Journal of Geotechnical and Geoenvironmental Engineering

The consolidation behavior and hydraulic conductivity $\left(k\right)$ of nine backfill mixtures modeling those used for soil-bentonite (SB) vertical cutoff walls are evaluated. The backfills include natural clay-sand mixtures with backfill fines contents $\left(F_B\right)$ of 20, 40, 60, 75, and 89% by dry weight and sand-bentonite mixtures with dry backfill bentonite contents $\left(B_B\right)$ of 2, 3, 4, and 5%. Test specimens of the backfills are mixed with a sufficient amount of 5% bentonite-water slurry to provide a $100\text{-}\mathrm{mm}$ slump, in accordance with standard field practice for SB vertical cutoff walls. The results indicate that both the compression index $C_c$ , and swell index $C_s$ increase essentially linearly with $F_B$ or $B_B$ . However, the increases in $C_c$ and $C_s$ with $B_B$ are approximately 19 and 5 times greater, respectively, than the corresponding increases in $C_c$ and $C_s$ with $F_B$ , because of a greater amount of higher plasticity fines (i.e., bentonite). The overall increases in $C_s$ with either $F_B$ or $B_B$ are relatively small $(⩽9\%)$ compared with those for $C_c$ with either $F_B$ or $B_B$ . Also, measured values for the coefficient of consolidation, $c_v$ , agree well with those reported in the literature, and $c_v$ decreases with an increase in $F_B$ or $B_B$ because of the decrease in $k$ with an increase in $F_B$ or $B_B$ . Finally, substantial amounts of fines $(⩾40\%)$ may be required in soil-bentonite backfills to achieve $k⩽{10}^{-9}\mathrm{m}∕\mathrm{s}$ when the backfill contains only low-plasticity fines. Alternatively, when backfill consists of a clean (i.e., little or no fines), coarse-grained material, a significant amount of dry bentonite (5% in this study) may be required to achieve $k⩽{10}^{-9}\mathrm{m}∕\mathrm{s}$ .

Predicting building damage due to ground movements caused by excavations is an important design consideration when building in a congested urban environment. Current predictive approaches range from empirical methods to detailed finite element calculations. Limitations inherent in the simpler of these models preclude them from accurately predicting damage in cases where important assumptions are invalid. A new simple model for representing buildings is presented to allow a designer to make realistic simplifications to a building system that is consistent with major features of the structure so that the response to ground movements can be adequately represented. This model assumes that the floors restrain bending deformations and the walls, whether load bearing or in-fill between columns, resist shear deformations. Closed-form equations are presented that relate bending and shear stiffness to normalized deflection ratios. The proposed model is shown to adequately represent the response of a three-story framed structure which was affected by an adjacent deep excavation. The proposed model represents a reasonable compromise between overly simplistic empirical methods and complex, burdensome detailed analyses.

The diffusion and sorption characteristics of a geosynthetic clay liner (GCL) are examined for a group of volatile aromatic hydrocarbons: benzene, toluene, ethylbenzene, m&p-xylene, and o-xylene (BTEX) at two different temperatures. It is shown that geotextile component of a GCL contributes to the sorption of hydrocarbons by the GCL. While the partitioning coefficients of the BTEX compounds have the order m&p-xylene $\approx \text{ethylbenzene}>o\text{-xylene}>\text{toluene}>\text{benzene}$ , the diffusion coefficients have the order $\text{benzene}>\text{toluene}>\text{ethylbenzene}>m\&p\text{-xylene}\approx o\text{-xylene}$ . The reduction in diffusion and sorption coefficients with decreasing temperature have opposite effects in terms of the rate of contaminant movement through a GCL. However, it is shown that the decrease in transport due to a reduced diffusion coefficient dominates and mass transport is reduced at lower temperature.

The understanding of soil behavior during the last 300 years has centered on mechanical principles, geological processes, and later on, mineralogy and the relevance of colloidal chemistry. More recently, research in biology and earth science has enabled important advances in understanding the crucial involvement of microorganisms in the evolution of the earth, their ubiquitous presence in near surface soils and rocks, and their participation in mediating and facilitating most geochemical reactions. Yet, the effect of biological activity on soil mechanical behavior remains largely underexplored in the geotechnical field. The purposes of this paper are to introduce microbiological concepts, identify and illustrate their potential roles in soils and rocks, and stimulate interest in seeking improved understanding of their importance and potential for advancing the states of knowledge and practice in geotechnical engineering. It is shown that microorganisms play an important part on the formation of many fine grained soils, can alter the behavior of coarse grained soils (including hydraulic conductivity, diffusion and strength), accelerate geochemical reactions by orders of magnitude, promote both weathering and aging, and alter the chemical and mechanical properties of specimens after sampling. While extensive research is needed to delineate the full impact of biomass and biomediated reactions on soil behavior, it is anticipated that a proper understanding of biological principles will lead to improved soil characterization, enhanced understanding of soil behavior, and even alternative geotechnical engineering solutions.

Two extension projects have been carried out recently on the Madrid Metro, including $97\mathrm{km}$ of large-diameter $\left(9.38\mathrm{m}\right)$ tunnels. Some technical specifications for the shields (thrust and torque) needed to excavate the tunnels have been analyzed in this work. The soil stability problem at the tunnel face has also been studied. Numerical tools based on a discrete method (particulate materials) have been used for these purposes. Results from the models are compared with real data and show the promising possibilities of the method to design both tunnels and tunneling machines.

This study focuses on how to determine an optimal radius minimizing the bending strains of vertical, cylindrical fixed-head piles embedded in a homogeneous elastic stratum in soil-pile-structure systems where the kinematic interaction dominates. In order to determine the appropriate radius, closed form formulae for the bending strains at the head of the piles are derived based on three-dimensional wave propagation theory. A general expression of the closed form formulae can be obtained by normalizing the bending strains with respect to a mean shear strain of the soil medium. The normalized bending strains can be expressed by the radius to height ratio of the piles, the ratio of soil to pile stiffness, and a factor representing the relative amplitude and the phase lag between the loading at the head of the piles and the deformation of the ground. The results of parametric analyses reveal the presence of an optimal radius that locally minimizes the bending strains of the piles. Criteria for determining the optimal radius of soil-pile-structure systems are presented.

The need for standardization of the measured blow count number $N_{\mathrm{spt}}$ into a normalized reference energy value is now fully recognized. The present paper extends the existing theoretical approach using the wave propagation theory as framework and introduces an analysis for large displacements enabling the influence of rod length in the measured $N_{\mathrm{spt}}$ values to be quantified. The study is based on both calibration chamber and field tests. Energy measurements are monitored in two different positions: below the anvil and above the sampler. Both experimental and numerical results demonstrate that whereas the energy delivered into the rod stem is expressed as a ratio of the theoretical free-fall energy of the hammer, the effective sampler energy is a function of the hammer height of fall, sampler permanent penetration, and weight of both hammer and rods. Influence of rod length is twofold and produces opposite effects: wave energy losses increase with increasing rod length and in a long rod composition the gain in potential energy from rod weight is significant and may partially compensate measured energy losses. Based on this revised approach, an analytical solution is proposed to calculate the energy delivered to the sampler and efficiency coefficients are suggested to account for energy losses during the energy transference process.

The hydraulic behavior of a residual gneiss soil compacted at conditions that produce collapsible characteristics was studied using a triaxial permeameter system that allows independent control of net stresses and matric suction. Wetting paths under differing but constant loads were utilized to reflect field conditions associated with a collapsing soil earth fill dam. The experimental results showed that different stress paths produce different amounts of volumetric collapse and distinct variations in the coefficient of permeability, which at relatively high matric suctions was mainly affected by the increase in degree of saturation. However, as the soil approached saturation, the coefficient of permeability became dependent on void ratio and net mean stress, with the saturated coefficient of permeability being reduced at larger amounts of collapse. The results also suggested that entrapped air in the soil voids may produce a significant reduction in the coefficient of permeability. A constitutive relationship for the coefficient of permeability that takes net mean stress changes into account was proposed based on best-fit analyses.

In this paper, the issue of model uncertainty is examined in detail within the framework of the first-order reliability method (FORM). The focus of the paper is on the characterization of the uncertainty of a shear wave velocity-based simplified model for liquefaction potential evaluation developed by Andrus and Stokoe. This simplified model is expressed as a boundary curve that defines liquefaction resistance as a function of the corrected shear wave velocity. The uncertainty of this simplified model is represented by a lognormal random variable, and characterization of the model uncertainty mainly involves the determination of its two statistics, namely, the mean and the coefficient of variation. A trial-and-error procedure is used to determine the two statistics of the model uncertainty based on a Bayesian mapping function that is calibrated with a database of case histories. This procedure is shown to be effective in the present study, and the uncertainty of the Andrus and Stokoe’s model is characterized. With the known model and parameter uncertainties, the probability of liquefaction can be determined through a routine FORM analysis.

Scour at bridges is the number-one cause of bridge collapse in the United States. Much research has been performed to improve the prediction of scour depths in coarse-grained soils, but little has been done for fine-grained soils. Starting in the early 1990s, the scour rate in cohesive soils-erosion function apparatus (SRICOS-EFA) method was developed for fine-grained soils. The first version of the method predicted the scour depth versus time curve for a cylindrical bridge pier in deep water subjected to a multiflood hydrograph and founded in a layered soil. Here, the SRICOS-EFA method is extended to the case of contraction scour, which is the lowering of the river bottom caused the narrowing of the river. Furthermore, the paper addresses clear-water scour only. The input to the new prediction method consists of the soil properties as tested in a special laboratory device called the EFA, the water parameters given by the velocity history over the design period considered, and the geometry of the contraction described by the contraction ratio, the contraction length, the contraction transition angle, and the water depth. This article focuses on the simpler case of a constant water velocity lasting for a limited time. The prediction equations are based on a combination of 14 model scale flume tests, 16 three-dimensional (3D) numerical simulations, and a verification (very limited). The step-by-step procedure is given, and a simple example is presented. The prediction process is automated by the program SRICOS-EFA, which can be downloaded free from http://ceprofs.tamu.edu/briaud/sricos-efa.htm. The advantages of the method are that it is based on site-specific soil testing (EFA), that it introduces the time effect in a simple manner, and that it therefore gives a more realistic prediction of the scour depth in cases where time effects significantly reduce the final scour depth. The drawback is that it requires soil testing.

Granular materials forming part of civil engineering structures are subjected to both static and dynamic loads. As a result of these loads, particle crushing occurs. This study focuses on the evolution of crushing in a simulated granular material subjected to a direct shear test. It was found that the discrete element method (DEM) can be used to visualize and understand the evolution of crushing experienced by a granular material during this test. Even though DEM does not normally consider particle breakage, it is possible to simulate crushing by replacing one particle that has failed in tension with a combination of many particles of different sizes. One simulation indicated that crushing did not develop uniformly throughout the sample, and the sample tended to achieve a fractal distribution of particle sizes. The changes in other properties of the simulated granular material such as porosity and shear strength were also recorded, analyzed, and compared to the changes produced during another simulation where crushing was not a predominant feature.

After a buried bell-and-spigot pipeline was installed at a site, an interior survey showed that some of the pipe sections were as much as $450\mathrm{mm}$ above the intended grade. One proposed explanation for this phenomenon was that the pipe sections were acting like teeter-totters, with one end settling and the other heaving, due to the variable foundation conditions. Later, when a similar pipeline was planned for the same vicinity, analyses were made utilizing a nonuniform Winkler soil model with randomized spring constants. The analyses showed that the calculated settlements were negligibly small; and there was no predicted teeter-totter behavior. Subsequent measurements confirmed the analyses.