Showing papers in "Journal of Geotechnical Engineering in 1988"

Lime-Induced Heave in Sulfate-Bearing Clay Soils

Abstract: Expansive reactions between lime and sulfate-bearing clay soils have attracted little attention until relatively recently. Lime treatment of Stewart Avenue in Las Vegas, Nevada, had induced heave in excess of 12 in. Heaved areas are found to contain abundant thaumasite, a complex calcium-silicate-hydroxide-sulfate-carbonate-hyd rate mineral. Thaumasite forms a solid solution series with ettringite, a calcium-aluminum-hydroxide-sulfate-hy drate mineral. In the presence of aluminum, ettringite forms first and is replaced by thaumasite only at temperatures below 15°C. The mechanism of heave is a complex function of available water, the percentage of soil clay, and ion mobility. Only the long-term possolanic chemistry of normal lime-soil reactions is disrupted. Cation exchange, agglomeration, and carbonation are unaffected. With the present state of knowledge, lime-induced heave is difficult to predict for all but most obvious conditions.

Lateral Load Behavior of Pile Group in Sand

Abstract: A large‐scale group of steel pipe piles and an isolated single pile were subjected to two‐way cyclic lateral loading. The tests were conducted in a submerged firm to dense sand that was placed and compacted around the piles. All of the piles were extensively instrumented so that the variation in soil resistance within the group could be determined. The response of the piles in the group was also compared with the response of the isolated single pile. The loss of efficiency of the piles in the group was related principally to “shadowing” (i.e., the loss of soil resistance of piles in the trailing rows). Piles in the leading row supported a large proportion of the group load and behaved similarly to the isolated single pile. Two‐way cyclic loading had little effect on the distribution of load to the piles in the group, but tended to densify the sand around both the single pile and the group piles.

Regression Models For Evaluating Liquefaction Probability

Abstract: Statistical models are developed to express the probability of liquefaction as a function of earthquake load and soil resistance parameters. Results are obtained based on a catalog compiled for this study, which consists of 278 cases of liquefaction/nonliquefaction occurrences. A method of binary regression is used to derive four models recommended for use in assessment of liquefaction probability. Two of them use the cyclic stress ratio (Seed and Idriss 1971) as the earthquake load parameter; the other two use, as load parameters, explicit functions of earthquake magnitude and distance, similar to the function proposed by Davis and Berrill (1981). All four models measure liquefaction resistance through the corrected/normalized SPT (N1)60 value. Recommendations for practical implementation are provided, and comparisons are made with other methods of liquefaction analysis.

Undrained Monotonic and Cyclic Strength of Sands

Abstract: Results of torsional shear tests on specimens of reconstituted 20-30 Ottawa sand are presented to resolve inconsistencies in prevailing interpretations of previously published test results regarding: (1) the conditions leading to limited or steady-state flow deformation under monotonic loading; and (2) the state conditions marking the initiation of strain softening behavior under either monotonic or cyclic undrained loading. It was found that the effective stress path in monotonic undrained shear appears to constitute a state boundary that controls the initiation of strain softening under undrained cyclic shear loading. Evidence is presented in support of a new concept of the collapse of sand fabrics. It is used to explain the sudden increase in pore-water pressure associated with the initiation of strain softening behavior on loading, or with the development of a condition of zero effective stress after repeated cyclic unloadings beyond a critical level of mean effective normal stress. The concept also explains why steady-state conditions in drained shear are not necessarily the same as in undrained shear. The implications of the new findings on the determination of the liquefaction potential of sands are discussed.

Initiation of Soil Liquefaction Under Static Loading Conditions

Abstract: Liquefaction of loose, saturated sands may be caused by cyclic or static (monotonically increasing) undrained loading. Most previous studies of static liquefaction behavior have emphasized liquefaction susceptibility and the behavior of liquefied soils. An experimental investigation is undertaken to evaluate the stress conditions required to initiate liquefaction and the influence of various parameters on those stress conditions. The static liquefaction resistance, defined as the shear stress increase under undrained conditions required to initiate liquefaction, is observed to increase with increasing relative density and confining pressure, and to decrease dramatically with increasing initial shear stress level. At high initial shear stress levels, initiation of liquefaction is observed to result from increases in shear stress under undrained conditions of only a few percent of the initial shear stress. The distinction between the initiation and the effects of liquefaction is discussed, and an expression for a factor of safety against the initiation of liquefaction is proposed.

Degradation of marine clays under cyclic loading

Abstract: A study of the effect of the overconsolidation ratio (OCR) on the cyclic shear modulus degradation of clay is presented. The research is based on a series of strain‐controlled, constant‐volume, cyclic, simple‐shear tests conducted on samples of an offshore Venezuelan clay consolidated to OCR=1, 2, and 4. The modulus degradation with number of cycles is successfully modeled for different OCR's using an expression applied previously to normally consolidated clays. The rate of cyclic modulus degradation decreases with increased OCR, and the dynamic stress‐strain backbone curves can be modeled by an extension of the SHANSEP method originally suggested for normalizing static stress‐strain curves. A chart is also developed for normally consolidated marine clays from Venezuela, California, and Alaska, which indicates that the modulus degradation rate parameter t, corresponding to a given cyclic strain, is similar for similar clays, with t decreasing as the plasticity of the clay increases. Also, a comparison bet...

Measured and predicted axial response of 98 piles

Abstract: This article deals with the prediction of the response to monotonic axial loading of single piles in various soil conditions. A 98-pile load test data base was obtained from the Mississippi State Highway Department and was used to evaluate 13 methods designed to predict the ultimate load of a pile and five methods designed to predict the settlement of a pile. The methods include SPT/\IS\du\N methods, cone penetrometer methods, a pressuremeter method, and a dynamic formula method. The accuracy and precision of each method is quantified statistically, and a risk analysis is performed in order to properly assess the factor of safety. A cost analysis is also performed in order to find the factor of safety that will minimize the cost of construction plus the cost of a potential failure.

Uplift behavior of horizontal anchor plates in sand

Abstract: The influence of anchor geometry, embedment, and soil density on the uplift capacity of one‐meter prototype anchors is investigated by subjecting 25‐mm models to an acceleration of 40 g in the Liverpool centrifuge. Uplift resistances expressed as dimensionless breakout facctors increase significantly with anchor embedment and soil density but reduce with increased aspect ratio. Failure displacements also increase with embedment but reduce with increased soil density and aspect ratio. The influence of anchor geometry is relatively insensitive to anchor size but increases with both embedment ratio and soil density. In general, the design approaches considered underestimate the observed capacity of one‐meter strip anchors in dense sand, although predictions using the Meyerhof and Adams and Rowe and Davis theories are acceptable. However, both these approaches appear overoptimistic for anchors in looser sand. In this case, Vesic's theory gives the closest agreement, while the formula of Majer yields overly co...

Study of soil-root interaction

Abstract: Soil reinforcement by roots is studied by considering the contribution of the tensile force in a root segment that intersects a potential slip surface in a soil‐root system. To evaluate the tensile force when the system is subjected to a shear displacement, the root segment is analyzed as a beam on elastic‐plastic support and as a cable for small and large displacements, respectively. Equilibrium and displacement compatibility at a branch point are used to analyze the distribution of forces between two root branches of a root system. Laboratory model tests and in situ root tests were performed to verify the analytical models. The analytical models and in situ root tests are used as means of evaluating the shearing resistance of the reinforced soil.

Three-dimensional stability analysis of concave slopes in plan view

Abstract: This paper proposes a simple, practical method of threedimensional stability analysis for concave slopes in plan view using the equilibrium concept. The force equilibrium and the moment equilibrium...

Constitutive Parameters Estimated by Plasticity Index

Abstract: A large testing program, consisting of triaxial compression, triaxial extension, and oedometer tests on 12 artificially prepared soils was performed. The soils exhibited a wide range in plasticity index, from 10 – 55. These tests were performed to study whether it is possible to determine parameters specifying a constitutive soil model simply by using the plasticity index. Linear correlations between the soil parameters for constitutive equations and the plasticity index were obtained with high values noted in the coefficients of correlation. Numerical illustrations to check the overall accuracy of the correlations were also developed. Direct application of these correlations to undisturbed natural clays will require further research.

Cyclic soil data for design of gravity structures

Abstract: The paper begins with a brief overview of some of the foundation design problems for gravity structures subjected to combinations of static and cyclic loads under undrained conditions and specifies soil data needed to analyze these problems. The paper then presents results from undrained triaxial and direct simple shear tests with various combinations of static and cyclic shear stresses on Drammen clay and describes how the data needed in the analysis can be derived from these tests. The results provide general knowledge about soil behavior under cyclic loading and constitute a database which can be used to determine soil parameters for early feasibility studies of gravity structures on clay. The database can also guide in setting up laboratory testing programs for soils from actual sites and provide a framework for interpretation of the results from such testing. Further, the results in the database can be used to develop and to check the validity of theoretical models.

In‐Situ Shear Test of Soil‐Root Systems

Abstract: In situ shear tests were performed on soils reinforced by roots. Analytical models of soil‐root interaction presented in a companion paper were used to compute the forces in the roots and the contribution of the roots to the shearing resistance of the soil‐root system. General agreement between measured and computed shearing resistances was taken as verification of the analytical models. Results of the computations also showed the influence of the dimensions of the shear box on the measured shear strength. The shear strengths measured by the in situ tests were found to be less than the shear strength along a potential slip surface in slope stability problems. Methods for estimating the shear strengths for stability analysis are presented.

Prediction of Field Collapse of Soils Due to Wetting

Abstract: A series of oedometer tests are used to provide data for a quantitative prediction of soil collapse. A full scale field test is conducted to provide a benchmark for comparison with laboratory test results and predictions. It is then found that the amount of field collapse can be accurately predicted using the procedure prescribed herein, provided that the extent of wetting is known.

Centrifuge modeling of transport processes for pollutants in soils

Abstract: The physico-chemical processes of advection, dispersion, adsorption, and degradation that control pollutant transport processes in groundwater are described. Dimensional analysis is presented, and the scaling requirements for centrifuge modeling of these processes is developed. The validity of these scaling laws is examined by conducting modeling of models tests using several types of soils in idealized models of one-dimensional flow situations. The importance of scaling gravity (by using a centrifuge) is highlighted. The centrifuge permits simulation of prototype stress levels and thus makes it possible to obtain identical soil properties such as permeability in a small-scale model as compared to a full-scale soil deposit. Simulation of capillary effects and a phreatic surface is also possible in a centrifuge model, but not in a 1-g scale model. It is concluded that the scaling laws are valid for adsorption and advection in the reported model tests, but in coarse-grained soils where the Peclet number is often greater than one, the dispersion process cannot be directly scaled from model to prototype. Even if direct scaling is not possible, the centrifuge is a useful tool for providing data to test or verify numerical models, since full-scale test data are not abundant, and the full-scale boundary and site conditions are poorly defined.

Vertical and torsional vibration of foundations in inhomogeneous media

Abstract: A study of the dynamic impedances for radially inhomogeneous, infinite viscoelastic layers with a circular hole, and for piles embedded in a medium represented by such layers is made. Systems in vertical and torsional modes of vibration are examined considering both a discontinuous variation in shear modulus and an exponentially increasing, continuous variation. The results are evaluated over wide ranges of the parameters involved and compared with those obtained for a homogeneous layer. In addition, the harmonic response of strip foundations supported at the surface of a vertically inhomogeneous viscoelastic half‐space is examined, and it is shown that within the framework of a previously proposed approximation, the impedances of such foundations for both horizontal and vertical modes of vibration may be deduced from those obtained for the vertically excited, radially inhomogeneous layer.

Bearing capacity for foundations with cyclic loads

Abstract: The paper presents a procedure to calculate the bearing capacity for foundations subjected to a combination of static and cyclic loads under undrained conditions. The term cyclic shear strength is defined, and laboratory tests are used to show how this strength and the type of failure of a soil element depend on the average and cyclic shear stresses and the number of load cycles. The calculation procedure is based on the strength determined from laboratory tests. It ensures strain compatibility of the soil elements along the potential failure surface and accounts for redistribution of average stresses during undrained cyclic loading. The procedure gives the failure load, the location of the critical failure surface, and indicates whether the foundation failure will occur as large cyclic displacements, large average displacements (e.g. settlements), or a combination of the two. The paper also presents examples with numerical values of cyclic shear strengths from triaxial and DSS laboratory tests on Drammen clay, both for given number of cycles and for typical storm loading.

Rational wave equation model for pile-driving analysis

Abstract: A one-dimensional wave equation model for pile-driving analysis is presented. In this model, the pile is represented by discrete elements, while the soil is represented by a series of springs and dashpots, the coefficients of which are derived using elasto-dynamic theory. The soil model incorporates the loss of wave energy to the soil through radiation or geometric damping. In addition, the effect of the increase in soil resistance to failure when subjected to rapid loading is taken into account. The capability of the proposed model is demonstrated by comparison with field data of two instrumented piles. The analyses include predictions of set, and driving stresses at various levels of the piles. Comparisons are made with the sets and driving stresses predicted by the Smith (1960) model. From the analyses by the proposed model and load test results, estimations of soil setup for the two piles are also presented.

Tension Crack Development in Soils

Abstract: A model is proposed for finite‐element modeling of tension crack propagation in soils. The essential features of this model are the splitting of a single node into two distinct nodes in the wake of an advancing crack tip to replicate separation of material on either side of the crack, and the use of a fracture mechanics criterion to predict crack propagation. The material parameter employed in this criterion, the critical energy release rate, is determined experimentally and shown to be reasonably constant over a range of crack lengths, thereby supporting the adoption of this parameter as a material constant for tension cracking in soils. The model is then applied to two classes of problems in which tension cracking is known to exercise significant influence, a stiff embankment on soft soil and an excavated slope. For both problems, stable and reasonable solutions are obtained, suggesting that fracture mechanics offers a feasible approach to the analysis of tension cracking in soils.

Settlement Response of Soft Soils Reinforced by Compacted Sand Columns

Abstract: Stone/compacted sand columns is a technique of soil reinforcement that is frequently implemented in soft cohesive soils to increase the bearing capacity of the foundation soil, to reduce the settlement, and to accelerate the consolidation of the surrounding saturated soft soil. The soil‐column interaction depends on several parameters, including the loading process and the loading rate, the replacement factor, the group effect, and the partial consolidation of the soft soil due to radial drainage through the column. This paper presents the results of a laboratory study that was conducted to investigate the effect of these various parameters on the settlement response of a soft foundation soil reinforced by compacted sand columns. Triaxial compression tests under different boundary conditions were performed on composite soil specimens made of annular silty soil samples with a central, compacted river‐sand column. These tests, performed in a specially modified triaxial cell, show that the group effect, the ...

Liquefaction Resistance of Artificially Cemented Sand

Abstract: This paper summarizes the experimental results of cyclic triaxial and resonant column tests with artificially cemented sand specimens. Since the samples for both types of tests were prepared with o...

Uplift Load‐Displacement Behavior of Spread Foundations

Abstract: The design of spread foundations for uplift loads is based primarily on capacity considerations, largely because there has been only a limited effort to characterize the load‐displacement response of these foundations. This paper examines the results of 75 full‐scale field tests and synthesizes the results in a convenient design procedure that incorporates estimated displacements. The effects of soil type (granular versus cohesive) and foundation type (steel grillage versus concrete slab or steel plate) are investigated, and it is found that: (1) Granular soils lead to a slightly stiffer response than cohesive soils in the initial portion of the load‐displacement curve; and (2) slab or plate foundations lead to slightly stiffer response than grillages for granular soils only. The type of foundation has little influence for cohesive soils, and for practical purposes, a single generalized load‐displacement relationship can be used to represent the available data for all four cases at the 95% confidence level.

Drained permanent deformation of sand due to cyclic loading

Abstract: An energy approach-based method is proposed to derive a correlation between the cumulative volume and cumulative shear strains (i.e. the first and second strain invariants). Capability of the derived relationship for modeling the dilative and contractive characteristics is demonstrated through the use of two sets of experimental data. This relationship is also validated in detail by comparing the predicted results with the measured ones obtained from cyclic triaxial tests on sands. The energy approach provides a relationship between cumulative strain ratio and static stress ratio. The soil behaviour characteristics shown by The derived relationship are listed.

Analysis of Laterally Loaded Piles in Soft Clays

Abstract: The results of an alternative procedure to the p‐y method for the elastoplastic analysis of laterally loaded piles are presented. This analysis is based on the boundaryelement method and assumes kn...

Cyclic Stability Diagram for Axially Loaded Piles

Abstract: This paper develops the idea of a cyclic stability diagram in which the mean and cyclic axial loads on a pile are plotted and three regions are identified: (1) A stable zone in which cyclic loading has no effect on pile capacity; (2) a metastable zone in which cyclic loading causes some limited reduction of load capacity; and (3) an unstable zone in which cyclic loading will result in failure of the pile within a specified number of cycles. An analysis that can be used to generate the stability diagram is described, and two examples are presented to demonstrate the characteristics of the three zones. One example also examines the relative importance of cyclic degradation and degradation due to a strain-softening shaft rexponse. Finally, a comparison is made between theoretical predictions of the lower boundary of the unstable zone and the results of some field and laboratory tests.

Determining OCR in Clays from Laboratory Strength

Abstract: The results of triaxial or simple shear tests may be used to estimate the in situ overconsolidation ratio (OCR) of clays using a SHANSEP database. A compilation of OCRs and normalized strengths from 114 different clays is presented to discern separate trends for isotropic and anisotropic triaxial compression, extension, and direct simple shear conditions. The method may be used to provide an independent estimate of OCR in clays or supplement the results of consolidation testing. It is observed that natural clays and artificially prepared clays exhibit distinctly different relationships. An example application involving a sensitive sandy clay deposit is used to illustrate the procedure.

Geotechnical properties of cemented volcanic soil

Abstract: A volcaniclastic formation, known as Cangahua, found in the Andes of Ecuador and Colombia is focused on. The deposit is composed of moderately cemented fine sand and silt‐sized particles. A pronounced linear correlation is shown between strengh, in terms of both uniaxial compressive and Brazil tensile strengths, and the dry unit weight of the deposit. The tensile strength is unusually high for soil, being between 18 and 29% of the uniaxial compressive strength. Brazil tensile, uniaxial compressive, and triaxial strength characteristics depend on the initial void ratio and degree of saturation. As the saturation declines from 90 to 40%, test results show a fourfold increase in tensile strength. Moreover, increasing degrees of saturation cause a shift from brittle to ductile failure. Slope failures in Cangahua develop from fractures which initiate at zones of high tensile stress. Material properties such as tensile strength and fracture toughness play an important role in explaining and evaluating slope fai...

Erosion rate of compacted na montmorillonite soils

Abstract: Erosion rates of unsaturated compacted Na‐montmorillonite clays are measured under a range of tractive stresses from surface flows in a rectangular flume. The degree of saturation of compacted samples ranges from 0.52–0.97. The Na‐montmorillonite (Volclay bentonite) is mixed with ground silica to obtain samples with various percentages of clay. Samples of 100, 70, 40, and 10% clay content by dry weight are tested. Samples are compacted under 700 Pa into sample containers with 160‐cm2 surface area and are subjected to flowing water in the flume. The results of the study show that the erosion rate of Na‐montmorillonite soil samples increases when clay content decreases and is independent of compaction water content. The relationship between erosion rate and tractive stress is linear for all Na‐montmorillonite samples. For the range of water content tested, an empirical relationship is developed to estimate the erosion rate of compacted Na‐montmorillonite clays as a function of percent clay content and tract...

Level Ground Soil-Liquefaction Analysis Using in Situ Properties: I

Abstract: Based on Maxwell's pioneering work, on the electrical conduction through heterogeneous media a fundamental approach utilizing the electrical properties of soils to charcterize their grain (particle shape) and aggregate (porosity and fabric anisotropy) characteristics is presented. Correlations between mechanical properties relevant to the analysis of soil liquefaction and electrical indices defining the structure of a soil are given, and the influence of fabric anisotropy on mechanical behavior of soils is demonstrated. The nondestructive nature of the proposed method provides a means to predict in situ properties and thus overcome the difficulty of retrieving undisturbed samples. Level ground soil-liquefaction analysis, which considers the pore pressure generation and dissipation during and after an earthquake, utilizing the method presented herein to obtain the necessary input properties, is presented in a companion paper (Arulanandan and Muraleetharan 1988).

Modulus and Damping Due to Uniform and Variable Cyclic Loading

Abstract: Laboratory tests are run on five different cohesionless soils to determine their modulus and damping characteristics. Torsional simple shear and resonant column tests are performed by the same test apparatus in order to compare results. Results indicate that the tests are interchangeable as long as there isn't a significant cycles effect. Number of loading cycles generally increases modulus in sands and decreases modulus in silts. Damping decreases with number of loading cycles for both silts and sands. Threshold strain levels are also studied with agreement between predicted and measured results. Ramberg‐Osgood parameters, taken with uniform cyclic tests, are applied to irregular loading tests along with the Masing criterion. Predictions compare very favorably with test results.