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.

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 reevaluation of using laboratory shear tests

1989 ◽  
Vol 26 (1) ◽  
pp. 162-164 ◽  
Author(s):  
G. Mesri
Keyword(s):  
Shear Strength ◽  
Correction Factor ◽  
Slip Surface ◽  
Undrained Shear Strength ◽  
Shear Tests ◽  
Text Data ◽  
Soft Clays ◽  
In Situ Data ◽  
Undrained Shear

The expression [Formula: see text] for the average undrained shear strength mobilized on a slip surface in the field resulted from in situ vane [Formula: see text] and oedometer [Formula: see text] data, combined with a correction factor μ obtained from the computed factor of safety of unstable embankments, footings, and excavations. It is shown here that the same expression for mobilized undrained strength of soft clays is also obtained from laboratory shear tests by taking into account anisotropy and time effects. This result is highly significant, since the laboratory undrained shear strength data, as well as the correction factor for the time effect, are completely unrelated to the in situ data that previously resulted in the expression for field mobilized undrained shear strength. Key words: mobilized undrained shear strength, in situ vane test, laboratory shear tests.

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.

scholarly journals Estimating the Small Strain Stiffness of Peat Soil Using Geophysical Methods

2021 ◽  
Vol 7 (1) ◽  
pp. 44-54
Author(s):  
Kasbi Basri ◽  
Adnan Zainorabidin ◽  
Mohd Khaidir Abu Talib ◽  
Norhaliza Wahab
Keyword(s):  
Peat Soil ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Small Strain ◽  
In Situ Stress ◽  
Design Parameters ◽  
Small Strain Stiffness ◽  
Geotechnical Design ◽  
Sample Disturbance

Geotechnical design commonly requires that the in-situ stiffness, strength and permeability of the ground be obtained. Laboratory based investigation often related with risk of sample disturbance and difficulties to replicate the in-situ stress condition which results in overestimation or underestimation. Application of geophysical methods in geotechnical investigation previously was limited to targeting and dimensioning sub-surface features due to lack of resolution. However, rapid developments of geophysical methods result in the application of these methods in providing geotechnical design parameters. Multichannel analysis of surface waves (MASW) and seismic refraction were among the geophysical methods capable of obtaining stiffness parameters including the maximum shear modulus (Gmax) and maximum elastic modulus (Emax). The study revealed the efficiency of these methods to measure the small strain stiffness of peat soil with high accuracy as the results obtained were found to be similar to those obtained by previous researchers. Overall, the Gmax and Emax values of peat soil obtained range from 0.49 to 1.72 MPa and 1.46 to 5.15 MPa respectively. The Gmax and Emax values obtained shows significant increase with depth governed primarily by the effective stress. Other parameters such as degree of decomposition and peat thickness also shows potential influence on the Gmax and Emax values obtained.

A statistical evaluation of some engineering properties of eastern Canadian clays

1990 ◽  
Vol 27 (3) ◽  
pp. 373-386 ◽  
Author(s):  
Étienne J. Windisch ◽  
Raymond N. Yong
Keyword(s):  
Shear Strength ◽  
Statistical Evaluation ◽  
Undrained Shear Strength ◽  
Plasticity Index ◽  
Engineering Properties ◽  
Plastic Limit ◽  
Liquidity Index ◽  
Marine Clays ◽  
Undrained Shear

Statistics for data collected on eastern Canadian clays (Champlain, Goldthwait, Tyrrell, and Laflamme marine clays and Barlow–Ojibway lacustrine clays) are computed and analyzed. These clays are divided into three groups: eastern Canadian marine clays, Champlain clays (as an important part of the first group), and Barlow–Ojibway lacustrine clays. The analysis reveals significant differences between eastern Canadian clays and Scandinavian clays. Some relationships proposed in the literature and based on plasticity index, liquidity index, and plastic limit are found to be inapplicable to eastern Canadian clays. On the basis of a proposed method for estimating the undrained shear strength of normally consolidated eastern Canadian marine clays, the overconsolidation ratio is found to be equal to the ratio of the in situ undrained shear strength to the estimated normally consolidated undrained shear strength. Key words: undrained shear strength, plasticity index, liquidity index, plastic limit, statistical evaluation, over-consolidation ratio, lacustrian clays.

In-Situ Undrained Shear Strength of Two Marine Clays

1976 ◽  
Vol 102 (9) ◽  
pp. 989-1005
Author(s):  
Demetrious C. Koutsoftas ◽  
Joseph A. Fischer
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Marine Clays ◽  
Undrained Shear

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.

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