Influence of cycling pore-water pressures and principal stress ratios on drained deformations in clay

1992 ◽  
Vol 29 (2) ◽  
pp. 326-333 ◽  
Author(s):  
K. D. Eigenbrod ◽  
J. Graham ◽  
J.-P. Burak
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Seasonal Changes ◽  
Triaxial Tests ◽  
Strain Rates ◽  
Natural Clay ◽  
Groundwater Levels ◽  
Deviator Stress ◽  
Pore Water Pressures ◽  
Stress Ratios

Seasonal changes in groundwater levels affect the rate of downhill creep movements in slopes. This process has been studied in triaxial tests on undisturbed specimens of a natural clay from Bluefish Lake, 50 km north of Yellowknife, N.W.T. Specimens were first anisotropically consolidated to low stresses that correspond to conditions at shallow depths in creeping slopes. Pore-water pressures (back pressures) in the specimens were then cycled systematically (over periods lasting 4–48 h) with the drainage leads open. Resulting axial and volumetric strains were measured, and shear and lateral strains deduced from them. Strain rates decreased with increasing total times of testing. They increased with increasing values of the ratio Δu/Δuf, with increasing values of deviator stress q, and with decreasing values of [Formula: see text]. Systematically increasing the pore-water pressures in the specimens produced clear estimates of failure at low stresses. Key words : slope, clay, creep, cyclic loading, ground water, triaxial.

Cyclic loading of an Ottawa area Champlain Sea clay

1977 ◽  
Vol 14 (1) ◽  
pp. 52-63 ◽  
Author(s):  
R. J. Mitchell ◽  
R. Douglas King
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Pore Water ◽  
Soil Structure ◽  
Shear Failure ◽  
Large Deformations ◽  
Cemented Soil ◽  
Pore Water Pressures ◽  
Excess Pore ◽  
Static Shear

Undrained cyclic loading of triaxial samples of a sensitive Champlain Sea clay at deviatoric stress levels in excess of 50% of the static shear strength is shown to produce large deformations and eventual shear failure. Continued deformation of the clay under repeated loadings is believed to result from a progressive destruction of the cemented soil structure. Effective stress failures result from an increase in the excess pore water pressures within the sample.

Melbourne's Southbank Interchange: a permanent excavation in compressible clay

2004 ◽  
Vol 41 (5) ◽  
pp. 861-876 ◽  
Author(s):  
Maxwell C Ervin ◽  
Neil D Benson ◽  
Jack R Morgan ◽  
Nick Pavlovic
Keyword(s):  
Ground Water ◽  
Pore Water ◽  
Design Criteria ◽  
Pressure Relief ◽  
Groundwater Levels ◽  
Flow Models ◽  
Site Monitoring ◽  
Pore Water Pressures ◽  
And Control ◽  
Groundwater Lowering

The Southbank Interchange of the Melbourne City Link Project links major freeways and access roads. The permanent excavation covers an area of 3 ha and extends to a maximum depth of 9 m, which is 6 m below the ground water table. Design and construction approaches were developed to (i) control seepage into the excavation to limit groundwater lowering beyond the site, and (ii) limit the effects of potentially damaging base heave during construction. Lateral flow of groundwater into the excavation was controlled by a cut-off wall extending through the compressible clay with a surrounding line of closely spaced recharge wells. Analyses showed the recharge wells in combination with the wall would be effective in limiting drawdown outside the site. Monitoring showed that pore water pressures were maintained within the design criteria, with the assistance of deep recharge of an underlying aquifer to control vertical seepage. Survey showed settlements outside the site were minimal. Shallow pressure relief drains were installed to limit uplift pressures and control base instability in the deepest parts of the excavation. Monitoring of the groundwater levels in the underlying aquifer and comparisons with results from flow models were used to successfully control uplift pressures during construction.Key words: clay, settlement, groundwater, excavation, recharge, construction.

scholarly journals Consolidation of Soils Under Cyclic Loading

1974 ◽  
Vol 11 (3) ◽  
pp. 420-423 ◽  
Author(s):  
N. E. Wilson ◽  
M. M. Elgohary
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Soil Layer ◽  
Saturated Soil ◽  
Theoretical Solution ◽  
Loading Cycle ◽  
Sustained Loading ◽  
Pore Water Pressures

A theoretical solution for the progress of consolidation of a saturated soil layer subjected to cyclic loading is obtained.Consolidation, proceeding inwards from the drainage face, is slower than consolidation under an equivalent sustained loading because positive and negative pore-water pressures, produced during the loaded and unloaded portion of the cycle, cause flow of water from and into the soil. An equilibrium, or finalized, consolidation ratio is reached which is dependent on the pattern of loading cycle; it is not possible to reach 100% consolidation under cyclic loading.

Stability of swelling clay embankments

1979 ◽  
Vol 16 (1) ◽  
pp. 140-151 ◽  
Author(s):  
R. A. Widger ◽  
D. G. Fredlund
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Back Analysis ◽  
Triaxial Tests ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Total Strength ◽  
Swelling Soils ◽  
Pore Water Pressures ◽  
Matrix Suction

A common occurrence in cuts or fills of swelling soils is their reduction in strength with time. At the time of compaction, the clay generally has a high matrix suction. Correspondingly, it has a high strength and will stand at relatively steep side slopes. With time, the soil generally tends towards saturation and the matrix suction reduces towards zero. There is a reduction in total strength and if the gravitational forces are too large, the slope fails.During the past several years, numerous cut and fill slopes have been observed in the Regina area of Saskatchewan. Many of these slopes have remained stable for 4–6 years and then failed. There has been a 20 year history of observations on the Belle Plaine overpass west of Regina. Field and laboratory investigations have been conducted.With a knowledge of the geometry of the slope and failure plane, the simplified Bishop method of stability analysis was used to perform a 'back-analysis' to assess the shear strength parameters. The shear strength parameters from the laboratory program are compared with those calculated from the stability analyses. The analyses indicate that the peak shear strength parameters from triaxial tests on the softened Regina clay (i.e., c' = 5 kPa and [Formula: see text]), with the appropriate pore water pressures, give a factor of safety of 1 for the failed surface. The effect of spring thawing appears to be to produce the condition of most serious pore water pressures.

Postfailure analysis: Tramping Lake causeway, Saskatchewan, Canada

1989 ◽  
Vol 26 (4) ◽  
pp. 687-704
Author(s):  
J. L. Labossiere ◽  
E. K. Sauer ◽  
E. A. Christiansen
Keyword(s):  
Pore Water ◽  
Slip Surface ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Lake Basin ◽  
Pore Water Pressures ◽  
Back Calculation ◽  
Vertical Subsidence ◽  
Sand And Gravel ◽  
Effective Friction

A traffic causeway placed on the sediments of saline Tramping Lake failed during construction in the summer of 1982. Vertical subsidence has continued until present (1988). The failure mechanism was controlled by sedimentary structure and artesian groundwater conditions. The shear zone is in a soft, near normally consolidated lacustrine sandy silt unit 22 m thick. The lake basin contains lacustrine, deltaic, and fluvial deposits of postglacial origin. Artesian conditions in the Upper Cretaceous Judith River Formation and postglacial fluvial sand and gravel dominate the hydrogeology at the site. The failure took place along a composite slip surface when excess pore-water pressures developed during loading [Formula: see text]. The estimated effective friction angle from triaxial tests and back calculation was 27° assuming c′ = 0. However, a parametric analysis showed that at very high pore-water pressures the effective friction angle required for equilibrium is very sensitive to small variations in ru. The calculated cohesion at [Formula: see text] required for equilibrium was 3.9 kPa, whereas the remolded vane strength measured in the field was 5.0 kPa. Key words: Foundation failure, artesian, saline environment, groundwater discharge, silty clays, postglacial fluvial and lacustrine deposits.

Study on Static Strength of Aeolian Sand before and after Cyclic Loading

2014 ◽  
Vol 580-583 ◽  
pp. 191-194
Author(s):  
Da Peng Liu ◽  
Xiao Hua Yang ◽  
Jing Wang ◽  
Zheng Jun Mao
Keyword(s):  
Cyclic Loading ◽  
Confining Pressure ◽  
Static Strength ◽  
Triaxial Tests ◽  
Aeolian Sand ◽  
Desert Region ◽  
Deviator Stress ◽  
Before And After ◽  
The Stability ◽  
Engineering Practices

Aeolian sand is one commonly used subgrade filling in Xinjiang Oasis-desert region, engineering practices also proved its applicability as subgrade filling. In order to find the law of Aeolian sand subgrade static strength after cyclic loading, the paper studied the static strength of Aeolian sand before and after cyclic loading through the dynamic and static triaxial tests. It is concluded that the greater cyclic loading is, the more Aeolian sand static strength peak decreases. When cyclic loading is small, the bigger confining pressure and consolidation ratio are, the static strength peak increases more after cyclic loading. The bigger initial static deviator stress is, the more Aeolian sand static strength peak reduces. The frequency of cyclic loading has little effect on static strength. In order to keep the stability of low embankment, we should restrict overload , ensure subgrade and foundation consolidation adequately, at the same time using gravel or geosynthetic materials to package edge of roadbed, so as to increase confining pressure. The research results can provide reference for the design and construction of Aeolian sand low subgrade in Xinjiang Oasis-desert region.

Determination of the Cyclic Properties of Silty Sands

2018 ◽  
pp. 416-445
Author(s):  
Eyyüb Karakan ◽  
Selim Altun
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Tests ◽  
Loading Conditions ◽  
Systematic Testing ◽  
Geotechnical Problems ◽  
Insight Into

Liquefaction may be triggered by cyclic loading on saturated silty sands, which is responsible of severe geotechnical problems. Development of excess pore water pressure in soil results in a liquid-like behavior and may be the reason of unavoidable superstructural damage. In this study, in order to investigate the behavior of saturated silty sands exposed to cyclic loading under undrained conditions, a systematic testing program of stress-controlled cyclic triaxial tests was performed on specimens of different silt contents, under different loading conditions and environment. The effect of parameters such as silt content on the liquefaction behavior of specimens was studied. Pore water pressure and shear strain curves were obtained for the silty sands. Furthermore, the boundaries existing in the literature on sands are compared with the results current research, on silty sands. Conclusively, the outcomes of this study were useful to develop insight into the behavior of clean and silty sands under seismic loading conditions.

Drained deformation and failure due to cyclic pore pressures in soft natural clay at low stresses

1987 ◽  
Vol 24 (2) ◽  
pp. 208-215 ◽  
Author(s):  
K. D. Eigenbrod ◽  
J.-P. Burak ◽  
J. Graham
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Stresses ◽  
Alternative Mechanism ◽  
Natural Clay ◽  
Deformation And Failure ◽  
First Approximation ◽  
Pore Water Pressures ◽  
Normal And Shear Stresses

Slow, recurring downslope movements in northern climates are frequently referred to as "creep movements," and are usually related to outwards freezing followed by vertical thawing movements. An alternative mechanism is examined in the reported test data.Undisturbed block samples of proglacial clay from a slope near yellowknife, N.W.T., have been tested by cyclically varying the pore-water pressure in triaxial specimens by an amount Δu, and measuring the resulting strains per cycle. The specimens were initially anisotropically consolidated with normal and shear stresses corresponding to those in the moving mantle. Drainage was permitted throughout the testing. This procedure represents changes that can occur in a natural slope from (a) seasonal groundwater level changes and (b) elevated pore-water pressures that accompany thawing. After 60–100 cycles, the pore-water pressure was systematically increased to the value Δuf at which the samples failed. This occurred on a steep, low-stress envelope, approximately c′ = 4 KPa, [Formula: see text]. The envelope is probably controlled by the nuggety macrostructure of the clay and appears to be slightly to the left of the [Formula: see text] locus.The strains per cycle were approximately linear in the range 30–100 cycles. As a first approximation they have been modelled as varying linearly with the ratio Δu/Δuf almost up to failure at Δu/Δuf = 1.0. Key words: downslope creep, solifluction, slope stability, clay, pore-water pressure, cyclic loading, low-stress failure.

scholarly journals Study on Cyclic Cumulative Deformation Characteristics and the Equivalent Cyclic Creep Model of Soft Clay

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Wenbo Zhu ◽  
Guoliang Dai ◽  
Weiming Gong
Keyword(s):  
Strain Softening ◽  
Soft Clay ◽  
Cyclic Creep ◽  
Creep Model ◽  
Triaxial Tests ◽  
Strain Accumulation ◽  
Test Results ◽  
Deviator Stress ◽  
Cumulative Deformation ◽  
Stress Ratios

Suction caisson foundations can be used to anchor tension leg platforms. The soil at the bottom of the caisson undergoes both unloading and cyclic loading under wind and wave loads. However, the problem of cyclic cumulative deformation of soft clay under unloading has rarely been addressed. So, the strain cumulative deformation and strain softening characteristics of soft clay are studied by cyclic triaxial tests. The test results show that under low static deviator stress ratios and dynamic deviator stress ratios, the soil has a low level of strain accumulation and softening. As the dynamic deviator stress ratios increase, the cumulative cyclic deformation gradually increases, which rapidly develops in the early stage and tends to stabilize in the later stage. Moreover, the softening index gradually increases and is linearly related to the logarithm of the number of cycles. The cyclic cumulative deformation of the soil increases with increases in unloading stress and dynamic deviator stress, showing a creep characteristic of attenuation and then stabilization. Based on the tests, an equivalent cyclic creep model is established to describe the strain accumulation and softening of soil and verified through comparison with the test results. Then, the model is extended to a three-dimension model, and a finite element subroutine is developed for studying the strain cumulative deformation and strain softening characteristics of soft clay.

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