Stress-strain Behavior Of Soil Research Articles

Non-linear soil stiffness in routine design

Soil stress-strain behaviour is highly non-linear and this has an important influence on the selection of design parameters for simple routine geotechnical calculations. Non-linear behaviour can be characterized by rigidity and degree of non-linearity and these can be determined from measurements of very small strain-stiffness, peak strength and failure strain. Very small strain-stiffness can be found from measurements of shear wave velocity in situ or in laboratory tests. Peak strength and failure strain can be measured in routine laboratory tests but are strongly influenced by initiation of shear bands. The important non-linear stiffness parameters for soil are related to its composition and to its current state. Back-analyses of the load settlement behaviour of full-scale and model foundations demonstrate the influence of non-linear soil behaviour. Variations of stiffness with settlement calculated from full-scale and model foundations agree well with non-linear soil stiffnesses based on rigidity and degree of non-linearity. These results suggest a simple method for routine design which takes account of soil non-linear stiffness.

Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils

This paper presents a new framework for elastic viscoplastic (EVP) constitutive modelling. In developing the model, a general one-dimensional elastic viscoplastic (1D EVP) relationship is first derived for isotropic stressing conditions using an "equivalent-time" concept. This 1D EVP model is then generalized into a three-dimensional EVP model based on Modified Cam-Clay and viscoplasticity. Fitting functions are proposed for fitting data when model parameters are being determined. Using these functions, a specific EVP model is developed which describes the time-dependent stress-strain behaviour of soils under triaxial stress states. This model has been calibrated using data from a densely compacted sand-bentonite mixture. The calibrated model is used to compute time-dependent (or strain rate dependent) stress-strain curves from a multistage shear creep test and a step-changed, constant strain rate undrained triaxial compression test. Predictions from the EVP model are in general agreement with measured values. It is demonstrated that the model can simulate accelerating creep when deviator stresses are close to the shear strength envelope in a q creep test. It can also model the behaviour in unloading-reloading and relaxation. Limitations and possible improvements are also indicated.Key words: equivalent time, stress-strain, time dependent, elastic, viscoplastic, triaxial.

A Triaxial Testing System to Evaluate Stress-Strain Behavior of Soils for Wide Range of Strain and Strain Rate

Abstract Some important modifications were made to an existing triaxial testing apparatus to more accurately evaluate the stress-strain behavior of geomaterials for wide ranges of strain and strain rate. An electro-mechanical loading device was specifically designed to control strain states and stress paths and to study the quasi-elastic properties of geomaterials at any given stress state. The device is now driven by an a-c servo motor, allowing for changing the strain rate about three orders of magnitude without any intermission in each test. A 16-bit A/D card has been adopted also to increase the resolution in data acquisition. The long-term stability of a local axial gage, LDT, has been ensured to evaluate creep deformations as well as post-creep behavior of geomaterials, which should be properly understood for many practical engineering applications. High performance of the system is demonstrated by presenting some typical results from undrained cyclic tests at very small strain levels for a wide range of strain rate and an undrained monotonic loading test for a wide strain range, both on a compacted silty sand. It is shown that the equivalent Young's modulus and damping ratio at very small strains have a clear sensitivity to both strain rate and ageing period. For monotonic shearing tests in a wide range of strain, the isotach property and the effects of changes in the strain rate are also presented.

Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils

Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils

Interpretation of Large-Strain Seismic Cross-Hole Tests

At sites in earthquake-prone areas, a reliable expression of the nonlinear dynamic stress-strain behavior of soil for the different depths of interest is needed for earthquake-response analyses. Most currently used geophysical seismic tests generate only small amplitude waves, which are in the linear stress-strain range, and the nonlinear behavior is inferred from laboratory tests. A seismic cross-hole test has been developed in which large dynamic forces are applied at different depths in a borehole. Velocity sensors located in three additional boreholes at various distances from the source hole measures the particle velocity and the time it takes the shear wave generated at the source borehole to travel horizontally to each of the receiver boreholes. The generated shear strains are well into the nonlinear stress-strain range. This paper provides a systematic interpretation scheme for the data from these large-strain geophysical crosshole tests. Use is made of both the measured particle velocities at each sensor and the travel times to each borehole to develop modulus degradation curves. The interpretation procedure is applied to a well-documented case study.

The geotechnical value of ground stiffness determined using seismic methods

Abstract Geotechnical design routinely requires that the in situ strength, stiffness and permeability of the ground be determined. Most satisfactory designs for constructions such as buildings, excavations and tunnels ensure that an adequate margin of safety is maintained, and, under these conditions, measurements of the stiffness of the ground are required so that movements in the ground, both during and after construction, can be calculated. Over the past two decades the careful back-analysis of the behaviour of the ground around constructions such as tunnels and excavations has repeatedly shown that the in situ stiffness of soils and rocks is much higher than was previously thought, and that stress—strain behaviour of these materials is non-linear in most cases. Numerical analyses, using finite element and finite difference computations and field observations, have demonstrated that when margins of safety are adequate the strain levels in the ground around retaining walls, foundations and tunnels are small, and typically of the order of 0.0-l%–0.1%. Improved measurements in the laboratory have confirmed the non-linear stress-strain behaviour of soil, and shown that stiffness is much higher when measured locally and at small strain levels than when determined using conventional laboratory techniques. The realization that strain levels around construction are small, and that field stiffnesses are much higher than previously measured in the laboratory, has led us to re-appraise the value of stiffnesses derived from field seismic geophysical methods. Such methods allow stiffnesses to be determined on representative volumes of the ground, and at the in situ stress state, and for this reason may provide valuable data. This paper reviews the importance of stiffness in geotechnical design and how seismic methods are used in ground stiffness investigations.

A Rotational Hardening Constitutive Model for Anisotropically Consolidated Clay

A constitutive relationship, known as CARMEL, is proposed to predict the behaviour of anisotropically consolidated clay. Based on the principles of critical state soil mechanics the model has a non-associated flow rule and accommodates both isotropic and rotational strain hardening. A characteristic of the CARMEL model is that it can represent the changes in stress-strain behaviour of soil caused by variations in stress induced anisotropy. This permits the modelling of long stress paths, during which the induced anisotropy of the soil can be greatly changed. To assess the model, data from stress path triaxial tests reported in the literature have been predicted. Comparisons between the experimental data and predictions of CARMEL show good correlations which significantly improve on predictions using Modified Cam Clay, an isotropic associated model.

Some Observations on the Kinematic Nature of Soil Stiffness

The Paper attempts to describe soil stress-strain behaviour by defining, in normalised stress-space, an outer Bounding Surface and three characteristic Zones which sub-divide the permissable interior region. The types of behaviour exhibited within each Zone are illustrated using experimental data. It is demonstrated that the Zone boundaries, or Sub-Yield Surfaces, are mobile and may be both re-positioned and modified by moving the current stress point. This scheme is found to offer a powerful way of envisaging many poorly understood aspects of soil stress-strain behaviour.

A Probabilistic Analysis of Seismically Induced Permanent Movements in Earth Dams

ABSTRACT The earth dams built with compacted cohesive soils or dense sandy materials are vulnerable to seismically-induced permanent displacements which in some cases may be excessive. Analysis of seismic response involves an uncertainty inherent in the specification of ground motion. In this study, a probabilistic analysis is developed for evaluating seismically-induced permanent displacements in earth dams. The ground motion is modelled as a stationary random process which is defined by the Kanai-Tajimi spectral density function. The dynamic response of the dam to vertically propagating shear waves is formulated in frequency domain. The nonlinearity in shear modulus and damping is incorporated by using an equivalent linear model for the stress strain behavior of soils. The permanent displacement in dams is assumed to be in the form of the cumulative movements of a block of soil mass detached from the body of the dam. Numerical results of an example analysis and a parametric study are presented.

The Preparation of Hollow Cylinder Specimens from Undisturbed Tube Samples of Soft Clay

Abstract The use of torsional-hollow cylinder testing apparatus for research into soil stress-strain behavior has grown over the past decade. Most studies have focused on sands or on cohesive materials reconstituted in the laboratory. Studies involving undisturbed soft clay have been neglected, in part due to the difficulties involved in specimen preparation. The present paper describes a procedure for the preparation of hollow cylinder specimens of very soft undisturbed clay and their mounting in the triaxial chamber. The procedure involves the use of electrosmosis in order to allow “frictionless” cutting of soft saturated cohesive materials. The specimen is supported laterally, axially, radially, and tangentially throughout the entire procedure. The procedure could easily be adapted for the preparation of specimens of soft clays for any geotechnical laboratory test.

Modelling small strains for analysis in geotechnical engineering : Stallebrass, S E Ground EngngV22, N9, Jan/Feb 1990, P26–29

This paper specifies factors which should be considered, when investigating the small strain stiffness of soils in order to obtain a realistic prediction of ground movement. For many structures in overconsolidated soils, most of the soil experiences shear strains less than 0.1%. At these small strains, the stiffness of overconsolidated soil is nonlinear, and depends on the current state, overconsolidation ratio and recent stress history of the soil. To predict both the magnitudes and the distributions of ground movements adequately, soil models should incorporate all these characteristics. This behaviour can be modelled, using a nonlinear elastic relationship derived empirically from appropriate data, but these data can be obtained only by using special stress path testing, which usually requires local axial strain measurement. A new kinematic yield model has been developed, which uses easily obtained basic soil parameters to model the stress-strain behaviour of soil. This approach provides a potentially simpler method of predicting ground movements.

Reliability of cyclic load deformation models for cohesive soil

The concepts of probability and structural reliability theories have been employed to assess the predictive capabilities of existing deterministic models of soil deformation under dynamic loads. The results reveal that the models are associated with appreciable error attributed to the assumptions involved in their original formulations. The results also clearly distinguish the investigated models into three categories defined by their relative degrees of conservatism in predicting failure strain. The anisotropic residual deformation model is very conservative, the hyperbolic and Ramberg-Osgood models are moderately conservative, while the cyclic stress-strain performance model is non-conservative. Hence the reliability analysis has enabled an indepth perception of the relative effectiveness and limitations of the models as descriptors of dynamic stress-strain soil behaviour.

Back analysis of the Nerlerk berm liquefaction slides: Reply

pressuremeter. 39th Canadian Geotechnical Conference, Ottawa. HIRD, C. C., and HASSONA, F. 1986. Discussion on A state parameter for sands. Giotechnique, 36(1), pp. 123132. HUNTSMAN, S. R. 1985. Dctcrmination of ir~ sitlc lateral pressure of cohesionless soils by static cone penetrometer. Ph.D. thcsis, University of California at Berkeley, Berkeley, CA. HUNTSMAN, S. R., M~TCMELL, J. K., KLEJBUK, L., and SIHINDE, S. 1986. Lateral stress measurement during cone penetration. ASCE Specialty Conference on Use of In Situ Testing in Gcotcchnical Engineering, Blacksburg, VA. JEFFERIES, M. G., STEWART, H . , THOMSON, R. A. A, , and ROBERTS, B. J. 1985. Molikpaq deployment at Tarsiut P-45. Plenary session paper, Proceedings, ASCE Specialty Confercncc on Civil Engineering in the Arctic Offshore, Arctic '85, San Francisco. MITCHELL, D. E. 1984. Liquefaction slides in hydraulically placed sands. Proceedings of 4th International Symposium on Landslides, Toronto. M. J. O'CONNOR A N D ASSOCIATES. 1982. An evaluation of the regional surficial geology of the southern Bcaufort seas. Geological Survey of Canada report. PARRY, R. H. G. 1971. Stability analysis for low embankments on soft clays. Stress-strain behaviour of soils. Roscoc Memorial Symposium, Cambridge. G. T. Foulis & Co., Henlcy-on-Thames, England. SLADEN, J. A,, D'HOLLANDER, R. D., and K R A ~ I N , J. 1985. The liquefaction of sands, a collapse surface approach. Canadian Geotechnical Journal, 22(4), pp. 564-578.

Pore pressure response of earth dams in random seismic environment

The progressive development of pore water pressure due to earthquake loading and associated loss of strength may be a major cause of instability in earth dams consisting of low to medium dense saturated sands and hydraulic fill materials. In this study a procedure is developed for the analysis of pore pressure response of an earth dam subjected to a random seismic environment. The ground motion is modelled as a portion of the stationary random process which may be defined alternatively by (a) Kani—Tajimi spectral density function, or (b) a design response spectrum. The earth dam is modelled as a series of shear slices and is considered to be homogeneous. The nonlinearity in shear modulus and damping are incorporated by using an equivalent linear model for the stress-strain behavior of soils. The dynamic response to vertically propagating shear waves is formulated in the frequency domain providing the transfer functions for various parameters, viz, stress, strain and acceleration, etc. The power spectra of these parameters are then readily obtained. Using a simple linear model for the generation of pore water pressure the expected value of associated damage is obtained. Numerical results of an example analysis and a parametric study are presented.

Advances in General Effective Stress Method for Prediction of Axial Capacity for Driven Piles in Clay

Summary Significant advances in the development of a general effective stress method for the prediction of the axial capacity of driven piles in clay are reported. These advances are in modeling and prediction of stress changes resulting from pile installation and reconsolidation after installation. Preliminary design charts (beta charts) are presented. Introduction An initial development of a general effective stress method for the prediction of the axial capacity of driven piles in clay was presented by Esrig et al. Their methodology is based on modeling, in sequence, the major events in the life of a pile (pile driving, reconsolidation after driving, and axial loading). Such an approach provides insight into the factors controlling pile capacity and should permit better estimates of pile capacity than are currently possible. possible. Two major uncertainties in the methodology were apparent in 1977:stress changes associated with pile driving were predicted from an analysis of a pile driving were predicted from an analysis of a cylindrical cavity expanded under conditions of plane strain in an elastic-plastic medium andstress changes and the stress path followed during reconsolidation of the soil surrounding the driven pile were estimated from the results of analysis of a pile were estimated from the results of analysis of a simple, mechanistic model of soil reconsolidation. Present analyses of the stress changes resulting from pile driving continue to use the model of a cylindrical cavity expanded under plane strain conditions to simulate pile driving. However, detailed consideration has been given to the use of more realistic stress-strain behavior of soil and/or to a plasticity approach to soil behavior. More refined studies have shown that, with minor modification, the simple elastic-plastic analysis is adequate.Two independent and philosophically different types of analyses of reconsolidation around a pile have replaced the mechanistic model. A closed-form elastic analysis of stress changes and the stress path followed during reconsolidation was generated first by Wroth. This analysis was generalized to permit consideration of materials with radially symmetric but variable elastic moduli by Leifer et al. The generalized elastic analysis forms the basis of the methodology presented in this paper. Subsequently, the elastic analysis was extended into the time domain by Randolph.Miller et al. were concerned about modeling soil as an elastic material during reconsolidation and produced a numerical solution for reconsolidation produced a numerical solution for reconsolidation that incorporates the concepts of plasticity and makes use of a model of soil behavior suggested by Roscoe and Burland. This work has been extended by Randolph et al.The differences between the results of the two available models are described subsequently, and the level of current uncertainty about the stress state after reconsolidation is indicated. Measurements reported by Cooke are cited that suggest that both analytical models are imperfect. A methodology for predicting axial capacity that is simpler in form than predicting axial capacity that is simpler in form than that presented by Esrig et al. is presented with the results of a verification study. The limitations of this improved methodology are described so that it can be used with appropriate caution and in conjunction with other available methods for predicting pile capacity. JPT P. 1793

Offshore Soil Sampling and Geotechnical Parameter Determination

In a study aimed at increasing the value of geotechnical analyses of piston and gravity core samples of marine sediments, nine core sampler systems were compared with each other and in-situ measurements. Conclusions are drawn regarding the extent of coring disturbance to be anticipated with each system and the applicability of two methods for correcting this disturbance. Introduction Geotechnical parameters are those characteristics of soil and rock that bear directly on the performance of engineering structures. They are the properties that determine whether a foundation will settle excessively, a pile will experience a bearing capacity failure, an anchor will pull out, or a slope supporting a structure will fail. On land, the list of pertinent geotechnical parameters is increasing steadily as more knowledge is gained about the stress-strain behavior of soil and rock and as computer codes are developed to handle increasing complexity. In the ocean we remain, in many ways, at a primitive level, designing structures so that their support anchors and foundations will not fail catastrophically. Less concern is shown during structural design toward small-scale deformations and settlements. The structures are built to withstand any smaller movements. There is, therefore, in the study of marine geotechnology, a greater interest in the soil properties that enter into the prediction of failure loads than there is on land. These failure properties generally can be summarized as shear strength, with different classes being delineated according to whether pore-water movement occurs during shear. if there is no water movement, as is generally the case in the short- and intermediate-term loading of clays, the critical parameter for use is the undrained shearing strength. If there is water movement as is generally the case with sands, the critical parameter is the drained strength, described by the friction angle. Because the risk of failure usually is much greater with clays than with sands, the undrained shearing strength of clays and other fine-grained materials can be taken as the most important single geotechnical parameter of marine soils.Undrained shearing strength has not been a simple property to measure in the hostile marine environment. Either a test device must be placed on or in the bottom to measure the property directly (in-situ test) or a sample must be brought back and tested for its strength in the laboratory. The in-situ test usually is an expensive and complicated venture involving a heavy piece of machinery equipped with electronic gear that must be maintained in one position on the seafloor for extended periods of time. Even then the soil has not been seen or felt directly, and a sample usually is required.Sampling has many problems as well. Sampling devices are somewhat crude lengths of pipe, topped with a heavy weight and dropped into the bottom. A piston attached by a line to the support vessel may be used to ride up inside the pipe and maintain the length of soil within the pipe at a level near the amount of pipe penetration into the seafloor. JPT P. 891＾

A Mechanical Model for The Stress-Strain Behaviour of Normally Consolidated Cohesive Soil

ABSTRACT A mechanical model on the stress-strain behaviour of normally consolidated cohesive soil is presented in this paper based upon the experimental results. Theoretical equations are derived based on the theory of elastoplasticity. Time effect is not taken into consideration. In the analysis, strain increment is divided into two components, i. e., elastic and plastic ones. The plastic component in strain increment is further divided into two components termed here as ƞ-component and p-component. These components of plastic strain increment occur due to effective stress increments in the directions of constant mean effective principal stress and constant stress ratio, respectively. Corresponding to two components of plastic strain increment, two sets of plastic potential, yield function and hardening function are proposed, and nonassociated flow rule is formulated. The strain increments due to the effective stress increments in various directions are calculated by this theory. The model thus obtained for the stress-strain behaviour of soil reasonably explains the dependency of the direction of plastic strain increment on that of effective stress increment. This model is applied to the analyses of triaxial drained shear tests along various stress paths and satisfactory result is obtained. The stress-strain behaviour by this model is compared with those obtained by theories by Roscoe et al. (1963, 1968) and Calladine (1971). Discussion on the stress-strain behaviour of soil predicted by these theories including the author’s one is given.

Plasticity Theory for Soil Stress-Strain Behavior

A general analytical model that describes both drained and undrained, anisotropic, elastoplastic, path-dependent stress-strain-strength properties of inviscid saturated soils is presented. For any loading (or unloading) history, the instantaneous configuration of the field of yield surfaces is determined by calculating the translation and contraction (or expansion) of each yield surface during successive changes in load. The material behavior can thus be determined for complex, and, in particular, for cyclic loading paths. The inverse stress-strain relations always exist and are uniquely defined if and only if the yield surfaces do not overlap. In order to avoid such overlappings, a new isotropic/kinematic hardening rule is introduced which couples the simultaneous translation of consecutive surfaces. The isotropic/kinematic hardening of the outer surfaces is thus made compatible with any isotropic/kinematic hardening rule assumed for the inner surfaces.

Pore pressures near moving underwater slope : 5F, 1T, 15R. Meijer, KL, Delft Hydr. Lab., Delft, NL Van Os, Ag, Delft Hydr. Lab., Delft, NL J. Geotech. Engng Div. ASCE, V102, GT4, 1976, P361–372

Pore pressures near a moving boundary of a saturated soil mass are calculated and compared with tests. For a more realistic approximation of the stress-strain behavior of soil, a dilatancy effect has been introduced that is based upon Rowe's stress-dilatancy relation and the assumption of a linear relationship between the principal stress ratio and the major principal strain. The field equations for the problem have been transformed to account for the traveling boundary. A psuedo three-dimensional consolidation theory is used to describe the fulid-soil skeleton interaction. The results of the computations were compared with pore-pressure measurements and showed reasonable agreement if dilatancy was taken into account. /ASCE/

Pore Pressures Near Moving Underwater Slope

Pore pressures near a moving boundary of a saturated soil mass are calculated and compared with tests. For a more realistic approximation of the stress-strain behavior of soil, a dilatancy effect has been introduced that is based upon Rowe’s stress-dilatancy relation and the assumption of a linear relationship between the principal stress ratio and the major principal strain. The field equations for the problem have been transformed to account for the traveling boundary. A psuedo three-dimensional consolidation theory is used to describe the fluid-soil skeleton interaction. The results of the computations were compared with pore-pressure measurements and showed reasonable agreement if dilatancy was taken into account.