IFCEE 2018: Innovations in Ground Improvement for Soils, Pavements, and Subgrades

Biofilm can interconnect porous media grains with exopolysacharide (EPS). This inter-particle bridging can affect the mechanical behavior of soils. However, the research on the mechanical behavior of biofilm-treated soil is very limited and shows contradictory conclusions. The goal of this paper is to further investigate the mechanical behavior of biofilm-treated sand. Three types of tests at variable conditions were conducted, including anaerobic tests, syringe tests, and triaxial tests. This study utilized Staphylococcus epidermidis (S. epidermidis, ATCC 35984), facultative anaerobic, and gram-positive bacteria, to induce biofilm formation in the sand matrix. The bacteria density (OD₆₀₀), pH, and nitrate concentration during biofilm treatment were monitored. S- and P-wave velocities were also monitored during biofilm treatment and loading of the triaxial test. After the tests, biomass content and scanning electron microscope (SEM) images of sand samples were analyzed for biofilm distribution and morphology in the sand matrix. It was concluded that the selected bacteria S. Epidermidis can grow and form biofilm in the sand matrix under anaerobic condition. The results of triaxial tests show a lower ultimate strength of biofilm-treated specimen compared to the untreated specimen.

Microbial calcium carbonate precipitation (MICP) has been studied widely as an environmentally friendly technology to stabilize coarse soil. Immersing method is one of laboratory methods to conduct MICP. This paper is to develop an improved immersing method with multiple treatments that can enhance the strength and uniformity of MICP treated soil. Experimental result shows the unconfined compression strength increased up to 6.4 MPa with multiple treatment. The CaCO₃ content of MICP-treated samples also increased with the increasing of cementation media concentration and treatment times. At the cementation media concentration of 0.25 M Ca, the MICP process can be repeated up to 4 times. When the cementation media concentration increased to 0.5 M Ca or 0.75 M Ca, double treatment can reach the optimum MICP treatment performance.

Scour adjacent to foundation systems is a contributing factor to significant structural damage. Microbial induced carbonate precipitation (MICP) is investigated as an approach to improve the soil’s shear strength and stiffness and reduce the potential to scour. In this study, a submerged impinging jet system (mini JET apparatus) is used to assess the erodibility of MICP-treated sand with results presented in the context of data in literature. The results indicated that the critical shear stresses of the MICP-treated specimens increased one to three orders of magnitude, while the erodibility coefficients decreased by up to four orders of magnitude as the cementation level increases. The micro image analysis confirmed that cementation is achieved via precipitated calcium carbonate at the particle contacts. These results suggest that moderate to high levels of cementation using the MICP process is potentially an effective approach to reduce the sand’s erodibility.

Sisal fibers were employed to enhance the performance of soil treated by enzyme induced carbonate precipitation (EICP). In EICP, free urease enzyme is used to catalyze the reaction between calcium chloride and urea that induces calcium carbonate precipitation in soil. The precipitation changes the mechanical properties of the treated soil through binding particles together, roughening particle surfaces, and filling pores. A laboratory study was conducted to investigate the effect of the addition of sisal fibers, including fiber ratio (as a percentage of the dry mass of fibers and sand) and the length of fiber, on the strength and ductility of EICP-improved soil. Two different lengths (10 and 20 mm) of sisal fibers were added at fiber ratios of 0 (control), 0.2, 0.3, 0.4, 0.75, and 0.85% to create specimens for unconfined compression strength tests. The optimal fiber ratio and fiber length with respect to the UCS were 0.3% and 10 mm, respectively. The UCS strength of EICP-treated sand at the optimum fiber content was four times higher than that of the control sample. The strain at failure (peak strength) was too variable to draw any conclusions regarding ductility.

Microbial induced calcium carbonate precipitation (MICP) is a ground improvement technique that can be employed to increase soil stiffness and shear strength. Based on the treatment’s objectives, soil properties are improved to reach different levels of cementation. Shear wave velocity and mass of calcium carbonate can be used to categorize treated soils into various levels of cementation. However, the obtained results show that these two parameters are not sufficient in categorizing cementation and may be misleading. Therefore, a new framework which considers particle size, the dependency of shear modulus on confinement, shear wave velocity, and calcium carbonate content is proposed. In this paper, three types of poorly graded sands with different particle sizes were used. Shear modulus was measured at varying levels of cementation and confinement pressures to find out the amount of dependency of small strain shear modulus on confining pressure. According to the results, the finest soil needs more calcium carbonate to reach heavily cemented level, but the final shear wave velocity is lower compared to the coarser sands. Based on the obtained results, n (the slope of log G_max against log of mean effective stress) values for lightly, moderately, and heavily MICP-sands are about 0.4, 0.3, and less than 0.1, respectively.

The establishment of the bio-inspired and bio-mediated sub-disciplines in the emerging field of biogeotechnology has led to the developments of many innovative methods and techniques. These methods and techniques potentially provide sustainable alternatives to conventional approaches that may be less desirable due to their use of high-embodied energy materials and processes. In particular, research within the bio-mediated sub-discipline over the past decade has fostered advancements in biocementation ground improvement methods that currently allow for possible field scale implementation. As a result, the ability to incorporate and sufficiently factor the associated mechanical enhancements during design is needed. The development of a constitutive model that properly assesses the level of improvement and adequately predicts the expected performance for a given level of cementation is underway. However, in order to accomplish the aforementioned goal, there is a need to develop components that are capable of capturing the behavior and transition from the cemented to uncemented state, while maintaining adherence to influential factors in the volumetric and stress states. This paper focuses on the development of strength in biocemented soils (via microbial induced calcite precipitation, MICP) and its evolution with cementation level under loading. The proposed strength correlation accounts for the observed nonlinearity of failure envelopes in sands and describes the strength of cemented sands as a function of density, confinement, mineralogy, and cementation.

The use of chemical additives to stabilize expansive soils is a common practice. However, the environmental concerns associated with the greenhouse gas generation during the production of these chemicals have launched engineers in search of sustainable stabilization alternatives. Microbial induced calcite precipitation (MICP) is a bio-cementation technique that could be a potential solution to this problem. Typically, MICP is achieved via bio-augmentation; however, bio-stimulation was argued to be a more realistic alternative due to its field implementation potential. Hence, in this research study, two expansive soils with varying plasticity characteristics were examined to understand the potential of MICP in treating expansive soils. These two soils were subjected to MICP treatments using enrichment and cementation solutions. The treatment effectiveness was studied via response measures such as Atterberg limits, unconfined compressive strengths, one-dimensional swell test, and calcium carbonate precipitation. The results indicate that MICP has potential in stabilizing expansive soils and further research is warranted to explore this idea.

The morphology and chemical composition of fly ash render the material unique in comparison to natural sediments. Fly ash deposited in ash ponds can possess a loose, saturated, and contractive structure with a tendency to collapse under induced shear stresses. Compressibility and hydraulic conductivity are the two main parameters affecting the stability of this material in ash ponds. Microbial induced calcium carbonate precipitation (MICP) is a novel approach, which has been widely studied to improve engineering properties of soils. In this study, the MICP treatment process is applied to a Class-F fly ash material to assess its effect on the two mentioned parameters. Modified odometer testing was developed with the ability to inject the treatment solution, measure the induced pressure during injection, and monitor the shear wave velocity of the test specimens. The specimens were successfully treated using MICP, reaching predetermined target shear wave velocities. The results of compressibility on treated and untreated specimens indicate that MICP decreases the compressibility of the studied material while the hydraulic conductivity decreased by only one order of magnitude or less. The shear wave velocity of the treated and untreated specimens converged to the same value while the vertical applied stress increased, indicating the calcium carbonate bond breakage between particles.

As compared with traditional turf, engineered equestrian surfaces typically use a mixture of geosynthetics such as geotextile pieces, fibers, and sometimes rubber crumbs to increase strength and improve response characteristics. Use of engineered surfaces is becoming increasingly widespread in the equestrian industry and the technology is used for some of the highest-grade competition arenas in the U.S. and worldwide. Despite their prominence, the effect of geosynthetic amendments on the response characteristics of a riding surface is not well understood. The complex horse-surface interaction introduces difficulties with designing surface material test procedures as well as interpreting and applying the test results. Research was undertaken at the University of New Hampshire that explored using direct shear testing to observe differences in shear behavior characteristics between surfaces with varying percentages of geosynthetic amendments. Shear strength and vertical displacement during shear were both used to characterize the behavior of surfaces. Engineering analysis was used to correlate lab test results to subjective professional rider experiences in the field. A unique opportunity arose that allowed for full-scale experimentation with varying quantities of geosynthetic amendments at a local riding arena. An arena surface that has been previously extensively studied was amended with a large quantity of geosynthetic fibers and fabric pieces. The resulting amended surface was found to have undesirable riding behavior, and thus was amended again with the addition of coarse sand and removal of some of the previously added geosynthetics. The procedure provided two amended surfaces, each with different quantities of geosynthetics, to test and compare to the baseline initial surface. In addition, professional rider experience was taken into account for each surface. The resulting analyses show both the capability of the direct shear test to characterize the behavior of a riding surface and the correlation of direct shear test data to subjective professional rider experience.

This paper presents the results of an experimental study on the shear behavior of soil-structure interfaces between snake skin-inspired surfaces and sand. Snakes were used as the model organism because the scales along their underbody (i.e., ventral scales) mobilize high frictional resistances when soil is sheared against them (i.e., cranial direction) to generate reaction for locomotion. On the other hand, these same ventral scales mobilize less frictional resistance when soil is sheared along them (i.e., caudal direction) in order to minimize friction during forward movement. The results presented consist of two-way cyclic interface shear tests between sand and bioinspired surfaces, and sand and a surface consisting of sand glued on steel. Two of the snake-inspired profiles are shown to mobilize significant frictional anisotropy, which is dependent on the shape of the asperities and the imposed testing sequence. The third snake-inspired surface, and the glued sand surface, mobilized negligible to moderate degrees of frictional anisotropies. This paper also provides a discussion of the practical implications for potential adoption of surfaces that mobilize frictional anisotropy in geotechnical design.

The current study evaluates the strength characteristics of tropical soil treated with nano calcium silicate (NCS) (synthesized with a proprietary method of the authors) and in combination with two different materials such as lime and fly ash added with dosages of 0.04% NCS, 6% lime and fly ash in the ratio of 1:1 with soil. The results of the investigation showed significant improvement in maximum dry density, plasticity index, and unconfined compressive strength. It was found that the strength development with various combinations were soil fly ash NCS, soil Lime NCS, and soil NCS. Nano calcium silicate particles promote pozzolanic reaction by transforming the calcium and silica of the mixtures into calcium silicate hydrate gel(s), which enhanced the strength characteristics of soil.

As part of an effort to lower the cost of urease enzyme used in enzyme induced carbonate precipitation (EICP) for soil improvement, urease enzyme was extracted from watermelon seeds. EICP is a biologically-based ground improvement technique in which a solution containing calcium, urea, and urease enzyme is used to induce calcium carbonate precipitation in a granular soil, enhancing strength, and stiffness. To reduce the enzyme cost by obtaining it from a waste material, the effectiveness of urease enzyme extracted from watermelon seeds, a urease-rich agricultural waste, was evaluated. Low-tech methods were employed for extraction and purification of the enzyme. The extracted enzyme, which showed urease activity of around 611 U/ml, was used to treat Ottawa 20/30 sand. Results of scanning electron microscope imaging and energy dispersive X-ray analysis demonstrated calcium carbonate precipitation. The ratio of the precipitated carbonate content to the theoretical maximum was found to be around 64%.

Biochar is a carbon rich compound produced through pyrolysis of organic matter. Over the past few decades, the material has been used for agricultural soil enhancement and environmental remediation. Recently, additional applications such the possibility of using biochar to supplement construction materials or to enhance engineering proprieties of problematic soils have been explored. Use of biochar to store carbon dioxide, and then mixing the material into soil and other construction materials, allows for stable storage of carbon for extended periods reducing carbon dioxide emissions. This study investigated the effects of locally produced biochar amendment on mechanical properties of Buckshot clay, a problematic soil in Mississippi. A set of mechanical tests, including compaction and unconfined compressive strength were performed on untreated and treated Buckshot clay with biochar. Mixtures using two different biochar sizes and four biochar dosages for each size were considered. To better understand the microstructure and surface morphology of untreated and treated soils, a field emission scanning electron microscopy (FESEM) test was performed on soil-biochar matrix. The results indicate that the biochar addition improves the mechanical properties of Buckshot clay with an optimum value of 10% by dry mass. For both particle sizes, a reduced density and increased strength over the unmixed material was found using the optimum value. The outcome of the research show that biochar can be used as an eco-friendly construction material for problematic soil improvement.

This paper describes a preliminary study of the effects of microbial induced calcite precipitation (MICP) on the desiccation cracking behaviors of bentonite. The drying shrinkage of bentonite mixed with bacteria and cementation medium is monitored in the petri dish under controlled temperature and relative humidity conditions. Three control groups are also monitored, in which bentonites are mixed with live bacteria + cementation medium without CaCl₂, dead bacteria + cementation medium, and dead bacteria + cementation medium without CaCl₂, in order to study the influence of MICP process and microbial activity on soil desiccation cracking. Scanning electron microscope images show bacteria survive on the surface of bentonite after dried. The MICP occurred at the early stage after mixing bentonite with cementation medium changes soil’s property and leads to more intact cracking polygons while drying. Bentonite mixed with live bacteria tends to form larger cracking polygons due to the increase of soil’s mechanical strength. It shows the MICP process as well as the microbial activity have a positive influence on bentonite’s cracking potential remediation.

Glycerol and xanthan gum were employed to enhance the viscosity of the cementation solution in soil treated with enzyme-induced carbonate precipitation (EICP). The effect of increasing the viscosity of the solution was investigated because it may facilitate EICP treatment by retaining cementation solution as precipitation occurs. Columns 51 mm in diameter and 102 mm in height of Ottawa 20/30 and F-85 sands were treated with EICP solution containing no thickener, 50% (v/v) glycerol, and 0.25% (w/v) xanthan gum. Some columns had open bottom to allow drainage and some were capped to retain the cementation solution. Xanthan-enhanced EICP solution showed the highest level of fluid retention. Results showed that EICP-treated sand can be cemented with the addition of a viscosity enhancer but that cementation quality may be affected. The level of retention did not have a strong relationship with uniformity of cementation and did not result in enhanced unconfined compressive strength.

Microbial-induced carbonate precipitation (MICP) has been used to improve soil properties for different geotechnical applications. This research focuses on evaluating the use of MICP for the wind erosion application. The results presented in this paper represent the initial attempt to optimize the field application/process of applying MICP. This will be followed by more detailed study and wind tunnel experiments in the future. A series of spray experiments were conducted on bar sand with different bacterial and calcium chloride (CaCl₂) applications. The sand was placed in a 279 × 216 × 25 mm tray at a relative density of 29%. Tests were designed to investigate different MICP treatment procedures to evaluate the effects of varying amounts of bacteria and cementation solutions on measured CaCO₃ content. After each test, samples were collected from each specimen to measure CaCO₃ content. The initial results presented in this paper show a non-uniform distribution of CaCO₃ content throughout the sample. Furthermore, increasing the number of bacteria applications improves the precipitation of CaCO₃ near the surface.

The pneumatic flow tube mixing (PFTM) was developed in Japan for land reclamation and land development, in which dredged clay is stabilized with a small amount of binder in a transporting pipeline. The soil mixture forms several separated mud plugs in the pipeline and is thoroughly mixed by means of turbulent flow during the transport. The PFTM has the potential to reduce treatment costs by eliminating costs associated with material transport and improve the final product by creating a more uniform amended sediment. This method was conducted at a sediment management site in Kearny, NJ from July through September of 2015, and demonstrated to be an efficient and rapid method for soft-sediment stabilization. In this study, the in-situ strength of the field stabilized soil by the PFTM was investigated to evaluate the long-term strength.

The interface shear strength is essential for the design and safety assessment of deep foundations, offshore and onshore pipelines, mechanically stabilized earth walls, and fiber-reinforced soils, among others. Despite the wealth of data on the interface shear resistance between soils and solid interfaces, there is limited information on the interface resistance between clays and natural fibers, which are currently being considered as a sustainable measure of soil improvement. In this study, a comprehensive experimental program is implemented to investigate the interface shear strength between a sandy clay and natural hemp fibers. It consisted of a series of direct shear tests conducted on both clay-clay and clay-hemp interfaces, in addition to another series of single fiber pullout tests at different rates of loading. Clay samples were compacted at optimum water content and maximum dry density. Results indicate that the interface shear strength parameters that characterize the fiber/soil interaction are significantly affected by the test mechanism and the rate of loading.

This study was performed to show the effects of incorporating different gradations and different percentages of crumb rubber into the local soil found in Memphis, TN and the surrounding area. Approximately 300 million tires are disposed of each year in the U.S. This has led to significant environmental concerns all over the nation. As a remediation to this negative environmental impact, the geotechnical engineering community has been working to use crumb rubber from these discarded tires in soil modification projects to improve the engineering properties of soils. In this study, consolidation tests are performed on loess, the primary soil found in the Memphis area. To gain insight on the use of crumb rubber as a fill material in regards to consolidation settlements, different percentages of different gradations of crumb rubber are mixed with the local loess. Results are presented that show the effect of different amounts and sizes of crumb rubber on consolidation properties of Memphis loess.

A study was conducted to see if soil properties, namely strength, could be improved by mixing highly organic, levee soils with local, naturally occurring pozzolans, in the form of volcanic ash, from the eruptions of Mt. Mazama. The results of this study are presented in this paper. These results include the suitability of the Mt. Mazama materials as a natural pozzolan, and strength testing of compacted soil samples mixed with various amounts of Mt. Mazama volcanic ash and other soil additives. Results indicate that in contrast to previous studies, the Mt. Mazama material does not improve soil strength without additional soil additives such as lime or fly ash. Mixtures of Mt. Mazama ash and lime improved soil strength to a higher degree than either fly ash or lime alone.

This study shows the effects of incorporating different gradations and percentages of crumb rubber into the local soil found in Memphis, TN and the surrounding area. The annual disposal of approximately 300 million tires in the U.S. has led to significant environmental concerns. To remediate this negative environmental impact, the geotechnical engineering community has been working to use crumb rubber from discarded tires in soil modification projects. Integrating crumb rubber into soil poses a potential hazard as permeating water may transport contaminants from crumb rubber through soil which can be harmful to plants and wild-life, and can pollute the ground water. In this study, pH, hardness, and chloride tests are performed on Memphis loess, with different percentages and gradations of crumb rubber mixed into the soil. Results show effects of different amounts and sizes of crumb rubber on the contaminant transport through the soil from the crumb rubber.

This study was performed to show the effects of incorporating anthracite into the local soil found in Memphis, TN and the surrounding area. Anthracite is a coal-based material that is commonly used as a filtration medium for the purification of contaminated water. Anthracite has the highest carbon content and the fewest impurities of all types of coal except for graphite. Because of this, it has the potential to be used as a light-weight fill in the loess found in the greater Memphis area. In this study, compaction and permeability tests are performed on brown loess, which is the primary soil found in the Memphis area. To gain insight on the use of anthracite as a fill material, different percentages and gradations of anthracite are mixed with the local loess to form a basis of comparison. Results are presented that show the effect of different amounts and sizes of anthracite on the maximum dry unit weight and coefficient of permeability of Memphis loess.

Characterization of soil-geosynthetic interaction is a key aspect in understanding mechanical performance of structures made using geosynthetics (e.g., geosynthetic-stabilized roadways and geosynthetic-reinforced soil walls). Pullout test has been one of the most widely used experimental techniques to characterize this interaction. This study implements t-z analysis approach, originally developed to evaluate load transfer mechanism in deep foundations, to predict pullout test results of geosynthetics. Formulations of the method and step-by-step solution algorithm are presented. Suitability of the method was evaluated by comparisons made between predictions of the t-z analysis approach and experimental pullout test results presented in literature. Specifically, geosynthetic and soil-geosynthetic characterization data presented in four studies with a wide range of soil and geosynthetic types, normal pressures, and test configurations were used in the t-z analysis framework presented in this study to simulate pullout test results. Results from the simulations were then compared to the experimental data presented in the four studies. This comparison underscored suitability of the t-z analysis approach in producing reasonably consistent results with the experimental data.

Small amounts of soil desaturation can substantially impact the undrained static and cyclic response of sand when compared to the fully saturated case. Due to its impact on undrained behavior, desaturation can increase the strain hardening behavior of loose sand subject to a monotonic static load and is an emerging technique for mitigation of the liquefaction potential of sands. Several investigators have demonstrated the increase in the cyclic strength, decrease in pore pressure generation, and reduction in seismic settlement that accompanies small amounts of desaturation in a loose sand. However, the potential impacts of desaturation on the undrained static response of dense soils is less well studied. In this work, results from the cyclic and static undrained testing of a natural beach sand and Ottawa 20-30 silica sand show that, while desaturation does significantly improve the cyclic response of dense sand, desaturation may also lead to a decrease in the monotonic compressive strength of sand initially dense of critical state. The impact of this result on the implementation of liquefaction mitigation via desaturation is discussed.

Liquefaction causes the most detrimental ground failure by strong earthquakes. Ground liquefaction leads to associated foundation and superstructure failures due to loss of bearing capacity and excessive deformation and an appropriate assessment of liquefaction is critical to the seismic safety evaluation of foundations and super structures. Cyclic triaxial tests (CTT) are traditionally used in experimental evaluation of liquefaction resistance. However, ground motion propagates from the soil-bedrock interface to ground surface in the form of cyclic simple shear, which can be more ideally simulated in a cyclic hollow cylinder (CHC) test than in a cyclic triaxial test. With appropriate dimensions, the distribution of stresses and strains in CHC sample is more uniform than that of cyclic triaxial test and CHC is an ideal substitute for CTT is evaluation of liquefaction during the earthquake shaking. While CHC is more ideal than CTT for evaluation of liquefaction resistance, CTT is much more prevalent due to its simplicity, and CHC is used to evaluate the correction factor, C_r as recommended by Seed and Idriss (1979).

Significant densification can be achieved using driven displacement piles, which act to mitigate liquefaction through both densification and reinforcement. Recent research on driven displacement piles was used as a basis to offer an alternative to earthquake drains for the mitigation of liquefaction of a 4-story structure along coastal South Carolina. The subsurface conditions consisted of fine, clean to slightly silty, very loose to medium dense sands over a deep, dense sand layer and the marl of the Cooper group. A test program was conducted in order to evaluate the change in cone tip resistance and estimated post-shaking settlements in the liquefaction susceptible layer following pile installation. Two 10-pile groups were driven as part of the test program: one with 1.2 m triangular spacing, and one with 1.8 m triangular spacing. Pre- and post-installation cone penetration tests and shear wave velocity tests were conducted at the center of each of the groups to enable comparisons between the two test pile groups. Liquefaction triggering and post-shaking settlement analyses were conducted and compared to the pre-treatment condition for the design seismic event. The paper concludes with a discussion of the design philosophy and performance criteria and basis for selection of the actual pile group spacing used for the project.

Blast densification has been used as a useful soil improvement technique for coarse-grained soils since the 1930s. The use of blast densification has been extended to include more soil types in recent decades, for instance, well-graded gravels, silty sands, silts. Ground condition strongly influenced on the effectiveness of blast densification; then trial-and-error is still used. The objective of this paper is to suggest “suitability line” for blast densification based on grain size distribution. The suitability line is defined as the demarcation line between effective and less effective on improving SPT N-value. The case histories from the six sites were collected to achieve the objective. Fine content (Fc), a coefficient of uniformity (Uc), and powder factor (PF) were considered on the improvement. The result showed that degree of improvement was sensitive to the ratio of Fc. The increment of SPT N-value deceased with an increase of Fc, and no improvement was expected for the soil that contains Fc over 30% regardless of explosive energy and gradation of grain size. Based on the observations, the suitability line was suggested.

In a 2015 study, case histories of lateral spreading after recent great (magnitude greater than 8.0) and long-duration subduction zone earthquakes in Peru, Chile, and Japan were organized into a spatial geodatabase. Afterwards, existing and widely-used empirical and strain-based models for predicting lateral spread displacements, which were developed primarily from shorter-duration and smaller crustal earthquakes, were compared with measured displacements for each case history in the database. The results of the comparison showed that the models poorly predict lateral spread displacements for great earthquakes because the ground motions are complex and strong shaking lasts significantly longer than for crustal earthquakes. In the years since the compilation of the initial great earthquake lateral spreading database in 2015, several additional subduction zone earthquakes have occurred with resulting additional case histories developed by international teams of geotechnical engineers. These additional case histories from Chile and Ecuador are briefly presented and compared to the existing case histories. The additional case histories confirm the findings of the initial database, while providing additional insights into lateral spreading during great and long duration earthquakes.

The compaction grouting (CPG) method is one of the liquefaction mitigation methods. Because the CPG method can be applied below or near the existing structures, there are many construction results at ports and airports. However, ground upheaval often becomes a problem. Therefore, the technical issue of the CPG method was to control the uplift that occurs with construction. In this study, a series of full-scale field tests was carried out by using 3 types of construction machines and various parameters, regarding the new up and down (U/D) method that control the upheaval of the ground. The results demonstrate that the developed U/D method reduced the ground upheaval quantity by more than 90 % compared with the conventional CPG method in the field.

A new jet grouting method (the V-JET method) was developed which can create columns larger and faster than conventional methods. Additionally, in order to improve the quality of construction, a new measurement technique, the JWM (jet wave monitoring) system, which is able to confirm the shape of the improved soil bodies in real time, was developed. Furthermore, through the application of these techniques, the MultiFan-Shaped jet grouting method for wall-form ground improvements was developed. This paper will introduce the V-JET method and examples of measurements obtained by utilizing the JWM system. Furthermore, we geometrically examined the effectiveness of the MultiFan-shaped column for wall-form ground improvements. Consequently, we were able to confirm that the shape of the improved soil body can be understood in real time by utilizing the JWM system, and that the MultiFan column is more effective for wall-form ground improvements than conventional jet grouting methods.

The authors have had intimate experience in the design, construction, and evaluation of remedial grout curtains for embankment especially dams during the “heyday” of the last 20 years in North America. Their experiences–and those of other active participants in such projects–have been widely published in the technical press, and have been incorporated in recent federal guidelines. However, not all the “lessons described” in such publications have been translated as “lessons learned,” and indeed many “lessons learned” have been ignored totally in certain quarters. The paper focuses on several topics which the authors feel merit particular attention in this regard, namely: drilling techniques for overburden and rock, design and testing of grout mixes, placement and sealing of standpipes and MPSP’s, data management systems (DMS), refusal and closure, allowable injection pressures, joint instrumentation monitoring plan, and long-term monitoring. The authors trust that the conclusions of the paper will provide guidance to engineers about to participate in a major grouting project for the first time, and comfort to more experienced engineers faced with conflicting “opinions” from unqualified but strongly opinionated “experts.”

Soil elements located at the toe of natural slopes and/or embankments are subject to extension stresses. This initial stress state is critical particularly when the elements are exposed to cyclic loading due to a seismic event. Using granular columns as a ground reinforcement and improvement alternative for clayey subgrades/natural soils is considered as an effective mitigation option to improve short and long term static stability, and increase the resistance to seismically-induced stresses. This paper investigates the effect of columnar granular inclusions on the cyclic resistance of anisotropically consolidated clay samples. Stress-controlled triaxial tests were conducted on both “control” and sand-column reinforced samples at a range of cyclic stress ratios. The effect of varying the density of the sand column inclusions is also explored as part of the testing program. Test results are analyzed and presented showing significant improvement due to the presence of the reinforcing columns along with a pronounced effect of the density of the inclusions.

Deformations in geosynthetic-reinforced column-supported embankments (GRCSE) can be calculated by performing fully-coupled consolidation analyses, which, depending on the system properties and the size of the numerical domain, can be computationally intensive and time consuming. In this paper, an alternative approach for numerically analyzing deformations in GRCSEs is presented. This approach captures the complex time-dependent deformations in the GRCSE through manual dissipation of excess pore pressures, where deformations are computed for known pore pressure distributions. Two validation examples were analyzed using the finite difference method as implemented in the computer program FLAC3D. They show that this alternative approach is computationally faster than fully-coupled analyses and provides comparable deformation results. This approach is adopted for the analysis of a GRCSE case history. Excess pore pressures developed in an undrained end-of-construction analysis are manually dissipated to solve for deformations in a drained long-term analysis. Numerical results are shown to envelope measured case history recordings in terms of settlement and vertical pressures on the subsoil and on the columns.

The use of column-support to facilitate rapid placement of fill over soft ground continues to gain wider acceptance and popularity. A soil arching mechanism and, often times, a geosynthetic reinforced load transfer platform partially transfers load to support columns beneath embankment and MSE wall fills. The mechanisms contributing to load transfer at the heads of columns has been the subject of extensive research for column-supported embankments. However, less attention has been given to the role of soil-column interaction at depth, and its influence on performance of these systems. This case study presents measured surface and subsurface deformations beneath embankments and retained MSE wall fills supported on concrete rigid inclusions. Movements were measured with settlement plates and extensometers. Stress changes beneath fill material was inferred from measured subsurface deformations and indicate soil-column interaction contributes to continued stress-reduction at depth. A quasi-3D finite element analysis was performed to examine the influence of soil-column interface shear strength in a near-surface layer of compressible clay. Computed results indicate soil-structure interaction in this layer plays an important role in the efficacy of settlement reduction, especially as clay thickness increases.

Proper design of column-supported embankments (CSEs) with or without a geosynthetic-reinforced load transfer platform involves careful consideration of the interaction among several natural and manmade materials. Variation in material properties, the thickness of soil layers, and the layout of columns can significantly affect service loads in the columns, tension developed in the reinforcement, and post-construction settlements. Probabilistic analyses enable the effects of uncertainty to be incorporated into design for serviceability by estimating the probability of acceptable performance. In cases where explicit functions relating parameter values to performance do not exist or are impractical to implement, Monte Carlo simulation or simplified reliability methods can be used in conjunction with a response surface to estimate the reliability of the design. A response surface is a function developed from the results of parametric analyses that defines the relationship between the design parameters and a performance parameter of interest. This paper describes the development of response surfaces for tension in the reinforcement and total settlement based on the load-displacement compatibility method for a hypothetical CSE constructed over a soil profile comprised of sand overlying soft clay. The design parameters selected for inclusion in the response surfaces frequently involve high degrees of uncertainty, especially, the thickness of the sand and clay, the stiffness of the sand and clay, and the interface friction angle between the sand and the columns. The response functions are applied using Monte Carlo simulation, the Hasofer-Lind method, and the Taylor Series method to estimate the reliability of the design with respect to the performance parameters. The analyses revealed that the thickness of a sand layer overlying the soft clay foundation and compression ratio of the clay have the greatest effect on total surface settlement and geogrid strain out of the five variables considered.

The paper analyzes a case history of a challenging jet grouting excavation shoring project carried out in North Vancouver, BC. The new building comprises up to four levels of above ground structures with three levels of underground parking. The construction required vertical excavation of 9–11 m below the ground surface, extending up to 9 m below the groundwater table along the north side of the site. The project was complicated by the requirement of the shoring wall to act as a seepage cutoff with no allowance for external or internal dewatering wells. The shoring would also be required to act as a blind form for the construction of the building foundation walls. The soil conditions present at site are typical of portions of the Vancouver North shore; comprising heterogeneous granular fluvial deposits overlying silty sand glacial till with clasts of running sands, frequent cobbles, and random large boulders. The paper will describe the design elements and effectiveness of the jet grout system to create a secant pile shoring wall system. It also describes the lessons learned in the execution of jet grouting in the challenging site conditions.

In this study, the effect of the soil mixing method on the swelling behaviour of expansive soils is investigated. Recent studies have demonstrated the modification effect of cement and inclusion of by-products such as pulverised fuel ash (PFA) and ground granulated blast furnace slag (GGBS) on the plasticity of expansive soils at a water–to–cement ratio of unity. In this study, the volume change of cement/PFA/GGBS improved expansive soil was evaluated using empirical correlations. One-dimensional oedometer experiment and tests to determine the index properties of both the natural and treated soils were performed. Complimentary numerical modelling of the loaded natural and treated soils using the SoilWorks MIDAS software were also carried out. Analyses of results indicated a significant influence of the binders on the plasticity properties of the expansive soil. Results obtained by the addition of 10% each of PFA and GGBS to the cement treated expansive soils showed a considerable reduction of plasticity. By using the index property–based correlations, the swelling potential of the treated soils were shown to be effectively reduced in the range of 10–80%. Comparisons with numerical analysis indicated slight variations.

This paper presents lateral loading test results on single soil-cement columns and groups of soil-cement columns for supporting foundation of high-rise buildings. The soil profile consists of a silty sand layer with 9 m thickness and underlain by clay layer. The soil-cement columns were 600-mm diameter and constructed into 7 m depth below ground surface by deep wet mixing method. Twenty days after construction, the static loading tests were performed on two single columns, the 3-column group and the 5-column group. The maximum test loads and movements ranged from 128 through 413 kN and 23 through 30 mm, respectively. The 28-days compression strength of columns was about 5.5 MPa. The correlation between single columns and the groups showed group factors of about 0.8 and 0.6 for the 3-column and 5-column group, respectively. The test results provides compelling evidences that the lateral bearing capacity of the soil-cement columns is adequate to support foundation of high-rise buildings.

The deployment of ocean-based renewable energy generation devices, including those utilizing wind, waves, and tidal and ocean currents, requires the installation of cost-effective anchoring foundations. Micropiles provide a viable option for cost-effective subsea anchoring foundations. However, due to the lack of an acceptable approach for the subsea formation of micropiles in sandy soils, no cases that we are aware of have been presented in the literature. The research work reported in this article seeks to investigate the effect of seawater during mixing and curing on compressive strength (f_c^′) of cement grout for marine micropile anchor systems. Grout mixes are tested at three water-cement ratios (w/c) and in two different curing liquids. Specimens mixed with and cured in fresh water are designated by (ff), those mixed with and cured in seawater as (ss) and those mixed with fresh water and cured in seawater as (fs). A total of 162 cubes and 162 cylinders were cast and exposed to curing liquids for 7, 14, 28, and 90 days. The results showed an appreciable high and early f_c^′ gain of ss specimens compared to the baseline ff specimens. The rate of f_c^′ gain of ss specimens reduced slightly at low w/c ratio, but increased at higher w/c ratios (0.5 and 0.6). The reasons for such behavior are related to the accelerated rate of hydration of alite and belite due to the presence of chloride ions (Cl⁻) in seawater, and the transformation of ettringite (AF_t) to monosulfate (AF_m) or monochloroaluminate. Scanning electron microscopy (SEM) showed the formation of those crystals at discrete Cl⁻ locations. The ff and fs specimens showed similar rate of f_c^′ gain (that was not affected by curing in seawater) due to the formation of impermeable layers of brucite [Mg (OH)₂] and aragonite (CaCO₃) beneath the surface of the fs specimens.

An important parameter used to predict the bearing capacity of a single stone column is the internal friction angle of the aggregate. Typically, constant friction angles are used to design stone columns regardless of the effects that particle shape, gradation, and aggregate-matrix soil interaction may have on the global performance of the pier. Because the bulging failure mechanism normally controls the global performance of single stone columns with L/D ratio greater than 4, a significant reduction in the internal friction angle could occur due to an increase in the confining pressure at the bulging zone during the load application. To examine this phenomenon, full-scale 3D discrete element method (DEM) simulations were developed to replicate field plate load tests on spread small circular foundations (0.76 m) supported on isolated stone columns in order to determine the corresponding load-displacement curves. The results demonstrate that incorporating a variation in the friction angle in the DEM models which is dependent on the level of confining pressure provides a better numerical representation of the load-displacement curve obtained from the field.

An expansive subgrade beneath a newly constructed roadway in Central Texas was instrumented using volumetric moisture content and matric suction sensors. Sensors were installed during construction, facilitating an evaluation of the hydraulic behavior in the subgrade beneath a temporary flexible base with a prime coat and a final asphalt surface. Monitoring indicated that the two surfaces had differing hydraulic boundary conditions. The asphalt surface acted as an impervious layer that reduced the infiltration of moisture into the subgrade, while the flexible base surface did not appear to provide a hydraulic barrier and allowed for more rapid moisture fluctuations through the entire subgrade. Additionally, monitoring of the pavement surface via total station surveying verified this behavior with the profile of the roadway undergoing differential movement at the edge for the asphalt surface but not for the flexible base surface. Overall, the hydraulic moisture fluctuations of the subgrade were affected by the different pavement surfaces, and total station technology was able to characterize the surficial profile movement.

Typically pavement structure is comprised of a surface layer (i.e., asphalt or concrete), underlying granular layers known as subbase and/or base, and a compacted subgrade soil layer. During wet seasons when the subgrade becomes saturated, cyclic loading caused by the moving traffic may result in pumping of fine particles from the subgrade up into the subbase. This presents a serious challenge to the pavement structure and may lead to failure of the pavement. The objective of this research is to investigate occurrence of migration of fine particles and to quantify the magnitude and rate of such migration. One-third scale model mobile load simulator (MMLS3), a type of accelerated pavement testing (APT) device, is utilized to simulate the cyclic traffic loading on scaled flexible pavement that simulates interstate highways. Kenlayer linear elastic program is used to determine the equivalent scaled pavement in the laboratory. The pavement section is constructed on a bed of non-plastic saturated silt as subgrade soil and partially saturated aggregate subbase. The lab testing reveals that under cyclic loading condition considerable amount of fine particles migrated into the subbase. The migrated soil in mass percentage increases with the simulated traffic loading cycles. The migration of subgrade soil into the subbase also varies with the depth in the subbase: more migration occurred in the lower section (closer to the subgrade) than in the upper section of the subbase.

Moisture flow dynamics in roadway systems affect the performance and serviceability of pavements. Accurate measurement of moisture requires direct collection of soil samples, followed by testing in the laboratory. Nondestructive measurements from neutron probes, time or frequency domain reflectometry, and radiometry in remote sensing are also used by researchers to record changes in moisture content. However, these methods either yield discrete point information or have depth limitations. Geophysical testing provides a continuous portrayal of the subsurface moisture flow. During this study, a geophysical testing method known as electrical resistivity imaging (ERI) was adopted. Monthly testing was performed on a selected two-lane highway slope. The objective of the study was to determine seasonal moisture fluctuations in a side slope of highway pavement. Over a monitoring period of 12 months, two distinct seasons were observed. April to October was determined to be the dry season, whereas November to March was found to be the wet season. Resistivity values ranged from as high as almost 25 Ohm-m in the dry period to as low as 10 Ohm-m in the wet period. In addition, the zone of moisture variation was found to be nearly 3 m. Moreover, the possible zone of moisture intrusion could be detected from resistivity imaging after rainfall. The ERI data was further statistically analyzed and correlated with temperature and precipitation data. The findings will further advance understanding of the dynamics of moisture flow in roads.

In addition to causing shrinkage and swelling in expansive subgrade, seasonal moisture variations may alter material properties, hence pavement serviceability. In order to prevent moisture variation in the subgrade, moisture barriers may be used. The current study observes the effects of a modified moisture barrier on subgrade moisture control. The modified moisture barrier that is used in this study is a combination of a 40-mi LLDPE (linear low density polyethylene) geomembrane and an 8-oz. HDPE (high density polyehtylene) geocomposite. In-situ moisture sensors were employed to observe subgrade moisture variation. Edge moisture intrusion was observed along farm-to-market (FM) 987 near Kaufman, Texas. Based on the observation of edge moisture intrusion, the moisture barrier consisting of a geomembrane and a geocomposite (geonet sandwiched between two nonoven geotextiles) was placed in a 50-ft section of FM 987. A 50-ft control section was also established along the roadway. Moisture sensors in both the barrier and control sections continuously monitor the moisture content of the subgrade soil. In the barrier section, preliminary results indicate a steady moisture content which is not influenced by rainfall. In the control section, the moisture content levels are influeced by rainfall. This ongoing study shows promise for using the modified moisture barrier to prevent subgrade moisture intrusion and provide for better pavement serviceability.

Fine coal refuse (FCR) is the waste material generated by the processing of raw coal. FCR is typically mixed in slurry form with a flocculant and placed hydraulically in on-site impoundments behind tailings dams, setting out over time to form a solid. Currently, little is known about the compressibility of these materials. In this study, FCR slurry was obtained from the inlet of the slurry discharge pipe of an active impoundment in Kentucky (U.S.). The liquid slurry was consolidated in columns over a range of stress to create samples representing the slurry in an adjacent established slurry impoundment. These results are compared with consolidation tests performed on in-situ samples obtained from the impoundment. The consolidation results indicate that both the fresh slurry samples and the in-situ FCR are highly compressible, and the in-situ FCR was found to exhibit values of the pre-consolidation stress that were much less than stresses corresponding to the equivalent overburden pressures. This implies that the impounded FCR has not yet reached the end of primary consolidation, even though the material was placed decades ago. Typical calculations suggest that the time for 99% consolidation is on the order of 90–300 years depending on the actual drainage.

Alabama Highway 5 is a farm-to-market road built directly on an expansive clay subgrade. Moisture fluctuations cause the soil to shrink and swell, resulting in severe pavement distress. Laboratory testing was performed to characterize the shrink-swell behavior of the subgrade soil. Swell pressures of up to about 72 kPa (1,500 psf) have been observed in the laboratory. Several remediation strategies have been implemented at AL-5 in an attempt to reduce the need for pavement maintenance. These techniques include increased drainage, vertical moisture barriers, lime columns, and paved shoulders. To evaluate the performance of these test sections and further characterize the soil behavior, field instrumentation has been installed including soil moisture sensors, soil suction sensors, pore water pressure sensors, and asphalt strain gages. This paper details the instrumentation placed in the improved test sections and evaluates the sections over time.

Lime kiln dust (LKD), which is a byproduct of lime production, has been increasingly used as an additive to improve the workability of clayey soils. However, limited research has been conducted to quantify the benefits of LKD used for this purpose. In this study, laboratory experiments were conducted to quantify the benefits of LKD for stabilization of subgrade soils. Two types of clayey soil from two different sites were selected and mixed with different percentages of LKD. The Atterberg limits, moisture-density relationships, swelling potential, durability, and unconfined compression strength of the native and LKD-treated soils were determined. The strength gain with time was also studied to assess the benefits of curing (if any). The LKD-treated samples were compacted and cured for 1–2 h and 1, 3, 7, and 28-day periods, and then tested to determine the unconfined compressive strength and volume expansion. A strength gain of more than 100% for the LKD-treated soil over the untreated soil was observed. The results also indicated that the strength of LKD-treated soil continuously increased with time. LKD also substantially reduced the plasticity and swelling potential of subgrade and improved the workability and durability of clayey soil. In general, LKD performed well and can be used for modifying and/or stabilization of clayey soil subgrades.

The technique of increasing load bearing capacities of sand using addition of waste materials is economically viable and eco-friendly. In 2013, India reportedly produced 530 million tones of construction and demolition waste (CDW), as a result of construction of new infrastructure and renovation of existing structures. The primary component of CDW is building derived materials (BDM). The present study primarily aims to utilize these waste materials in improving the load bearing capacities of cohesionless soil having low relative density. Laboratory investigations are carried out to determine the strength and load carrying capacity of sand partially replaced with different percentages of BDM. Test results indicate that addition of 17–23% of BDM effectively increases shear strength and load carrying capacity of sand. A finite element model is developed in commercially available software to simulate the behavior of sand-BDM mix as a foundation material and it shows a good agreement with the experimental results. Experimental and the numerical studies indicate that naturally available loose sand can be partially replaced with BDM to improve its properties as a foundation bed, while simultaneously reducing the need for disposal of BDM as solid waste.

In this research, lime sludge, a byproduct of the lime softening process, was investigated as an alternative stabilizer to increase its use for soil stabilization. For this purpose, lime sludge was used alone and with class C fly ash to stabilize a loess soil which is a silty soil. Atterberg limits, unconfined compression (UC), and freeze-thaw (F-T) tests were performed. The UC test results of the specimens cured up to 90 days showed that the use of lime sludge alone increased the strength of the loess soil. Besides, the UC test results of the 7-day cured specimens pointed out that lime sludge can be mixed with class C fly ash to provide a further increase in the strength of the loess soil. However, the UC test results performed after the F-T tests showed that there was no considerable benefit of using lime sludge either alone or with class C fly ash to increase the durability of the loess soil.

Volume change behavior of the Moreland clay, which is full of montmorillonite mineral, is one of the major causes of building and pavement damage in northern Louisiana. Using class C fly ash geopolymer (CFAG) to stabilize expansive soil is not new and becoming more accepted in the industry nowadays. However, stabilizing the Moreland clay using CFAG has never been extensively studied or well documented. In this research, the Moreland clay stabilization with CFAG (5, 10, and 20%) was studied and then its performance was compared with a traditional soil stabilizer which is cement (10%). Consolidation tests were performed 7, 14, and 30 days after the samples were prepared. From the compression index (C_C) and swelling index (C_S) values it was concluded that even though cement is by far the best soil stabilizer the application of a higher percentage of CFAG, a satisfactory level of soil stabilization can be achieved.