Clay Embankment Research Articles

Deformation of centrifuge models of clay embankments due to ‘bumpy road’ earthquakes : Kutter, B L Soil Dynam Earthq EngngV2, N4, Oct 1983, P199–205

Deformation of centrifuge models of clay embankments due to ‘bumpy road’ earthquakes : Kutter, B L Soil Dynam Earthq EngngV2, N4, Oct 1983, P199–205

Effects of freeze–thaw and softening on a natural clay at low stresses

Weathering processes such as softening and freeze–thaw cycling affect the properties of clays. Care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes, compacted clay embankments, and trench excavations in which significant proportions of the cross section can be affected by climatic weathering.Samples of plastic Lake Agassiz clay from Winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure. They were therefore all overconsolidated with respect to the field preconsolidation pressure. The samples were then loaded under drained or undrained conditions along steeply rising stress paths in p′, q stress space. One group of samples was tested immediately to identify the "undisturbed" behavior, a second group was subjected to freeze–thaw cycles, and a third group allowed to swell freely before testing.The freeze–thaw cycling produced increased compressibility and pore-water pressures, and reduced strengths at low stresses compared with the behavior of undisturbed clay. Freezing also caused the development of a clearly defined fissure structure. Softening at low stresses with access to water produced less marked effects. Key words: clay, undisturbed, freeze–thaw, softening, strength, yielding, pore-water pressures.

Earthquake Deformation of Centrifuge Model Banks

A modified sliding block analysis, which allows the sliding resistance to be nonlinear visco‐elastoplastic, has been developed to predict deformations of embankments during earthquakes. Contrary to the assumption (of the original Newmark sliding block analysis) that a distinct slip surface forms, the centrifuge models were observed to deform along relatively wide shear bands during base shaking. The sliding resistance provided by a wide shear band is better characterized by visco‐elastoplastic than rigid‐plastic behavior. A detailed analysis concerning rational parameter selection is included. The modified analysis is used to predict the deformation of clay embankment centrifuge models during simulated earthquakes, with good agreement between experiment and theory. The centrifuge modeling technique is shown to be a useful tool for development, tuning, and verification of analytical models, especially in the subject of earthquake engineering where detailed field evidence is in acute shortage.

841208 Triaxial test — field stresses in compacted clay embankment : Ostlid, H Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981V2, P549–551. Publ Rotterdam: A. A. Balkema, 1981

841208 Triaxial test — field stresses in compacted clay embankment : Ostlid, H Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981V2, P549–551. Publ Rotterdam: A. A. Balkema, 1981

Deformation of centrifuge models of clay embankments due to ‘bumpy road’ earthquakes

A model study of deformations of kaolin embankments during earthquakes has been carried out using a ‘Bumpy Road’ actuator to impose earthquake-like base accelerations on centrifuge models. This paper begins by briefly describing the earthquake simulating apparatus. The results of the model tests indicate that predictions of displacement using sliding block type calculations need to take account of softening of the soil during the earthquake. A simple mathematical model for degradation of strength with increasing block displacement is shown to satisfactorily account for softening. In one model test, strain softening and pore pressures caused by an earthquake apparently induced a collapse of the model a few seconds after the earthquake. Delayed failure produced deformations of an order of magnitude larger than any measured during actual base shaking.

Motorway slip report warns ‘go easy’ with clay embankments : Byrd, T New Civ Engr, N516, 11 Nov 1982, P18–20

The final report on the failure of a massive M25 embankment has not blamed a terram separation membrane, although the fabric possibly promoted a soft clay layer. Failure involved a 200 M long section of the batter slope breaking away with secondary rotation of the fill behind. It was concluded that the ground probably contained shear surfaces, that it was saturated with rain at the time of loading and the drainage blanket was not draining freely above it. A loss of strength due to softening of the clay immediately above the separation membrane occurred and possible segregation of the finer size clay particles during migration of moisture through the membrane made the problem worse. Tendency of the original ground to spread all contributed to the collapse. Very careful sampling and evaluation of the top-most layer of the foundation are needed to assess the influence of discontinuities and pre-existing shear surfaces. The effect of rainfall on the natural ground and the effectiveness of any drainage blanket need to be carefully assessed. Also a short break in construction of an embankment on saturated clay should allow local excess pore water pressures to dissipate through fissures and drainage blankets. (TRRL)

Influence of shrinkage cracks on pore-water pressures within a clay embankment : Anderson, M G; Hubbard, M G; Kneale, P E Q J Engng Geol, V15, N1, 1982, P9–14

Influence of shrinkage cracks on pore-water pressures within a clay embankment : Anderson, M G; Hubbard, M G; Kneale, P E Q J Engng Geol, V15, N1, 1982, P9–14

Simulation of Earthquake Motions in the Centrifuge

The present study is mainly concerned with the design of an earthquake simulator package for the generation of a sinusoidal motion during a centrifuge test. It was then used to excite the dynamic response of a clay embankment in the centrifuge. A comparison of measurements made during the tests with results calculated using a computer program with an equivalent-linear material model (QUAD IV), for the test condition is presented. The results demonstrate the potential beneficial use of dynamic testing using the centrifuge. (Author)

The influence of shrinkage cracks on pore-water pressures within a clay embankment

Summary For slope stability estimations, the soil pore-water conditions need to be accurately specified. The influence of cracks in clay was previously observed significantly to modify soil water response. In this study shrinkage cracks were monitored in a clay embankment where the soil water response to precipitation had been shown to be more rapid than the clay micro-permeability would predict. The cracks were shown to increase the hydraulic conductivity of the clay at all times of the year and to be the cause of the rapid soil water potential responses monitored. X-ray examinations of closed crack sites indicated that fractures at these sites formerly extended to greater depths.

Stability of swelling clay embankments : Widger, R A; Fredlund, D G Can Geotech J, V16, Feb 1979, P140–151

Stability of swelling clay embankments : Widger, R A; Fredlund, D G Can Geotech J, V16, Feb 1979, P140–151

Parametric Elastoplastic Analysis of Clay Fills

Plasticity theory has not yet been used extensively in the modelling of the behaviour of clay embankments. This paper uses a linearly elastic-plastic model and the finite element method to investigate the influence of different forms of plastic behaviour on the stresses and displacements in the body of a clay embankment during undrained construction. Twelve cases are studied and their results are compared. These include a linearly elastic case, a strain softening case, two cases of perfect plasticity and eight cases of strain hardening.The results show that the type of plastic stress-strain curve greatly influences the displacements and only to a much lesser extent the stresses. The pattern of influence of the type of plasticity on the stresses depends on the location of the element whose stresses are examined. Similarly, the pattern of expansion of the plastic zone depends on the geometric configuration of the embankment.

Pore water pressure and stability conditions on a motorway embankment

AbstractPrior to the occurrence of a shallow surface slip on a clay embankment a tensiometer system was installed to continuously monitor pore water conditions. It is shown that high pore water pressures can develop in clay embankments after periods of continuous low intensity precipitation. Using stability analyses it is demonstrated that for this first time slide, the clay fill material had a shear strength above residual values and a small but finite cohesion.

Stability of swelling clay embankments

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.

Simplified Procedure for Estimating Dam and Embankment Earthquake-Induced Deformations

The method uses the concept of yield acceleration but is based on the evaluation of the dynamic response of the embankment rather than a rigid body behavior. The yield accelerations, for a potential sliding mass, is estimated on the basis of the static undrained shear strength (with some reduction due to effects of cycling) using pseudostatic methods of stability analysis. The permanent deformations are estimated by numerical double integration of the time history of induced accelerations for various depths of the potential sliding mass. Design curves are presented that were developed on the basis of finite element response computations of embankments subjected to base accelerations representing earthquakes of magnitudes ranging between 6-½ and 8-¼. The simplified procedure is illustrated by an example computation. The permanent deformations are estimated for a 135-ft (40-m) high sandy clay embankment that was shaken by a magnitude 8-¼ earthquake and the results are compared with the observed field behavior.

The Efficiency of Horizontal Drainage Layers for Accelerating Consolidation of Clay Embankments

Synopsis The efficiency of drainage layers to accelerate consolidation of clay fill embankments is considered and the influence of such factors as layer thickness, length and permeability is examined. It is shown that in order to be fully effective a drain should have, typically, a permeability at least 106 times that of the surrounding clay fill, although an acceptable efficiency would be achieved with a ratio of about 3 × 104. A drainage blanket only 103 times more pervious than the fill is likely to be useless. L'efficacité de couches de drainage pour accélérer la consolidation de remblais en argile est prise en considération et l'on examine l'influence de facteurs tels que l'épaisseur, la longueur et la perméabilité des couches. On montre qu'afin d'être complètement efficace un drainage doit posséder, d'une façon typique, une perméabilité au moins 106 fois celle du remblai d'argile environnant, quoiqu'une efficacité acceptable serait obtenue avec un rapport d'environ 3 × 104. Un tapis de drainage seulement 103 fois plus perméable que le remblai sera vraisemblablement inutile.

Electro-osmosis in Frozen Soil

WATER can be transported in unfrozen soil under an electrical gradient. This process, which is called electro-osmosis, is due to an excess of positive ions over negative ions in the water near a solid surface. The amount of water which can be transported by electro-osmosis is such that in some instances it has been used to stabilize soft clay embankments. The purpose of our experiment was to measure the extent to which water can be moved through the films of unfrozen water in a frozen soil.