Journal of Geotechnical and Geoenvironmental Engineering

The use of fly ash in highway applications as a stabilizing agent and soil amendment for embankments has become very common owing to its economical advantages. However, fly ash may contain toxic constituents that may pose environmental risk if they leach through the soil and reach groundwater. A series of water leach tests (WLTs), toxicity characteristic leaching procedure (TCLP) tests, and column leach tests (CLTs) were conducted to define the leaching of aluminum, arsenic, chromium, and zinc from a self-cementitious fly ash and four different off-spec high-carbon ashes. Laboratory results indicated that an increase in fly ash contents generally yields an increase in pH and leached metal concentrations regardless of the type of fly ash and metals. Furthermore, it was determined that there were significant differences in the leached metal concentrations measured in the three different laboratory tests, i.e., ${\text{C}}_{\text{CLT}}>{\text{C}}_{\text{TCLP}}>{\text{C}}_{\text{WLT}}$. Analyses conducted using a numerical groundwater model indicated that predicted field metal concentrations for the mixtures prepared with high-carbon fly ash were generally lower than the concentrations measured in the laboratory and decreased to concentration levels that do not possess any environmental risk.

Vertically loaded anchors (VLAs) are installed in a manner similar to drag-embedded anchors, except that after initial drag installation the anchor shank is released to enhance pullout capacity. Because of their lightness and relatively low installation cost, VLAs offer an attractive alternative for mooring systems. However, existing design procedures are largely empirically based, and uncertainties with regard to anchor trajectory and load capacity have limited their application to temporary mooring systems. This paper presents a design model for predicting VLA performance during drag installation, shank release, and subsequent loading beyond the installation load. Model-based parametric studies on the effects of VLA fluke–shank angle and anchor line angle at the mudline are also presented. Some aspects of the model have been benchmarked against limited available field data, but a broader validation is still needed.

It is well known that saturated silt and fine sand are susceptible to instability during undrained shearing. Coarse granular soils may also be unstable during undrained shearing or during rainfall infiltration starting at an unsaturated state. This paper investigates the instability of three saturated and unsaturated granular soils with different fines contents ($f=50,32,\text{and}\hspace{0.17em}10\%$). Isotropic consolidation tests and mercury intrusion porosimetry tests were first conducted to investigate the instability of the microstructures of these granular soils. Then drained and undrained triaxial tests were conducted to investigate the instability behavior under the saturated condition. Subsequently, wetting tests under the constant shear stress condition were carried out on unsaturated specimens to investigate the instability of the same soils during water infiltration. The instability in the microstructures is in accordance with the compressibility of the soils. The instability during undrained shearing under saturated conditions is described using relations between the state parameter and the peak shear strength or slope of the instability line of the soil. The instability of an unsaturated soil along a wetting path depends on the stress ratio and net confining pressure. Using the equivalent mean effective stress concept, a unified instability line is defined for both saturated and unsaturated soils.

Aggregate piers, also known as stone columns, are commonly used to improve ground for the support of structure foundations. Despite the number of existing analytical and semiempirical methods available to predict the displacement of shallow foundations resting on aggregate pier reinforced clay, the accuracy of these models remains uncertain. After a brief review of existing load-displacement estimation methods, the accuracy of those models valid for isolated spread footings was investigated using a database of high-quality footing load test data. The methods were compared using the bias (i.e., the ratio of measured bearing capacity to that calculated) and were shown to exhibit a high degree of variability in the prediction of load and displacement. Then, the database was used to develop a multiple linear regression model for the prediction of footing displacements for aggregate pier reinforced clay under a wide range of pier configurations and soil conditions. The proposed statistical model is shown to produce unbiased displacement estimates with low prediction variability that is appropriate for planning and designing ground-improvement projects.

Elastic moduli (Young’s modulus and shear modulus) are material properties that describe a material’s elastic stress-strain relation, and are therefore two of the most important properties in geotechnical engineering design and analysis. For soils, in addition to their well-known dependence on stress, these moduli depend on volumetric water content and/or matric suction, particularly for silty and clayey soils. This study proposes a simple power law to describe the dependence of these two moduli on volumetric water content for all types of soils. A series of uniaxial compression tests are conducted on various compacted soils under varying volumetric water content. Young’s moduli are measured and used to test the validity of the proposed power-law relationship. Additional validation and comparative analyses are conducted using other compacted soils studied by previous investigators and empirical models for shear modulus from the literature. It is shown that the proposed power law agrees well with the other models, but is much simpler because the other models use both matric suction and volumetric water content as independent variables and involve more fitting parameters. A practical three-point testing procedure is provided to determine the single fitting parameter that defines the power law for any type of soil. The procedure involves measuring elastic moduli at three states of water content: dry, wet (nearly saturated), and the middle points. Test results for 16 soils demonstrate that the proposed three-point testing procedure can accurately capture the dependence of Young’s moduli for all types of soils from sandy to silty to clayey soils ($R^2>95\%$ for most soils). The proposed power law provides a simple and practical way to describe changes in elastic moduli of soils under variably saturated conditions.

A logical framework is developed for the LRFD of slopes based on reliability analysis. The LRFD of slopes with resistance factors developed in this manner ensures that a target probability of slope failure is not exceeded. Three different target probabilities of failure (0.0001, 0.001, and 0.01) are considered in this paper. The ultimate limit state for slope stability (formation of a slip surface and considerable movement along this slip surface) is defined using the Bishop simplified method with a factor of safety equal to 1. Gaussian random field theory is used to generate random realizations of the slope with values of strength and unit weight at any given point of the slope that differ from their mean by a random amount. A slope stability analysis is then performed for each slope realization to find the most critical slip surface and the corresponding driving and resisting moments. The probability of slope failure is calculated by counting the number of slope realizations for which the factor of safety did not exceed 1 and dividing that number by the total number of realizations. The means of the soil parameters are adjusted, and this process repeated until the calculated probability of failure is equal to the target probability of failure. Resistance and load factors are obtained by dividing the resisting and driving moments corresponding to the most probable ultimate limit state (the design point) by the nominal values of resisting and driving moments. Although this paper focuses on the presentation of the methodology of resistance factor determination, resistance and load factors are calculated for some slope cases, and preliminary load and resistance factors are suggested for use in applicable codes.

Torsional load on pile foundations is induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twist at the pile head, but also reduces its axial capacity significantly associated with increased settlement of the foundation. Inadequate design of piles under torsion may lead to disastrous consequences. Although several theoretical and experimental investigations have already been carried out on piles under torsional load as evidenced from the available literature, there is ample scope for further contributions on the influence of torsional load on pile foundation. This paper presents a novel numerical model (boundary element method) to analyze the response of a single, vertical, floating pile subjected to pure torsional load. The nonlinear stress-strain response of soil has been incorporated in the model by hyperbolic correlation, whereas the pile material has been idealized as elastic–perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. Apart from predicting the load-displacement response with incremental angle of twist of pile under pure torsion, the profiles for shear stress and angle of twist and the depth of interface slippage are some of the salient features captured by the proposed model. Validation of the model developed by comparing with existing models and experimental data indicate the suitability and accuracy of the solutions developed. However, minor discrepancies in the solution appeared owing to the simplified assumptions of perfectly plastic postpeak soil behavior and the absence of residual stress in the soil owing to pile installation. The proposed model is also applied successfully to selected case studies on concrete piles ($L/D$ ranged from 10–40) in medium-soft clay, medium-dense sand, and layered soil, and a set of design curves have been constructed.

Soil stress-strain behavior is highly nonlinear and considerably influences the performance of a foundation. The response of single piles under axial load can be predicted from the load-transfer, or t-z, curve. This paper presents a new approach to predict the load-transfer curve and subsequently the load-settlement curve. This new approach incorporates nonlinear soil stress-strain behavior and accommodates differences in soil behavior in laboratory and field conditions. Expressions are given for the load-transfer curve, which capture the hardening and softening behavior of soil-pile interactions. Predictions of load-transfer curves and load-settlement curves from the proposed approach have been compared with the measured values from two case studies. The predictions show good agreement with the measured values.

Applied during pile driving, the Case Method offers an immediate estimate of the static resistance to driving (SRD) after each hammer blow. It has been used in its original form both in the onshore and offshore piling industries for more than 40 years to provide an indication of the pile static capacity. The Case Method requires measurements of force and velocity near the pile head as the hammer strikes the pile and produces an analytical estimate of the SRD using a number of assumptions, one of which requires the pile to be of constant impedance (or cross section) along its length. However, for reasons of economy, driven piles are often composed of several sections of different cross sections. In that case, the Case Method provides an inaccurate estimate of the SRD. This paper presents an improved version of the original Case Method, which takes into account possible variations of impedance along the pile. A numerical validation shows that for piles displaying impedance changes, the modified Case Method presented herein provides an estimate closer to the actual SRD than the original Case Method. That conclusion is further validated by applying the modified method to pile driving records and comparing its results to SRD estimates obtained through more reliable modeling.

Liquefaction-induced lateral spread has caused substantial damage to buildings, bridges, embankments, buried utilities, and other critical components of infrastructure in numerous past earthquakes. Although many practitioners use analytical Newmark-based seismic slope displacement models to estimate liquefaction-induced lateral spread displacements, empirical regression models remain popular among most practicing professionals today. However, all lateral spread estimates have a significant level of uncertainty. This paper introduces a procedure to develop performance-based estimates of liquefaction-induced lateral spread displacement by incorporating a widely used empirical model into a probabilistic framework. Utilizing the same principles used in probabilistic seismic hazard analysis, the empirical lateral spread equation is modified and inserted into a performance-based framework modeled after the framework introduced by the Pacific Earthquake Engineering Research Center. Lateral spread hazard curves are developed for 10 sites located across the United States using a generic soil profile. The results of the performance-based lateral spread method are compared with those of conventional pseudoprobabilistic methods. Consistent application of the conventional methods is shown to produce inconsistent actual lateral spread displacement hazards in different seismic environments. Practical design implications for the proposed performance-based procedure are discussed, and a simple example application is presented.

The resonant-column test is widely used for dynamic characterization of soils under different confinement and shear-strain conditions. The free-decay response of a soil specimen in resonant-column testing shows a nonlinear behavior when the strain levels exceed a threshold shear strain. However, the dynamic parameters are commonly determined assuming a linear single-degree-of-freedom (SDOF) model. This paper presents a new analysis methodology based on the complex exponential method (CEM) for the nonlinear dynamic characterization of soil specimens using the free-decay response in torsional fixed-free resonant-column testing. This analysis methodology represents a solution to the chronic problem of evaluating the dynamic properties of soils while avoiding the negative effects of imposing many loading cycles at strain levels greater than the threshold shear strain, which, in turn, change the original dynamic properties of soil specimens. The effectiveness of the proposed analysis methodology is demonstrated on a dry-sand specimen tested under isotropic loading and unloading conditions, two confining pressures (40 and 100 kPa), and different shear-strain levels ($1.34\times {10}^{-5}\le \gamma \le 1.52\times {10}^{-3}$). The results from the CEM are compared with the results from traditional linear SDOF methods (transfer function and free-decay response). Damping ratios obtained from the CEM are also compared with values obtained using the empirical-mode-decomposition–Hilbert-transform (EMD-HT) method. The results show that the damping ratio can be underestimated up to 80% at strain levels greater than the threshold shear strain when computed using linear SDOF models. In a nonlinear free-decay response in resonant-column testing analyzed using the CEM, it is possible to observe that the dry-sand specimen becomes denser (stiffer). Thus the shear-wave velocity (resonant frequency) increases at the low shear-strain levels imposed during the same test.

Rocking isolation is a relatively new design paradigm advocating the intense rocking response of the superstructure as a whole, instead of flexural column deformation. This is accomplished through intentionally underdesigning the foundation to guide plastic hinging below the ground surface rather than in the columns. A 2-story, 2-bay asymmetric frame is used to explore the effectiveness of this novel design approach. Finite-element dynamic analyses are performed using as seismic excitation idealized pulses and 20 real accelerograms, taking into account material (soil and superstructure) and geometric (uplifting and $P\text{-}\mathit{\Delta }$ effects) nonlinearities. A conventionally, Eurocode-designed frame and its foundation are compared to a design featuring the same frame but with substantially underdesigned (unconventional) footings. It is found that the performance of the unconventional system is advantageous, as not only does it escape collapse but it also suffers reparable damage. Despite their reduced width, the residual settlements of the underdesigned footings are comparable to those of the conventional ones. However, the analyses also reveal that residual rotation and differential settlement of the underdesigned footings may be unavoidable and must be critically evaluated—a need exaggerated by the asymmetry of the examined frame. Three possible ways of improvement at the foundation level are studied: (1) a single conventional tie beam, monolithically connected to the footings; (2) two separate tie beams hinged at each footing (allowing rotation, but resisting axial deformation); and (3) a hybrid system, comprising a single continuous tie beam connecting the three footings but externally hinged to each of them. The first solution hardly offers improvement, as it hinders rocking, and the second fails to reduce differential settlements. The hybrid solution provides encouraging results in terms of residual rotation and differential settlement, while it does not hinder the development of beneficial rocking isolation mechanisms and fully restrains horizontal differential movements.

This paper presents a systematic experimental investigation into the impact of specimen preparation on the cyclic loading behavior of saturated sand, including the deformation pattern, pore-water pressure generation, stress-strain relationship, and cyclic shear strength. Moist tamping and dry deposition were used in the laboratory to prepare sand specimens with distinct fabrics for cyclic triaxial tests under a range of conditions. It is found that the soil fabric formed by dry deposition can lead to unique failure modes different from those of moist-tamped samples in certain situations. These failure modes are hybrid in nature, characterized by a contractive response in the form of limited flow followed by cyclic strain hardening in the form of either cyclic mobility or plastic-strain accumulation. The hybrid nature of the failure patterns makes defining failure for liquefaction-resistance evaluation crucial; the conventional failure criteria based on a certain level of strain or pore-water pressure do not appear to properly represent the failure mechanism involved and may lead to a substantial overestimation of liquefaction resistance. The experiments reveal that the method used to reconstitute specimens or the soil fabric they form plays a role that is far more complicated than previously thought. Depending on the combination of relative density, confining stress, and degree of stress reversal in cyclic loading, a change of reconstitution method can have a marked or little effect on the nature of the response in terms of deformation pattern and failure mechanism; nevertheless, the two reconstitution methods always give significantly different liquefaction-resistance values under otherwise similar testing conditions.

Difficulties are often encountered in a variety of seabed sediments during extraction of spudcan foundations of mobile jack-up rigs. This paper reports results from centrifuge model tests undertaken to provide insight into spudcan foundation behavior during vertical extraction through single, double, and multilayer soils. The model tests included half-spudcan tests against a transparent window, allowing the soil flow to be captured continuously by a digital camera and subsequently quantified through particle image velocimetry (PIV) analysis and separate full-spudcan tests to measure the uplift resistance. The observed soil-failure mechanisms provide insight with respect to the profile of extraction resistance. The mechanisms reveal evolving failure modes at different spudcan extraction depths and, in particular, changes in the failure patterns because of varying layer geometry, soil types, and properties. For single, double, and multilayer clays, suction at the spudcan base, shearing along a truncated cone above the spudcan, and weight of the soil above the spudcan constitute the extraction resistance. Maximum extraction resistance occurs in the stiffer soil layer. The extent to which suction is sustained at the spudcan base is critical in determining the extraction resistance. The presence of a sand layer beneath the penetrated spudcan, for example as part of the soil plug pushed down during spudcan penetration, allows the base suction to be released within a short distance of uplift and results in relatively low extraction resistance. Improved understanding of spudcan extraction mechanisms through layered soils resulting from this study will allow development of analytical solutions to model spudcan extraction behavior, assisting jack-up operators to plan properly for leg extraction based on seabed conditions.

The procedures used to freeze and sample a Pleistocene sand deposit near Charleston, South Carolina to preserve and study the effects of diagenesis are presented in this paper. Based on the results of geotechnical tests and a feasibility ground freezing study, a freezing system with a central freeze pipe was installed to target a column of clean sand 1 m in radius and 2.3 m in length. Liquid nitrogen was continuously supplied to the freeze pipe fabricated to freeze the sand between depths of 1.8 and 3.8 m below the ground surface for 270 h. Frozen sand cores taken from five locations 0.65 to 0.7 m away from the central freeze pipe indicate the ground was frozen between depths of 1.8 and 3.8 m at all but one location. Ground temperature measurements, growth of the frozen zone, and the amount of liquid nitrogen consumed are presented and compared with predicted values. Recorded temperatures indicate that the freezing was influenced by the direction of groundwater flow, the flow rate of liquid nitrogen, and the location of the liquid nitrogen inlet pipe within the central freeze pipe.

This study examined the energy transfer ratio (ETR) of Central Mine Equipment (CME) automatic standard penetration test (SPT) hammers utilizing a large database of SPT energy measurements. The database consisted of energy measurements from 17,825 SPT hammer blows obtained from 33 CME automatic hammers over a 5-year period, many of which were tested multiple times. The average ETR for all 17,825 CME automatic hammer blows in the database was 82.9% with a COV of $\pm 7.4\%$. The database also provided an opportunity to determine the impacts of hammer calibration, test depth, and calibration interval on the measured ETR. The impact on average ETR of eliminating hammer blows due to D4633-10 restrictions was also demonstrated.

This paper presents the results of a series of laboratory model free-falling penetrometer (FFP) tests in kaolin clay. A thin-shafted FFP has been allowed to free fall and has also been pushed at a relatively slow constant rate into clay beds. Different configurations are used to examine the influences of various properties (FFP mass, tip diameter, tip shape, impact velocity, and clay-bed strength) on the rate effects in FFP tests. The rate effects are determined by comparing the dynamic and static penetration resistances measured from the free-fall and constant rate of penetration tests. The rate effects are found to be independent of the FFP mass, tip shape, and tip diameter but are influenced by the clay-bed strength and FFP velocity.

This study is part of an extensive research program carried out at the Treporti test site (Venice, Italy), where a cylindrical trial embankment was constructed and monitored from the beginning of its construction until complete removal, 4 years later. This paper concentrates mainly on the evaluation of overconsolidation and stiffness of the Venice lagoon sands and silts. The possibility of estimating the overconsolidation ratio (OCR) in sand by the combined use of seismic dilatometer (SDMT) tests and piezocone (CPTU) tests is investigated. A tentative correlation for estimating the OCR in sand from the ratio $M_{\text{DMT}}/q_t$ is constructed. Field compression curves have been back-figured from 1-m field oedometer curves reconstructed from local vertical strains measured by a sliding deformeter under the embankment center. The SDMT and CPTU soundings performed before embankment application and postremoval have permitted analyzing how the OCR caused by the embankment was reflected by the before/after SDMT and CPTU results. The paper also illustrates the possible use of the SDMT to assess the in situ decay of stiffness with the strain level, by comparison with the stiffness decay curves of the elements on the centerline back-figured from the observed embankment behavior under increasing loading.

Organic matter is frequently encountered in both naturally occurring and engineered particulate media. Charged functional groups in the organic matter can lead to cation exchange within the clay interlayer, which results in the formation of an organic coating on the clay surfaces and alters the interfacial frictional regime in the soil mass. This study investigated the triaxial shear frictional behavior of montmorillonite particles coated with a controlled organic phase composed of quaternary ammonium cations. Through cation exchange, organic cations were loaded onto the clay’s interlayer exchange sites, with control on the density of organic coverage and structure of the organic cation. Results demonstrated that increasing the total organic carbon content of the clay resulted in increasing frictional resistance regardless of whether the increase in carbon content was attributable to increased density of organic loading, increased cation size, or increased cation tail length. Concentrating organic carbon in one of the quaternary ammonium cation branch positions led to measureable gains in strength compared with distributing the carbon over all four branch positions. Measured critical-state friction angles for the organoclays ranged between 34 and 61°, whereas all tested organoclays demonstrated peak strength coupled with contractive tendencies. The presence of the organic cations in the clay interlayer led to alteration of the structure within the interlayer and is believed to have combined with forces from electrostatic bonding between the organic cation head groups and the clay surface, as well as chain entanglement and dewatering, to contribute to the increased frictional resistance of the modified organoclays.

Soils are generally known not to be isotropic materials. The inherent anisotropy of clays results from the deposition process, which tends to induce a horizontal bedding plane in the soil layer. In this paper, the anisotropy of clays was studied to obtain more accurate analytical results for geotechnical problems, especially for deep excavations in soft clay with nearby structures. A series of ${\mathrm{K}}_0$-consolidated undrained triaxial compression (${\text{CK}}_0\text{UC}$) tests thus was conducted on tube samples of natural Taipei silty clay with multidirectional bender elements. A newly designed triaxial testing system equipped with a high-precision servo motor and local strain sensors was developed. A new soil suction-control system was also developed to perform soil saturation for triaxial tests. The suction-control system was used to reduce the change in the void ratio during saturation in the triaxial tests. Soil samples were retrieved from a site near a well-documented excavation case in Taipei. The anisotropy ratios for both the shear modulus and the undrained Young’s modulus were obtained by performing small-strain triaxial tests. The test results indicated that the anisotropy ratios of the shear moduli at the end of reconsolidation ranged from 1.15 to 1.44. Soils with higher overconsolidation ratio values had higher anisotropy ratios. Numerical simulations for an excavation case history were performed using a developed small-strain soil model that incorporates the anisotropy in the soil stiffness. The analysis results showed that differences between the anisotropic and isotropic models for the wall displacements, ground-surface settlements, and lateral soil movement behind the wall ranged from 10 to 43% at specified depths.

A simple hyperbolic equation is used to best fit measured piezocone pore pressure dissipation data. The same hyperbolic equation, albeit with slight differences in its coefficients, fits well the existing theoretical solutions/charts for piezocone dissipation response. Coefficient of consolidation $c_h$ can be conveniently expressed in terms of the hyperbolic parameters corresponding to the measured data and the existing solution charts. Field piezocone dissipation test data for Busan clay is successfully fitted using the provided hyperbolic equation. The $c_h$ values thus determined over a range of degree of consolidation ($10–90\%$) compare well with $c_h$ values obtained by the traditional direct use of the same existing theoretical solutions or charts.

A series of full-scale micropiles was installed at a site in mid-Missouri for a load-test program to study the effect of combined loading. The micropiles were installed with a 178-mm (7-in.) outer diameter steel casing to a depth of 4.6 m (15 ft) and a bond zone length of 3.0 m (10 ft). The surficial soils at the site consisted of stiff-to-hard clay underlain by weathered silty/sandy shale where the bond zone of the micropiles was located. The load-test program included axial, lateral, and combined-load tests. The ultimate axial and lateral capacity of the piles was initially determined. A series of combined-load tests was then performed by applying a static axial load and incrementally increasing the lateral load on the micropiles. The pile-head load-deformation response and distribution of load and bending moment with depth were measured with concrete-embedded strain gauges along the micropile length.