Showing papers in "Journal of Geotechnical Engineering in 1991"

Effect of Soil Plasticity on Cyclic Response

Abstract: A study on the influence of the plasticity index (PI) on the cyclic stress‐strain parameters of saturated soils needed for site‐response evaluations and seismic microzonation is presented. Ready‐to‐use charts are included, showing the effect of PI on the location of the modulus reduction curve G/Gmax versus cyclic shear strain γc, and on the material damping ratio λ versus γc curve. The charts are based on experimental data from 16 publications encompassing normally and overconsolidated clays (OCR=1-15), as well as sands. It is shown that PI is the main factor controlling G/Gmax and λ for a wide variety of soils; if for a given γc PI increases, G/Gmax rises and λ is reduced. Similar evidence is presented showing the influence of PI on the rate of modulus degradation with the number of cycles in normally consolidated clays. It is concluded that soils with higher plasticity tend to have a more linear cyclic stress‐strain response at small strains and to degrade less at larger γc than soils with a lower PI. ...

Formulas and charts for impedances of surface and embedded foundations

Abstract: A complete set of algebraic formulas and dimensionless charts is presented for readily computing the dynamic stiffnesses (\IK\N) and damping coefficients (\IC\N) of foundations harmonically oscillating on/in a homogeneous half-space. All possible modes of vibration, a realistic range of Poisson’s ratios, and a practically sufficient range of oscillation frequencies are considered. The foundations have a rigid basemat of any realistic solid geometric shape. The embedded foundations are prismatic, having a sidewall-soil contact surface of height \Id\N, which may be only a fraction of the embedment depth \ID\N. Two numerical examples illustrate the use of the formulas and charts and elucidate the role of foundation shape and degree of embedment on radiation damping for various modes of vibration. A companion paper (Gazetas and Stokoe 1991) presents supporting experimental evidence from model tests. The two papers aim at encouraging the practicing engineer to make use of results obtained with state-of-the-art formulations, when studying the dynamic response of foundations.

Stability Evaluation during Staged Construction

Abstract: Staged construction uses controlled rates of load application to increase the foundation stability of structures founded on soft cohesive soils and to improve the slope stability of tailings dams. Because construction causes positive excess pore pressures and because actual failures usually occur without significant drainage, stability analyses should compute the factor of safety against an undrained failure as the most critical and realistic condition. This requires an undrained strength analysis (USA) that treats predicted or measured in situ effective stresses as equal to consolidation stresses in order to calculate variations in undrained shear strength during construction. The recommended USA methodology requires a detailed evaluation of changes in vertical stress history profiles, uses undrained strength ratios obtained from CK0U tests to account for anisotropy and progressive failure, and is more rational than stability evaluations based on UU and CIU triaxial compression testing. Conventional effe...

Diffusion in Saturated Soil. I: Background

Abstract: Recent studies suggest that diffusion may be an important, if not dominant, mechanism of contaminant transport through waste containment barriers. This paper represents the first of two papers pert...

The Mechanical Aging of Soils

Abstract: Soils age Their engineering properties often improve significantly during aging times of practical interest to engineers This paper provides examples from research and practice It includes a review of the triaxial IDS test, followed by examples of its use to investigage the question of whether the aging improvements result from frictional or cohesive effects Contrary to most current thinking, the soil stiffening and strengthening appears entirely frictional in effect The aging effects described appear mechanical, resulting from dispersive particle movements and internal stress arching under drained conditions The paper concludes with suggestions for using these mechanical aging effects in practice

Pb(II) Removal from Kaolinite by Electrokinetics

Abstract: Electro-osmosis tests are conducted on saturated kaolinite specimens loaded with Pb(II) to investigate the efficiency and energy requirements of the process in removing this heavy metal. Kaolinite specimens were loaded with 118 μ\Ng to 145 μ\Ng of Pb(II) per gram of dry soil, below the cation-exchange capacity of the mineral. The test results pertaining to the flow and the associated electrochemistry (voltage, current, resistance, pH gradients, and conductivity) are presented. The flow in electro-osmosis with open electrodes is time-dependent, and it is strongly influenced by electrochemistry resulting from the pH gradients. The adsorbed Pb(II) was removed 75–95% by the process. The extent of removal is directly related to the pH gradients developed in the process. The total charge passed to remove Pb(II) varied between 1,400 and 2,000 amp-hr per cubic meter of soil. The energy requirement for the removal of Pb(II) in these tests was less than 29 kwhr–60 kwhr per cubic meter of soil processed.

Three-dimensional nonlinear study of piles

Abstract: The main objective of this work is to examine the effect of nonlinear soil behavior on the axial and lateral response of piles to monotonic and cyclic loading with a view towards developing simplified, yet realistic models for representing pile‐soil‐pile interaction effects. The specific role of pile‐soil slippage and separation, and the overall nonlinear soil behavior on the response of single piles and pairs of piles is studied by means of a three‐dimensional finite element elastoplastic model that includes interface elements for representing slippage and pile‐soil separation. Numerical results indicate that material nonlinearity can significantly affect pile and soil response. Pile‐soil slippage is dominant under purely axial loading, while for lateral loads pile‐soil separation and generalized inelastic soil deformation are the crucial factors. In fact, ignoring these sources of nonlinearity can lead to greatly overestimating the amount of interaction between piles. Guided by the results of this work,...

Simplified design for vibration screening by open and in-filled trenches

Abstract: Rectangular open or in‐filled trenches (wave barriers) are often used in engineering practice to reduce the ground vibrations caused by propagating surface (Rayleigh) waves of relatively small wavelengths. This paper presents simple design expressions for estimating the vibration screening effectiveness of rectangular wave barriers in homogeneous soil deposits. The design formulas are developed by conducting an extensive numerical investigation on the influence of various geometrical and material parameters on the vibration screening effectiveness of the barriers. An advanced direct Boundary Element Method (BEM) incorporating higher‐order isoparametric elements and a sophisticated self‐adaptive numerical integration scheme is used for this study. Dimensionless parameters that govern a barrier's performance are then identified, and models are developed taking these parameters into account in a simplified way. Through some comparisons with results from the rigorous BEM code and available experimental data, ...

Diffusion in saturated soil. ii: results for compacted clay

Abstract: The effective diffusion coefficients, \ID\N*, of three anions (Br\u-, Cl\u-, and I\u-) and three cations (Cd²\u+, K\u+, and Zn²\u+) diffusing in two compacted clay soils, kaolinite and Lufkin clay, are measured. The ions are contained in a simulated waste leachate. The effects of molding water content and method of compaction on the measured \ID\N* values are evaluated for kaolinite. The calculated \ID\N* values varied between 4 × 10\u-¹\u0 m²/s and 2 × 10\u-\u9 m²/s and, based on the results for chloride diffusion in kaolinite, are relatively insensitive to molding water content and compaction method. The measured \ID\N* values for Cl\u- and Br\u- in kaolinite are in excellent agreement with previous studies, but the \ID\N* values for the cations are relatively high. High \ID\N* values for the cations are attributed to nonlinear adsorption behavior at relatively high concentrations and to the possibility of chemical precipitation of the heavy metal species (Cd²\u+ and Zn²\u+). Also, \ID\N* values determined from reservoir concentrations typically are higher than \ID\N* values determined from soil concentration profiles.

Smear effects of vertical drains on soft bangkok clay

Abstract: Smear effects due to the installation of prefabricated vertical drains were studied in the laboratory using special equipment and in the field using a full‐scale test embankment. The prefabricated vertical drains were installed by two different sizes of mandrel. The test results showed that the smear zone can be assumed to be twice the equivalent mandrel diameter and the horizontal permeability coefficient in the smeared zone, kh′, was approximately equal the vertical permeability coefficient in the undisturbed zone, kv. A faster settlement rate and higher amounts of compression were observed in the small mandrel area than in the large mandrel area, suggesting lesser smear effects in the former than in the latter. The total settlement prediction using the method of Skempton and Bjerrum of 1957, with stress distribution using Poulos's 1967 method, yielded reasonable agreement with the observed values. More accurate settlement‐rate predictions can be obtained using Asaoka's 1978 method when the prediction w...

Kinematic Seismic Response of Single Piles and Pile Groups

Abstract: This paper presents a comprehensive set of dimensionless graphs that could be readily utilized in practical applications A comparative study of these graphs leads to interesting conclusions that may contribute towards an improved appreciation of the nature of seismic pile-soil-pile interaction The graphs should be of practical value in determining the 'effective' seismic input motion at the base of structures, if the free-field motion is known The discussion of the study results focuses on elucidating the role of the key parameters, and aims at developing engineering insight into kinematic soil-pile and pile-pile interactions during earthquakes

Earthquake‐Induced Permanent Deformations: Probabilistic Approach

Abstract: A simple procedure for estimating earthquake‐induced permanent deformations of earth dams, embankments and slopes is presented. The analytical model is based on computed permanent deformations obtained by using Newmark's sliding‐block analysis and actual recorded acceleration time histories. The model incorporates the effect of earthquake magnitude through the use of equivalent uniform cycles of motion. Uncertainties in the model and the parameters used are accounted for through the use of modeling error theory. Normalized plots and a computer program are presented that provide the probability that the permanent deformation of a critical sliding mass will exceed a specified value. The results from this probabilistic procedure can be expressed in terms of damage probabilities in the form of a seismic performance analysis matrix. The use of a seismic performance analysis matrix in an overall seismic risk analysis for an earth dam, embankment or a slopes is described in a companion paper.

Modified vlasov model for beams on elastic foundations

Abstract: Realizing the inadequacy of the classical Winkler model to represent an elastic continuum, Vlasov and Leont'ev developed a two‐parameter model for a beam on an elastic foundation. The Vlasov model required an estimation of a parameter, 7, that controls the decay of stresses in the continuum. Vallabhan and Das developed a unique iterative technique to determine a consistent value of the y parameter. Their model is called a “modified” or “refined Vlasov” model. Here, the finite different technique is employed to solve the fourth‐order differential equations. The results of sample problems obtained by using the modified Vlasov model are compared with more sophisticated finite element solutions.

Combining Industrial Wastes with Lime for Soil Stabilization

Abstract: Using a geotechnical viewpoint, this paper proposes a potential, partial solution to solve some of the problems posed by increasing amounts of certain types of sludgy industrial waste. The primary objective of this study is to examine the potential for burning various industrial wastes combined with lime, in certain proportions, to produce a by-product having cementing characteristics similar to ordinary portland cement (OPC). It is found that the percentages of main cementitious compounds in this new cement-like stabilizer are comparable to those of OPC. The by-product also shows promise for use in stabilizing a loam soil. The contribution of ettringite to strength development is discussed. It is found that this new type of additive can be used to stabilize loam soil for subgrade purposes.

Hyperbolic method for consolidation analysis

Abstract: The analysis of consolidation in the field is not easy, because the soil properties are often difficult to determine, especially when the clay deposit is very soft and nonhomogeneous. To monitor th...

Uplift behavior of screw anchors in sand. i: dry sand

Abstract: Experimental and theoretical investigations on the behavior of single‐screw helical anchors in sand are presented. A testing program included 56 tests conducted on five model anchors installed in dense, medium, and loose dry sands. A sand‐placing technique was developed and utilized over the testing program in order to achieve the predetermined unit weight. The experimental setup was instrumented to allow the measurement of the pullout load, the upward displacement of the anchor, and the deflection of the sand surface. It was observed that the failure mechanism as well as the pullout load varied with the installation depth of the anchor and the angle of shearing resistance of the sand. A mathematical model is developed using the limit‐equilibrium method of analysis and the observed failure mechanism of the anchor from the present experimental work. Based on experimental results, a simple equation is proposed to introduce the degree of shear mobilization on the coefficient of passive earth pressure. Compar...

Performance of axially loaded pipe piles in sand

Abstract: This paper summarizes the parameters that influence the axial capacity of pipe piles driven into sands. The parameters that affect pile behavior are for convenience divided into four categories: (1) Soil characteristics; (2) pile characteristics; (3) method of pile installation; and (4) type of loading. When possible, the influence that these parameters have on the capacity is quantified. In addition, the paper describes supporting evidence from pile load test data, small‐scale laboratory tests, and in situ cone probings that has been used to justify limiting values for unit shaft and toe resistances. The use of limiting values has significant economic impact on long piles, especially those used for offshore applications. This information is, therefore, evaluated and critiqued to place the use of limiting values in proper perspective. The results of this paper are based on a synthesis of literature on (1) pile load test data on piles in sand, (2) data from cone penetrometer tests in sands, and (3) informa...

Dynamic interaction factors for floating pile groups

Abstract: A comprehensive set of dimensionless graphs of complexvalued dynamic interaction factors versus frequency is presented for vertical, horizontal, and rocking harmonic excitation at the head of each ...

Three-dimensional analysis of traffic-induced ground vibrations

Abstract: A new numerical method is introduced to analyze traffic‐induced ground vibrations three‐dimensionally on the basis of a dynamic elastic finite element method. A set of examples are examined to investigate the effect of pavement structures on reduction of ground vibrations. This technique, using an extended thin‐layered element method, can account not only for irregularities in near fields, including pavement structures, but also for traveling waves to far fields. Furthermore, weights, velocities, intervals, and vibrating conditions of vehicles can be taken into account. Now, given that moving loads are composed of static and dynamic components, the analytical results indicate that the dynamic component is a much more significant factor in causing ground vibrations than the static components. It is understood from the results that pavement structures have a large influence on ground vibrations, and that stiffness and damping of the pavement materials are the important factors. This statement confirms that ...

Finite Element Analyses of HDR‐4 Excavation

Abstract: Simulations of construction of a 40-ft-deep braced excavation in saturated clays in Chicago have been made using a coupled finite element formulation. Surface and subsurface ground movements, pore water pressures, and sheet-pile deflections are measured throughout construction at the site and are compared to results of the simulations at key stages of the excavation. The finite element simulations closely modeled all phases of construction including sheet-pile installation and the actual duration of construction. Computed sheet-pile deformations agreed quite well with those observed throughout all stages of excavation and bracing. Soil deformations, ground surface settlements, and pore pressures agreed reasonably well with observations until an incipient shear surface developed within the soil mass as the unsupported height of the wall reached as much as 19 ft. Parametric studies assess the importance of modeling the sheet-pile installation, the effects of different types of assumed constitutive responses, the impacts of assumed boundary conditions, and importance of closely modeling the actual construction process. The importance of the available resistance of the soil on the passive side of the excavation in controlling ground movements is demonstrated. Anisotropy is a factor that must be considered when evaluating potential ground movements associated with a proposed excavation through soft to medium clays.

Dielectric Method for Prediction of Porosity of Saturated Soil

Abstract: The electromagnetic theory of Maxwell‐Fricke for the electrical conduction through heterogeneous media is extended to develop a theoretical relationship for fluid‐saturated porous media, accounting for the orientation of particles, the porosity and the dielectric constants of the pore fluid, the solid phase and the mixture. Based on this relationship, it is shown that a knowledge of the dielectric constants of saturated soils in the horizontal and vertical directions at high frequencies around 50 MHz provides the necessary data for the evaluation of the porosity for most soils when the dielectric constants of the particle and the solution are known. The method provides a rapid means for laboratory evaluation of the porosity of any saturated soil. It may also be adopted to in situ evaluations of the porosity of any saturated soil.

Stress ratio effects on collapse of compacted clayey sand

Abstract: A“double‐triaxial” test procedure similar to the double‐oedometer test was developed to determine the wetting‐induced collapse potential of soils subjected to anisotropic stress states. Based on a series of double‐triaxial tests performed on a slightly expansive clayey sand, it was established that the magnitude of volumetric strain resulting from a change in stress state or from wetting depends on mean normal total stress and is independent of principal total stress ratio. The individual components of axial and radial strain, however, depend significantly on stress ratio. For a given mean normal total stress, axial collapse increases and radial collapse decreases with increasing stress ratio. Comparison of oedometer and triaxial results indicates that the ratio of horizontal to vertical effective stress after wetting under zero‐lateral‐strain conditions varies as a function of the wetting‐induced axial strain. In the swell region, effective lateral stresses tend toward active, and in the collapse region ...

Free vibration of embedded foundations : theory versus experiment

Abstract: Comprehensive experimental results of 54 free-vibration tests on model footings embedded at various depths in moist dense sand and having circular, square, and rectangular base shapes were reported by Erden and Stokoe in 1974 and 1985. The results for vertical and coupled swaying-rocking oscillations are used in this paper to verify the homogeneous-half-space solutions given in a companion paper published by Gazetas in 1991 in the form of algebraic formulas and graphs for dynamic stiffnesses and damping factors. Particular attention is accorded to selecting appropriate values of the effective S-wave velocity, using either Erden’s original measurements and recommendations of 1974 or the measured response of the corresponding surface footings. It is demonstrated beyond significant doubt that: (1) The lower value of shear modulus around the footing sides and slippage at the footing side-soil interface may have contributed to not more than 25% of the shortfall in the experimental values; and (2) boundary wave reflections, primarily at the vertical interface between the sand and the high-damping soft boundary layer, are responsible for at least 75% of the observed discrepancies, having essentially eliminated the contribution to radiation damping from the swaying component of motion.

Load transfer for pipe piles in highly pressured dense sand

Abstract: Large-scale loading tests were conducted on closed-toe and open-toe piles driven into dense submerged sand confined in a pressure chamber. Unit load-transfer relations were developed and related to stress conditions in the chamber. Ultimate shaft resistance in compressional loading was found to be approximately equal to the ambient lateral effective stress in the chamber before driving, and was generally not dependent on the geometry of the toe. From this observation it can be inferred that because of installation and loading effects the operative earth-pressure coefficient on the pile shaft approximately doubled from the ambient value that existed before driving. In uplift, ultimate shaft resistance was about 20% lower than in compression, regardless of depth. The open-toe piles consistently remained plugged during static testing but nonetheless exhibited lower bearing capacity than the closed-toe piles. This can be explained by deformation and compression of the soil within the plug as a means of effectively reducing the rigidity index of the soil against which the toe bears.

Estimation earth pressures due to compaction

Abstract: When soil is compacted in layers by rollers, vibrating plates, or rammers, the horizontal earth pressures within the compacted soil mass are increased. Charts are presented that can be used to estimate compaction‐induced earth pressures quickly and reliably. These charts are developed using the hysteretic theory developed by Duncan and Seed, with a computer program called EPCOMP2. The charts offer the advantages of being easy to use, and providing very rapid results, while retaining most of the accuracy of the detailed computer analyses. Because earth pressures can be estimated quickly, it is easy to evaluate the effects of changes in the factors that influence the magnitudes of the compaction‐induced earth pressures. Comparisons of earth pressures calculated using these charts with the results of computer analyses indicate that the values calculated using the charts are sufficiently accurate for practical purposes. Field measurements of compaction‐induced earth pressures indicate that the horizontal eart...

Design of wave barriers for reduction of horizontal ground vibration

Abstract: Wave barriers are often installed in the ground to reduce high-frequency ground vibrations induced by man-made sources such as traffic or machine foundations. This type of ground vibration could be a major problem in densely populated urban areas and for structures housing sensitive equipments. This paper investigates the effectiveness of rectangular wave barriers (solid obstacles) in reducing the horizontal ground vibration caused by propagating surface waves. A rigorous boundary element method (BEM) algorithm incorporating higher-order elements is used to conduct an extensive numerical study of the influence of various key geometrical and material parameters on the screening efficiency of a rectangular barrier. Important dimensionless parameters are identified. Based on the influence of these parameters, a simple model is developed for the design of wave barriers for horizontal vibration screening. Finally, some numerical examples are presented and through comparisons with results from the rigorous BEM technique, the applicability and usefulness of the developed model is established.

Effects of saturation and back pressure on sand liquefaction

Abstract: The influence of saturation and back pressures on the liquefaction resistance of a sand is investigated by conducting cyclic triaxial tests on four sets of sand samples with different degrees of saturation and on five sets of samples with different back pressures. The tested sand is taken from the site of Tong Jaizhi Water Power Station in China. Test results show that the conspicuous effect of saturation on the liquefaction resistance of the tested sand cannot be improved by keeping back pressures on samples during the test. On the other hand, the application of back pressures otherwise results in higher liquefaction resistance. The effect of back pressures is further explained by analyzing the internal interaction of soil particles. It is concluded that the back pressure method should not be used in cyclic liquefaction tests for improving the degrees of saturation of sand, and Terzaghi’s effective stress principle is not valid unless additional conditions are included for the actions of interparticle forces in soils.

Bearing Capacity of Eccentrically Obliquely Loaded Footing

Abstract: The bearing capacity of an eccentrically obliquely loaded footing is determined by limit equilibrium analysis. The footing is considered rigid with a rough base. It is assumed that the rupture surface is a log spiral and that failure occurs on the same side as the eccentricity, with respect to the center of the footing. The resistance mobilized on this side is fully passive and partial on the other. The footing is assumed to lose contact with an increase in eccentricity; the results are given in the form of bearing capacity factors, \IN\N\dγ, \IN\dq\N, and \IN\dc\N. For the verification of analytical solutions, model tests were conducted on sand. Footings were tested both at the surface and at a depth such that \ID\df/B\N = 0.5, eccentricity of load ranged from 0.1\IB\N to 0.3\IB\N, and inclination of load varied from 5° to 20°, in which \ID\df\N and \IB\N are, respectively, depth and width of footing. The results of the previous investigators are also analyzed and compared with the proposed theory. A reasonable agreement was found between the theory and the test data.

Modeling One‐Dimensional Compression Characteristics of Soils

Abstract: This Technical Note proposes an extended power function for modeling one-dimensional compression of normally consolidated and overconsolidated soils. The function has 3 parameters, and a single set of these parameters is sufficient for representing void ratio-effective stress relations from zero effective stress to any desired stress level. The model proposed by Hardin (1989) is discussed, and it is noted that both models have problems in fitting data of highly sensitive clays, but from the limited comparison presented in the paper, it appears that for these cases Hardin's model is more suitable.