Journal of Geotechnical and Geoenvironmental Engineering

Frictional resistance between soil and steel reinforcements develops as a result of relative displacement at the soil-reinforcement interface and is typically characterized using interface shear or reinforcement pullout tests. The soil-reinforcement interaction between uniformly-graded soils and metal reinforcements has been well-characterized. However, the interface response of well-graded gravelly soils and ribbed steel strips is primarily based on lower-bound estimates of pullout resistance using databases of single isolated reinforcement pullout tests. Increases in horizontal stresses that develop in tall mechanically stabilized earth (MSE) walls are often accounted for in design by reducing the reinforcement spacing; however, the effect of possible frictional interference between closely spaced inextensible reinforcements has not been explored. Two reinforcement pullout apparatuses have been developed to study the soil-reinforcement interaction and effect of reinforcement proximity in a well-graded sandy gravel. A single strip pullout apparatus was developed to establish the baseline frictional resistance, comparable to typically-conducted pullout tests. The assessment of reinforcement strip interaction effects possible in closely spaced reinforcements was evaluated using a multistrip pullout apparatus. The effects of passive resistance at the front facing that alters the load-displacement response and contribute to epistemic uncertainty were mitigated using a well-characterized, soft boundary condition. Generally, the available resistance was observed to increase with increases in the localized stiffness, whereas the secant stiffness of the resistance-displacement response reduced with increases in localized stiffness. Current pullout resistance factor models are shown to be conservative and biased, and recently proposed calibrated exponential models more accurately capture the measured responses. Fitted isolated and confined strip models presented in this paper should help practitioners estimate the frictional resistance of ribbed steel strips in sandy gravel soils and incorporate increases resulting from closely spaced reinforcements into design methodologies and numerical simulations.

Large repetitive wheel loads from heavy haul and passenger trains can cause significant track deformation that leads to poor track geometry and safety issues. The inclusion of geosynthetics and rubber mats (i.e., shockmat) in critical sections in the track for reducing these adverse effects was further examined through an extensive field trial in the town of Singleton, New South Wales (NSW), Australia. Four types of geosynthetics and a shockmat were installed below the ballast layer in selected sections of track constructed on three different subgrades (soft alluvial clay, hard rock, and concrete bridge), and the performance of the instrumented track was monitored for five years under in-service conditions including tamping operations. The measured stress-deformation response indicates that the geosynthetics effectively control the long-term and transient strains in the ballast layer, with the obvious benefit of reducing maintenance costs. The study also showed that the aperture size of geogrids in the range of 1.1 times the mean particle size of the ballast was most effective. The placement of shockmat on a concrete bridge contributed to reduced ballast breakage. The dynamic amplification of stresses induced by moving trains was observed, and it became more pronounced at higher axle loads and train speeds. The dynamic track modulus was evaluated adopting the concept of modified beam on an elastic foundation (BOEF), and this approach was found to be largely influenced by the axle load, train speed, placement of synthetic inclusions, and type of subgrade.

This paper explores the possibility of using high-resolution fiber-optic distributed sensing for in situ geotechnical estimation of soil shear modulus distribution with depth. It is shown that a recursive analysis of an elastic problem together with a measured vertical strain can assist in evaluating the sought stiffness values. It is suggested that high-resolution fiber-optic distributed sensing can provide the necessary strain for the proposed process. The approach was demonstrated in a field trial, entailing a stratified soil profile including a thin sand layer encapsulated between two clay layers. Results of the suggested profiling method are compared against data from a geophysical survey and against correlations with conventional in situ testing. Excellent agreement is exhibited between the different methods, indicating aptitude and viability of the idea for implementation as a geotechnical investigative tool.

Sodium bentonite (Na-bentonite) is a high-swelling clay with low hydraulic conductivity ($k$) that is commonly used for hydraulic and chemical containment applications (e.g., engineered barriers, seals, and grouts) to limit advective (hydraulic) flow and chemical transport. In Na-bentonite pastes and other paste-like substances (e.g., high slump backfills, filter cakes, well seals, and slurried mine tailings) that exhibit low values of $k$ ($<{10}^{-9}\mathrm{m}/\mathrm{s}$), diffusion can be a significant chemical transport process such that measurement of diffusion properties of these materials may be necessary. Based on these considerations, diffusion of NaCl from Na-bentonite pastes with porosities ranging from 0.96 to 0.98 was evaluated by adapting standardized test methods for diffusive leaching of contaminants from stabilized/solidified waste to a dialysis procedure commonly used for clay purification. The apparent diffusion coefficients ($D_a$) measured with the proposed dialysis-leaching test method ranged from ${2.26\times 10}^{-10}$ to $1.37\times {10}^{-9}{\mathrm{m}}^2/\mathrm{s}$ for initial NaCl concentrations ranging from 1.0 to 0.1 M, respectively. Values of $D_a$ decreased as the exchangeable sodium percentage of the bentonite increased and as the average concentration of NaCl remaining in the bentonite decreased. The diffusion results were in agreement with expectations based on the literature and diffuse double layer theory. The dialysis-leaching test method may offer a simple, fast ($\le 2\mathrm{weeks}$), and inexpensive ($<\$300$ per setup) approach to measure diffusion in bentonite pastes and other paste-like substances.

Deep excavations may cause settlement and damage to adjacent buildings, even if they are found on piles. The corresponding pile deformations are determined by axial and lateral effects. This paper describes an analytical model relating axial pile deformation to the vertical soil displacement resulting from the deep excavation and also suggests ways to determine the pile response to lateral displacements. The axial pile-soil interaction is clearly different for end-bearing and friction piles. Common generalizations that end-bearing piles settle the same as the soil settlement at the base level and friction piles with the ground surface settlement present lower and upper bounds, which are only valid for certain idealized cases. The settlement of piles with a large component of shaft friction is determined mainly by the actual load on the pile relative to the pile ultimate capacity. The lateral pile response is governed mainly by the relative stiffness of the pile to the soil. The proposed model was validated with measurements of the North South Line project in Amsterdam.

Pile driving is a complex dynamic process where little insight has been garnered in terms of the energy transfer from the driver to the soil and surrounding structures. Ground motion measurements during driving of full-scale steel H-piles with diesel hammers are presented. The key feature of this work is the in-depth sensor installation starting very close to the pile (0.2 m), at other radial distances from the pile, and at various depths in the ground. Differences in wave sources from the tip and the shaft of the pile as well as wave attenuation coefficients are revealed from the sensor measurements. Attenuation relationships fitted through the data could be used to predict ground motion that could cause shakedown settlement. A conventional line array of surface-mounted geophones was also used and results are presented.

A generalized framework is applied to predict consolidated undrained VHM failure envelopes for surface circular and strip foundations. The failure envelopes for consolidated undrained conditions are shown to be scaled from those for unconsolidated undrained conditions by the uniaxial consolidated undrained capacities, which are predicted through a theoretical framework based on fundamental critical state soil mechanics. The framework is applied to results from small-strain finite-element analyses for a strip and circular foundation of selected foundation dimension and soil conditions, and the versatility of the framework is validated through a parametric study. The generalized theoretical framework enables consolidated undrained VHM failure envelopes to be determined for a practical range of foundation sizes and linearly increasing soil shear-strength profiles through the expressions presented in this paper.

Hydraulic conductivity was evaluated for eight commercially available geosynthetic clay liners (GCLs) permeated with leachate characteristic of low-level radioactive waste (LLW) disposal facilities operated by the U.S. Department of Energy (DOE). Two of the GCLs (CS and GS) contained conventional sodium bentonite (Na-B). The others contained a bentonite–polymer mixture (CPL, CPH, GPL1, GPL2, and GPH) or bentonite–polymer composite (BPC). All GCLs (except GPL2 and GPH) were permeated directly with two synthetic LLW leachates that are essentially identical, except one has no radionuclides (nonradioactive synthetic leachate, or NSL) and the other has radionuclides (radioactive synthetic leachate, or RSL). Hydraulic conductivities to RSL and NSL were identical. For the CS and GS GCLs, the hydraulic conductivity gradually increased by a factor of 5–25 because divalent cations in the leachate replaced native sodium cations bound to the bentonite. The CPL, GPL1, and GPL2 GCLs with low polymer loading (1.2–3.3%) had hydraulic conductivities similar to the conventional GCLs. In contrast, hydraulic conductivity of the CPH, GPH, and BPC GCLs with high polymer loading ($\ge 5\%$) to RSL or NSL was comparable to, or lower than, the hydraulic conductivity to deionized water. Permeation with leachate reduced the swell index of the bentonite in all of the GCLs. A conceptual model featuring pore blocking by polymer hydrogel is proposed to explain why the hydraulic conductivity of bentonite–polymer GCLs to LLW leachates remains low even though the leachate inhibits bentonite swelling.

Boiler slag is a by-product that is derived from coal combustion in wet bottom boilers. Due to its low bulk density, in the compacted state it is an attractive alternative for use as structural fill material. Compared with other coal combustion by-products, the geotechnical and leaching properties of boiler slag are less known. This paper presents the results of laboratory and field investigation of boiler slag, produced in boilers where brown coal is used as fuel. Chemical and mineralogical composition, as well as mechanical properties were studied in the laboratory. A test embankment was constructed in order to identify compaction behavior and the achieved layer stiffness. A lysimeter was installed as part of the test embankment for the long-term monitoring of the quality and quantity of percolated water.