Journal of Geotechnical and Geoenvironmental Engineering

This paper addresses the one-dimensional compression behavior of a highly organic sapric soil in both its natural intact and reconstituted states, based on the results of constant rate of strain and incremental loading oedometer tests. The soil investigated contains 40–60% organic matter, comprised mainly of highly processed humic substances, and represents a “transitional” material between inorganic clays and peats. The inorganic portion is entirely finer than $0.075\mathrm{mm}$ , with over 60% in the clay fraction $(<2\mu \mathrm{m})$ , which XRD analyses indicate contains smectite and vermiculite. Testing of the soil in its intact state relies on high quality block samples and shows that the natural intact soil displays intermediate behavior between that typical of inorganic soft clays and that observed in peats, in terms of compressibility, hydraulic conductivity, and change in hydraulic conductivity with void ratio. As in the case of peats, the coefficient of consolidation is observed to decrease with increasing stress level and the soil shows a high tendency to creep, with $C_{\alpha }∕C_c$ at the high end of values reported in the literature. Comparison of the compression results for the natural and the reconstituted soil serves to illustrate the degree of structuring of the natural soil, which is found to be consistent with that typical of natural sedimentary inorganic clays.

Liquefaction triggering assessments are often performed for individual locations, providing little information in regard to the expected spatial extent of liquefaction events. The present paper proposes a method to quantify the potential extent of liquefaction by accounting for spatial dependence of soil properties and potential future earthquake shaking. Random-field theory and geostatistics tools are used to model soil properties and earthquake shaking intensity; this approach facilitates incorporation of measurement results obtained at individual locations within the area of interest. An empirical liquefaction triggering criterion is then used to model liquefaction occurrence as a function of the random-field realizations. The framework components are briefly described and an example analysis is performed to illustrate the details of the approach. The area of liquefied soil under a building in Adapazari, Turkey, is considered in the example, conditional upon soil property measurements obtained from nearby standard penetration tests.

Model uncertainty associated with normalized shear modulus and material damping ratio relationships developed in a previous study is discussed in terms of standard deviations in this paper. The relationships were originally developed by separating resonant column and torsional shear test results of 122 specimens into three general geologic groups (Quaternary-age soils, Tertiary-age and older soils, and residual/saprolite soils) and determining mean regressional model parameters (i.e., $\alpha$ , $k$ , ${\gamma }_{r1}$ , and $D_{\min 1}$ ) for each group. Statistical variability of the regressional parameters is quantified and expressed by standard errors of prediction. The determined uncertainty of the regressional parameters is then propagated through the recommended relationships using the point-estimate method to estimate the model uncertainty of the relationships. The point-estimate method is a simple and effective method of uncertainty propagation. For uncertainty estimation, the regressional parameters are assumed to be uncorrelated for the sake of simplicity. The influence of this assumption on the model uncertainty of normalized shear modulus and material damping ratio values, as well as the sensitivity of the model uncertainty to the uncertainty of various regressional parameters, are also discussed.

As an alternative to a field-based liquefaction resistance approach, cyclic triaxial tests with bender elements were used to develop a new correlation between cyclic resistance ratio (CRR) and overburden stress-corrected shear-wave velocity $\left(V_{S1}\right)$ for two nonplastic silts obtained from Providence, Rhode Island. Samples of natural nonplastic silt were recovered by block sampling and from geotechnical borings/split-spoon sampling. The data show that the correlation is independent of the soils’ stress history as well as the method used to prepare the silt for cyclic testing. The laboratory results indicate that using the existing field-based $\mathrm{CRR}\text{-}{V}_{S1}$ correlations will significantly overestimate the cyclic resistance of the Providence silts. The strong dependency of the $\mathrm{CRR}\text{-}{V}_{S1}$ curves on soil type also suggests the necessity of developing silt-specific liquefaction resistance curves from laboratory cyclic tests performed on reconstituted samples.

In this paper, the sedimentation behavior of two kaolinite samples with distinct fabric associations is characterized using mechanical and electromagnetic wave-based techniques. The two different fabric formations, the edge-to-face (EF) flocculated structure (i.e., Sample A) and the dispersed and deflocculated structure (i.e., Sample B), were produced by changing the pH of the pore fluid. The anisotropy of the shear-wave velocity and DC conductivity was not observed in the sediment of Sample A because of EF isotropic fabric associations, but it was detected in Sample B as a result of face-to-face aggregation. An open card-house structure of the Sample A sediment results in a higher relaxation strength of the bulk water, $\Delta {\kappa }_w$ owing to a higher water content; the smaller $\Delta {\kappa }_w$ measured in the Sample B sediment indicates denser packing. In both samples, sediment consolidation gives rise to a decrease in the bulk-water relaxation strength, but an increase in the bound-water relaxation strength owing to increasing particle content. During sediment consolidation, the sediment conductivity of Sample A continuously decreases because of the reduced contribution from the fluid conductivity. In Sample B, the surface conduction overcompensates such a decreased contribution so that the sediment conductivity increases with increasing particle content.

Within hydraulic earth structures (dikes, levees, or dams), internal seepage flows can generate the entrainment of the soil grains. Grain transportation affects both particle size distributions and porosity, and changes the mechanical and hydraulic characteristics of the earth’s structure. The occurrence of failures in new earth structures due to internal erosion demonstrates the urgency of improving our knowledge of these phenomena of erosion. With this intention, a new experimental device has been developed that can apply hydraulic stresses to reconstituted consolidated cohesive soils without cracks in order to characterize the erosion evolution processes that might be present. A parametric study was conducted to examine the influence of three critical parameters on clay and sand erosion mechanisms. When the hydraulic gradient was low, it was concluded that the erosion of the structure’s clay fraction was due to suffusion. When the hydraulic gradient increased, it was concluded that the sand fraction erosion initiation was due to backward erosion. The extent of the erosion was dependent on the clay content. The study underlines the complexity of confinement stress effects on both erosion phenomena.

The results of two series of accelerated aging tests are reported. Both series of tests were conducted at temperatures of 85, 70, 55, and $26°\mathrm{C}$ over a period of about $3\text{years}$ . In the simulated liner series, the top of the geomembrane was covered with a geotextile (protection) layer that was exposed to simulated municipal solid waste (MSW) landfill leachate while the bottom of the geomembrane was in contact with a hydrated geosynthetic clay liner. In the immersion series, the geomembrane was immersed in the simulated MSW leachate, and hence, both sides were exposed to leachate. The results from oxidative induction time tests indicate that the antioxidant depletion is about 2.2–4.8 times faster for the leachate immersed geomembrane than for geomembrane in a composite liner. The higher rates are attributed to the higher extraction of antioxidants from two sides of the geomembrane immersed in leachate. The measured antioxidant depletion rates are extrapolated to a range of temperatures $(0–60°\mathrm{C})$ using Arrhenius modeling. At a liner temperature of $35°\mathrm{C}$ , the calculated time for the depletion of antioxidants is about $40\text{years}$ for a geomembrane in a composite liner compared to $10\text{years}$ if it is simply immersed in leachate. These tests suggest that to obtain realistic estimates of geomembrane service life one needs data from tests that simulate the expected field conditions and that prediction based on immersion tests may underestimate the service life.

Mechanical behavior of the waste body controls many aspects of landfill lining system design and performance, including stability issues and integrity of the geosynthetic and mineral lining components. The constituents of municipal solid waste deposits vary between countries and regions and are constantly altering as a result of changes in lifestyle and legislation. This paper describes an investigation using a family of synthetic wastes to assess the relationship between classification and mechanical behavior of the waste body via a program of one-dimensional compression and direct shear tests. Measured mechanical behavior is compared with results for real wastes to assess the validity of using synthetic samples. Compression and shear behavior of the synthetic wastes were found to be within the range of published values for real waste. Both stiffness and shear strength values for a synthetic “real” waste were found to be at the lower bound of published values. Lower unit weights and dry conditions for the synthetic wastes are considered to be responsible for the observed differences with real waste behavior. It is concluded that synthetic wastes can be used to assess the relationship between classification and mechanical behavior and that compression and shear behavior can be related to waste classification.

Electrokinetic remediation technology is one of the developing technologies that offers great promise for the cleanup of soils contaminated with heavy metals. However, the performance of an electrokinetic remediation system depends on the interaction of a complex set of interrelated system variables and parameters. Many of these interactions were addressed in this study by incorporating geochemical reactions into electrokinetic remediation modeling. A one-dimensional transport model was developed to predict the transport and speciation of heavy metals (chromium, nickel, and cadmium) in soil during electrokinetic remediation as a function of time and space. The model incorporates: (1) pH-dependent adsorption of contaminants to the soil surface; (2) sensitivity of soil surface potential and electroosmotic flow to the pore water properties; and (3) synergistic effects of multiple chemical species on electrokinetic remediation. The model considers that: (1) Electrical potential in the soil is constant with time; (2) surface complexation reactions are applicable in the highly concentrated clay suspensions; (3) the effect of temperature is negligible; and (4) dissolution of soil constituents is negligible. The predicted pH profiles, electroosmotic flow, and transport of chromium, nickel, and cadmium in kaolin soil during electrokinetic remediation were found to reasonably agree with the bench-scale electrokinetic experimental results. The predicted contaminant speciation and distribution (aqueous, adsorbed, and precipitated) allow for an understanding of the transport processes and chemical reactions that control electrokinetic remediation.

Penetration of skirts is an essential design issue for offshore skirted foundations and anchors in sand. Skirts may not penetrate far enough into dense sand by the available submerged weight alone. It may therefore be necessary to apply underpressure inside the skirt compartment to produce an increased driving force and to reduce the penetration resistance. This paper recommends procedures to calculate penetration resistance and required underpressure for skirts penetrated in dense sand with and without interbedded clay layers. The recommendations are based on interpretation of skirt penetration data from prototypes, field model tests, and laboratory model tests in dense sand. The paper first presents a model to calculate the penetration resistance of skirts penetrated by weight, or other external vertical load that does not cause flow of water in the sand. Two models are considered; one based on bearing capacity equations with friction angles from laboratory tests, and the other one based on empirical correlations with CPT tip resistance. The bearing capacity model gives more consistent correlations with the empirical data than the CPT model. Thereafter, a model to account for the effect of underpressure applied inside the skirt compartment is proposed. This model is developed based on interpretation of available prototype and model test data from skirts penetrated by underpressure. The results show that underpressure facilitates skirt penetration in sand considerably by providing both an additional penetration force and a reduced penetration resistance. It is also shown that interbedded clay layers can prevent flow of water through the sand and eliminate the beneficial reduction in penetration resistance.

Experimental evidence and analyses of results of three-dimensional (3D) tests show that the shape of the failure surface for soils is influenced by the intermediate principal stress, shear banding, and cross anisotropy. Presented here is a formulation of a general 3D failure criterion for cross-anisotropic soils for both nonrotating and rotating stresses. The formulation relates the loading direction to the principal directions of the cross-anisotropic microstructure of the soil. The criterion is based on a function of stress, previously used as the 3D failure criterion for isotropic frictional materials, which is set equal to a scalar that varies over a sphere. The formulation is specialized for true triaxial tests and torsion shear tests and determination of material parameters is demonstrated. The failure criterion for cross-anisotropic soils is compared with experimental results from the literature to show that it is able to capture the conditions obtained in true triaxial tests without stress rotations as well as the conditions in torsion shear tests performed to study effects of stress rotation. Sets of data from some classic true triaxial tests are reinterpreted to show their true cross-anisotropic behavior.

By representing the assembly by a simplified column model, a constitutive theory was recently developed for a two-dimensional assembly of rods. This theory, referred to as the sliding-rolling theory, is extended in this paper to represent the triaxial stress-strain behavior of granular materials. The sliding-rolling theory provides a dilatancy rule and an expression for the slope of the line of zero dilatancy in the stress space. These rules are then combined with triaxial observations to provide a microstructural interpretation of the critical state of granular materials. According to the theory, the slope of the critical state line in the stress space depends on the interparticle friction angle and the degree of contact normal anisotropy. To verify the basic ideas of the sliding-rolling theory, numerical experiments are conducted using the discrete-element method on three-dimensional assemblies of spheres.

When a loose sand specimen is loaded under an undrained condition, it may become unstable. The instability conditions may be specified by an instability line determined using undrained tests. However, the instability behavior of sand has seldom been studied under plane-strain conditions. Experimental data obtained under both triaxial and plane-strain conditions are presented in this paper to define the instability conditions of loose sand under plane-strain conditions. Using the state parameter, a unified relationship can be established between the normalized slope of instability line and the state parameters for both axisymmetric and plane-strain conditions. Using this relationship, the instability conditions established under axisymmetric conditions can also be used for plane-strain conditions.