The Critical-State Pore Pressure Parameter from Consolidated-Undrained Shear Tests

2009 ◽  
pp. 410-410-21 ◽  
Author(s):  
PW Mayne ◽  
PG Swanson
Keyword(s):  
Pore Pressure ◽  
Critical State ◽  
Shear Tests ◽  
Pressure Parameter ◽  
Undrained Shear

Undrained shear behaviour of sands subjected to large shear displacement and estimation of excess pore-pressure generation from drained ring shear tests

2005 ◽  
Vol 42 (3) ◽  
pp. 787-803 ◽  
Author(s):  
Yasuhiko Okada ◽  
Kyoji Sassa ◽  
Hiroshi Fukuoka
Keyword(s):  
Pore Pressure ◽  
Triaxial Compression ◽  
Excess Pore Pressure ◽  
Compression Tests ◽  
Shear Tests ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Triaxial Compression Tests ◽  
Undrained Shear ◽  
Excess Pore

Undrained shear behaviour of fine silica and weathered granitic sand subjected to large shear displacement is examined. Parallel experiments using ring shear and the triaxial compression tests on soil specimens through a wide range of initial void ratios were conducted to investigate undrained shear strength as the key factor in the flow-like motion of landslides. The steady-state undrained shear strengths achieved in ring shear tests were, in general, smaller than those in the triaxial compression tests, probably because of the excess pore-pressure generation by grain crushing within the shear zone that occurred in ring shear. Very low steady-state shear strengths were achieved, however, in triaxial compression tests on the dense silica sand in which well-defined shear surfaces developed in the cylindrical specimens. In these triaxial compression tests, shear deformation must have been concentrated on these surfaces to generate excess pore pressure similar to that found in ring shear tests. An attempt was made to estimate excess pore pressure generated in undrained ring shear tests using the results of drained ring shear tests. The equivalent normal stress calculated as the ratio of volumetric strain in the drained test to the coefficient of volume change was introduced as a parameter for the estimation of excess pore-pressure generation for the large shear displacement that is usually found in landslides. Equivalent normal stress from drained tests was almost the same as the generated excess pore pressure in undrained tests with up to 1 m of shear displacement, at which the steady state was reached.Key words: undrained shear strength, excess pore pressure, equivalent normal stress, ring shear test, triaxial compression test, liquefaction.

scholarly journals Consolidated and Undrained Ring Shear Tests on the Sliding Surface of the Hsien-du-shan Landslide in Taiwan

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Hung-Ming Lin ◽  
Jian-Hong Wu ◽  
Erik Sunarya
Keyword(s):  
Pore Pressure ◽  
Rock Avalanche ◽  
Excess Pore Pressure ◽  
High Water Content ◽  
Sliding Surface ◽  
Shear Tests ◽  
Typhoon Morakot ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Excess Pore

A new consolidated undrained ring shear test capable of measuring the pore pressures is presented to investigate the initiation mechanism of the Hsien-du-shan rock avalanche, triggered by Typhoon Morakot, in southern Taiwan. The postpeak state of the landslide surface between the Tangenshan sandstone and the remolded landslide gouge is discussed to address the unstable geomorphological precursors observed before the landslide occurred. Experimental results show that the internal friction angle of the high water content sliding surface in the total stress state, between 25.3 and 26.1°, clarifies the reason of the stable slope prior to Typhoon Morakot. In addition, during the ring shear tests, it is observed that the excess pore pressure is generated by the shear contractions of the sliding surface. The remolded landslide gouge, sheared under the high normal stress, rendered results associated with high shear strength, small shear contraction, low hydraulic conductivity, and continuous excess pore pressure. The excess pore pressure feedback at the sliding surface may have accelerated the landslide.

Seismic triggering of catastrophic failures on shear surfaces in saturated cohesionless soils

2005 ◽  
Vol 42 (1) ◽  
pp. 229-251 ◽  
Author(s):  
Aurelian Catalin Trandafir ◽  
Kyoji Sassa
Keyword(s):  
Shear Stress ◽  
Shear Resistance ◽  
Shear Displacement ◽  
Sliding Surface ◽  
Shear Tests ◽  
Shear Surface ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Stress Reversals ◽  
Undrained Shear

This paper is concerned with an analysis of the seismic performance of infinite slopes in undrained conditions. The material assumed on the sliding surface is a loose saturated sand susceptible to a gradual loss in undrained shear strength after failure with the progress of unidirectional shear displacement. The undrained monotonic and cyclic shear behavior of this sand was investigated through an experimental study based on ring shear tests, with initial stresses corresponding to the static conditions on the sliding surface of the analyzed slopes. These tests provide the experimental framework for a modified sliding block method to estimate the earthquake-induced undrained shear displacements for conditions of no shear stress reversals on the sliding surface. The proposed estimation procedure incorporates the shearing resistance obtained from undrained monotonic ring shear tests to approximate the undrained yield resistance at a certain displacement during an earthquake. The term catastrophic failure is used in this study to define the accelerated motion of a potential sliding soil mass due to the static driving shear stress exceeding the reduced undrained yield resistance of the soil on the shear surface. The critical displacement necessary to trigger a catastrophic failure on the shear surface under seismic conditions was derived based on the shear resistance – shear displacement curve obtained under monotonic loading conditions. Using the shear resistance – shear displacement data from undrained monotonic ring shear tests and several processed horizontal earthquake accelerograms, the minimum peak earthquake acceleration necessary to cause a catastrophic shear failure under various seismic waveforms was estimated for conditions of no shear stress reversals on the sliding surface.Key words: earthquakes, slopes, critical shear displacement, sand, ring shear tests, undrained shear strength.

Structure characteristics and mechanical properties of kaolinite soils. II. Effects of structure on mechanical properties

2006 ◽  
Vol 43 (6) ◽  
pp. 601-617 ◽  
Author(s):  
Y -H Wang ◽  
W -K Siu
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Shear Modulus ◽  
Critical State ◽  
Soil Structure ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Undrained Shear Strength ◽  
Interparticle Forces ◽  
Undrained Shear

This paper reports the effects of structure on the mechanical responses of kaolinite with known and controlled fabric associations. The dynamic properties and strength were assessed by resonant column tests and undrained triaxial compression tests, respectively. The experimental results demonstrate that interparticle forces and associated fabric arrangements influence the volumetric change under isotropic compression. Soils with different structures have individual consolidation lines, and the merging trend is not readily seen under an isotropic confinement up to 250 kPa. The dynamic properties of kaolinite were found to be intimately related to the soil structure. Stronger interparticle forces or higher degrees of flocculated structure lead to a greater small-strain shear modulus, Gmax, and a lower associated damping ratio, Dmin. The soil structure has no apparent influence on the critical-state friction angle (ϕ′c = 27.5°), which suggests that the critical stress ratio does not depend on interparticle forces. The undrained shear strength of kaolinite is controlled by its initial packing density rather than by any interparticle attractive forces, and yet the influence of the structure on the effective stress path is obvious.Key words: interparticle forces, shear modulus, damping ratio, stress–strain behavior, undrained shear strength, critical state.

Controlled displacement-rate in situ shear tests with pore pressure measurements

1985 ◽  
Vol 22 (1) ◽  
pp. 136-142 ◽  
Author(s):  
F. S. Shuri ◽  
D. D. Driscoll ◽  
S. J. Garner
Keyword(s):  
Shear Strength ◽  
Pore Pressure ◽  
Shear Zone ◽  
Large Scale ◽  
Bedding Plane ◽  
Western Canada ◽  
Shear Tests ◽  
Plane Shear ◽  
Clay Seam

Two large-scale in situ shear tests were conducted at a damsite in western Canada. The rock at the site is a Cretaceous shale containing a thin clay seam tentatively identified as a bedding-plane shear zone. The material in this seam is significantly weaker than the intact rock and influences the design of certain features of the dam and structures. In order to provide shear strength data for design, two large blocks of shale were sheared along the clay seam. These tests differed from conventional in situ shear tests in two significant ways: the rate of shear displacement was strictly controlled, and pore pressures (both positive and negative) in the shear zone were carefully monitored throughout the test. This note presents the material properties of the shear zone, describes the test equipment and techniques, and discusses the results obtained. Key words: shear strength, in situ testing, pore pressure, shale.

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