Effects of sample disturbance and consolidation procedures on measured shear strength of soft marine Norwegian clays

2006 ◽  
Vol 43 (7) ◽  
pp. 726-750 ◽  
Author(s):  
Tom Lunne ◽  
Toralv Berre ◽  
Knut H Andersen ◽  
Stein Strandvik ◽  
Morten Sjursen
Keyword(s):  
Shear Stress ◽  
Shear Resistance ◽  
Engineering Properties ◽  
Large Strains ◽  
Stress Strain ◽  
Soft Clays ◽  
Effective Stresses ◽  
Small Strains ◽  
Sample Disturbance

After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.

scholarly journals Effect of sample disturbance on triaxial and oedometer behaviour of a stiff and heavily overconsolidated clay

2014 ◽  
Vol 51 (8) ◽  
pp. 896-910 ◽  
Author(s):  
Toralv Berre
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
In Situ Stress ◽  
Undrained Shear Strength ◽  
Stress Strain ◽  
Effective Stresses ◽  
Sample Disturbance ◽  
Oedometer Tests ◽  
Undrained Shear

The tests in this investigation were performed on a natural soft clay with plasticity index around 32%, which was K0 consolidated to a vertical stress of 2942 kPa and then K0 unloaded to a vertical stress of 74 kPa (i.e., to the “in situ” stress). The specimens so created were disturbed in various ways to study the effect of sample disturbance on the stress–strain relationships during undrained shearing and during drained K0 loading (i.e., K0 triaxial and oedometer tests). The results for two testing alternatives may be summarized as follows. Alternative 1: Allow the specimen to swell at the correct in situ effective stresses, but accept an initial water content that is higher than the in situ value. This alternative was found to give the best stress–strain relationships around the in situ effective stresses for undrained triaxial tests, but with undrained shear strength values up to about 20% too low, due to the swelling taking place during consolidation to the in situ effective stresses. Alternative 2: Prevent swelling by starting the test at effective stresses that are higher than the in situ stresses, but with a water content that is closer to the in situ value than if alternative 1 is chosen. Using only isotropic stresses prior to shearing, this alternative was found to give better undrained shear strength values (although up to about 14% too high) but strain values much too small around the in situ effective stresses. For oedometer tests, only alternative 2 was investigated. Also, for these tests, the strains around the in situ stress were too small, but preconsolidation stresses estimated from stress–strain curves were typically only around 60% of the true value.

A numerical solution of cavity expansion problem in sand based directly on experimental stress-strain curves

1998 ◽  
Vol 35 (4) ◽  
pp. 541-559 ◽  
Author(s):  
Branko Ladanyi ◽  
Adolfo Foriero
Keyword(s):  
Numerical Solution ◽  
Strain Path ◽  
Shear Resistance ◽  
Cavity Expansion ◽  
Large Strains ◽  
Volume Changes ◽  
Stress Strain ◽  
Stress Variation ◽  
Cylindrical Cavity Expansion ◽  
State Of Stress

A numerical solution of a spherical and cylindrical cavity expansion problem in sand is presented herein. The underlying theory is unbiased in that it is based directly on experimentally determined stress-strain curves. The solution makes it possible to follow the continuous variation of strains, stresses, and volume changes produced by cavity expansion. It essentially uses the "strain path" approach to determine the state of stress around the cavity, taking into account large strains and the effect of spherical stress variation on the mobilized shear resistance and the associated volume strains. A limited comparison with experimental data shows a reasonable agreement between theory and measurements.Key words: cavities, expansion, sand, stress-strain curves, numerical solution.

Potential improvements of design parameters by taking block samples of soft marine Norwegian clays

2007 ◽  
Vol 44 (6) ◽  
pp. 698-716 ◽  
Author(s):  
Toralv Berre ◽  
Tom Lunne ◽  
Knut H Andersen ◽  
Stein Strandvik ◽  
Morten Sjursen
Keyword(s):  
Undrained Shear Strength ◽  
Design Parameters ◽  
Shear Tests ◽  
High Quality ◽  
Soft Clays ◽  
Direct Simple Shear ◽  
Sample Disturbance ◽  
Marine Clays ◽  
Oedometer Tests

Undrained triaxial and direct simple shear tests on samples reconsolidated to the in situ effective stresses and oedometer tests have been carried out on standard piston tube and on high quality block samples from 12 deposits of soft Norwegian marine clays. Based on the results of a selected number of these tests, empirical procedures for estimating the effect of sample disturbance have been developed. These procedures can be used to show the potential increase that may be achieved in undrained shear strength and apparent preconsolidation stress by taking high quality block samples. Suggestions are also given regarding corrections for rate of loading and temperature effects; as well, examples are given regarding possible consequences for design if higher strengths are utilized.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour.

Finite element investigation into the torsion test in the range of large strains and deformations

2001 ◽  
Vol 36 (4) ◽  
pp. 401-409
Author(s):  
X Peng ◽  
Y Qin ◽  
R Balendra
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Shear Strain ◽  
Twist Angle ◽  
Large Strains ◽  
End Effect ◽  
Stress Strain ◽  
Strain Relationship ◽  
Thin Walled ◽  
Tubular Specimens

Torsion tests with thin-walled tubular, solid cylindrical and Lindholm-type tubular specimens were simulated using the finite element code ABAQUS, in the range of large strains and deformations. The results showed that for thin-walled tubular and solid cylindrical specimens the radii of the specimens almost remained straight during torsion; for Lindholm-type tubular specimens the twist angle of the cross-section at the two ends of the gauge section did not stay constant, due to the change of the specimen geometry (i.e. the end effect). A correction which considers the end effect should therefore be introduced when the stress-strain relationship is characterized. Compared with the stress-strain relationship obtained previously from experiment, a distinct difference was noted when conventional formulae were used to convert the torque and twist angle into the shear stress and shear strain. Further, the influence of axial constraint conditions at the two ends of the specimen was examined; the results showed that axial strains and stresses had no significant influence on the definition of the shear stress-shear strain relation, and hence these can be neglected when the stress-strain relationship is characterized.

In situ sampling, density measurements, and testing of foundation soils at Duncan Dam

1994 ◽  
Vol 31 (6) ◽  
pp. 927-938 ◽  
Author(s):  
Howard D. Plewes ◽  
V. Sitham Pillai ◽  
Michael R. Morgan ◽  
Brian L. Kilpatrick
Keyword(s):  
Soil Sampling ◽  
Frozen Soil ◽  
Engineering Properties ◽  
Energy Calibration ◽  
Penetration Test ◽  
Cone Penetration ◽  
Field Investigations ◽  
Sample Disturbance ◽  
Penetration Tests

As part of the B.C. Hydro Dam Safety Review of Duncan Dam, a comprehensive two-phased program of field and laboratory investigations was carried out between 1988 and 1992 to evaluate the potential for liquefaction of the foundation soils during an earthquake. The initial screening level phase 1 field investigations comprised basic soil sampling, standard penetration tests, and cone penetration tests to determine the spatial distribution of the foundation soils beneath the dam and to characterize the basic engineering properties of the soil units. A screening study using Seed's liquefaction assessment method indicated that soil unit 3c consisting of uniform fine-grained sand would be susceptible to liquefaction. The phase 2 investigations consisted of detailed and careful soil sampling to obtain high-quality in situ samples of the unit 3c sand for laboratory triaxial and simple shear tests. Samples were obtained using a conventional fixed piston sampler and a specially modified Christensen double core barrel sampler. The samples were frozen to minimize sample disturbance during handling and transport. Ground freezing was also conducted using liquid nitrogen, and the frozen soil was sampled using a CRREL core barrel. Borehole density logging was performed to assess the quality and level of disturbance of the soil samples. This paper discusses the procedures and results of the phases 1 and 2 field investigations. Key words : standard penetration test, cone penetration test, geophysical logging, energy calibration, soil sampling, freezing.

Stress history and sampling disturbance effects on monotonic and cyclic responses of overconsolidated Bootlegger Cove clays

2014 ◽  
Vol 51 (6) ◽  
pp. 599-609 ◽  
Author(s):  
David G. Zapata-Medina ◽  
Richard J. Finno ◽  
Carlos A. Vega-Posada
Keyword(s):  
Shear Stiffness ◽  
Natural Soil ◽  
Stress Strain ◽  
Stress History ◽  
Effective Stresses ◽  
Subsequent Response ◽  
Significant Difference ◽  
History Of ◽  
And Behavior

This paper examines the influence of reproducing the stress history of a natural soil deposit during laboratory reconsolidation on the subsequent response and behavior of heavily overconsolidated Bootlegger Cove Formation (BCF) clays under both monotonic and cyclic loadings. The results are compared with a conventional reconsolidation technique wherein a specimen is directly K0-reconsolidated to the in situ effective stresses, and no stress history of the overconsolidated soil deposit is reproduced. Monotonic and cyclic experiments under triaxial conditions were conducted and their results compared in terms of stress–strain–strength responses with emphasis on shear stiffness degradation, to show the significant difference in the responses between the stress-probe sets. Additionally, comparison with field and in situ measurements are presented to validate procedures, judge the accuracy of the experiments, and evaluate the effects of tube sampling.

Dynamics of Nanoparticle Chain Aggregates of Carbon Under Tension

2003 ◽  
Vol 778 ◽  
Author(s):  
Rajdip Bandyopadhyaya ◽  
Weizhi Rong ◽  
Yong J. Suh ◽  
Sheldon K. Friedlander
Keyword(s):  
Mechanical Properties ◽  
Carbon Black ◽  
Polymer Film ◽  
Elastic Behavior ◽  
Small Strains ◽  
Transmission Electron ◽  
Chain Aggregates ◽  
Nanoparticle Chains ◽  
Reinforcing Filler

AbstractCarbon black in the form of nanoparticle chains is used as a reinforcing filler in elastomers. However, the dynamics of the filler particles under tension and their role in the improvement of the mechanical properties of rubber are not well understood. We have studied experimentally the dynamics of isolated nanoparticle chain aggregates (NCAs) of carbon made by laser ablation, and also that of carbon black embedded in a polymer film. In situ studies of stretching and contraction of such chains in the transmission electron microscope (TEM) were conducted under different maximum values of strain. Stretching causes initially folded NCA to reorganize into a straight, taut configuration. Further stretching leads to either plastic deformation and breakage (at 37.4% strain) or to a partial elastic behavior of the chain at small strains (e.g. 2.3% strain). For all cases the chains were very flexible under tension. Similar reorientation and stretching was observed for carbon black chains embedded in a polymer film. Such flexible and elastic nature of NCAs point towards a possible mechanism of reinforcement of rubber by carbon black fillers.

In Situ Characterization of Soils for Prediction of Stress-Strain Relationship

1983 ◽  
Author(s):  
K. Arulanandan ◽  
Y. Dafalias ◽  
L. R. Herrmann ◽  
A. Anandarajah ◽  
N. Meegoda
Keyword(s):  
In Situ Characterization ◽  
Stress Strain ◽  
Strain Relationship

scholarly journals Laboratory and In Situ Determination of Hydraulic Conductivity and Their Validity in Transient Seepage Analysis

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1131
Author(s):  
Soonkie Nam ◽  
Marte Gutierrez ◽  
Panayiotis Diplas ◽  
John Petrie
Keyword(s):  
Hydraulic Conductivity ◽  
Field Measurements ◽  
Natural Soil ◽  
In Situ Tests ◽  
Seepage Analysis ◽  
Soil Deposits ◽  
Seepage Modeling ◽  
Sample Disturbance

This paper critically compares the use of laboratory tests against in situ tests combined with numerical seepage modeling to determine the hydraulic conductivity of natural soil deposits. Laboratory determination of hydraulic conductivity used the constant head permeability and oedometer tests on undisturbed Shelby tube and block soil samples. The auger hole method and Guelph permeameter tests were performed in the field. Groundwater table elevations in natural soil deposits with different hydraulic conductivity values were predicted using finite element seepage modeling and compared with field measurements to assess the various test results. Hydraulic conductivity values obtained by the auger hole method provide predictions that best match the groundwater table’s observed location at the field site. This observation indicates that hydraulic conductivity determined by the in situ test represents the actual conditions in the field better than that determined in a laboratory setting. The differences between the laboratory and in situ hydraulic conductivity values can be attributed to factors such as sample disturbance, soil anisotropy, fissures and cracks, and soil structure in addition to the conceptual and procedural differences in testing methods and effects of sample size.

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