pp. 895-904 ◽  
Author(s):  
Poul V. Lade
Keyword(s):  
Shear Strength ◽  
Stress State ◽  
Yield Surface ◽  
Failure Surface ◽  
Triaxial Tests ◽  
Analysis Method ◽  
Trigger Mechanism ◽  
Plastic Properties ◽  
Static Instability ◽  
Undrained Conditions

According to stability postulates by other authors, soils that exhibit nonassociated flow may become unstable when exposed to certain stress paths inside the failure surface. Several series of conventional triaxial tests on fully saturated specimens have been performed to study the regions of stable and unstable behavior. For saturated specimens that tend to compress, undrained conditions lead to effective stress paths directed within the region of potential instability, and instability is observed, provided the yield surface opens up in the outward direction of the hydrostatic axis. Thus, instability occurs inside the failure surface. Instability is not synonymous with failure, although both lead to catastrophic events. The location of the region of potential instability and its determination are discussed. The submarine Nerlerk berm, which suffered six slides during its construction, is analyzed using a newly developed method of instability analysis. It is shown that conventional slope stability methods do not capture the mechanics of instability and subsequent liquefaction. The proposed analysis method is based on the location of the region of potential instability and the stress state in the ground. In addition, a trigger mechanism is required to initiate the instability. These topics are discussed with reference to the slides in the Nerlerk berm. Key words : instability, nonassociated flow, plastic properties, sand, shear strength, submarine slope.

scholarly journals Stress-Dilatancy for Soils. Part II: Experimental Validation for Triaxial Tests

2016 ◽  
Vol 38 (4) ◽  
pp. 59-65 ◽  
Author(s):  
Zenon Szypcio
Keyword(s):  
Test Data ◽  
Experimental Validation ◽  
Triaxial Compression ◽  
Shear Resistance ◽  
State Theory ◽  
Triaxial Tests ◽  
Macro Scale ◽  
Undrained Conditions ◽  
Particle Rolling ◽  
Drained And Undrained Conditions

Abstract Different forms of the stress-dilatancy relations obtained based on the frictional theory for the triaxial condition are presented. The analysed test data show that the shear resistance of many soils is purely frictional. The angle Φ0 represents the resistance of the soil as a combined effect of sliding and particle rolling on the macro-scale during shear at the critical frictional state. The stress-plastic dilatancy relations differ not only for triaxial compression and extension but also for drained and undrained conditions. The experiment investigated shows the correctness of the frictional state theory in the triaxial condition.

Hydromechanical behaviour of overconsolidated unsaturated soil in undrained conditions

2019 ◽  
Vol 56 (11) ◽  
pp. 1609-1621 ◽  
Author(s):  
Shengshen Wu ◽  
Annan Zhou ◽  
Jie Li ◽  
Jayantha Kodikara ◽  
Wen-Chieh Cheng
Keyword(s):  
Effective Stress ◽  
Unsaturated Soils ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Conventional Triaxial Compression ◽  
Hydromechanical Behaviour ◽  
Undrained Conditions

Hydromechanical behaviour of an unsaturated silt with various suctions and different overconsolidated ratios (OCRs) was investigated through a series of undrained triaxial tests (constant water contents, CW). All the samples were prepared from the slurry state. Different OCRs (= 1, 2, 4, and 8 in net stress) were achieved by unloading the samples to 400, 200, 100, and 50 kPa from an initial confining net pressure of 400 kPa. Then the samples were dried to various suctions (0, 100, 200, 300, and 400 kPa). Unsaturated samples with different OCRs were then sheared at CW conditions following the conventional triaxial compression (CTC) paths. Full hydromechanical responses including the changes in deviator stress, stress ratio, volumetric strain, suction, and degree of saturation with axial strain were monitored and are presented in this paper. Some key findings include (i) the critical state for unsaturated soils with different OCRs can be well defined by Bishop’s effective stress; (ii) the peak strength in Bishop’s effective stress increases with increase of OCR, but decreases with increase of suction in the undrained condition; and (iii) the volume change of unsaturated soils in undrained conditions is related to OCRs and the volume of pore air.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

Effects of Stress Path and Stress History on the Stiffness of Reconstituted London Clay

1986 ◽  
Vol 2 (1) ◽  
pp. 139-144 ◽  
Author(s):  
J. H. Atkinson ◽  
J. S. Evans ◽  
D. Richardson
Keyword(s):  
Stress Path ◽  
Triaxial Tests ◽  
Soil Parameters ◽  
Stress History ◽  
Strain Behaviour ◽  
Reconstituted Soil ◽  
Path Dependent ◽  
London Clay ◽  
Soil Behaviour

AbstractSoil behaviour is stress history dependent and stress path dependent and soil parameters, particularly those for stress-strain behaviour, measured in conventional triaxial tests may not represent the behaviour of soil in many civil engineering works.To obtain more realistic parameters it may be necessary to conduct laboratory tests which more closely represent in situ conditions before and during construction.The paper describes equipment developed at The City University to carry out stress path tests simply and economically. A series of CU triaxial tests and stress path tests on reconstituted soil illustrate the dependence of measured soil parameters on stress history and stress path.

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