Mode of shear effects on yield and liquefied strength ratios

A database of 386 laboratory triaxial compression, direct simple shear, rotational shear, and triaxial extension test results was collected to examine yield and liquefied strength ratio concepts used in liquefaction analysis of sloping ground. These data envelope the yield and liquefied strength ratios obtained from back-analyses of liquefaction flow failure case histories. Generally, triaxial compression exhibits the highest yield and liquefied strength ratios, triaxial extension yields the lowest ratios, and direct simple shear – rotational shear shows intermediate responses. However, mode of shear appears to have a considerably smaller effect on laboratory-measured liquefied strength ratios for specimens with a positive state parameter (i.e., difference in consolidation void ratio and steady state void ratio at the same effective stress).

Download Full-text

Undrained shear strength of clean sands to trigger flow liquefaction

Canadian Geotechnical Journal ◽

10.1139/t99-047 ◽

1999 ◽

Vol 36 (5) ◽

pp. 891-906 ◽

Cited By ~ 50

Author(s):

M Yoshimine ◽

P K Robertson ◽

C E (Fear) Wride

Keyword(s):

Shear Strength ◽

Simple Shear ◽

Laboratory Testing ◽

Triaxial Compression ◽

Undrained Shear Strength ◽

Simple Shear Test ◽

Flow Failure ◽

Toyoura Sand ◽

Triaxial Extension ◽

Undrained Shear

This paper attempts to evaluate the undrained shear strength of sand during flow failures, based on both laboratory testing and field observations. In the laboratory, the minimum shear resistance during monotonic loading was taken as the undrained strength, based on the criterion of stability. Triaxial compression, triaxial extension, and simple shear test data on clean sand were examined and it was revealed that the undrained shear strength ratio could be related to the relative density of the material provided that the initial stress, piprime, was less than 500 kPa. Three previous flow failures involving sand layers with relatively low fines contents and reliable cone penetration test (CPT) data were studied. Using existing calibration chamber test results, the Toyoura sand specimen densities in the laboratory tests were converted to equivalent values of CPT penetration resistance. The undrained shear strengths measured in the laboratory for Toyoura sand were compared with those from the case studies. It was found that the behaviour of sand in simple shear in the laboratory was consistent with the field performance observations. Triaxial compression tests overestimated the undrained strengths, and triaxial extension tests underestimated the undrained strengths. From both the simple shear test result and the CPT field data, the threshold value of clean sand equivalent cone resistance for flow failure was detected. Based on these observations, a CPT-based guideline for evaluating the potential for flow failure of a clean sand deposit is proposed. Key words: liquefaction, flow, laboratory testing, in situ test, case histories.

Download Full-text

Estimating the undrained strength of sand: a theoretical framework

Canadian Geotechnical Journal ◽

10.1139/t95-082 ◽

1995 ◽

Vol 32 (5) ◽

pp. 859-870 ◽

Cited By ~ 44

Author(s):

Catherine E. Fear ◽

Peter K. Robertson

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Void Ratio ◽

Triaxial Compression ◽

State Parameter ◽

In Situ Tests ◽

Initial State ◽

Undrained Strength

A framework for estimating the ultimate undrained steady state shear strength of sand (Su) from in situ tests, which combines the theory of critical state soil mechanics with shear wave velocity measurements, is presented. For a particular direction of undrained loading, samples of a given sand at a constant void ratio will reach the same Su, despite the magnitude of the initial effective confining stresses. Unique Su/p′ or [Formula: see text] ratios for a given direction of loading exist for a particular sand only if state parameter is constant throughout the deposit. Normalized shear wave velocity, Vs1, can be correlated with void ratio and is therefore used to estimate Su for a given initial state and direction of loading. Strengths in triaxial compression are examined in this paper; however, the same framework can be used to estimate strengths under other directions of loading. The Su–Vs1 relationship is shown to be relatively sensitive and should be used more as a screening tool rather than an accurate means of predicting Su. Vs1 is converted to equivalent values of SPT (N1)60 and CPT qc1, and the results are compared with the current methods of estimating Su. Key words : in situ testing, liquefaction, sand, undrained strength.

Download Full-text

Use of laboratory data to confirm yield and liquefied strength ratio concepts

Canadian Geotechnical Journal ◽

10.1139/t03-058 ◽

2003 ◽

Vol 40 (6) ◽

pp. 1164-1184 ◽

Cited By ~ 22

Author(s):

Scott M Olson ◽

Timothy D Stark

Keyword(s):

Shear Strength ◽

Steady State ◽

Yield Strength ◽

Triaxial Compression ◽

Sandy Soils ◽

Friction Angle ◽

Strength Ratio ◽

Case Histories ◽

Direct Simple Shear ◽

Flow Failure

A laboratory database of triaxial compression test results was collected to examine the use of strength ratios for liquefaction analysis. Specifically, the database was used to: (i) validate the yield strength ratio concept (or yield friction angle); (ii) demonstrate the parallelism of the consolidation line and steady state line of many sandy soils; and (iii) validate the liquefied strength ratio concept. The yield strength ratio of contractive sandy soils in triaxial compression ranges from approximately 0.29 to 0.42 (corresponding to yield friction angles of 16°23°), while the yield strength ratio from flow failure case histories (which correspond approximately to direct simple shear conditions) ranges from 0.23 to 0.31 (or yield friction angles of 13°17°). As expected, the yield friction angle is greatest in triaxial compression, smaller in direct simple shear, and likely smallest in triaxial extension. The steady state line and consolidation line of many contractive sandy soils are parallel for a wide range effective stresses, steady state line slopes, fines contents, and grain sizes and shapes that are applicable to many civil engineering structures. As such, the liquefied strength ratio is a constant for many sandy soils deposited in a consistent manner. The liquefied strength ratio is inversely related to state parameter and ranges from approximately 0.02 to 0.22 in laboratory triaxial compression tests. Flow failure case histories fall near the middle of this range.Key words: liquefaction, liquefied shear strength, yield shear strength, collapse surface, steady state line, penetration resistance.

Download Full-text

Void ratio redistribution in undrained triaxial extension tests on Ottawa sand

Canadian Geotechnical Journal ◽

10.1139/t98-006 ◽

1998 ◽

Vol 35 (2) ◽

pp. 351-359 ◽

Cited By ~ 9

Author(s):

A Ayoubian ◽

P K Robertson

Keyword(s):

Phase Transformation ◽

Void Ratio ◽

Large Strains ◽

Ultimate State ◽

Ratio Distribution ◽

Ottawa Sand ◽

Effective Stresses ◽

Softening Behavior ◽

Triaxial Extension Test ◽

Triaxial Extension

Water-pluviated samples of Ottawa sand were tested in monotonic, undrained triaxial extension tests. The specimens exhibited similar "limited strain softening" behavior, and they all experienced phase transformation from contraction to dilation at small axial strains. The tests were stopped at different stages and the samples were frozen to obtain void ratio distribution along the length of the specimens. It was shown that void ratio redistribution can start at very low axial strains in an undrained triaxial extension test. Before phase transformation, void ratio redistribution was very small, but after phase transformation void ratio redistribution started rapidly and continued until the end of the tests at ultimate state. The location of the ultimate state line in a void ratio - mean normal effective stress plot was shown to be affected by localized failure at large strains in undrained triaxial extension tests. The actual ultimate state line with respect to void ratios and effective stresses within the failure zone in the samples can be located above the average ultimate state line obtained from average measurements of void ratios and effective stresses of the entire specimens.Key words: liquefaction, testing, void ratio.

Download Full-text

Stress–strain behaviour of sands in triaxial and direct simple shear tests

Canadian Geotechnical Journal ◽

10.1139/t91-033 ◽

1991 ◽

Vol 28 (2) ◽

pp. 276-281 ◽

Cited By ~ 5

Author(s):

Gianni Rossato ◽

Paolo Simonini

Keyword(s):

Simple Shear ◽

Triaxial Compression ◽

Compression Modulus ◽

Shear Tests ◽

Stress Strain ◽

Natural Sand ◽

Shear Moduli ◽

Dimensionless Analysis ◽

Direct Simple Shear ◽

Strain Behaviour

The behaviour of a natural sand in triaxial compression and direct simple shear tests was compared by means of dimensionless analysis of parameters controlling the evolution of stresses and strains. The secant triaxial compression and direct simple shear moduli were interpreted in a dimensionless form. A criterion based on the equivalence between major principal strain in the two tests was considered to compare the results. Key words: sand, stress–strain behaviour, triaxial test, direct simple shear test, shear modulus, triaxial compression modulus.

Download Full-text