Journal of Geotechnical and Geoenvironmental Engineering

The observational method was used to design and construct an embankment over a deposit of soft sludge. The first part of the paper describes the case history of the project. The second part describes the use of analytical models as part of the observational method. The finite-element method and one-dimensional consolidation solution were used as prediction models. Bayesian updating was used to revise the material properties with observed performance. Advantages and limitations of updating are presented.

Erosion was one of the major causes for the failure of New Orleans levee system during Hurricane Katrina. Protection of flood walls from erosion failure can be achieved in many different ways. This study consisted of experimental research to develop engineered flood wall surfaces that can reduce the erosion energy of the plunging water before the water hits the levee surface, so that the flood protection system becomes more resilient. Test results were compared to hydrodynamics simulation results by using FLOW3D. The results revealed that the erosion resistance of levees can be substantially reduced by providing protective structures at the surface of the flood walls. An effectively designed protective structure could reduce the erosion depth as much as 40% and extend the erosion time as much as 400%.

Design of laterally loaded cast-in-place shafts that pass through the reinforcement behind a mechanically stabilized earth (MSE) wall often requires isolation of the shafts from the MSE mass and socketing of the shafts into the underlying stable foundation material, such as bedrock. Sizeable cost and time savings could be realized, while maintaining stability if the shaft could be supported by the MSE mass alone with no rock socket. Construction, instrumentation, and testing of multiple 0.9-m-diameter shafts solely supported by the geogrid-reinforced mass behind a 6-m-high MSE block wall were conducted for the Kansas Department of Transportation (KDOT). This paper describes the design, construction, and instrumentation of the wall and shafts and the results from the lateral load tests of three shafts tested together as a group compared with shafts that were tested individually. This testing protocol was adopted to evaluate the shaft group effect and the effect of shaft distance from the back of the wall facing. All shafts discussed had lengths that were equal to the full height of the wall. Results for both load and deflection of the shafts and the deflections of the wall facing during loading are presented with preliminary design recommendations.

There is currently a lack of established calculation methods for the geotechnical design of heat exchanger piles, although the technology is experiencing a fast expansion. Instead of quantifying the effects of temperature changes on the static behavior of heat exchanger piles, the common geotechnical practice is to apply a large overall security factor. This is done to be on the side of safety with respect to thermal effects. The few existing in situ experiments show that applying a thermal load induces a significant change in the stress-strain state of a pile. This paper presents a geotechnical numerical analysis method based on the load-transfer approach that assesses the main effects of temperature changes on pile behavior. The method is validated on the basis of in situ measurements of the loads and deformations experienced by heat exchanger test piles. The occurrence of critical design situations is further discussed. Some conclusions are formulated on concrete failure and the full mobilization of the pile shaft friction and base resistance during the operation of the heat exchange system.

This paper presents the results from an experimental investigation designed to examine the effect of soil-core development and cyclic loading on the shaft resistance developed by open-ended piles in sand. An instrumented open-ended model pile was installed either by driving or jacking into an artificially-created loose sand deposit in Blessington, Ireland. The tests provided continuous measurements of the soil-core development and the radial effective stresses during installation and subsequent load tests. The equalized radial effective stresses developed at the pile-soil interface were seen to be dependent on the degree of soil displacement (plugging) experienced during installation, the distance from the pile toe, and the number of load cycles experienced by a soil element adjacent to the pile shaft. A new design method for estimating the shaft capacity of piles in sand is proposed and compared with measurements made on prototype field-scale piles.

Recent large-magnitude ($M>7$) earthquakes have caused numerous failures induced by surface faulting, demonstrating the need to account for tectonic deformation in seismic design. Thanks to their usually high rigidity, embedded (e.g., caisson) foundations may divert the fault rupture and lead to favorable performance, whereas surface or piled foundations may fail. We present a series of centrifuge model tests to investigate the response of caisson foundations embedded in a cohesionless soil stratum, the base of which is subjected to reverse faulting. We elucidate the interplay between the propagating fault rupture and the caisson, focusing on the role of the location of the outcropping rupture relative to the caisson. The rigid-body of the caisson causes diversion and/or bifurcation of the shear localization, which is forced to develop preferentially around the edges of the caisson. The observed failure pattern and the consequent caisson response depend strongly on the exact caisson position relative to the fault. We employed three-dimensional (3D) finite-element (FE) modeling and validated it by comparing to centrifuge test results. The numerical method captures the general interaction mechanisms, showing satisfactory (if not always perfect) agreement with experiments. We then employ the validated numerical method in a parametric investigation, providing further insight into the different possible modes of foundation response.

The sliding-block model is often used for the prediction of permanent coseismic displacements of natural slopes and earth structures. This model assumes motion in an inclined plane but does not consider the decrease in inclination of the sliding soil mass as a result of its downward motion, which is the usual condition in the field. The paper studies the above effect and proposes an empirical equation correcting the predictions of the sliding-block model. The investigation is performed by using a recently developed multiblock model. The equation correcting the predictions of the sliding-block model depends on the slip length, the difference in inclinations of the upper and lower part of the slip surface, the seismic displacement predicted by the sliding-block model and the maximum value of the applied horizontal acceleration.

This study investigates the interaction between soil and pipeline in sand subjected to lateral ground displacements with emphasis on the peak force exerted to a bended elbow-pipe. A series of three-dimensional (3D) finite-element (FE) analyses were performed in both opening and closing modes of the elbow section for different initial pipe bending angles. To model the mechanical behavior of sands, two soil models were adopted: Mohr-Coulomb and Nor-Sand soil model. Investigations also included the effects of pipe embedment depth and soil density. Results show that the opening mode exhibits higher ultimate forces and greater localized deformations than the closing mode. Nondimensional charts that account for pipeline location, bending angle, and soil density are developed. Soil-spring pipeline analyses of an elbow-pipe were performed using modified $F-\delta$ soil-spring models based on the 3D FE results and were compared to the findings of conventional spring model analyses using the standard two-dimensional soil-spring model. Results show that the pipe strain does not change in the closing mode case. However, in the opening mode case, the pipe strain computed by the modified analysis is larger than that by the conventional analysis and the difference is more pronounced when the pipe stiffness is stiffer.

A new type of ground treatment method is developed to improve the engineering properties of coarse-grained soils. By using biochemical concepts derived from recent discoveries into how organisms produce silicified skeletons, a silicification process is reported that offers environmental and physical advantages over some traditional methods by using nontoxic, commercially available components with a low potential for adverse environmental effects. Silicification begins by first pretreating the soil with a commercially available cationic polyelectrolyte, which is then followed by injecting a mixture of commercial sodium silicate and buffer. The silicification solutions have a pH of 5.0–5.5, weakly acidic values that are within the range of surface soil environments in temperate weathering regions. Gel time is regulated by the sodium silicate or polyelectrolyte concentration. The compressive strengths are measured as a function of polyelectrolyte type and concentration by using samples of Ottawa $20/30$ sand silicified with a 20% sodium silicate by volume. Unconfined compressive strengths range from 150 to 198 kPa and are shown to be equal to or higher than soils treated at similar silicate concentrations with traditional and alternative formulations. Drained triaxial compression test results show that silicification improves strength and initial stiffness and increases the amount of volume change attributable to dilation. In principle, the methods developed in this paper for coarse-grained soils are also applicable to fractured rock and to fine-grained soils. Developing materials and processes for ground treatment by using inspiration from biological systems offers the promise of improved geomechanical performance, lower embodied energy, and lower cost than current treatment methods.

The embodied energy (EE) and gas emissions of four design alternatives for an embankment retaining wall system are analyzed for a hypothetical highway construction project. The airborne emissions considered are carbon dioxide (${\mathrm{CO}}_2$), methane (${\mathrm{CH}}_4$), nitrous oxide (${\mathrm{N}}_2\mathrm{O}$), sulphur oxides (${\mathrm{SO}}_X$), and nitrogen oxides (${\mathrm{NO}}_X$). The process stages considered in this study are the initial materials production, transportation of construction machineries and materials, machinery operation during installation, and machinery depreciations. The objectives are (1) to determine whether there are statistically significant differences among the structural alternatives; (2) to understand the relative proportions of impacts for the process stages within each design; (3) to contextualize the impacts to other aspects in life by comparing the computed EE values to household energy consumption and car emission values; and (4) to examine the validity of the adopted EE as an environmental impact indicator through comparison with the amount of gas emissions. For the project considered in this study, the calculated results indicate that propped steel sheet pile wall and minipile wall systems have less embodied energy and gas emissions than cantilever steel tubular wall and secant concrete pile wall systems. The difference in ${\mathrm{CO}}_2$ emission for the retaining wall of 100 m length between the most and least environmentally preferable wall design is equivalent to an average 2.0 L family car being driven for 6.2 million miles (or 62 cars with a mileage of $10,000\mathrm{miles}/\mathrm{year}$ for 10 years). The impacts in construction are generally notable and careful consideration and optimization of designs will reduce such impacts. The use of recycled steel or steel pile as reinforcement bar is effective in reducing the environmental impact. The embodied energy value of a given design is correlated to the amount of gas emissions.

The evolution of the field saturated hydraulic conductivity of four covers located on a reclaimed saline-sodic shale overburden from oil sands mining is presented. Three covers consisted of a surface layer of peat/glacial topsoil over a mineral, soil. and one cover was a single layer of mixed peat and mineral soil. Measurements of the field saturated hydraulic conductivity of the cover and shale materials were made with a Guelph permeameter between 2000 and 2004. The hydraulic conductivity of the cover materials in the multilayered covers increased by one to two orders of magnitude over the first few monitoring seasons. The hydraulic conductivity of the single-layer cover system, which was placed three years before the multilayered covers, marginally increased from 2000 to 2002 and then remained relatively unchanged. The hydraulic conductivity of the shale underlying all four covers increased approximately one order of magnitude. Soil temperature measurements indicated that one freeze/thaw cycle occurred each year within all cover soils and the surficial overburden. This suggests that freeze/thaw effects were the cause of the observed increases in hydraulic conductivity, as previously observed by other researchers working on compacted clays.

Small-scale tests were carried out on a monopile and fin piles to determine the effect the length of fins had upon the lateral displacement of cyclically loaded piles. A variety of loading conditions were applied to model piles in a dense sand by using a mechanical loading system. Ten thousand cycles were used in each test to represent 20 years of environmental loading on offshore structures. Variables included the magnitude, frequency, and direction of the load; the type of pile tip; and the length of the fins. The reduction in pile head displacement was used as a measure of the efficiency of the fins. The tests show that the fins reduced the lateral displacement by at least 50% after 10,000 cycles.