A reevaluation of undrained shear strength mobilised on the failure surface using laboratory shear tests. Note

1989 ◽  
Vol 26 (6) ◽  
pp. 294
Keyword(s):  
Shear Strength ◽  
Failure Surface ◽  
Undrained Shear Strength ◽  
Shear Tests ◽  
Undrained Shear

scholarly journals Geotechnical Centrifuge Modelling of Retrogressive Sensitive Clay Landslides

2020 ◽  
Author(s):  
Ray Kennedy ◽  
W. Andy Take ◽  
Gregory A. Siemens
Keyword(s):  
Shear Strength ◽  
Slope Angle ◽  
Physical Modelling ◽  
Failure Surface ◽  
Undrained Shear Strength ◽  
Stability Number ◽  
Surface Stability ◽  
Geotechnical Centrifuge ◽  
Sensitive Clay ◽  
Undrained Shear

Sensitive clay landslides represent a significant geohazard due to their well-known potential for extensive retrogressive failures, on the scale of multiple hectares, which could encompass surrounding communities and infrastructure. Interpretation of retrogression mechanisms is often limited since only forensic investigations are possible. This work presents the results of a physical modelling study to examine retrogressive failures, analysis of each failure episode, and interpretation of the results using published relationships. Five novel centrifuge model tests were conducted under a defined range of undrained shear strength and slope angle conditions. The models are constructed of a sensitive cement-soil mixture that allows for a consistent contractile material with bespoke shear strength. Results indicate the observed retrogression distance correlates with Taylor’s stability number. The addition of a 5-degree slope angle to invoke a static shear stress on the model provoked notably larger retrogression distances. Post-test undrained shear strength measurements quantified softening of the material along the failure surface. Stability analyses on each failure episode captured the observed failure geometry and factor of safety. Results indicate that the geometric parameters of a slope, specifically the slope angle, may be able to explain a component of the scatter for relating the Taylor’s stability number with retrogression distances.

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.

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.

scholarly journals Evaluation of Undrained Shear Strength of Miocene Clay from the Weight Sounding Test (WST)

2017 ◽  
Vol 62 (2) ◽  
pp. 367-384
Author(s):  
Sebastian Olesiak
Keyword(s):  
Shear Strength ◽  
Field Testing ◽  
Field Investigation ◽  
Undrained Shear Strength ◽  
Cohesive Soils ◽  
Strength Parameters ◽  
Additional Measurement ◽  
Carpathian Foredeep ◽  
Innovative Solution ◽  
Undrained Shear

Abstract Soil strength parameters needed for the calculation of bearing capacity and stability are increasingly determined from field testing. This paper presents a method to determine the undrained shear strength cuWST of the soil, based on the Weight Sounding Test (WST). The innovative solution which allows for a significant reduction of equipment needed for geotechnical field investigation is presented. The proposed method is based on an additional measurement of the torque during testing. It then becomes possible to estimate the undrained shear strength, cuWST of the soil, using the correlation given in this paper. The research results presented in this paper were carried out on selected cohesive soils, Miocene clays from the Carpathian Foredeep.

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