Journal of Geotechnical and Geoenvironmental Engineering

This paper describes the development and multistep validation of a one-dimensional, large strain consolidation coupled contaminant transport model with nonlinear and nonequilibrium sorption kinetics. The RCM-XPORT2K model uses the CS2 large strain consolidation approach for modeling the deforming saturated porous medium consolidating under a surcharge stress, coupled with reactive advective/dispersive solute transport through the medium, capped with a thin-layered reactive sequestering geocomposite known as a reactive core mat (RCM). In addition to assumptions made in previously developed, one-dimensional consolidation coupled contaminant transport model RCM-XPORT2, the RCM-XPORT2K model accounts for sediment- and sorbent-specific sorption kinetics to model nonlinear, and nonequilibrium sorption behavior. Validation of the model is presented by simulating: (1) sorption kinetics tests performed on sediment sampled from Neponset River, Milton, Massachusetts, USA and a commercial product, CETCO Organoclay PM-199; (2) solute transport from the large strain consolidation coupled contaminant transport tests with ${\mathrm{Br}}^{-}$ and ${\mathrm{Cl}}^{-}$ using a high water content inert silt sample (New York Silt); and (3) the naphthalene transport and breakthrough times observed in upflow column tests with Neponset River sediment with various overlying cap layers.

In this study, the uplift load-carrying capacity of micropiles was investigated, focusing on the effect of various installation conditions including installation angle ($\theta$), spacing ($S$), and group configuration. For this purpose, a series of uplift model load tests was conducted using single micropiles (SMP) and group micropiles (GMP). The uplift load capacity of both SMP and GMP increased with $\theta$ up to 30° but decreased for a higher installation angle of $\theta =45°$. Micropile spacing had less effect on the uplift load capacity for GMP. The uplift load-carrying mechanism of inclined micropiles is proposed based on decomposed axial and lateral loads and resistance components. Based on the proposed load-carrying mechanism, axial and lateral load capacity ratios were proposed and adopted to formulate the uplift load-capacity equation for inclined micropiles. For GMP, the group-effect factor was proposed based on the reduction effect of group micropiles on the overall uplift load capacity. Full-scale uplift load tests were conducted to check the validity of the proposed method. Both SMP and GMP were constructed and tested. It was observed that the estimated results using the proposed method were in good agreement with the measured results.

Ballast degradation or fouling often associated with deteriorating railroad track performance refers to the condition of a new ballast layer changing its aggregate particle size and shape properties with usage. Fouling is mainly due to degradation or breakage of ballast aggregates under traffic loading, although other fine materials intruding can also contaminate a clean and uniformly graded ballast layer. Previous research efforts have focused on studying the degraded ballast behavior of clean ballast aggregates mixed with finer materials such as sand, mineral filler, subgrade clay, and coal dust. However, this approach cannot fully represent the cases where fouled ballast composition is made up of aggregate particle breakdown or intrusion of foreign materials. In the field, over two-thirds of the ballast fouling cases are due to ballast aggregate particle abrasion and breakage, which necessitates a better basic understanding of the field degradation trends and the related changes in ballast gradation and aggregate particle morphology. This paper describes an experimental approach to quantify ballast gradation and aggregate morphological properties at different stages of degradation studied through Los Angeles (LA) abrasion testing and aggregate image analysis technique in the laboratory. The results from this experimental study were intended to quantify changes in ballast gradation and aggregate morphological properties due to the LA abrasion–based degradation process and link different physical properties of the ballast material to the previously defined fouling index (FI) as a practical indicator of fouling conditions. A good correlation was found between percent changes in aggregate shape properties quantified by image analysis of ballast particles larger than 9.5 mm ($3/8\text{in.}$) and the number of turns of the LA abrasion drum. Further, the study findings are also linked to the field degradation trends reported in the literature, which necessitates ballast gradation and aggregate shape property changes also be tracked in the field and better documented to the FI when studying fouled ballast behavior.

Wrinkles were quantified and compared for 1.5-mm-thick, high-density polyethylene (HDPE) geomembranes in 20-m-long and 13-m-wide control sections that were identical except for color—one had a black geomembrane, whereas the other, a coextruded white surface. On the two particular sunny summer days when wrinkles were compared, the peak temperature of the white geomembrane was 21–23°C cooler than that for the black geomembrane. Relative to the black geomembrane, wrinkles on the white geomembrane formed later in the morning and went away sooner in the evening and, at the hottest part of the day, were less frequent (approximately 12 versus 24% of the area) and had a much shorter maximum connected length (21% of maximum black length).

The complex behavior of unsaturated soils can be partly attributed to the co-existence of networks of liquid bridges and saturated pockets in the soil void space. Past studies have examined how the water bridges and pockets behave when suction changes in soils. The study described here uses microfocused industrial X-ray computed tomography (X-ray μCT), to closely examine unsaturated geomaterials. In this study, an unsaturated glass bead sample was scanned in a suction-controlled setup. Images of the interphase microstructure were processed using image processing techniques. Water-air and solid-water interfaces were distinctively identified using phase-based segmentation. The soil water characteristic curve (SWCC) of the tested granular specimen was quantified by processing microstructural images that were obtained with X-ray computed tomography (CT) scanning. Values of interfacial contact angle were measured on orthogonally projected planes, and the associated results are presented and discussed.

The geotechnical properties (e.g., density, friction angle, and cohesion) of waste material in landfills and dumpsites vary significantly, depending on the waste composition and compaction practices. This variability results in a major source of uncertainty in slope stability analysis for municipal solid waste (MSW) disposal sites. This study presents a novel probabilistic approach for slope stability analysis by backcalculation, assigning probability distributions to waste material properties. Using backanalysis of historical, well-documented failed waste slopes, probability distributions for the density, friction angle, and cohesion of MSW are assigned based on the disposal method (landfill or dumpsite) and waste material composition (fibrous or food waste materials). MSW with (1) major food waste contents has lower shear strength (friction angle = 22.2° and cohesion = 19.2 kPa) in comparison with MSW with major fibrous waste contents (friction angle = 34° and cohesion = 14 kPa) and (2) compaction practices in landfills compared to dumpsites result in 20% higher shear-strength properties for the waste material. The application of this new approach and its advantages is demonstrated/validated using four case studies (Rumpke, Durban, Istanbul, and Sarajevo).

Drilled shaft foundations commonly experience torsional loads, in addition to axial and lateral loading. Such cases include loads on mast arm traffic sign and signal poles, or seismically induced inertial loading of foundations supporting skewed or curved bridges. Despite the prevalence of drilled shafts, the understanding of the actual resistance to torsion provided by these deep foundation elements is not well established. To help address this gap in knowledge, two instrumented drilled shafts were constructed to evaluate the torsional capacity and load transfer at full scale. Both monotonic quasi-static and cyclic loading tests were performed. The imposed rotation and corresponding torque was monitored using string potentiometers and load cells, respectively. Strain gauges installed to measure shear strains facilitated computation of the torsional load transfer, which is described in detail. Design procedures for the calculation of the ultimate total and unit torsional resistances of drilled shafts are proposed and resulting estimates compared against the resistances observed in the testing program and other studies reported in the literature. The rational design methodology proposed herein overpredicts or underpredicts the torsional capacity, indicating the need for the development of improved methods for assessing the torsional resistance of drilled shaft foundations.

Soil erosion is a major problem in civil engineering. It is involved in bridge scour, meander migration, levee overtopping, internal erosion of earth dams, surface erosion of embankments, and cliff erosion. The best way to predict the erodibility of a soil is to measure it directly on a site-specific basis by in situ testing in the field or by testing samples in the laboratory. The borehole erosion test (BET) is a new in situ soil-erosion test proposed to measure the erosion of the walls of a borehole while wet rotary drilling takes place. The increase in diameter of the borehole is measured with borehole calipers as a function of time and for a given flow velocity. The result is a profile of soil erodibility as a function of depth. Tests in clay and in sand conducted at the National Geotechnical Experimentation Sites at Texas A&M University are presented and compared with laboratory soil-erodibility tests with the erosion function apparatus (EFA) on samples taken from the same borehole. Computational fluid dynamics (CFD) numerical simulations of the velocity and shear stress field for the BET are also presented. The experimental and numerical results show the lessons learned and lead to an evaluation of the advantages and drawbacks of this new test.

Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses.

Soil classification systems worldwide capture great physical insight and enable geotechnical engineers to anticipate the properties and behavior of soils by grouping them into similar response categories based on their index properties. Yet gravimetric analysis and data trends summarized from published papers reveal critical limitations in soil group boundaries adopted in current systems. In particular, current classification systems fail to capture the dominant role of fines on the mechanical and hydraulic properties of soils. A revised soil classification system (RSCS) for coarse-fine mixtures is proposed herein. Definitions of classification boundaries use low and high void ratios that gravel, sand, and fines may attain. This research adopts $e^{\max }$ and $e^{\min }$ for gravels and sands, and three distinctive void ratio values for fines: soft $e_F{|}^{10\mathrm{kPa}}$ and stiff $e_F{|}^{1\mathrm{MPa}}$ for mechanical response (at effective stress 10 kPa and 1 MPa, respectively), and viscous $\lambda ·e_F{|}^{\mathrm{LL}}$ for fluid flow control, where $\lambda =2\log (\mathrm{LL}-25)$ and $e_F{|}^{\mathrm{LL}}$ is the void ratio at the liquid limit. For classification purposes, these void ratios can be estimated from index properties such as particle shape, the coefficient of uniformity, and the liquid limit. Analytically computed and data-adjusted boundaries are soil-specific, in contrast with the Unified Soil Classification System (USCS). Threshold fractions for mechanical control and for flow control are quite distinct in the proposed system. Therefore, the RSCS uses a two-name nomenclature whereby the first letters identify the component(s) that controls mechanical properties, followed by a letter (shown in parenthesis) that identifies the component that controls fluid flow. Sample charts in this paper and a Microsoft Excel facilitate the implementation of this revised classification system.

Elevated temperatures in municipal solid waste landfills can pose health, environmental, and safety risks because they can generate excessive gases, liquids, pressures, and heat that can damage landfill infrastructure. This paper discusses mechanisms that can lead to elevated temperatures in the landfill and presents a case history to establish trends in gas composition, leachate collection, settlement, and slope movement. In general, landfill gas composition changes from predominantly methane [50–60% volume-to-volume ratio (v/v)] and carbon dioxide (40–55% v/v) to a composition of carbon dioxide (60–80% v/v), hydrogen (10–35% v/v), and carbon monoxide [$>\mathrm{1,500}$ parts per million per volume (ppmv)] as temperatures elevate. As waste temperatures increase, gas and leachate pressures also increase, resulting in odors, leachate outbreaks, and potential slope instability. These observations are summarized in a progression of elevated temperature indicators that are related to field manifestations and possible remedial measures. Finally, biological and chemical processes are proposed to explain the changes in internal landfill processes.