Journal of Geotechnical and Geoenvironmental Engineering

A modified conventional direct shear device was used to measure unsaturated shear strength of two silty soils at low suction values ($\sim 0–50\mathrm{kPa}$) that were achieved by following drying and wetting paths of soil-water characteristic curves (SWCCs). The results revealed that the internal friction angle of the soils was not significantly affected by either the suction or the drying-wetting SWCCs. The apparent cohesion of soil increased with a decreasing rate as suction increased. Shear stress–shear displacement curves obtained from soil specimens subjected to the same net normal stress and different suction values showed a higher initial stiffness and a greater peak stress as suction increased. A soil in wetting exhibited slightly higher peak shear stress and more contractive volume change behavior than that of soil in drying at the same net normal stress and suction.

Failure of foundations induced by earthquakes occurred many times in the past. There is a general lack of data recorded during earthquakes in the field about seismic response of such foundations. According to the results of some previous laboratory tests and numerical analyses, anisotropy of fabric of soil grains has significant influence on dynamic soil response. However, there is hardly any realistic physical data available to analyze the influence of fabric anisotropy on the response of foundations during earthquakes. Centrifuge tests are small scaled model tests which have been widely used to study the mechanism of response and to verify and validate design methods and numerical simulations. In this study, 12 centrifuge tests were carried out to study the effect of fabric anisotropy on seismic response of foundations. Important parameters in the response are evaluated and implications for design are discussed.

Geotechnical engineers can and should take a leading role in incorporating sustainable development goals into the selection of ground improvement design alternatives and construction methods through quantitative assessment of environmental impacts. Since all valid design alternatives must meet project performance requirements, overall cost and environmental impact become two key factors in the decision process. Although methods of cost estimation are well established within geotechnical engineering, simplified methods for assessing impacts to the environment have remained a largely unfulfilled need. In this paper, life cycle analysis, embodied energy, and carbon footprinting are reviewed in the context of geotechnical ground improvement. It is proposed that estimates of life cycle embodied energy and carbon dioxide emissions may be used during the design process by geotechnical engineers to quantify some of the effects of ground improvement on the environment. The life cycle is considered to extend from raw material extraction to the completion of construction. The background presented herein forms the basis for a streamlined energy and emissions assessment model (SEEAM), described in a companion paper.

A streamlined energy and emissions assessment model (SEEAM) is presented that is based on life cycle analysis (LCA) methods. The SEEAM provides geotechnical engineers with the means to quantify the embodied energy (EE) and carbon dioxide (${\mathrm{CO}}_2$) emissions associated with ground improvement projects. A companion paper (Shillaber et al. 2015) provides detailed background for sustainable development and environmental impact assessment, which are at the foundation of the SEEAM. This paper presents the boundary conditions and methodology for this model. Construction of levee LPV 111 in New Orleans, LA is used as a case history example to illustrate the use of the model. This project involved supporting an earthen embankment by deep soil mixing (DSM) elements. Results of a SEEAM analysis of the DSM supported embankment indicate that constructing the levee involved 1,174,000 GJ of EE and 147,000 t of ${\mathrm{CO}}_2$ emissions. For comparison, the SEEAM was also used to estimate the EE and ${\mathrm{CO}}_2$ emissions associated with two other LPV 111 design alternatives; one utilizing prefabricated vertical drains (PVDs) to increase the rate of primary consolidation in the foundation soils, and the other a pile-supported reinforced-concrete T-wall. The results show that the PVD design has the lowest EE and ${\mathrm{CO}}_2$ emissions at 809,000 GJ and 64,000 t, respectively. The concrete T-wall has the greatest EE and ${\mathrm{CO}}_2$ emissions, at 2,755,000 GJ and 211,000 t, respectively (for the materials alone). Despite having the lowest EE, ${\mathrm{CO}}_2$ emissions and cost, the PVD design was not a viable solution because it could not meet a 20-month time constraint placed on the construction to achieve the needed flood protection. When performance criteria are met, quantitative information about environmental impacts, such as EE and ${\mathrm{CO}}_2$ emissions, is useful for making geotechnical decisions for sustainable development.

A component of geotechnical applications involving nonisothermal conditions is the determination of the thermal properties of the ground. This paper presents a new test, called the thermal cone dissipation test (TCT), which overcomes most of the drawbacks observed in current in-situ techniques used to determine the thermal properties of soils. The equipment consists of a cone penetrometer equipped with thermocouples located behind the cone point. The TCT is pushed in the ground at the standard penetration rate of $2\mathrm{cm}/\mathrm{s}$, and the friction between the cone and the soil increases the cone temperature. The temperature decay is recorded as a function of time (for approximately 30 min) and this information is used to estimate the thermal conductivity and other thermal properties of soils. The calibration of the curves proposed in this work to estimate the thermal properties of the ground was based on three main activities: (1) in-situ experiments, carried out at three different locations involving different soil types; (2) laboratory investigation, aimed at obtaining the thermal conductivity of the soils studied in the field; and (3) numerical simulations, used to validate the proposed numerical models against the experimental data and to populate the proposed calibration curves including ground conditions to explore in the field. Very good agreements between field, laboratory and numerical results were obtained for the 11 TCTs studied in this research. It is expected that the proposed calibration curves will be enhanced in the future as additional experimental data become available.

This study presents 3M, an analytical method to estimate the skin friction of bored piles in sands. It is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading. These include the development of a shear band, its potential expansion as induced by soil dilatancy, and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils. The resulting analytical equations are easy to apply and insert in a worksheet. The procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load, whereas the increment of horizontal stresses is evaluated by the closed-form solution for the expansion of a cylindrical cavity into a dilatant elastic–perfectly plastic medium. The effectiveness of the 3M method in predicting shaft friction has been checked against numerical results, centrifuge, and full scale pile load tests. Nevertheless, prior to use in design practice, preliminary validation is required with more well-documented experimental data from load tests on instrumented bored piles.

This paper presents a systematic approach for relating fundamental (soil element) strength-degradation models with cyclic full-flow penetration tests. The approach is then employed to enhance the commonly-used exponential strain-softening model by adding a parameter that regulates the slope of degradation. Using the developed methodology, a new relationship between ${\xi }_{95}$ and $N_{95}$ (the shear strain and cycle number associated with 95% degradation in strength and penetration resistance, respectively) is established for the enhanced strain-softening model. The additional parameter of the enhanced model is optimized against various cyclic field test results and found to be roughly constant. It is demonstrated that the new model independently reproduces the field test results when introduced into advanced numerical analyses of cyclic penetration tests.

Ground improvement via jet grouting is commonly used to strengthen weak ground and/or create hydraulic barriers. Delivering soilcrete columns with tightly controlled and known diameters is critical to performance; however, techniques to assess jet grout geometry during construction are lacking. This paper reports the results of a study on electrical resistivity imaging of soilcrete by investigating the effects of electrode configuration and electrical protocol type on laboratory scale soilcrete columns constructed in a tank filled with sand. Experimental results are verified via numerical modeling and the model is used to analyze the changes in soilcrete resistivity that result from geometric variation. The results of this study indicate that resistivity imaging with direct contact electrodes can estimate the diameter of laboratory scale jet grout columns to within $\pm 5\%$ of the as-built column diameter. A relationship between electrode spacing and column diameter is identified and quantified to more readily extend the diameter estimation approach developed in this research to field-scale geometries. Additionally, time lapse monitoring of soilcrete resistivity was performed over the course of curing. Results indicate that resistivity imaging should be performed as early as possible to obtain the greatest resistivity contrast between the soilcrete and in situ soil.

Simplified performance-based liquefaction triggering procedures have sought to address observed inconsistencies in predicted liquefaction triggering hazards across the United States resulting from conventional, pseudoprobabilistic analysis procedures. Unfortunately, current simplified performance-based procedures are limited to use with a single liquefaction triggering curve. This paper introduces a modified performance-based procedure and applies it to a different liquefaction triggering curve that is currently used by many engineering practitioners. The modified procedure is derived, and the concept of liquefaction loading parameter maps is introduced. Validation of the modified procedure against the full performance-based procedure is performed for multiple U.S. cities and soil profiles at three different return periods. The results of the validation demonstrate that the modified performance-based procedure reasonably approximates the full performance-based procedure across multiple return periods, though it tends to slightly underpredict the full performance-based results on average. Some discussion regarding the limitations and potential benefits of this modified procedure is provided.

Miniature cone penetration tests were conducted in centrifuge models to investigate the effects of various testing conditions on the tip resistance including the particle size, centrifugal acceleration related to stress level and prototype cone diameter, container wall boundary, and penetration rate. Two sand materials were selected: (1) Saemangeum and (2) silica sands. The former is natural sand with high fine contents and the latter is clean sand. A series of penetration tests was performed in six saturated soil models using an in-flight robot. Three Saemangeum sand models were prepared by means of the moist compaction method. The silica sand models were made by the air-pluviation method. Modeling of models was adopted to investigate the particle size effect using 7-, 10-, and 13-mm-diameter cones. The centrifugal acceleration effect also was studied by comparing the tip resistance profiles obtained at different g-levels using the 10-mm-diameter miniature cone. The results indicated that the particle size effect was negligible for both sands using 7- to 13-mm-diameter cones. However, the tip resistance decreased with increasing g-level at a shallower depth than a given critical depth ($D_{cr}$), especially for dense sand. Then, it merged to a single value at a deeper depth than $D_{cr}$. The $D_{cr}$ was affected by g-level and soil density. Finally, an empirical correlation to estimate the soil density from the tip resistance in the centrifuge was proposed.

This paper presents an investigation of the effect of clay consolidation on contaminant transport through compacted clay liner (CCL) and composite geomembrane liner (GML)/CCL landfill bottom liner systems. Numerical simulations were conducted using the CST2 model and consider coupled consolidation and contaminant transport with representative geometry, material properties, and applied stress conditions. Simulation results indicate that, depending on conditions, consolidation can have important effects on contaminant breakthrough time, mass flux, cumulative mass outflow, and concentration distribution within the CCL, not only during the course of the consolidation process but also long after consolidation has completed. In general, the effects of CCL consolidation increase with increasing CCL thickness, increasing magnitude of applied stress, decreasing loading time, increasing CCL organic carbon fraction, and increasing variation of effective diffusion coefficient. Traditional advective-dispersive transport analyses fail to consider transient advection and associated changes in material properties caused by CCL consolidation, and thus can lead to significantly different results. Considering the complexity of the process and the number of variables involved, case-specific analysis is recommended for the evaluation of the significance of CCL consolidation for contaminant transport through a CCL-based liner system.