Journal of Geotechnical and Geoenvironmental Engineering

The deformation and degradation of ballast is influenced by the size of the aggregates. In this study, a series of cyclic drained triaxial tests was conducted on ballast with different sizes using the large-scale cylindrical triaxial apparatus designed and built at the University of Wollongong, and two different frequencies of cyclic loading were used to simulate low-speed and high-speed trains. From the laboratory results, coarse particles experience less vertical and lateral strains, whereas the volumetric strains decrease and then increase as the coefficient of uniformity increases, regardless of the loading frequency. Resistance to deformation and degradation is found to be improved by increasing ballast density. Different trends between the extent of breakage and particle size are observed for different breakage indices, and accordingly the extent of breakage is characterized into two distinct zones, depending on the coefficient of uniformity ($C_u$), where the significantly reduced breakage corresponds to a value of $C_u$ larger than 1.8. The variation of particle shape before and after test is also quantified. A new particle size distribution that incorporates the size characteristics is proposed, as a result of this study.

Stiffened slabs-on-grade are one of the most economical solutions for 1- to 3-story buildings on shrink-swell soils. They consist, for example, of 1-m-deep, 0.3-m-wide beams resting on the soil, spaced 4 m apart in both directions covered by a 0.1-m-thick slab-on-grade. The challenge is to optimize the beam depth, width, and spacing for the slab to be stiff enough that the movement of the soil at the edges of the slab will not cause undue bending of the foundation and the structure above it. Indeed, shrink-swell soils are affected by the weather and/or by the irrigation at the edges of the foundation and will swell and shrink as a result. This article presents a new method to design stiffened slabs on grade such that the differential movement divided by the length over which this movement takes place is within tolerable limits. The method gives the beam depth necessary to achieve such stiffness as well as the bending moment and shear force to be resisted. The method is automated in a spreadsheet called TAMU-SLAB.

A methodology for cost-effective design of jet grouted water-sealing bottom plugs is presented in this paper. These massive barriers, made of partially overlapping jet grouted columns, are required to ensure temporary waterproofing to excavation areas and adequate uplift resistance against water loads. Therefore, the proposed calculation procedure simultaneously focuses on the structural performance and continuity of the plug. The design may be optimized by considering the possibility of reducing column length, performing injections only in the lower part of the plug, and leaving the upper part of the plug untreated. The reduction in column length may then result in a very slender slab, and a structural check has to be performed to avoid tension fracturing or overall structural collapse. Additionally, in spite of strict controls, jet grouted columns are never perfectly cylindrical or exactly aligned along their prescribed position, and thus the plug may present imperfections. Statistical evaluation of defects with experimental data from different field trials and their simulation with the Monte Carlo method shows that the imperfections are less relevant for the structural performance of the plug, but must be carefully taken into account in the analysis of seepage. Imperfections have been thus introduced in the structural analysis by means of partial factors evaluated from probabilistic analysis. The latter calculation provides a rule to control the effects of incomplete watertightness of the plug. The introduced relations are expressed with design charts.

Several different phenomena are involved in the formation and performance of self-hardening slurry walls, including slurry contamination by soil, penetration of slurry into the ground, confining with the trench, filtration, sedimentation, consolidation, and chemical reactions between the slurry constituents. To evaluate the relative influence of these phenomena, a case study is analyzed—the cutoff wall of Santa Clara-a-Velha Monastery, built in 2001–2002. The performance of this wall is related to the in situ phenomena through data obtained during construction and from a site investigation conducted in 2011. An extensive laboratorial program was performed on samples cored from the wall and on laboratory-made samples. It was found that consolidation was the major contributor to the significant settlement of the wall that occurred after trench excavation, whereas filtration and sedimentation made only a secondary contribution. Contamination by sand only interfered with the physical properties and compressibility of the slurry. The unusual hydromechanical behavior of the wall material, when compared with soils, was attributed to the combined effect of consolidation, cement hydration, and pozzolanic reactions.

The available simplified analytical methods for the seismic design of underground structures either assume yielding or rigid-unyielding conditions. Underground reservoir structures do not fall into either of these categories. In this paper, we present the results of three centrifuge experiments that investigate the seismic response of stiff-unyielding buried structures in medium dense, dry sand and the influence of structure stiffness and earthquake motion properties on their performance. The structure to far-field spectral ratios were observed to amplify with increased structural flexibility and decreased soil-confining pressure at the predominant frequency of the base motion. Lateral earth pressures and racking displacements for a range of structural stiffnesses were compared with procedures commonly used in design. Pre-earthquake measured lateral earth pressures compared well with expected at-rest pressures. However, none of the commonly used procedures adequately captured the structural loading and deformations across the range of stiffness and ground motions for which these reservoirs must be designed. Further, it is unclear whether the current methods of analysis provide results that are conservative or not conservative for engineering design purposes. This identifies a critical need for improved methodologies to analyze and design underground reservoir structures.

The containment function of soil-bentonite (SB) cutoff walls can be enhanced when the adsorption capacity of the SB backfill for targeted contaminants is increased. In this regard, the potential use of three commercially available zeolites, i.e., two chabazites and a clinoptilolite, as SB backfill amendments to enhance the adsorption capacity for two metal sorbates, potassium (K) and zinc (Zn), was evaluated via batch equilibrium adsorption testing. The adsorptive behaviors of K and Zn to both the unamended and zeolite-amended backfill sorbents were nonlinear over the concentration ranges of interest. Depending on the specific zeolite, the addition of only 5% zeolite increased the adsorption capacity relative to that for the unamended backfill sorbent by a factor ranging from 6.2 to 7.3 for K and from 2.8 to 3.4 for Zn, whereas 10% zeolite amendment increased the adsorption capacity by a factor ranging from 7.5 to 13.5 for K and 3.1 to 3.7 for Zn. The lower increase in adsorption capacity for Zn relative to K was attributed to preferential selectivity of K relative to Zn. The adsorption behavior of both K and Zn was consistent with cation exchange as the dominant mechanism, provided that the chemical speciation (complexation) of Zn was taken into account. The results show that adding zeolite to SB backfills can enhance the containment of metals via an increase in adsorption capacity, but the enhanced adsorption capacity will be a function of both the metal and the type and amount of zeolite, such that material specific adsorption studies will be required for practical applications.

The evolution of the soil-water retention curve (SWRC) for cemented paste backfill (CPB) undergoing cement hydration is evaluated in this paper. A pressure plate apparatus and insertion tensiometers in a continuous drying configuration were used to apply and measure suction, respectively, at different CPB curing ages. In addition to this, a novel experimental setup that combines the previously mentioned techniques was developed and validated in an effort to reduce the time associated with SWRC determination. Unconfined compressive strength (UCS) tests and shear wave velocity measurements on CPB specimens provided complementary information regarding the rate of change of material properties attributable to cementation. An exponential maturity relationship commonly used for cement hydration was used to fit this data. The results showed that the SWRC evolved in a continuous manner from low to high suction ranges as cement hydration progressed. The evolution of the air entry value with hydration time was found to be well described by a simple exponential function, regardless of the technique used. The suctions measured in the pressure plate were observed to be, in general, larger than those found by means of insertion tensiometers. Similarly, the overall shape of the SWRC was observed to differ slightly, depending on which testing technique was used.

The installation of dense granular columns by various construction techniques can be used to mitigate liquefaction through a combination of densification, increase of lateral stresses, reinforcement, and drainage. The contributing mechanism of shear reinforcement is isolated and explored using nonlinear three-dimensional (3D) finite-element (FE) analysis. FE models representing both dry and saturated conditions were developed to evaluate cases with and without generation and dissipation of excess pore-water pressures. The shear stress and strain distributions between the granular columns and surrounding soil, and the level of shear stress reduction, were investigated for a practical range of treatment geometries, relative stiffness ratios, vertical stresses, and relative densities of the surrounding soil. A set of 10 acceleration time histories were used as input motions. The FE results show that granular columns undergo a shear strain deformation pattern that is noncompatible with the surrounding soil. As such, the achieved reduction in cyclic stress ratios imposed on the treated soil is far less than that predicted by the conventional shear strain compatibility design approach. Reductions in cyclic stress ratios are insensitive to the applied surface pressure, granular column length/diameter ratio (L/D), and relative density of the surrounding soil for the range of area replacement ratio and column–soil shear modulus ratio examined. A modified design equation to estimate the reduction in cyclic stress ratio provided by dense granular columns is shown to provide good agreement with the FE simulation results.

Dense granular columns can be used to mitigate liquefaction hazards through a combination of densification, increases in lateral stress, reinforcement, and drainage effects. Three-dimensional (3D) nonlinear dynamic finite-element analyses are used to examine the effectiveness of dense granular columns for reducing liquefaction-induced deformations in the event that the triggering of liquefaction in the native soils is not prevented. The finite-element analyses consider unit cells with dense granular columns (improved case) and without granular columns (unimproved case). Parametric analyses are used to isolate aspects related to the different improvement mechanisms. The parametric studies consider a range of area replacement ratios, shear modulus ratios, diameter of granular columns, liquefiable soil depth, hydraulic conductivity, surface pressures, slope angle, penetration resistances in the native soil, and spatial variations in those penetration resistances. A set of 10 acceleration time histories were used as input motions. Dense granular columns were shown to be effective in reducing lateral spreading displacements of sloping ground, even if liquefaction triggering is not prevented. The reductions in lateral spreading displacement are primarily attributable to the reinforcing and strengthening effects of the granular columns, with drainage being a secondary benefit for cleaner sand profiles. The effect of spatially varying penetration resistances as develops around a column are examined and recommendations are developed for selecting an equivalent uniform value for design.

Difficulties in obtaining high-quality soil samples from offshore sites and heavy involvement of lab testing and engineering judgment have necessitated increasing reliance on in situ penetrometer tests, giving continuous penetration resistance profiles. This paper reports a framework for estimating spudcan penetration resistance directly from continuous resistance profile of a full-flow penetrometer (T-bar) test in single-layer clays and calcareous silts. The framework was validated chiefly against centrifuge test data, supplemented by some reported field data.

This work provides a detailed description of the full-scale experimental tests performed on the dynamic behavior of a shallow foundation under intermediate strains. A wind tower supported by the foundation was subjected to a snap-off test, i.e., it was first pulled with a cable and then suddenly released, thus inducing free oscillations of nonnegligible amplitude in the whole system. The motion induced was measured with a digital camera, seismometers, and accelerometers attached to the surrounding ground surface and to the wind tower. An innovative interpretation technique based on optimizing a few meaningful parameters obtained from the recorded time histories was required by the heterogeneity of the data collected and the accuracy needed to deduce the behavior of the foundation plinth. The analyses showed that the rotational stiffness of the foundation plinth was approximately 10 times greater than that of the base joint, which in turn was approximately one order of magnitude greater than that of the wind tower. As a result, the vibration phenomenon was driven by the wind tower, which induced a sort of forced, damped, harmonic excitation in the foundation such that the tower’s oscillations and the foundation’s rocking were decoupled from one another. Seismometer measurements performed on the ground surrounding the foundation plinth enabled an assessment of the geometrical attenuation of the surface vibrations induced by foundation rocking. To the best of the authors’ knowledge, the geometrical attenuation assessments reported in this study are the first to be published on the deformations of the ground surrounding a rocking foundation, and could serve as a useful reference to validate constitutive models for simulating small-strain soil response.

A pair of large centrifuge tests was conducted to evaluate the effect of soil-cement grid reinforcement on the seismic response of a deep soft soil profile. The soil profile consisted of a 23-m-thick layer of lightly overconsolidated clay, underlain and overlain by thin layers of dense sand. Each centrifuge model had two separate zones for a total of four different configurations: a zone without reinforcement, a zone with an embedded soil-cement grid that penetrated the lower dense sand layer and had a unit cell area replacement ratio of $A_r=24\%$, a zone with an embedded grid with $A_r=33\%$, and a zone with a floating grid in the upper half of the clay layer with $A_r=33\%$. Models were subjected to 13 shaking events with peak base accelerations ranging from 0.005 to 0.31 g. This paper examines the effect of the soil-cement grids on the global responses of the soil profiles, and the internal interaction between soil-cement grids and their enclosed soils. Nonlinearities in the dynamic responses and interaction mechanisms are examined using (1) time series of accelerations, shaking-induced excess pore-water pressures, and postshaking reconsolidation settlements; (2) response spectra and spectral ratios; (3) back-calculated composite stress-strain responses; (4) analyses of internal stress distributions between the grids and enclosed soils; and (5) dynamic crack detections and posttest crack mapping in the soil-cement grids. The results provide insights on the dynamic performance of soil-cement grids and an archived dataset for evaluating design procedures and numerical analysis methods.

Past researchers have introduced performance-based methods to simultaneously account for the various sources of uncertainty in the prediction of lateral spread displacements through the incorporation of a probabilistic analytical framework. Although these methods can effectively handle the various sources of uncertainty associated with empirical lateral spread displacement prediction, they are difficult for engineers to perform without the use of specialized numerical tools. This paper introduces a simplified procedure that approximates the results of the performance-based method through the use of lateral spread reference parameter maps. Equations are provided to correct mapped reference parameter displacements for site-specific geotechnical and topographical information to produce hazard-targeted estimates of lateral spread displacement. The simplified performance-based procedure is validated through a comparative study using several soil profiles across several cities in the United States. Results show that the simplified procedure approximates the results from the full performance-based procedure at all evaluated return periods within 3% and/or 4.0 cm.

Slope monitoring is routinely conducted, and observational information such as surface/underground displacements, groundwater levels, and rock bolt forces at multiple locations is collected. How to make use of the monitoring information to reveal failure mechanisms and assess the slope stability is a key issue in slope engineering. This paper presents a method for assessing the slope stability by integrating monitoring parameters with physical analysis. The observed information first was used to back analyze the strength and loading parameters, and then the updated basic parameters were used to calculate the factor of safety or failure probability of the slope. The dominant basic parameters whose uncertainties influence the observed results the most were identified from the probabilistic back analysis. Alert levels were defined in the monitoring parameter space on the basis of a factor of safety or failure probability criterion. A rock slope example was worked out to illustrate the application of the proposed method.

Two parallel adjacent river-crossing bridges performed differently in response to strong shaking (peak ground acceleration $\sim 0.27\mathrm{g}$) and liquefaction-induced lateral spreading during the 2010 M 7.2 El Mayor-Cucapah earthquake. A railroad bridge span collapsed, whereas the adjacent highway bridge survived, with one support pier near the river having modest flexural cracking of cover concrete and a second settling approximately 50 cm. Cone penetration and geophysical test results are presented along with geotechnical and structural conditions evaluated from design documents. This investigation employed an equivalent-static beam-on-nonlinear-Winkler foundation analysis to accurately predict observed responses when liquefaction-compatible inertia demands were represented as spectral displacements that account for resistance from other bridge components. Pier columns for the surviving bridge effectively resisted lateral-spreading demands in part because of restraint provided by the superstructure. Collapse of the surviving bridge was predicted when liquefaction-compatible inertial demands were computed for the individual bent in isolation from other components, and were represented by forces instead of displacements. The poor performance of the settled pier column resulted from bearing-capacity failure in a thin liquefiable layer at the shaft tip.

Earthen slopes encountered in engineering practice typically consist of unsaturated or partially saturated soils. During rainfall, water infiltrates into the slope and causes a reduction in suction. Slope stability is affected by the increase in the degree of saturation as a result of the reduction in normal stress and cohesive strength along potential failure surfaces. Therefore, to determine the geohazard potential, it is important to know the degree of saturation within slopes at shallow depths. Resistivity imaging (RI) is one of the most convenient techniques available for geohazard studies; however, only qualitative saturation profiles can be obtained using this method. Quantification of the degree of saturation has become important for using RI in the evaluation of the geohazard potential of slope failures. The objective of this study was to quantify the degrees of saturation at shallow depths using RI. Electrical resistivity tests were conducted in the laboratory on high plasticity clay (CH) and lean clay (CL) specimens, and to identify the effects of the degree of saturation and cation exchange capacity (CEC). Multiple linear regression (MLR) analyses were carried out on the laboratory resistivity test results, using statistical analysis software SAS. Two MLR models were developed that correlated electrical resistivity with the degree of saturation and CEC. RI tests were conducted on earthen slopes, and using MLR models, degrees of saturation were determined from electrical resistivity values observed at field conditions.