Journal of Geotechnical and Geoenvironmental Engineering

This article presents a study on 15 concrete face rockfill dams (CFRDs) carried out to characterize in situ rockfill compressibility. The stress-strain-time behavior of rockfill for each CFRD was evaluated at the embankment centerline, during and after construction and before the onset of reservoir impoundment. By comparing the behavior in different case studies, the rockfill in situ compressibility parameters were defined and related to key material properties. It was shown that short-term and long-term response of rockfill to changes in stress level is a function of two parameters: the strength of individual rock particles and the void ratio of the rockfill assemblage. Moreover, the time-dependent and short-term rockfill compressibility parameters are connected. This study provides a good framework to characterize and estimate the behavior of rockfill during and after construction of embankments. Moreover, the concepts presented in this paper can be used for predicting postconstruction deformations of structures constructed by using compacted rockfill on the basis of their behavior during construction.

This paper presents an extended formulation of the Sobol’ sensitivity index for geotechnical reliability assessments involving spatially variable soil properties. It incorporates the subsurface spatial correlation structure with the response surface method, which is then assimilated into the context of the Sobol’ index approach. A Sobol’ index map can be generated for the entire subsurface domain, identifying the sensitive zones that also represent the optimal sampling locations. In addition, the approach allows the derivation of the mean and variance of system response conditional to any sample value, without the need to conduct separate conditional random field simulations. This is adopted for the assessment of the reliability of slopes, where design charts are established for cases in which a single sample is obtained within slopes of $c_u$ or $c-\varphi$ soils, with various conditions of geometries and spatial variability. The approach can also be applied to multiple sampling points, thereby facilitating a feedback mechanism where the planning of geotechnical investigation and evaluation of performance uncertainty can be considered in a holistic manner.

Tests were conducted on eight soils to determine how coal combustion product (CCP) leachates may affect the hydraulic conductivity of compacted soil liners (CSLs) used for CCP disposal facilities. The soils represent a broad range of particle-size distributions, Atterberg limits, and mineralogy, and meet minimum compositional recommendations for CSLs. Hydraulic conductivity tests were conducted with five characteristic CCP leachates from the Electric Power Research Institute (EPRI) database of CCP leachates. The testing confirmed that seven of the soils are suitable for a CSL. Five of the seven suitable soils have hydraulic $\text{conductivity}<1\times {10}^{-9}\mathrm{m}/\mathrm{s}$ when permeated with any of the CCP leachates at 28 kPa effective stress (disposal facility with first lift of CCP placed), as do all but one soil when the effective stress is 450 kPa. Larger increases in hydraulic conductivity are associated with soils having lower hydraulic conductivity to deionized water and significant montmorillonite content. Soils exhibiting the smallest increases in hydraulic conductivity have little to no montmorillonite. Hydraulic conductivity to CCP leachate is not related systematically to any of the primary index properties, indicating that mineralogy is a better indicator of sensitivity to CCP leachates than index properties. Increasing the effective stress from 28 to 450 kPa ($\approx 2$ to 30 m CCP depth) results in an average reduction hydraulic conductivity of $10\times$. The average reduction is $2\times$ at 100 kPa and $5\times$ at 250 kPa.

Scour is responsible for approximately 60% of all bridge collapses in the United States. A large number of bridges are listed in the National Bridge Inventory as scour critical; however, evaluating scour potential based on soil sampling and laboratory testing can be cost prohibitive, as erosion testing using available apparatuses is time consuming. Various soil characteristics that affect the erosion of soil also influence in situ bulk electrical resistivity (ER) measurements collected using electrical resistivity tomography (ERT). The objective of this study was to predict soil erodibility using ERT. Fourteen bridge sites were used for ERT and erosion testing. The results of this study indicate that an ER over 50 Ωm has a 93% probability of classifying the soil as high erodibility. As such, ERT can be used to rapidly prioritize existing bridges where soils near the surface are likely classified as highly erodible. These bridges would then require a more detailed investigation to characterize soil erosion potential. The application of using ERT to predict soil erodibility was validated using an additional experimental site.

The paper presents an experimental study on the volumetric behavior of two compacted soils (Boughrara and Châtaignier clays) through suction-controlled drying-wetting and oedometric tests. During hydraulic loading (drying-wetting tests), the changes in void ratio, degree of saturation, and water content of both materials are plotted against the logarithm of suction, providing relatively comprehensive experimental results to validate recent empirical correlations on the wetting path and to derive the suction yield curve on the drying path. For mechanical loading (oedometric tests), volumetric changes are presented in the ${\log }_{10}({\sigma }_v)$-e plane, and an increase in yield stress and a monotonic decrease in compressibility coefficient $\lambda (s)$ with suction are observed. These results show the suction hardening effect on soil stiffness, which is further illustrated by the analysis of the pore-size distribution curve. In addition, a new osmotic oedometric cell which takes advantage of the electrical resistivity technique is developed and used to measure the variation of degree of saturation and volumetric water content in oedometric tests, highlighting in particular how the hydraulic parameters change in a different way from the mechanical parameters (void ratio). The Barcelona Basic Model is examined and a new empirical correlation is proposed to determine the yield stress.

The characteristic features of undrained behavior of a silty sand are investigated for a range of initial conditions $(e,p^{\prime })$ for both isotropic consolidation (CIU) and ${\mathrm{K}}_0$ consolidation (${\mathrm{K}}_0\mathrm{U}$). The silty sand contains approximately 10% natural fines. The steady-state line (SSL) for ${\mathrm{K}}_0$-consolidated specimens is slightly below the SSL for isotropic consolidated specimens. The so-called reverse behavior for silty sand is not observed for CIU, although it is observed in some cases for ${\mathrm{K}}_0\mathrm{U}$. Earlier studies claimed that the shape and location of the consolidation line with respect to the SSL can explain such behavior. The findings of this study suggest that the liquefaction potential, a key parameter for observing reverse behavior, depends on the state of the soil and shows a unique relation to the state parameter ($\psi$) irrespective of the type of consolidation. However, the stress ratio at the triggering of liquefaction, ${\eta }_{IS}$, and liquefaction resistance, $q_{IS}$, show slightly different relationships with $\psi$ for isotropic and ${\mathrm{K}}_0$ conditions. This finding has practical importance for estimating liquefaction strengths, triggering of liquefaction, and developing a $\psi$-dependent constitutive model both for isotropic and ${\mathrm{K}}_0$ consolidation.

The performance of two urban cofferdams is presented in this paper. The first case history is a cofferdam built for the One Museum Park West structure (OMPW), braced with segmental steel ring beams. The second is a cofferdam braced with cast-in-place reinforced concrete ring beams. The main goal of this paper is to study the excavation-induced ground deformations arising from these two cofferdams built in similar geologic settings but different bracing systems, installation sequences, and material responses to time-dependent effects. The deformations at the OMPW cofferdam are attributed to the compliance in the overall retaining system caused by a large initial unsupported cantilever depth and gaps left open between segmental steel ring beams and sheet piles. For the cofferdam at Site 2, observed ground movements are attributed to a rapid construction sequence, low temperatures during concrete curing, and concrete material time-dependent behavior of the concrete ring beams.

This study examines the use of a numerical model to predict the reduction in permeability of bioclogged specimens observed from column experiments. The numerical model uses the two-dimensional (2D) segmented scanning electron microscope (SEM) images of the initial microstructure of soil and simulates the growth of biofilm assuming uniform grain coating around particles. The corresponding Navier-Stokes equation in free pore space and the flow within the biofilm described by the Brinkman equations are solved using finite-element analysis. The numerical results are shown to match the experimental data very well. The predictions by the different analytical models used in the current literature are also compared. The numerical model, utilizing the uniform grain coating criterion for biofilm growth, is shown to predict well the permeability reduction of porous medium as a function of biofilm saturation.

Drying shrinkage results in cracks in mud in nature, and the patterns of the cracks are complex because of multiple combinations of various physical processes. Mudcrack growth may be induced by the internal friction caused by the differences between the shrinkage ratios of the soil skeletons, but the mechanical details remain unknown. In this study, the authors determined the fractal dimensions and its behavior to quantify the geometric characteristics of mudcracks on bentonite paste. Subsequently, the strain distribution of the mudcracks occurring on the bentonite paste was observed by the digital image correlation (DIC) method, and the mudcrack characteristics were clarified. Lastly, a novel numerical model for mudcrack growth in/on mud paste was described based on the results of DIC analyses. This is a new model for mudcrack simulation based on the techniques of three-dimensional solid dynamics. In order to validate the proposed model, the Hausdorff fractal dimension of the numerical crack patterns was compared with that of the data obtained. As a result, some reasonable fracture patterns were obtained, and the fractal dimension of the cracking patterns by numerical simulation was fairly consistent with the experimental results.