Journal of Geotechnical and Geoenvironmental Engineering

This study presents the results of a treatability study for dredged material (DM) stabilization using 20 combinations of pozzolanic agents (lime, cement kiln dust, high alkali and slag cements, and fly ash). The DM consisted of CH/OH soil excavated from the U.S. Army Corps of Engineers Craney Island confined disposal facility in Hampton Roads, Virginia, having an in situ moisture content of approximately 130% and void ratio of 3.35. Mix designs were prepared for each stabilized DM (SDM) blend using a 3-day mellowing period for the SDM blends to become compactable. Typical maximum dry unit weights were on the order of $11.9–12.9\text{kN}/{\text{m}}^3$ $(76–82\text{lb}/{\text{ft}}^3)$ , for total dry pozzolan doses to wet DM between 5 and 95%, the upper dosing limit being unconstrained for potential use of the SDM blends as fill. Unconfined compression strength (UCS) testing of the SDM blends using DM with an initial MC of 132.5% was completed in accordance with ASTM D1632 and ASTM D1633 for curing times of 7, 28, and 180 days. The 28-day cured specimens had UCS values up to 800 kPa (115 psi). Leaching analyses of the various SDM blends for Resource Conservation and Recovery Act metals using toxicity characteristic leaching procedure and deionized water solutions for extended durations and contact times illustrated that the SDM blends were nonhazardous and virtually identical to the raw DM. Overall, the use of industrial by-products in SDM blends suggests that it may be possible to undertake large-scale fill construction that is sustainable, cost-effective, and environmentally protective of human health and the environment.

This study presents the results of a detailed geotechnical evaluation of six stabilized dredged material (SDM) blends incorporating various combinations of lime, cement kiln dust, high alkali and slag cements, and Class F fly ash. The dredged material classified as CH/OH soil with an in situ moisture content (MC) of approximately 130% and void ratio of 3.35. Mix designs and unconfined compression strength tests were completed for each SDM blend based on 3-day mellowing characteristics. Compacted dry densities were on the order of $7.8–11.2\text{kN}/{\text{m}}^3$ $\left(49–71\text{lb}/{\text{ft}}^3\right)$ , with MCs on the order of 34–73%. Peak effective friction angles ranged from 20–50° with cohesion intercepts on the order of 30–235 kPa $\left(4–34\text{lb}/{\text{in.}}^2\right)$ using a maximum stress obiliquity criterion. Postpeak effective friction angles (15% axial strain) were routinely in excess of 40° with low cohesion ( $<40\text{kPa}$ ; $6\text{lb}/{\text{in.}}^2$ ). One sample exhibited very strong soil-fabric effects (cohesion) having an effective friction angle of only approximately 9°, but cohesion on the order of 450 kPa $\left(65\text{lb}/{\text{in.}}^2\right)$ . Negligible consolidation of a 28-day cured sample was measured. Also, contrary to expectations based on the high sulfate contents (10,000–30,000 mg/kg) of the SDM blends, negligible swell $\left(<1\mathrm{\%}\right)$ was measured in five of six SDM blends. The main finding of this research is the SDM blends exhibit the strength, compressibility, and bulking characteristics that make them favorable for large fill applications and subgrade improvement applications at costs equivalent to or less than conventional construction materials.

The prior two papers in this series reported on the geoenvironmental and geomechanical properties of 20 stabilized dredged material (SDM) blends using dredged material (DM) from the U.S. Army Corps of Engineers Craney Island confined disposal facility. The pozzolans included lime, cement kiln dust (CKD), class F fly ash, and two cements (portland and slag cement). This paper reports on the mineralogical evolution of the SDM blends over a 6-month curing period using techniques new to mainstream geotechnical engineering: X-ray diffraction (XRD) with Rietveld quantification analysis which allows direct quantitative mineralogical comparisons between soil samples. Despite being classified as a high plasticity clay-organic clay (CH/OH soil), XRD showed that the DM contained no montmorillonite, illite or kaolinite, and was thus mineralogically unreactive. The quartz, feldspar, and mica contents were numerically tracked and were shown to remain stable 6 months after blending. The chlorite (in DM) content decreased over time and with the fly ash served as the sources of soluble silica and alumina for pozzolanic reactions especially in the lime-based SDM blends. Lime in the lime-based blends persisted in significant quantities (3%) as unreacted portlandite $\left[\text{Ca}{\left(\text{OH}\right)}_2\right]$ even at 6 months curing, indicating that the solubility of silica in the DM was the limiting factor for strength development. New (ettringite and hydrocalumite) mineral formation was quantified. CKD provided high early strength (7 and 28 days) when used in combination with small amounts of lime that provided prolonged pH buffering; CKD alone or in combination with fly ash did not maintain elevated pH $\left(>10.8\right)$ over 6 months. Overall, the unconfined compressive strength, pH, and mineralogy results at 6 months were substantially different compared to the standard curing time of 28 days, confirming similar findings of previous long-term stabilization-solidification studies.

A new centrifuge permeameter was developed with the specific objective of expediting the measurement of the hydraulic characteristics of unsaturated soils. The development, theoretical basis, and typical results associated with using the centrifuge permeameter for concurrent determination of the soil-water retention curve (SWRC) and hydraulic conductivity function ( $K$ function) of unsaturated soils are presented in this paper. Components developed for the centrifuge permeameter are described, including the centrifuge, permeameter, water flow control system, and instrumentation used to concurrently and nondestructively measure the infiltration rate (flow pump and outflow transducer), volumetric water content (time domain reflectometry), and matric suction (tensiometers) in flight during steady-state infiltration. A companion paper focuses on definition of the SWRC and $K$ function for a clay soil using the procedures described in this paper. While conventional geotechnical centrifuges are used to reproduce the response of earth structure prototypes, the centrifuge developed in this study is used to accelerate flow processes. Accordingly, it required a comparatively small radius (0.7 m) but high angular velocity (up to 875 rpm or 600 $g$ ’s) to impart a wide range of hydraulic gradients to an unsaturated soil specimen. Analytical solutions to Richards’ equation in the centrifuge indicate that steady-state infiltration allows direct determination of the relationships between suction, volumetric water content, and hydraulic conductivity from the instrumentation results. Typical instrumentation results during a drying stage are presented to illustrate determination of data points on the SWRC and $K$ function at steady state. These results were found to be consistent with analytical flow solutions.

This paper presents the hydraulic characteristics of an unsaturated, compacted clay, including its soil-water retention curve (SWRC) and hydraulic conductivity function ( $K$ function), determined using a new centrifuge permeameter developed at the University of Texas at Austin. A companion paper describes the apparatus, its instrumentation layout, and data reduction procedures. Three approaches are evaluated in this study to define the SWRC and $K$ function of the compacted clay under both drying and wetting paths, by varying the inflow rate, the $g$ level, or both. For imposed inflow rates ranging from 20 to 0.1 mL/h and $g$ levels ranging from 10 to 100 g, the measured matric suction ranged from 5 to 70 kPa, the average volumetric water content ranged from 23 to 33%, and the hydraulic conductivity ranged from $2\times {10}^{-7}$ to $8\times {10}^{-11}\text{m}/\text{s}$ . The SWRCs and $K$ functions obtained using the three different testing approaches were very consistent, and yielded suitable information for direct determination of the hydraulic characteristics. The approaches differed in the time required to complete a testing stage and in the range of measured hydraulic conductivity values. The $g$ level had a negligible effect on the measured hydraulic characteristics of the compacted clay. The SWRCs and $K$ functions defined using the centrifuge permeameter are consistent with those obtained using pressure chamber and column infiltration tests. The $K$ functions defined using the centrifuge permeameter follow the same shape as those obtained from predictive relationships, although the measured and predicted $K$ functions differ by two orders of magnitude at the lower end of the volumetric water content range.

Most of the rock medium possesses intrinsic grain orientation or preferred bedding and joint directions, thus requiring the use of at least transverse isotropy to describe its elastic behavior. This paper presents a series of charts, based on extensive finite element parametric studies along with nonlinear regression analysis of FE simulation results, for estimating the subgrade reaction modulus (or initial tangent to the $p\text{-}y$ curve) using five elastic constants of a transversely isotropic rock mass. The proper characterization of subgrade reaction modulus is critical for accurate prediction of the elastic lateral deflection of a rock socketed drilled shaft under the applied lateral loads. The sensitivity of the response of a laterally loaded drilled shaft to the degree of anisotropy and orientation of the plane of anisotropy (bedding plane direction of the rock medium) was demonstrated in this paper for an actual lateral load testing case in Ohio. It is highly recommended to use five elastic constants to estimate subgrade reaction modulus of rock medium exhibiting high degree of cross anisotropy.

The mechanical performance of pavement systems depends on the stiffness of subsurface soil and aggregate materials. The moduli of base course, subbase, and subgrade soils included in pavement systems need to be characterized for their use in the new empirical-mechanistic design procedure (NCHRP 1-37A). Typically, the resilient modulus test is used in the design of base and subbase layers under repetitive loads. Unfortunately, resilient modulus tests are expensive and cannot be applied to materials that contain particles larger than 25 mm (for 125-mm diameter specimens) without scalping the large grains. This paper examines a new methodology for estimating resilient modulus based on the propagation of elastic waves. The method is based on using a mechanistic approach that relates the $P$ -wave velocity-based modulus to the resilient modulus through corrections for stress, void ratio, strain, and Poisson’s ratio effects. Results of this study indicate that resilient moduli are approximately 30% of Young’s moduli based on seismic measurements. The technique is then applied to specimens with large-grain particles. Results show that the methodology can be applied to large-grained materials and their resilient modulus can be estimated with reasonable accuracy based on seismic techniques. An approach is proposed to apply the technique to field determinations of modulus.

Compaction characteristics of municipal solid waste (MSW) were determined in the laboratory and in the field as a function of moisture content, compactive effort, and seasonal effects. Laboratory tests were conducted on manufactured wastes using modified and 4X modified efforts. Field tests were conducted at a MSW landfill in Michigan on incoming wastes without modifications to size, shape, or composition, using typical operational compaction equipment and procedures. Field tests generally included higher efforts and resulted in higher unit weights at higher water contents than the laboratory tests. Moisture addition to wastes in the field was more effective in winter than in summer due to dry initial conditions and potential thawing and softening of wastes. The measured parameters in the laboratory were ${\gamma }_{d\text{max-mod}}=5.2\text{kN}/{\text{m}}^3$ , $w_{\text{opt-mod}}=65\mathrm{\%}$ , ${\gamma }_{d\text{max-}4\times \text{mod}}=6.0\text{kN}/{\text{m}}^3$ , and $w_{\text{opt-}4\times \text{mod}}=56\mathrm{\%}$ ; in the field with effort were ${\gamma }_{d\text{max-low}}=5.7\text{kN}/{\text{m}}^3$ , $w_{\text{opt-low}}=70\mathrm{\%}$ ; ${\gamma }_{d\text{max-high}}=8.2\text{kN}/{\text{m}}^3$ , and $w_{\text{opt-high}}=73\mathrm{\%}$ ; and in the field with season were ${\gamma }_{d\text{max-cold}}=8.2\text{kN}/{\text{m}}^3$ , $w_{\text{cold}}=79.5\mathrm{\%}$ , ${\gamma }_{d\text{max-warm}}=6.1\text{kN}/{\text{m}}^3$ , and $w_{\text{warm}}=70.5\mathrm{\%}$ . Soil compaction theory was reasonably applicable to wastes with the exception that the $G_s$ of waste solids increased with compactive effort resulting in steep degree of saturation curves and low change in $w_{\text{opt}}$ between efforts. Moisture addition to wastes during compaction increased the workability, the unit weight, and the amount of incoming wastes disposed, and reduced the compaction time. The combined effects have significant environmental and economic implications for landfill operations.

The interslice force function $f\left(x\right)$ is a major assumption of the limit equilibrium method, which is important but has not been adequately considered in the past. In this paper, $f\left(x\right)$ is taken as the control variable, and the upper and lower limits of the factor of safety for a general slope will be determined by a global optimization analysis. Based on this approach, $f\left(x\right)$ will be determined and investigated. We demonstrate that $f\left(x\right)$ cannot be arbitrarily assigned if a set of acceptable internal forces is required. The present approach can be presented practically as a lower bound approach with the advantage that failure to converge is virtually eliminated, which is not possible with all other existing “rigorous” methods. The “present proposal” attempts to answer several important questions in the basic theory of slope stability analysis, and provides a $f\left(x\right)$ based on the lower bound approach statically admissible forces throughout the whole failure zone. Currently, different assumptions will give different factors of safety to the same problem, and this situation will be overcome by the use of the present proposal. The present proposal is also proven to give a result equal to the slip line solution for a simple footing on clay which is not possible for other classical slope stability methods, which has demonstrated that the applicability of the “present proposal” for general difficult problems.

Load and resistance factor design (LRFD) is a method that aims at meeting specified target reliabilities (probabilities of failure) of engineered systems. The present work focuses on ultimate side friction resistance for axial loads on single cylindrical drilled shaft foundations in the presence of spatially variable rock/soil strength. Core sample data are assumed to provide reliable information about local strength in terms of mean, coefficient of variation and spatial correlation structure (variogram) at a site. The geostatistical principle of support up-scaling is applied to quantify the reduction in variability between local strength and the average ultimate shaft side friction resistance without having to recur to lengthy stochastic finite difference/element simulations. Site and shaft specific LRFD resistance factors ( $\Phi$ values) are given based on the assumption of lognormal load and resistance distributions and existing formulas recommended by the Federal Highway Administration. Results are efficiently represented in dimensionless charts for a wide range of target reliabilities, shaft dimensions, and geostatistical parameters including nested variograms of different types with geometric and/or zonal anisotropies. Field data of local rock strength is used to demonstrate the method and to evaluate the sensitivity of obtained resistance factors to potentially uncertain variogram parameters.

Representative interpretation criteria are examined to evaluate the capacity of nonrigid drilled shaft foundations under lateral loading. A wide variety of lateral load test data are used for analysis, and these data are divided into drained and undrained databases. The interpretation criteria are applied to these load test data to establish consistent lateral interpretation criteria. Among these criteria, the results are generally comparable for both drained and undrained loading. The statistical results show that the smaller the displacement or rotation is, the higher the coefficient of variation. Moreover, the undrained load test results present somehow less variability than the drained results. Based on these analyses, the relative merits and interrelationships of these criteria are established, and specific design recommendations for the interpretation of lateral drilled shaft load test are given in terms of capacity, displacement, and rotation.

We outline the development of a computational procedure for finite-element analysis of suction-caisson behavior, highlighting its unique features and capabilities. The procedure is based on a description of clayey soil as a two-phase medium: a water-filled porous solid. Nonlinear behavior of the solid phase is represented by means of a bounding-surface plasticity model. An algorithm is developed for frictional contact in terms of effective normal stress. Furthermore, a special remeshing scheme is introduced facilitating the simulation of the installation process, tracking the caisson penetration path and avoiding numerical complications in the vicinity of the caisson-soil interfaces. To illustrate the use of the proposed computational procedure and examine its validity, complete simulations of available laboratory tests on model suction caissons are conducted. Results are presented and discussed for test-bed preparation (consolidation) followed by caisson installation by self-weight and suction, setup (reconsolidation), and axial pullout. The overall agreement between computations and measurements is good. Possible improvements are identified and recommendations are made regarding future studies.

This paper presents the results of a numerical investigation into the performance of geosynthetic-encased stone columns (GESCs) installed in soft ground for embankment construction. A three-dimensional finite-element model was employed to carry out a parametric study on a number of governing factors such as the consistency of soft ground, the geosynthetic encasement length and stiffness, the embankment fill height, and the area replacement ratio. The results indicate among other things that additional confinement provided by the geosynthetic encasement increases the stiffness of the stone column and reduces the degree of embankment load transferred to the soft ground, thereby decreasing the overall settlement. It is also shown that the geosynthetic encasement has a greater impact for cases with larger stone column spacing and/or weaker soil. Also revealed is that unlike isolated column loading conditions, full encasement may be necessary to ensure maximum settlement reduction when implementing GESCs under an embankment loading condition. Practical implications of the findings are discussed in detail.

Modern methods for designing drilled shafts in soft rock require knowledge of the compressive strength and modulus of the rock. However, rock jointing at many sites prohibits the recovery of samples of sufficient length and integrity to test rock cores in either unconfined or triaxial compression tests. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the rock. The surrogate methods considered in this study was Texas cone penetrometer tests, and performed at several sites in North Central Texas. In order to develop the relationships between Texas cone penetrations and side and base resistances of rock socketed drilled shafts, three field load tests were conducted. Based on the field study and literature reviews, a relationship between Texas cone penetration tests and axial resistances of rock socketed drilled shafts was proposed.