Cyclic Deviator Stress Research Articles

Behaviour of lignosulfonate-treated soil under cyclic loading

In this paper, the effectiveness of an environmentally-friendly stabilising agent for soil, lignosulfonate (LS), is examined through a series of cyclic triaxial tests. The deformation characteristics of the contents of LS-treated sandy silt when subjected to undrained cyclic triaxial loading are investigated at different confining pressures and cyclic stress levels. Test results indicate that under a given confining pressure and cyclic deviator stress, the rate of increase in axial strain is controlled by the addition of LS, which results in a smaller value of plastic axial strain (εa,p). For all the untreated and LS-treated specimens, the rate of increase in εa,pincreases with the increasing cyclic stress ratio (CSR). A critical value of CSR exists for a given LS content (i.e. CSRCR), below which the specimens could remain stable irrespective of the number of load cycles. The longevity of treated specimens is improved significantly, especially for the specimens with LS = 2% by weight. As the treated specimens are subjected to a high level of cyclic stress, the excess pore pressure shows a decreasing trend with the increasing number of cycles, but then increases again rapidly when the failure becomes imminent. Compared with the untreated soil, the resilient modulus increases significantly as a result of LS treatment, especially for LS = 2%. When the LS > 2%, there is no additional advantage, implying that 2% LS treatment is an optimum for this soil.

Effects of mean net stress and cyclic deviatoric stress on the cyclic behavior of normally consolidated unsaturated kaolin

Experimental study of the cyclic behavior of unsaturated materials is more complex than that of the saturated materials due to the required equipment, experience and time. Furthering investigations in the field of unsaturated materials is necessary to better understand its complexity and sensitivity of unsaturated cyclic parameters to different determinants such as suction path, stress path, loading speed, deviatoric stress amplitude, physical specifications, and etc. To this end, the main focus of this study has been to analyze the effects of factors such as mean net stress and deviatoric stress levels in fast cyclic loading on the cyclic behavior of a normally consolidated unsaturated fine-grained trade soil, namely the Zenoz kaolin. Various unsaturated tests were performed in three mean net stress levels and three amplitudes of cyclic deviatoric stress levels. Results showed that increase of suction in the same strain level leads to increase in stiffness in normally consolidated samples (i.e. increase in elastic modulus and shear modulus and decrease in damping ratio). Also, in the same suction value and strain level, increase of the mean net stress during the isotropic consolidation causes to the denser normally consolidated samples and results to increase of elastic modulus and shear modulus, and decrease of damping ratio.

Effects of cyclic confining pressure on the deformation characteristics of natural soft clay

To investigate the coupling effects of cyclic deviator stress and cyclic confining pressure on the deformation behavior of natural soft clay under partially-drained conditions, a series of one-way cyclic triaxial tests with and without cyclic confining pressure were carried out. Test results show that, at the same amplitude of cyclic deviator stress, the increase of cyclic confining pressure amplitude will accelerate the accumulation of both permanent volumetric and axial strain significantly. The comparison between test results for different amplitudes of cyclic confining pressure shows that tests with a cyclic confining pressure corresponding to a stress path of ηampl=pampl/qampl=1 lead to a 1.4 times larger permanent volumetric strain and a 1.2 times larger permanent axial strain compared to the conventional cyclic triaxial tests with constant confining pressure (ηampl=1/3). In case of ηampl=2 the permanent strains are found to be even 2.0 or 1.5 times larger compared to the standard tests. Finally, an empirical formula is proposed for the prediction of permanent axial deformations of natural soft clays under partially-drained conditions, considering the effects of cyclic confining pressure.

Dynamic Feature Analysis for Silty Sand

Dynamic shear modulus is proportional to average principal stress.Cyclic varied surrounding pressure isn't proportional to cyclic varied pore water pressure.The dynamic triaxial test with cyclic surrounding pressure can apply cyclic surrounding pressure.The dynamic triaxial test with cyclic surrounding pressure can apply cyclic surrounding pressure in addition to the cyclic deviator stress and it can simulate the coupling of cyclic shear stress and it can simulate the coupling of cyclic shear stress and cyclic normal stress in an earthquakes.

Evaluation of cyclic shear strength of mixtures with sand and different types of fines

ABSTRACTSoils are classified as sandy soils and clayey soils in most soil classification systems, and appropriate equations are used for practical design, depending on soil type, to represent each soil behavior. Sand-clay mixtures, however, need a special standard to evaluate their specific behaviors since they are categorized as intermediate soils or transitional soils and typically show intermediate properties. In this article, a series of cyclic triaxial tests were conducted on specific sand-fines mixtures with three fine types and various fine contents. The behaviors of various soil mixtures (silica sand with Iwakuni natural clay, Tottori silt, and Kaolin clay) were investigated by considering a concept of granular void ratio expressed in terms of sand structure. The cyclic shear strengths of the soil mixtures were also evaluated by increasing the fine content but no more than the threshold fine content. In the results, the cyclic deviator stress ratio decreased in dense soils whereas it increased in loose soils by increasing the fine content. In addition, a simple equation was proposed to predict the liquefaction resistance of sandy soils by evaluating the cyclic deviator stress ratio with a concept of equivalent granular void ratio.

Cyclic triaxial tests to aid offshore pile analysis and design

Renewable offshore energy structures experience unusually high levels of cyclic loading under storm and operating conditions. Laboratory and full-scale tests provide one route to develop rational foundation design approaches for such structures. Analytical approaches may also be developed from soil element testing and modelling. This paper outlines preliminary results from such a study. Computer-controlled stress path triaxial equipment, employing high-resolution local strain instrumentation, is adopted for experiments on Dunkerque and Fontainebleau sands designed to support parallel full-scale field and laboratory-model testing programmes involving axial pile loading. The triaxial experiments comprise suites of constant-volume uniform cyclic tests on K0 over-consolidated specimens employing different amplitudes, performed in conjunction with static and multi-stage experiments that examine the effects of non-uniform cyclic loading. Preliminary results reveal the relationships between cyclic deviator stress, mean effective stress changes and number of cycles, as well as patterns of permanent and cyclic strain development.

모래-세립분 혼합토에 대한 반복전단강도특성 평가

토질분류법에서 흙은 크게 사질토와 점성토로 분류되며, 실제 설계에서도 이와 같이 분류된 흙 종류에 따라 다른 예측식을 사용하여 흙의 거동을 평가하고 있다. 그러나, 모래-세립분 혼합토는 전형적으로 중간토(intermediate soil or transitional soil)로 구분되어 모래와 점토의 중간적인 성질을 나타내기 때문에, 이러한 혼합토에 대한 거동특성을 평가할 수 있는 기준이 필요하다. 본 논문에서는 입도분포를 조정한 특정 모래에 세 가지 종류의 세립분으로 구성된 다양한 세립분함유율을 갖는 시료를 대상으로 일련의 반복 삼축압축시험을 수행하였다. 모래가 골격을 이루는 간극비(골격간극비)를 고려하여, Silica sand와 세립분(Iwakuni natural clay, Tottori silt, kaolinite)을 다양한 건조 중량비로 혼합하여 그 특성을 파악하였으며, 실험결과로 전환 세립분함유율(threshold fines content)을 넘지 않는 혼합토의 반복전단강도를 세립분 함유율 증가에 따라 평가하였다. 그 결과, 반복 전단응력비는 세립분 함유율 증가에 따라 조밀한 시료에서는 감소, 느슨한 시료에서는 증가하는 결과를 나타냈으며, 혼합토의 반복전단응력비를 등가골격간극비의 개념을 이용하여 평가했다. In most design codes, soils are classified as either sandy or clayey soils, and appropriate design equations for each soil type are used to estimate their soil behaviour. However, sand-fine mixtures, which are typically referred to as intermediate soils, are somewhere at the middle of sandy or clayey soils, and therefore a unified interpretation of soil behaviour is necessary. In this paper, a series of cyclic shear tests were carried out for three different combinations of sand-fine mixtures with various fines content. Silica-sand mixture and fines (Iwakuni natural clay, Tottori silt, kaolinite) were mixed together with various mass ratios, while paying attention to the changes of void ratios expressed in terms of sand structure. The cyclic shear strengths of the mixtures below the threshold fines content were examined with the increasing fines contents. As a result, as the fines contents increased, their cyclic deviator stress ratios decreased for dense samples while it increased for loose samples. Additionally, cyclic deviator stress ratio of the mixtures was estimated using the concept of equivalent granular void ratio.

Undrained cyclic triaxial behavior of saturated clays under variable confining pressure

A laboratory study on the undrained dynamic behavior of saturated clays in cyclic triaxial tests with a variable confining pressure (VCP tests) is presented. Tests were performed on remolded clayey samples using a dynamic triaxial device where the deviatoric stress and confining pressure can be varied simultaneously. Various cyclic stress paths have been applied on the specimens through varying the ratios or phase differences between the cyclic deviatoric stress and cyclic confining pressure. Specifically, the stress paths used in the present study were designed to simulate the coupling effects of simultaneously varying shear and normal stresses in clays due to earthquakes and other vibration sources. Test results obtained from this study show that the undrained response of saturated clays is strongly influenced by the variation of confining pressure, in terms of pore water pressure, development speed of cyclic strain and magnitude of cyclic strength. It is found that when strong P-waves are propagating in soil layers, VCP tests are more appropriate for the simulation of in situ stress fields than the conventional cyclic triaxial tests with a constant confining pressure (CCP tests).

Effect of Microfabric on Undrained Static and Cyclic Behavior of Kaolin Clay

Microfabric plays an important role in the engineering behavior of soils. Although many studies are available in the literature on the effect of microfabric on the static behavior of soils, the effect on the cyclic behavior is less understood. In the present study, samples with different microfabric were prepared in the laboratory by reconstituting commercially available kaolin clay with different pore fluids under a consolidation pressure of 100 kPa. Consolidated undrained triaxial tests were carried out on these samples under static and cyclic loading conditions. Dispersed samples were found to have monotonic stress-strain behavior with a peak deviatoric stress and higher peak undrained shear strength than the flocculated samples. However, the dispersed samples were found to offer less resistance to cyclic loading. When subjected to cyclic loading, dispersed samples failed within a few cycles under a cyclic stress ratio (defined as the ratio of cyclic deviatoric stress to the undrained shear strength) close to 0.6, whereas in flocculated samples, sudden failure was not observed even at a higher cyclic stress ratio of 0.9, although strains and pore pressures accumulated to higher values. Postcyclic monotonic tests conducted on samples that did not fail under cyclic loading showed an apparent overconsolidation effect caused by cyclic loading in a similar manner, as reported in the literature.

Design of Foundations on Sensitive Champlain Clay Subjected to Cyclic Loading

Sensitive clay subjected to cyclic loading may experience gradual loss of its shear strength, which may lead to liquefaction. Foundations built on this clay would suffer extensive settlement and significant loss of bearing capacity or perhaps catastrophic failure. This paper presents an experimental investigation on sensitive (Champlain) clay obtained from the city of Rigaud, Quebec (Canada). Consolidation tests, static and cyclic undrained and drained triaxial tests were performed on representative samples of this clay. The objective of this investigation was to examine the influence of the physical and mechanical parameters, which govern the shear strength of sensitive clay subjected to cyclic loading. Based on the results of the present investigation and those available in the literature, it can be reported herein that the undrained response is the most critical for these foundations; furthermore, the preconsolidation pressure is considered as an important parameter in establishing the shear strength of sensitive clay. A design procedure is developed to determine the safe zone for the undrained and drained responses, within which a combination of the cyclic deviator stress and the number of cycles for a given soil/loading/site conditions can achieve a quasielastic resilient state without reaching failure. The proposed design procedure is applicable to all regions around the world, where sensitive clays can be found. Furthermore, this procedure can be adopted to examine the conditions of existing foundations built on sensitive clay at any time during its lifespan.

Liquefaction, Cyclic Mobility, and Failure of Silt

It is known that the mechanical properties of low-plasticity silt are similar to those of sand, and yet silts are frequently used as coastal reclamation materials in many cities and industrial areas and will thus be susceptible to liquefaction. Samples of a low-plasticity silt have been tested under monotonic and cyclic loading under isotropic and anisotropic stress conditions to characterize liquefaction, cyclic failure, and to develop an empirical model describing its cyclic strength. A sedimentation technique produced samples that had the highest susceptibility to liquefaction. Contractive behavior of monotonically loaded samples was triggered when the stress path reached an initial phase transformation (IPT) in both compression and extension tests. The samples became dilative after reaching a phase transformation (PT) point. The cyclic shear behavior of the silt samples prepared using the sedimentation method and consolidated at various initial sustained deviator stress ratios was examined in terms of two different failure criteria: a double amplitude axial strain εa,DA=5% for reversal conditions; or axial plastic strain εa,P=5% for nonreversal. For isotropically consolidated samples the initial phase transformation determined from undrained monotonic extension tests was the boundary between stable and contractive behavior. For anisotropically consolidated samples failure was defined by a bounding surface formed by undrained monotonic compression tests. An empirical model was developed relating the number of cycles to failure under conditions of both liquefaction and cyclic mobility to the initial anisotropic sustained deviator stress and cyclic deviator stress ratio.

Residual Strains in Calcareous Sand due to Irregular Cyclic Loading

This paper describes a procedure for predicting the residual strains developed in calcareous sand under irregular cyclic triaxial loading conditions. The rates of accumulation of volumetric and shear strains are treated separately, with the volumetric strain response being used as the basis for characterizing the effects of cyclic loading. The residual volumetric strain developed as a result of repeated loading is related to the mean and the amplitude of the cyclic deviator stress. Thus, by using empirical correlations between the applied deviator stresses, the number of cycles, and the measured residual strains, the effect of cyclic loading under one set of cyclic loading conditions can be expressed in terms of an equivalent number of cycles under a different set of cyclic loading conditions. By using this equivalent number of cycles for the cyclic loading stresses, the residual strains developed as a result of further loading are then determined, so that the residual strains developed at any stage during irregular cyclic loading can be evaluated.

Cyclic Loading of Silty Clay with Drainage Periods

Undrained repeated load triaxial tests are carried out on anisotropically (Ko) normally consolidated specimens of a silty clay. Each specimen is subjected to five periods of loading at 0.1 Hz. The loading periods have a maximum duration of approximately 2,000 cycles, and are separated by drainage periods. A variety of cyclic loading magnitudes are applied. The experiments show that large permanent shear strains and pore pressures develop during the first few loading periods, particularly during the application of high cyclic deviator stress amplitudes, leading to failure. This is defined as an accumulated shear strain of 0.6% during a particular loading period. Drainage periods have a significant strengthening effect, even though the changes in water content are small, and it is observed that during the later loading periods very little permanent strain or pore pressure development occurs. The number of drainage periods required to produce this condition increases as the magnitude of the cyclic loading amplitude increases.

Estimation of Subgrade Resilient Modulus from Standard Tests

Mechanistic pavement design procedures based on elastic layer theory require the specification of elastic moduli for each material in the pavement section. Repeated load tests yielding a resilient modulus are frequently used to characterize the soil subgrade. Due to difficulties associated with cyclic testing, approximate methods are often used for design estimates of resilient modulus. These approximations are often based only on shear strength measures and do not account for the dependence on the magnitude of cyclic deviator stress. A procedure is described to relate the soil‐index properties and the moduli obtained from uncon‐fined compression tests, to resilient modulus. Two statistical models are described and demonstrated for 11 soils from throughout the state of Tennessee. One model provides an estimation of the breakpoint resilient modulus, or the modulus at a deviator stress of 6 psi (41 kPa). The second model provides a general nonlinear relationship for the modulus of fine‐grained soils as a function of deviator stress. Both models are demonstrated for a range of soils and are shown to provide a good characterization of the response for the soils investigated. Similar relationships can be developed for other subgrade soils, and may prove useful to agencies that use deterministic pavement design procedures, but lack the capability for high‐production repeated‐load testing.

Cyclic loading triaxial testing of crushed rubble and lava

This paper describes a laboratory investigation into the suitability of crushed rubble as a substitute for conventional road base materials. The rubble investigated was a mixture of crushed concrete and crushed bricks, whilst lava from the Eifel was chosen as a reference material. Standard highway engineering tests (Proctor, CBR) and durability tests (Los Angeles Abrasion, Slake Durability and the standardized Dutch crushing test) were performed to provide reference date with every-day engineering practice. Cyclic loading triaxial tests were performed on both materials. The resilient moduli were determined at various levels of confining stress and the cyclic deviator stress. The susceptibility to plastic strain development (rutting) of both materials was determined in triaxial tests with up to 106 load applications. The degradation of the materials in the plastic strain tests was determined through sieve analyses prior to and after the tests.

Cyclic Triaxial Tests with Continuous Measurement of Dissipated Energy

Abstract This article describes conventional cyclic triaxial tests on a uniform sand in which the amount of energy dissipated by the specimen was continuously monitored. Energy monitoring was achieved by means of a digital circuit that automatically integrated the force-displacement signals as the test progressed. The resulting energy trace was plotted against the pore pressure buildup within the specimen. From a total of 21 tests, it appears that pore pressure generation and dissipated energy are functionally related, but this relationship appears to depend strongly on the level of cyclic deviator stress.

Cyclic Undrained Triaxial Strength of Sampled Sand Affected by Confining Pressure

The effects of confining pressure on the cyclic undrained triaxial strengths of intact sandy specimens obtained by sand sampling methods were investigated. It was found that the ratio of cyclic deviator stress amplitude to initial confining pressure required to cause a certain value of cyclic axial strain amplitude at a certain number of loading cycle in an intact triaxial specimen increased significantly with the decrease in confining stress when the laboratory confining pressure was less than the in situ confining pressure. However, it was also found that cyclic undrained triaxial strength expressed by stress ratio decreased only slightly with the increase in confining pressure when the laboratory confining pressure was larger than the in situ confining stress. (Author/TRRL)

Soil Failure Modes in Undrained Cyclic Loading

The failure modes of saturated sand in undrained cyclic loading are explored. A typical soil element subject to dynamic load exists initially under a nonhydrostatic state of stress. Anisotropically-consolidated samples in triaxial tests with a superimposed cyclic deviator stress represent such elements, except for the rotation of principal stress directions during cycling. The response of these samples depends on the degree of anisotropy and whether shear stress reversal occurs. For isotropically-consolidated undrained tests on saturated sand samples, the pore pressure increases with each cycle, thus decreasing the effective confining stress. The axial cyclic strain also increases as the effective stresses approach the failure state. However, the static axial strain should remain close to zero. For anisotropically-consolidated undrained tests with no shear stress reversal, the pore pressure generally, but not always, increases. In this case, the static axial strain will increase with each cycle, and the cyclic strain will remain smaller than the static strain.

Influence of cyclic load input on the mechanical properties of a sensitive soil from Orleans, Ontario

The importance of disturbance and remoulding to the alteration of mechanical properties of sensitive soils has been well documented in the geotechnical literature both in terms of laboratory and field behaviours. Man-made transient dynamic input such as dynamite blasting, heavy vehicles, and train movement have been suspected of being capable of causing a reduction in the in situ strength parameters of sensitive clays. A laboratory test program was undertaken to determine whether dynamic loading at peak stress levels below normal failure strength caused similar changes in the mechanical properties, and specifically to quantify the phenomena.In order to simulate highly overconsolidated conditions most of the tests were carried out under conditions of no confining pressure, although supplemental data were obtained from consolidated undrained tests. Some of the variables examined in this program were confining pressure, mean deviatoric stress, cyclic deviatoric stress, cyclic strain, number of applications, frequency, and reference strength. In order to compare the effect of dynamic input with the long-term creep phenomena, a simultaneous constant load program was undertaken.In general terms, the study indicates that under the prestated laboratory test conditions no major reduction in peak strength was found under dynamic loading, and that failure would occur at comparative stress levels under dead-load conditions, but required a greater time. In addition, examination of the sample after failure revealed that any remoulding of the sample appeared to be restricted to the area adjacent to the shear zone.