Geo-Congress 2022: Soil Improvement, Geosynthetics, and Innovative Geomaterials

Rigid inclusions (RI), a form of ground improvement, has become accepted in the United States as a cost-effective alternative to support low- to mid-rise buildings, parking garages, tanks, retaining walls, and embankments, especially in areas with marginal, soft, and compressible ground. RI systems are commonly implemented as a cost-effective alternate to deep foundations for the growing warehouse, distribution, and data center markets. Originally developed by specialty contractors in Europe, this system of support was imported to the US in the early 2000s. For the purposes of this paper RI are defined as unreinforced grout or concrete columns. These systems are typically procured through a design build process and though similar in appearance, the drilling equipment, installation methods, inclusion material, and design methodology, are often proprietary and specific to each specialty contractor. As with other methods of ground improvement, the lack of Building Code regulation, misunderstanding of the technology and poor-quality project specifications can lead to variability in performance, project team expectations, quality control, and verification testing. This paper addresses the authors’ local industry approach of RI systems as support for buildings in New England, specifically in the presence of soft compressible soils such as soft organic or clay deposits. This paper will discuss sites where RI can be considered and will highlight areas of design risk including load transfer layers (i.e., aggregate pads that are used to separate the inclusions from the supported structural foundations), bearing capacity, element structural capacity, settlement of the system, and interactions with building foundations and slabs. Construction risks may be mitigated with thoughtful pre-mobilization planning between Owners, Consultants and Specialty Subcontractors, and robust quality control procedures to address project specific risks (including load testing of elements). This paper will distinctly identify design and construction considerations that should be considered by the engineer and contractor as the use of this technology continues to grow and evolve.

A one- to two-story-high behavioral health hospital, designed with shallow foundations for an allowable bearing pressure of up to 95.8 kPa, was proposed in Dearborn, Michigan. Due to the presence of a 23-m-thick deposit of very soft to soft Great Lakes clays, the 1.2-m raise-in-grade and the proposed building were expected to induce as much as 12.7 cm of long-term consolidation settlement, negatively impacting the structure performance. The design-build team proposed hybrid ground improvement methods consisting of Prefabricated Vertical Drains (PVDs) and high modulus Rigid Inclusions (RIs) to overcome design performance and construction time-constraint challenges. Integrated ground improvement systems, coupled with detailed construction monitoring, are more cost and schedule effective than conventional deep foundations for similar projects and geologies. Aided by a thorough instrumentation program, the ground improvement design team was able to make timely decisions to adjust surcharging duration, achieve the necessary settlements, and still meet the project delivery schedule.

The shores of Lake Erie are known for having areas with deep soft clay deposits. These soft clay profiles often result in the need for expensive deep foundation solutions to limit the potential for unfavorable total and differential settlements. Advancements in ground improvement, such as aggregate piers and rigid inclusions, are rapidly becoming a cost-effective foundation solution at these challenging sites. This paper discusses one such site in Sandusky, Ohio, where a relatively heavily loaded sports complex was supported on rigid inclusions extending through 12–13 m of very soft clays to tag limestone bedrock. This paper presents the geotechnical conditions at the project site, discusses the selected ground improvement solution and associated design approach, outlines the quality control program used during construction, and presents the results of the load testing program. The paper details the importance of the load testing program to verify the stiffness and continuity of the rigid inclusion elements so that the building performs as expected through the design life.

This paper will provide an introductory explanation regarding the use of rigid inclusions as bearing elements combined with high strength reinforced load transfer platform (LTP). The system resolves issues related to lateral squeeze, excessive deformation, and global failures that can occur due to the low-bearing capacity of the foundation soil. The combination of the columns and LTP (reinforced with high strength, high tensile modulus geosynthetic reinforcement) offers highly improved factors of safety against global stability failures, significantly reduces total and differential settlements, and stabilizes column tops to minimize lateral displacement. The narrative will discuss how the rigid inclusions are designed and built and provide an explanation on how excessive lateral deformation of perimetral columns can be prevented by the system. It will also present information about the different types of high strength geosynthetic reinforcements that can be used. The paper will present case studies illustrating the use of the solution on recent projects and discuss performance results and observations.

Among different soil improvement methods, stone columns are widely used to enhance the engineering behaviour of deep soft soil deposits. In general, the deep soil deposits consist of multilayer soil having different hydro-mechanical behaviour characteristics. The design and performance of stone columns in the multi-layered soil profile are not well understood. As available guidelines for the design of stone columns mostly consider homogeneous clay deposits, an approximation would be wrong for the multi-layered sites. To understand the effect, a 3D finite-element (FE) analysis was performed on the representative unit cell with homogenous and multi-layered soil profiles. The performance of the unit cell in terms of the settlement, horizontal deformation, and stress concentration ratio were investigated. The results indicated that the variations of stress concentration ratio and stone column bulging levels are different in multi-layered stratification profiles and depend on the location of soft soil layers and their relative stiffness levels.

The interaction between the stone column and the soft soil is an important design factor that affects the bearing capacity and the settlement of the composite system. Most studies have neglected this phenomenon and have always assumed there will be a perfect bond between the column and the soil. The results of this analysis might not represent the reality of the composite system, because the difference in stiffness and load carrying capacity in these materials might cause differential settlement. This project conducted a finite element analysis using ABAQUS to identify the appropriate contact type that accurately simulates the interaction between the stone column and the surrounding soft clay soil with the effect of the material properties. The results demonstrated that the interaction between these two materials could be simulated in two directions with either soft normal-penalty contact or hard-penalty contact. The interaction was influenced by the friction angle and the Young’s modulus of the materials. As a result, the effect of the interaction on the bearing capacity of the column is recognized.

Settlements due to subjected dead and live loads induce normal, lateral, and shear stresses that affect the geotechnical capacity of the stone column. Excessive vertical loads can cause bulging failure near the top of the end bearing of the stone column to the relative displacement at the interface with the surrounding soil. Most studies have neglected the elastic–plastic behavior of the soil and column due to the complexity of the problem and propose the serviceability limit state to estimate the bearing capacity and settlement. The objective of the current model is to represent more realistically the interaction of the column-soil behavior considering the elastic–plastic model and determine the bearing capacity of the column in a composite foundation subjected to extreme vertical loads. Finite element analysis was carried out on a single-end bearing stone column installed in soft clay soil. Empirical correlations were developed for stresses via settlement acting on the top of the column up to failure. The validity of the solution was verified through a comparison with the measurement data and other existing analytical solutions.

This paper describes the results of two modulus load tests and two-dimensional finite difference analyses (FDA) conducted to evaluate the load-displacement responses of isolated aggregate piers. Aggregate piers were constructed with two different aggregate materials; aggregate pier 1 with base coarse materials and aggregate pier 2 with subbase coarse materials. The numerical analyses provided reasonable predictions of the measured settlement and load-displacement responses of the isolated aggregate piers. Parametric analyses using the validated numerical model illustrate that the lateral stress increment on the soil around the pier during the installation process of the pier should be considered in the numerical analyses, otherwise the settlement can be overestimated. The friction angle of the aggregate pier could also significantly alter the resulting displacement.

Structures built over expansive soils undergo severe volume change due to seasonal moisture fluctuations. Increased suction with loss of moisture leads to desiccation cracking and soil curling (upward and downward curling) which is a common phenomenon during the soil drying process. To address the detrimental effects of shrinkage, conventional materials such as lime, cement, and fly ash are used as soil stabilizers. In contrast to this, recent studies on soil improvement paying attention to bio-inspired materials due to reduced negative impact on the environment. Among them, biopolymers are recognized as an effective stabilizer to improve soil properties. However, the shrinkage behavior of biopolymer treated soil is not fully understood under different testing conditions. Investigation of surface characteristics (i.e., curling and cracking) is important to assess the effectiveness of biopolymer in soil stabilization. In view of this, the present paper aims to evaluate the shrinkage characteristics of xanthan gum (XG)/guar gum (GG) treated expansive soil at various dosages subjected to uncontrolled boundary conditions. Bar linear shrinkage tests were performed at biopolymer (XG/GG) dosages of 0.5%, 1.0%, 2.0%, and 4.0% by weight of dry soil mass. Results indicate that untreated samples exhibited shrinkage cracks (without curling) with 18.25 mm deformation and 12.9% linear shrinkage value. Xanthan gum treated soil exhibited soil curling behavior (Convex upward) with lift-off height 12.5 mm and 23.5 mm at 0.5% and 4.0% dosage, respectively; whereas guar gum treated soil exhibited surface cracking phenomenon at 0.5% dosage with deformation value of 21 mm and linear shrinkage value of 15.2%; non-uniform division of polygons and minor convex-up curling is observed at 1%, 2%, and 4% dosage. The factors which affect the moisture evaporation, cracking phenomenon, curling state, particle rearrangement, and lift-off height are identified and possible mechanisms are discussed. The current study creates a basis for in depth investigation on shrinkage characteristics of biopolymer treated soil when it is proposed as a subgrade material for pavement application, in erosion control works (slopes), and as landfill cover material.

Compacted expansive soil undergoes swelling and shrinkage during seasonal moisture fluctuations and causes distress to highway and railway structures built over them. Shrinkage of expansive soil is accompanied by the development of large desiccation cracks. The present research work is focused on studying the effect of lime treatment on crack propagation characteristics of compacted expansive soil along with its shrinkage response. Soil-shrinkage curves (SSC) were obtained for both untreated and lime treated compacted expansive soil specimens. Digital images of soil specimens were captured during the desiccation process. A Python program was developed to study the evolution of desiccation cracks by performing digital image analysis. A marked reduction in the rate of shrinkage process was observed accompanied with 36.4% reduction in volumetric shrinkage at 6% lime addition. Crack analysis results showed an increase in the intensity of cracks on lime addition followed by reduction in crack width, higher crack network connectivity, and microcracking phenomenon.

Carbonation is a chemical reaction that occurs invariably throughout the service life of lime-stabilized soil. Carbonation results in densification owing to the precipitation of reaction product calcite within the pore structure. However, the pore structure of lime-stabilized soil varies during curing due to the progressive surface modifications and pozzolanic reactions. Given this, the present study investigates the effects of carbonation on the compressive strength of lime stabilized compacted expansive soil by varying the dosage of lime content and curing period. The chemical, molecular, and microstructure changes upon carbonation were assessed using a thermogravimetric analyzer, Fourier transform infrared spectrometer, and mercury intrusion porosimeter. Results showed that the porosity of lime stabilized soil increased with initial lime content and curing period. Also, the permeation of gas and consequent changes in the mechanical performance upon carbonation is observed to be highly dependent on the availability of macropores and residual lime in a stabilized expansive soil.

Due to their low undrained shear strength and compressibility, soft soils are considered problematic. Numerous methods, including the addition of fibers, shredded rubber tires, and geosynthetics, have been used to increase the shear strength. The present study investigated the addition of magnetic particles and the use of a magnetic field to rotate the orientation of the particles in order to increase the shear strength of soft soil. Laponite, a transparent material, was used to simulate the geotechnical properties of soft soil and to visualize the magnetic particles’ rotation. The addition of magnetic particles increased the undrained shear strength significantly. By applying a controllable electromagnet to the transparent soil specimen and creating a magnetic field around it, the magnetic particles can be rotated by controlling the current. Overall, this study’s findings indicated that adding magnetic particles to soft soil improved its shear strength.

The wet method of deep mixing employs cement-water slurry to increase the strength, reduce the compressibility, and reduce the hydraulic conductivity of the soil. Organic soils can be challenging to treat because organic matter can interfere with cementitious reactions. Some types of organic matter reduce the mixture strength at early curing times while having little effect on the long-term strength, and other types of organic matter reduce both the short- and long-term strengths. A research program is underway to develop a framework for quantitatively representing the impact of organics on the strength development of soil-cement mixtures. Reproducible fabricated organic soils will be employed to develop the framework, and then the ability of the framework to represent the strength development of natural organic soils will be assessed. As a first step, the influence of the following six readily available organic compounds on the strength development of cement-water slurries was investigated: humic acid, tannic acid, sucrose, ethylenediaminetetraacetic acid (EDTA), ethylene glycol, and xanthan gum. These organic compounds were separately mixed with the cement-water slurry at dosages of 10% and 2% by dry weight of cement and cured at room temperature for 7, 12, and 28 days. The results showed that tannic acid and sucrose significantly reduce the unconfined compressive strength (UCS) of the cement-water slurry. EDTA also had a negative effect on UCS, but the effect disappears at low concentrations and after long curing times. Humic acid, ethylene glycol, and xanthan gum had little or no effect on UCS compared to the other three organic compounds. Tannic acid was selected for further testing over a wide range of concentrations of tannic acid with cement-water slurry because tannic acid can have a dramatic detrimental effect on UCS, and it occurs in natural soils. The findings from the further tests include the following: (1) increasing tannic acid concentration reduces UCS, and (2) the detrimental effect of tannic acid appears to decrease as curing time increases. The test results indicate that tannic acid may be a suitable organic compound for fabricating organic soils to use in a laboratory investigation to develop a quantitative framework for representing the influence of organic matter on the strength development of soil-cement mixtures.

This study reports on the thermodynamics and kinetics of the cementitious reactions between two pure clay minerals (sodium bentonite and kaolinite) and slaked lime. The optimum moisture content (OMC) for strength development was first investigated for each mineral, through an evaluation of both the proctor compaction curves and the 7-day Unconfined Compressive Strength (UCS) results. Particle size of kaolinite was observed to have little influence on the 7-day UCS of specimens treated with 5% slaked lime or 5% Portland cement. A water content dry of optimum was observed to generate the highest UCS values for two different particles sizes of kaolinite, for both the binders. Conversely, bentonite yielded higher UCS wet of optimum (1.4 times the OMC) for both cement and lime. Long-term strength tests for the lime blends up to 180–360 days showed that bentonite mixed with 8% slaked lime plateaued at 400 kPa after 28 days of curing. The pore solution extract indicated that pH dropped from 13 to 10 within the same time frame, then remained constant. The Thermogravimetric analysis (TGA) confirmed that this trend was associated with a rapid consumption of free lime. Conversely, kaolinite maintained a pH of 13 up to 180 days and free consumption of lime was gradual. The strength increased almost linearly with time in kaolinite, and the rate of increase was in step with the apparent rate of calcium silica hydrate (CSH) formation. Future work includes full pore solution analysis as well as quantitative analysis of the solid with Nuclear Magnetic Resonance (NMR) and X-Ray Diffraction (XRD) to enhance the TGA data. The solid and pore solution data will be combined to obtain a full kinetic quantitative model for the two minerals.

Soft or highly compressible soils often undermine the stability and overall integrity of structures through excessive shear failure and settlement. Past research efforts have established the effectiveness of Ordinary Portland Cement (OPC) binder in improving the strength of these highly soft or compressible soils. Unfortunately, a pronounced shortcoming of OPC is its energy-intensive production, and large quantities of CO₂ emissions. This environmental concern has led to the use of geopolymers as a viable alternative to OPC with desirable properties such as high strength and low-energy consumption. The present study investigates the effect of polypropylene fiber (PF) and curing methods on the Unconfined Compressive Strength (UCS) of geopolymer stabilized kaolin clay. The kaolin clay was infused with 20% fly ash and varying PF percentages 0.25%, 0.5%, and 1.0% by dry weight of clay. The alkali precursor NaOH:Na₂SiO₃ was prepared at a ratio of 1.5:1.0 and molarity of 8 M used for the geopolymer synthesis. Two curing methods were employed, that is, Ambient Curing Temperature (ACT, 23°C) and Elevated Curing Temperature (ECT, 70°C) for a period of 7 and 28 days. Results showed a maximum 28-day UCS value of 32.28 MPa for curing at ECT. This clearly shows that geopolymer-stabilized kaolin clay exhibits a significant increase in 28-day strength under sustained ECT compared to ACT. Hence, ECT was found to be more effective with increasing curing period and PF content compared to ACT. However, the maximum UCS was attained at a 0.25% PF content for ACT and 1.0% for ECT; beyond 0.25% PF, the UCS decreased under ACT, while under ECT, the peak UCS was recorded at 1.0% PF. Scanning Electron Microscope (SEM) test was also conducted to analyze the microstructure of the virgin and geopolymer-stabilized kaolin clays.

Cement is widely utilized to mix with soft clays to improve their properties such as strength, stiffness, and permeability. The characteristics of soils mixing cement (soilcrete) depend on the change of soilcrete microstructure. However, the microstructure of soilcrete has still limit data. This paper investigated the variation of soilcrete microstructure with time using scanning electron microscopy (SEM). The two identical soilcrete specimens were made from dredging sand taken in the Mekong Delta, Vietnam, mixing the OPC cement at a content of 300 kg/m³ for the permeability and SEM tests. The results indicate that the permeability of soilcrete (k_s) was lower 1,000 times than that of the unmixed sand. k_s decreases with the curing time of 120 days. The soilcrete microstructure was denser than that of the untreated sand sample due to the cement-water-soil chemical reactions forming cementitious products and causing reduction of k_s with the curing time.

The impact of the use of sand treated with Colloidal Silica (CS) on a model 80 m high-earthfill dam was assessed through numerical modelling. The hydro-mechanical properties of the CS-treated soil were taken from a previous laboratory study. Different strategies of treatment placement were studied, with increasing volumetric fractions of the dam being replaced by the treated material. Staged construction of the earthwork was simulated to evaluate the horizontal and vertical displacements at critical points within the dam. Different kinematics have been observed, depending on the quantities of CS-treated material included in the soil structure. Moreover, the use of the treated soil was beneficial in terms of water outflow and upstream slope stability, in correspondence with different water reservoir levels. Different strategic patterns of CS-treated sand placement are proposed herein to fully exploit the storage capacity of the dam, optimizing its stability.

Collapsible soils cover vast areas around the world and may cause severe damage to civil engineering structures. In this paper, the application of grouting clay nanoparticles for improving mechanical behavior of low permeable collapsible soils has been investigated. Dilute grout of nano-clay particles was injected into undisturbed soil columns, where oedometer specimens were acquired from the axis and the side of the grouted columns and tested after 7, 14, and 18 days of curing. Results compared with soils grouted using ordinary Portland cement (OPC) revealed that clay suspensions feature high mobility in the ground and remarkable performance in reducing the collapse potential. Findings encourage the application of clay nanoparticles over cement for a sustainable, economical, and eco-friendly grouting approach to improve mechanical behavior of loose deposits.

Deep Soil Mixing (DSM) is adopted in various applications to improve the mechanical and hydraulic properties of different soil types, granular, plastic, or organic. Activity of plastic soils often inhibits the disaggregation of particles and their mixing with cement, with the result that lumps of untreated soil remain entrapped in the cement paste causing flaws to its homogeneity and mechanical properties. The paper presents the results of an experimental study aimed at testing the applicability of a chemical additive to improve workability and homogeneity of the paste and the mechanical performance of the aggregate. Two different materials, a kaolinite and a smectite, have been tested mixing them with Portland cement and an additive formed by a clay dispersant polymer dosed with various proportions. The modified performance is evaluated with a series of laboratory tests aimed at determining consistency limits, viscosity, and uniaxial compressive strength. The obtained results are interpreted in the light of the physio-chemical modification induced by the additive to the clay-water mixes.

Poor subgrade often requires in-place stabilization or removal by excavation and replacement with suitable material. Chemical stabilization with cement or lime is a common remediation practice. This study investigated the use of No. 10 screenings, a quarry byproduct finer than the 4.75-mm (No. 4) Sieve, as a means to improve poor subgrade conditions. Three sources of screenings with two marginal soil types at various mixture rates were studied in the laboratory to determine an appropriate field application. The engineering improvements were determined by the California bearing ratio (CBR), density, plasticity reduction, drainage characteristics, and resilient modulus. At a mix rate of 50% by weight, increased density and reduced plasticity were observed. But the resilient modulus improvement depended on the moisture condition. When subgrade is not saturated, amendment with screenings could provide a benefit in terms of higher resilient modulus at the equilibrium moisture condition, which is usually lower for amended soil and depends on the depth of the groundwater table (GWT).

During Tunnel Boring Machine (TBM) excavation in hard rock, it is possible to encounter at the excavation zone, weak areas composed by weathered rocks, which need to be improved. In this paper, a laboratory study about a grouted cataclasite fragmented rock and its mechanical behavior is reported. Two non-conventional binders, that is, a colloidal silica with 15% SiO₂ content and very low viscosity and a two-component low-viscosity hydrophilic acrylic resin (both about 3 mPa∙s) were tested in laboratory to evaluate their performance improving the cataclasite. Permeation tests in a column of 0.5 m height and 0.05 m diameter were performed. The cataclasite was placed loose in the column, with a porosity n = 0.6 and the two products were injected with a pressure between 3.5 and 4 bars. After that, multi-stage triaxial CU on single samples for each grouted product with 100 mm height and 50 mm diameter. Strain rate of 0.3 mm/min was applied. Results show that the binders are valid products to improve the mechanical properties of cataclasite.

In recent years, a new method for soil stabilization was discovered that involves combining an anionic surfactant with alkaline earth metals. Combination of these ions with soil creates a matrix that adheres soil particles together and leads to improved strength. This soil improvement method has been dubbed surfactant-induced soil strengthening (SISS). In this study, beach sand from Atlantic Beach, FL, was strengthened via SISS by hand-mixing various combinations of sodium dodecyl sulfate and calcium chloride. Specimens were tested for strength improvement using unconfined compressive strength testing. Results showed that significant strength improvements may be possible using this method, and an approximate optimization point was established as a function of pore volume. Next, a surface percolation treatment method was tested using bench-scale sandboxes where surface erodibility and strength were tested using a modified rut erosion test and pocket penetrometer. Results showed that surface percolation may increase soil strength and reduce erodibility associated with vehicle tires, but surface percolation is much less effective than hand mixing. In addition, results from sandbox testing appeared to show that calcium mobilization is much more important than stoichiometric balance in terms of realizing strength and tire erosion improvement. Finally, dissolution testing was conducted on several specimens. Results showed that soils treated via SISS tended to revert to their untreated state over time in the presence of freshwater and saltwater.

The durability and performance of pavements and other lightweight structures constructed over expansive soils are persistent causes of concern due to moisture-induced volumetric fluctuations. Typically, traditional calcium (Ca)-based stabilizers, especially lime, effectively mitigate the problems associated with such problematic soils by reducing their swell-shrink potential and improving their strength properties. However, the treatment of sulfate-rich expansive soils using the Ca-based stabilizers results in detrimental heave due to the formation of a highly deleterious mineral, ettringite. This research study was performed to investigate the efficacy of utilizing an eco-friendly metakaolin-based geopolymer (MKG) stabilizer for treating sulfate-rich expansive soils. A comparative study was conducted by performing engineering tests such as free swell tests and unconfined compressive strength (UCS) tests on untreated, lime-treated, and geopolymer-treated soils for different curing periods. The effects of geopolymer dosage, curing period, and moisture intrusion on swelling characteristics and strength properties of treated soils were investigated. In addition, microstructural analyses were performed to study the changes in the soil after chemical treatment with geopolymer and lime. The results of engineering tests and microstructural studies indicate that geopolymer can effectively stabilize sulfate-rich expansive soils and could be used as a sustainable and eco-friendly alternative to traditional Ca-based stabilizers.

Rapid stabilization of expansive soils has significant potential to support infrastructure development, particularly highway pavements. Historically, several studies have attempted to develop a stabilizer that can rapidly convert weak soils to strong soils with little manipulation and straightforward construction protocol. Often, such studies have recommended the use of non-traditional stabilizers that have not been widely implemented. This study aimed to develop and evaluate the use of a mixture composed of conventional stabilizers such as lime, metakaolin, and sodium silicate for rapid strength gain of expansive soils. A simulant soil composed of smectite, kaolinite, and quartz was used to evaluate the stabilizer. The optimum mix design for rapid strength gain was determined by varying the amount of lime, metakaolin, and sodium silicate. The proposed mixture was composed of 4% lime, 3% metakaolin, and 3% sodium silicate by weight of soil, respectively. Engineering characterization results showed a 170% increase in strength within 24 h of treatment. The durability of the treated soil was also evaluated by recording the strength after 3, 7, and 9 cycles of wetting and drying, respectively. The results indicate that the stabilizer performance is on par with the simulant soil treated with the optimal amount of lime and cement. Microscale characterization using scanning electron microscopy-energy dispersive spectroscopy and nanoindentation provided insights into the stabilization mechanism of the treated soil. Scanning electron microscopy demonstrated the formation of pozzolanic products such as (C,N)-A-S-H, which is attributed to the soil’s rapid stabilization.

Expansive soil possesses inferior mechanical behavior with periodic variability in heave/shrink, causing distortion and premature failure to the pavement structures. In the present study, an attempt was made to strengthen the expansive subgrade soils by combining alkali-activated binder (AAB) with naturally available hemp (HF) and banana fiber (BF). HF and BF were chemically treated (10M of KaOH) to improve their durability. The influences of varying dosages of fibers and slag in fiber-reinforced alkaline soil significantly improved California Bearing ratio (CBR) and flexural strength. Microstructural and morphological studies using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were also carried out to understand the behavior of HF and BF-AAB soil mixture at varying slag and fiber content. It was observed that HF-alkaline soil achieved higher interfacial bonding with good interlocking density relative to BF-AAB soil. Furthermore, the uncertainties associated with subgrade strength in terms of CBR were expressed in the form of a reliability index (β_CBR) using Monte Carlo simulation (MCS). The results showed that the optimum dosages of slag and fiber in the alkaline soil mixture were essential factors for regulating the linear shrinkage tensile crack and strengthening the stiffness of subgrade soil.

Hydromechanical performances and pore-structure evolution in in situ lime-treated soil is influenced by the implemented methodology of execution. In situ lime-treated soil experiences kneading action during soil compaction; however, little is investigated regarding the contribution of the kneading mechanism towards hydromechanical and pore-structure evolution. This study evaluates the evolution of Unconfined Compressive Strength (UCS), hydraulic conductivity, and pores of different categories in laboratory kneaded soil. The evaluation involves results from lime-treated soil subjected to different curing times and temperatures. The results obtained from laboratory kneaded and cured soils are interpreted with the one obtained from in situ sampled soil of the same configuration after 7 years of atmospheric curing. The obtained interpretation provides an acceptable insight towards the expected long-term hydromechanical and pore-structure evolution of lime-treated soil. Thus, the study highlights the importance of reproducing an implementation mechanism in the laboratory which closely represents the field compaction.

A research study was designed and conducted to investigate the effect of polymer emulsion treatment on permeability characteristics of subgrade soils. A commercially available polymer emulsion was used to stabilize cohesionless and cohesive soils, and an attempt was made to understand the impact of polymer dosage and curing time on the permeability characteristics of treated soils. A double-walled triaxial test setup was used to measure the hydraulic conductivity of untreated and treated soils. The changes in the microstructure of the polymer emulsion treated cohesionless soil specimens were examined using field emission scanning electron microscope (FE-SEM) imaging. The laboratory test results indicated that polymer treatment decreased the hydraulic conductivity of the soil, and the degree of reduction in hydraulic conductivity was more prominent at higher dosages and longer curing periods. The SEM images of untreated and treated soil specimens corroborated the change in hydraulic conductivity before and after chemical treatment.

Most quarries in the United States have an abundance of the No. 10-screenings (i.e., stone dust) byproduct, which is often considered a byproduct material from the production of conventional aggregates. The use of byproduct materials will become necessary in the future. One potential application is to use stone dust in inverted pavements systems by improving their engineering properties with cement treatment. The concept inverted pavements were developed in South Africa about 50 years ago; however, their use is relativity new in the United States. This paper explores the use of No. 10-screenings to create a cement-treated base for a pavement test section at the Turner-Fairbank Highway Research Center. No. 10-screenings and 21A aggregate were collected from a local quarry and tested for gradation and density. Specimens were then made with both soils at 2, 4, and 6 percent cement and tested after a 7-day cure for permeability, unconfined compressive strength, and resilient modulus. The percentage of cement in the soil showed a negative relationship with the permeability and a positive relationship with soil stiffness. Without any added cement, No.10-screenings and 21A have similar permeability, but the No. 10-screenings were 30 percent less stiff than the 21A soil. Adding 2 percent cement to the No. 10-screenings resulted a cement-treated material equivalent to the 21A in stiffness.

Biomineralization is a popular reinforcement technology, for soil materials in current stages, but which is rarely studied at different temperature environment. Some potential application targets are different temperature environment. Therefore, it is essential to study the feasibility of biomineralization at different temperature environment. In this article, plant urease was selected as a cost-effective enzyme for enzyme-induced carbonate precipitation (EICP) at different temperature environment. Urease activity and urease enzyme-induced carbonate precipitation were studied as a function of temperature, and N-(n-butyl)-thiophosphoric triamide (NBPT) addition. The effects of NBPT addition on the curing efficiency of sand columns were studied by unconfined compressive strength tests and by determining the resulting concentration of CaCO₃. The results demonstrated that the urease activity could be inhibited by NBPT, but the urease activity would recovered with the temperature increasing. In addition, the initial rate of calcium carbonate production would be reduced with NBPT, which could relieve the plugged port during perfusion. Therefore, the distribution of calcium carbonate in sand columns was more uniform. And the experiment has proved that NBPT was proposed as a new way to control urease activity, which resulted in a high unconfined compressive strength (UCS) of the sand columns formed at different temperature environment.

Microbial induced carbonate precipitation (MICP) has been widely investigated to enhance the mechanical properties of soils. However, MICP applications have encountered challenges such as having a brittle CaCO₃ bond that breaks at small strains when subjected to shearing. The Silicatein–α enzyme, which is naturally found in sea sponges, was produced in the laboratory and applied in biomineralization to control the CaCO₃ crystal morphology. In this study, bio-inspired flexible calcite (BiFC) was precipitated in soils using Silicatein-α enzyme. Silicatein-α enzyme protein was engineered and expressed in modified Escherichia coli bacteria and then extracted and purified for lab use. Syringe tests were conducted to characterize the morphology and the structure of the BiFC precipitation in soils. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the CaCO₃ at the microscale. Spicule (needle-like structures) morphology of BiFC precipitates was observed from the syringe tests compared to the cubic morphology of the CaCO₃ precipitates treated by MICP and enzyme (urease enzyme) induced carbonate precipitation (EICP).

To explore the possibility of providing additional reinforcement to bio-cemented sand through fiber inclusions, a series of laboratory tests were conducted to investigate the effects of the addition of two different types of fibers (polypropylene fiber and basalt fiber) on the mechanical properties of bio-cemented sand, respectively. Samples were prepared at five different fiber ratios (0%, 0.2%, 0.4%, 0.6%, and 0.8% by volume of sand). Unconfined compression tests and calcium carbonate content tests were carried out to characterize the mechanical properties and calcite amounts, respectively. The results show that the unconfined compressive strength (UCS) of basalt fiber-reinforced samples monotonically increases with increasing fiber content, whereas for samples mixed with polypropylene fibers, the UCS increases first and then decreases with increase of fiber content. Moreover, fiber inclusions transit the bio-cemented sand from brittle to ductile failure modes. Scanning electron microscopy (SEM) photographs show that the calcium carbonate precipitations change the surface texture of sand particles and fibers, increase the internal friction, and transform discrete sand particles into a cemented sand cluster.

Microbially induced calcium carbonate precipitation (MICP) is a soil improvement technique that has the potential to meet the expanding needs of society with marginal environmental consequences. In this method, biological activities of bacteria lead to formation of calcium carbonate at particle–particle contacts. Precipitated cementation links soil grains together and improves engineering behavior of soil. In recent years, the method has demonstrated promising results in a wide range of geotechnical applications where soil stabilization is mainly performed under unsaturated conditions. However, the deformation and compressibility behavior of unsaturated MICP-treated soil is yet to be investigated. A series of consolidation tests were performed on untreated and MICP-treated sand specimens. Specimens were treated by percolation in unsaturated conditions. Tests were performed in a modified consolidation setup equipped with bender element sensors. Consolidation test results indicated that unsaturated MICP-treatment significantly reduced compressibility of soils. A sudden collapse in shear wave velocity measurements with stress increment was observed in moderately cemented specimens that was less pronounced in lightly and heavily cemented specimens.

Microbially induced carbonate precipitation (MICP) is a bio-cementation process using microbes to hydrolyze urea and form carbonate-based minerals with the presence of Ca ion. This reaction produces bonding among soil grains and improves stiffness and strength of soils. The MICP implementation in offshore construction would gain a significant benefit from use of sea water owing to its abundance. However, the effect of various chemical constituents in sea water, such as Na⁺, Cl^–, Ca²⁺, and Mg²⁺, on the MICP process remains poorly understood. This study investigates the effect of artificial salt water on the MICP process through batch tests, soil column tests, and microscopic analyses. The batch tests revealed that the level of urea hydrolysis with the salt water was higher than that with the deionized water. We also confirmed that the MICP-treated sand with salt water showed the greater improvements in small-strain shear modulus and unconfined compressive strength than the one treated with deionized water. Microscopic imaging showed that use of salt water results in different morphology of precipitated minerals though most precipitates still consisted of CaCO₃. The experimental results provide clear evidence that various cations in salt water facilitates MICP treatment of soils, and the MICP can be effectively implemented using salt water.

Wind erosion (dust) is a severe problem for mine tailings industry, as it poses environmental and safety concerns to public. In this study, microbiologically induced carbonate precipitation (MICP) based on urea hydrolysis was used to stabilize the surface of different tailings materials. An experimental study was performed on soil-filled pans that were prepared using loosely packed tailings material and treated using percolation of reactive solutions. Penetration testing and calcium carbonate content analysis were used to optimize the treatment strategy and assess the strength and durability of the cemented crusts. The MICP treated pans showed an increase in strength and durability with increasing concentration of the cementation solution and number of treatments.

Microbial induced carbonate precipitation (MICP) is a bio-mediated cementation process that uses biological activity to improve the geotechnical properties of granular soils. MICP, or more generally bio-cementation, has the potential to improve the resilience of granular materials to prevent phenomena such as liquefaction and erosion. Bio-cementation processes have also been previously used to stabilize byproduct materials such as coal ash and mature fine tailings. Fine-grained mine tailing sediments, or “slimes,” are typically weakened layers that negatively affect the overall performance of tailings impoundments and dams, and have previously contributed to catastrophic failures of these structures. In this study, two sets of fine-grained tailings from gold and iron mines are tested to determine their compatibility with MICP. The remolded undrained shear strength was assessed for these byproduct materials over a range of different water contents to compare with bio-cemented samples. The bio-cemented samples indicated significant increases in remolded undrained shear strength, ranging from two to five times the natural samples’ strength. Analytical microscale testing methods were utilized to determine the soil fabric and structure (i.e., X-Ray Diffraction and Cryo-Scanning Electron Microscopy). In particular, the mineralogy of the soils was examined to better understand the physical and chemical interactions of the soil grains, both before and after cementation. The results of this study indicate that MICP strengthens the fabric of the fine-grained tailings, which may result in improved performance of fine-grained mine tailings.

Microbially induced desaturation and precipitation (MIDP) is being investigated for its potential as a ground improvement method. The MIDP process involves stimulation of native denitrifying microorganisms by injecting a solution containing nitrate, calcium, and a source of dissolved organic carbon. Metabolic conversion of substrates into biogenic gas (nitrogen and carbon dioxide), biominerals (calcium carbonate), and biomass in sufficient quantities can mitigate liquefaction hazards in granular soils. This study aimed to investigate how soil stratification affects the distribution of substrates and metabolic products during and after MIDP treatment. A tank set-up simulating two-dimensional flow conditions was used. Multiple treatment cycles were applied to reach a significant amount of calcium carbonate. Bulk electrical conductivity measurements were used to monitor the distribution and consumption of ionic substrates throughout tank during treatment cycles. Post-treatment carbonate analysis showed that despite the spatially and temporally varying distribution of substrates, calcium carbonate was precipitated in all layers, both at the inlet and outlet, but the distribution was not homogeneous.

A series of thermal experiments was conducted to investigate the effect of ureolysis-driven calcite precipitation technique using the ureolytic bacterium Sporosarcina pasteurii on thermal properties of bio-cemented sand. The sand used in this study was Ottawa F-65 sand and thermal properties of the sand were measured using a TR-3 sensor connected to a portable, battery-operated thermal properties analyzer. The effects of different injection methods of the injected fluids on the efficiency of calcium carbonate precipitation and the uniformity of bio-cementation through the soil specimen were investigated. The amount of urea hydrolyzed, and the amount of calcium precipitated were determined using the modified colorimetric Jung assay and calcium assay, respectively. Calcium concentration along the bio-cemented soil column was determined using acid washing method followed by use of a colorimetric calcium assay. Thermal conductivity measurements were used to evaluate the changes as mineral develops in time.

Bio-cementation, notably microbial induced calcite precipitation (MICP), and Enzyme induced calcite precipitation (EICP), binds soil particles together through calcium carbonate (CACO₃) precipitation (cementation). Both MICP and EICP have significant potential for many scientific and engineering applications including improvement of strength, reducing soil liquefaction potential, surface erosion control, reducing permeability, and heavy metal contaminant remediation. However, the catalytic mechanism and the precipitation of CACO₃ in MICP and EICP mainly depends on the source of urease enzyme and the treatment process used. This study evaluates the mechanical and microstructural behaviour of bio-cementation using the standard MICP and EICP treatment process. The results indicate that, for the same number of treatment cycles (N_TC), a higher amount of precipitated CACO₃ was achieved for MICP than EICP which affects the strength. For similar average CACO₃ content (A_C), the standard treatment method used in EICP produced a higher chemical efficiency (defined as the amount of CACO₃ precipitated relative to the quantity of urea-CaCl₂ used) than in MICP. The results from scanning electron microscopy (SEM) imaging shows that the morphologies of the precipitated CACO₃ in MICP and EICP are similar, however, a high amount of vaterite was found in EICP than MICP. The outcome of this study indicates that the standard treatment processes used in MICP and EICP may influence the chemical efficiency, the amount, distribution, and polymorph of the precipitated CACO₃ which may directly affect the strength.

Bio-mediated soil improvement has become an important research area in recent years due to the societal need for eco-friendly ground improvement solutions. This technique utilizes the hydrolyzation capacity of ureolytic bacteria to induce carbonate precipitation in order to improve the shear strength properties of sandy soil. Even though Microbial induced calcium carbonate precipitation (MICP) is now an experimentally proven technique, work remains to advance the modeling of the strain-softening pattern of bio-cemented granular soils. In general, widely used models such as conventional elasto-plastic models do not fully capture the behavior of cemented soils. Work herein explores the use of the hypoplastic constitutive model in capturing the strain-softening behavior of MICP treated soil. A sensitivity analysis is performed to investigate the influence of hypoplastic parameters needed to model the material behavior on the obtained stress–strain behavior. Hypoplastic material model parameters are calibrated and the stress–strain responses for data from drained triaxial tests have been simulated for different levels of cementation.

Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that uses microbial enzymatic activity to catalyze the precipitation of CaCO₃ minerals on soil particle surfaces and contacts. Extensive research has focused on understanding various aspects of MICP-treated soils including soil behavioral enhancements and process reaction chemistry, however, almost no research has explored the permanence of bio-cemented geomaterials. As the technology matures, an improved understanding of the longevity of bio-cementation improved soils will be critical towards identifying favorable field applications, quantifying environmental impacts, and understanding their long-term performance. In this study, a series of batch experiments were performed to investigate the dissolution kinetics of CaCO₃-based bio-cemented sands with the specific aim of incorporating these behaviors into geochemical models. All batch experiments involved previously bio-cemented poorly graded sands that were exposed to different dissolution treatments intended to explore the magnitude and rate of CaCO₃ dissolution as a function of acid type, concentration, initial pH, and other factors. During experiments, changes in solution pH and calcium concentrations indicative of CaCO₃ dissolution were monitored. After experiments, aqueous measurements were compared to those simulated using two different dissolution kinetic frameworks. While not exhaustive, the results of these experiments suggest that the dissolution behavior of bio-cementation can be well-approximated using existing chemically controlled kinetic models, particularly when surrounding solutions are more strongly buffered.

While experimental studies on the use of microbial-induced calcium carbonate precipitation (MICP) for soil improvement have focused on assessment of cemented soil properties, there is a gap between small-scale laboratory experiments and modeling for the design of large-scale field implementation. Numerical analyses are conducted herein to explore the influence of various layouts and configurations of injection wells in delivering effective deployment of the MICP process. Metrics of evaluation include continuity and level of cementation as well as associated by-products. The bacterial transport/attachment/decay, and ureolysis rate parameters are included in the transport model. The model is calibrated using column-scale experimental data. Under the same flow rate and injected volumetric solutions, results indicated that 2-, 3-, and 4-well configurations with distance between wells equal to 1 m produce the highest average CaCO₃ in the target area. Among the well configurations which induce the highest CaCO₃ content, 4-well configuration with 1 m distance between wells provided more uniform distribution of CaCO₃ (less standard deviation), with relatively lower by-product ammonium (NH₄).

This study investigates the feasibility of using macro-synthetic fiber to improve the mechanical properties of Enzyme Induced Carbonate Precipitation (EICP) treated soils. The fiber used in this study is macro-synthetic composed of polypropylene and polyethylene. Unconfined compressive strength (UCS) test was used to investigate the effect of incorporating the fibers into the EICP-sand matrix. The effect of fibers on stress–strain behavior, peak and residual compressive strength, secant modulus of elasticity, energy absorption, and calcium carbonate distribution was evaluated. Three levels of fiber were used in the study: 0.1%, 0.3%, and 0.5% (by weight of the dry soil). Generally, the results have shown an increase in EICP-treated soil residual compressive strength and strain at failure by adding fiber to the EICP-treated soils. The increase in the macro-synthetic content has initially slightly decreased the EICP treated soil UCS followed by an increase in UCS at the fiber content of 0.5%. The UCS of soil treated with both EICP and fiber has reached a UCS of 274.1 kPa with an 87.5% increase compared to soil treated with EICP alone. This improvement is accompanied by more ductile behavior with an increase by 54.3 kPa in residual compressive strength compared to zero in the case of EICP alone.

As one of the electrokinetic phenomena, electro-osmosis has been used since 1970s as a soil improvement method to assist dewatering from soil, especially soft clay. The application of electro-osmosis for dewatering or consolidation involves installing anodes and cathodes, which induces directed water movement toward cathode. Over the past decade, due to the invention of different conductive materials, the electrodes can now be made from polymer; as a result, the electrodes can be made into the form of Prefabricated Vertical Drains (PVDs) to serve dual functions. Such development facilitated the wider adoption of electro-osmosis to treat clay soil. G-I sponsored Soil Improvement Committee a scan tour in China in 2018. A large land reclamation project in Taizhou, China, was visited during that scan tour. The soil at the site consisted of 3–4 m of dredging fill that was underlain by approximately 20 m of peat. The reclaimed land will be used for warehouse, roads, and office buildings. The estimated post-construction settlement would be in the magnitude of meters if soil was not treated before construction. Multiple soil improvement methods were utilized to drain the water from dredging soil and peat, among which electro-osmosis was used in one test section. Totally, two hundred electrodes were installed in the sections and connected to DC power. The electric current was monitored and adjusted in real time by a central control unit to ensure a good progress of the dewatering. During our site visit, the measured settlements was in a ranged from 500 to 750 mm, 32 days since the start of electro-osmosis dewatering/consolidation. The settlement values were significantly higher than these obtained from the neighboring sections with conventional vacuum preloading to consolidate the clay. The average energy consumption of the electro-osmosis ranged from 4 to 7 kwh/m³ for the project. The project indicates that the electro-osmosis has great potential to treat clay with the newly developed polymeric electrodes.

Analysis of ‘Rate of consolidation’ by ‘Laurent series and transformations’ is done here and a clear comparison is made between the Fourier series and Laurent series regarding the variation of the degree of consolidation with the time factor. Laurent series is proven to be very important for achieving consolidation of soil with low permeability more clearly as compared to Fourier series. As it is a type of convergent series, therefore, all the variation in sample thickness and pore water pressure converges to a single value. The curve obtained by the Laurent series is exponential in nature. With the help of the Laurent series process of consolidation can be studied even at a microscopic level and for any kind of soil. It is also helpful in determining the consolidation of stiff clays and can be achieved at a faster rate as compared to the Fourier series.

Particle migration through porous media is a complex phenomenon where the stability of the ground against deformation gets enhanced by virtue of the reduction in hydraulic conductivity. Factors such as constriction size distribution of the porous media, rheology of the injecting fluid, injection pressure/flow rate, and boundary stresses predominantly govern the particle migration. Studies have focused on controlling some of these factors and developing filtration models to quantify the maximum penetration depth. In the present study, a specially designed laboratory experimental setup is utilized to understand the effect of porosity and its corresponding constriction size distribution (CSD) of the granular media, at a particular injecting fluid viscosity and injection pressure on the particle migration characteristics. Exponential decay in injecting fluid velocity due to particle plugging, and penetration decay rate is quantified by employing imaging techniques. Image subtraction along with other image processing algorithms are used to quantify and analyze the flow stoppage mechanism due to the formation of internal filter cake. Further, existing empirical relations are found to overestimate the maximum penetration depth when compared with the experimental results.

Organo-silane (OS) modification has been shown experimentally to render soil water repellent. Engineered water repellency has the potential for widespread use in geotechnical and geoenvironmental applications. One such application is mitigating the effects of frost action in susceptible subgrade soils, particularly for unbound, unsurfaced roads. As part of a larger project to evaluate the feasibility of post-construction treatment of such roads, testing was performed with two commercially available OS products at varying dosages. This paper summarizes experimentally observed relationships between treatment, apparent contact angle, and water entry head for four samples of frost-susceptible soil collected from different regions across Iowa. Soil water characteristic curves were used to estimate the prevailing pore size and to relate that to water entry head for a given sample. Modification with two different OS chemicals yielded apparent contact angles between 119° and 143°. The water entry head was determined to range from 15 to 63 cm of water. Inverse relationships were observed between average pore radius and water entry head. These results are expected to be useful to agencies interested in evaluating engineered water repellency for use in new construction as well as rehabilitation of existing infrastructure underlain by frost susceptible soils.

The presence of frost susceptible soils makes the design, construction, and maintenance of geostructural systems such as pavement difficult. This pronounced in areas that experience seasonally cold weather characterized by freezing sub-zero temperatures. An innovative approach in mitigation is to render frost susceptible soils hydrophobic. This is achieved by treating soils with cost-effective and environmentally compatible polymers in a process that makes them water repellent (Engineered Water Repellency). This paper investigates the treatment of selected frost susceptible soils using commercially available chemicals (ATS-100, Terrasil, DOWSIL IE6683) at varying concentration dosages. The degree of hydrophobicity imparted, and performance was determined using contact angle measurements and Water Drop Penetration Tests. Treatment using ATS-100 and Terrasil were found to be effective even at small concentrations with values ranging from 73° to 144° for ATS-100 and from 103° to 145° for Terrasil. Effective values for DOWSIL IE6683 were obtained at a ratio of 1:10.

To overcome the dearth of natural sand, usage of the marginal fills has become inevitable in mechanically stabilized earth walls. The paper investigates the suitability of two waste materials, namely, steel slag and construction and demolition waste (CDW) for backfill applications. A series of strain-controlled static triaxial tests were conducted on geogrid reinforced sand, slag, and CDW at 70% relative density. Test results reveal that the performance of both the fill materials was found to be superior than the conventional fill material sand. Slag found to have the maximum shear strength, whereas CDW sustained higher strain at failure. Geogrid reinforcement increased the apparent cohesion of the materials without significantly affecting the friction angle. The geogrid found to enhance the peak shear strength of the slag by 2.5 times. The experimentally obtained stress–strain response was further approximated using the Duncan-Chang hyperbolic model, which effectively captured the non-linear shear behavior of geogrid reinforced materials.

This paper presents the results from laboratory tests on the pullout behaviour of polyester geogrid (GG) and polyester strips (PS) embedded in sands of different morphology and gradation. Pullout tests were carried out for three normal stresses of 20 kPa, 40 kPa, and 80 kPa in dense and loose conditions. The gradation and shear strength characteristics of sands confirmed to codal provision for reinforced soil structures (RSS). The test results showed that peak pullout resistance (P_R) of GG is lower in dense conditions and occurs at higher strains than PS due to constrained dilatancy. Pullout resistance of under compacted sample shows significant reduction as compared to the dense sample. The interface apparent coefficient of friction was reduced 50%–60% in GG and 70%–75% in PS. The study reveals that proper compaction is an essential requirement for RSS built using either GG or PS.

This paper presents a study on the interface behavior of geogrids and sub-ballast (capping) using a series of large-scale direct shear tests and discrete element modelling (DEM). Direct shear tests were carried out on sub-ballast with and without geogrid inclusions. The laboratory test data show that the interface shear strength is governed by normal stress and types of geogrid. The three-dimensional DEM was used to study the interface shear behavior of the sub-ballast subjected to direct shearing loads. Irregular-shaped particles of capping aggregates were modelled by clumping of many balls together in appropriate sizes and positions. Different types of geogrids were modelled by bonding small spheres together to form the desired grid geometry and apertures. The DEM model was then used to investigate the evolutions of contact force distributions and fabric anisotropy during the shear tests and the role of geogrid in micro-mechanical perspective.

The primary objective was to evaluate a data and quality-based alternative to long-established geomembrane destructive seam sampling approaches. The authors present the background of long-established geomembrane destructive seam sampling approaches and outline an alternative using a data and quality-based geomembrane field seaming framework as implemented on a pilot project and field study. Energy companies nation-wide are closing ash basins and will rely on thousands of acres (hectares) of polyethylene geomembrane (high-density or linear-low density) and millions of linear feet (meters) of geomembrane seams. The proposed data and quality-based geomembrane field seaming framework has the potential to reduce geomembrane installation costs while improving seam quality.

This paper presents a method to develop a Simplified Ground Reaction Curve (SGRC) for 3D vertical load transfer associated with soil arching in column supported embankments (CSEs). The SGRC is comprised of three piecewise linear relationships for the normalized differential settlement between columns and the normalized vertical stress between the columns. The differential base settlement is normalized by the column diameter to establish a percent relative displacement as opposed to plane strain trapdoor tests which use the clear span. Peak arching is modeled using approximations of the Concentric Arches (CA) or Hewlett and Randolph (HR) models, while terminal arching is modeled using the Adapted Terzaghi (AT) model. The Approximate Concentric Arches (ACA) and Approximate Hewlett and Randolph (AHR) models were developed herein using fitted relationships between the AT model for arching and the CA and HR models. The ACA and AHR models are assumed to be applicable to triangular as well as rectangular column arrangements. Measurements of the load transfer due to soil arching in full-scale CSEs were used to compare the predictions using the SGRC to those using the AT, ACA, and AHR models alone. Based on the results of the comparison with 13 measurements from five case histories, the authors do not see a compelling reason to use an SGRC due to the added complexity and lack of performance gains over simpler options such as the Bilinear Adapted Terzaghi (BAT) method used in Load-Displacement Compatibility Analysis.

A significant number of published studies acknowledged geocell as a pavement material with numerous benefits. While the geocell applications in highways are in transition from research to practice, practitioners need a systematic methodology to understand the economic viability of the geocells. Thus, this study proposed a method to estimate the maximum allowable cost (MAC) of geocell layer by combining case-based methodology, a product cost estimating technique, with life cycle cost analysis (LCCA). Also, the proposed method is demonstrated by calculating the MAC of the geocell layer for four low-volume roads in different counties of Texas. The case study indicated that the geocell layer’s MAC varied ($6–$20 per square yard) across different counties within Texas, showing geocell MAC is project-specific. This study identified that the geocell MAC is governed by two factors: the geocell layer’s load-carrying capacity compared with the conventional road materials and the price of the local construction materials. Thus, the proposed approach supports practitioners in justifying their decisions to include or exclude the geocell layer in road designs through MAC assessment.

“Geofoam” refers to a geosynthetic closed cell foam product used in civil engineering applications. An example application is the use of geofoam behind retaining walls as an alternative to conventional soil fill material. This paper discusses the use of geofoam blocks as retaining wall backfill and the authors’ experiences from past design/construction projects. A particular case study presented in this paper is the geofoam-backfilled hybrid retaining wall at Yeager Airport in Charleston, West Virginia. The case study project included a 48 foot of expanded polystyrene (EPS) fill for the upper portion of an 83 foot tall hybrid retaining wall. The project goal was to regain useable area lost as a result of a slope failure. The authors discuss design and construction challenges encountered and present lessons learned that can be applied to other geofoam projects.

Geosynthetic covers, including the exposed geomembrane cover and engineered turf cover, have been used as alternatives to conventional soil-geosynthetic covers for closure of landfills and other waste containment facilities. Because the geomembrane component in geosynthetic covers is not overburdened with a soil layer, uplift of geomembrane due to wind loads is of a concern in the design and construction of such covers. A wind tunnel study was performed to evaluate performance of an exposed geomembrane cover and the ClosureTurf engineered turf cover under wind loads on small-scale test models that were built to simulate a landfill cross section. The wind tunnel test results are presented in the form of dimensionless wind pressure coefficients. The wind-induced uplift pressure is found to be affected by the surface roughness of the cover and the slope ratio. The measured maximum uplift pressure coefficient values for the ClosureTurf engineered turf cover are approximately 30% of those for a smooth exposed geomembrane cover, demonstrating significant improvement of wind uplift resistance of the engineered turf cover. An example calculation of the maximum wind uplift pressure on the engineered turf cover is presented.

Two full-scale unsurfaced pavement test sections containing multi-axial geogrids and a control test section were constructed at the US Army Engineer Research and Development Center (ERDC). Each unsurfaced pavement section consisted of 250 mm of crushed limestone aggregate base (AB) over a soft high-plasticity clay subgrade. Geogrid stabilized pavements were prepared by placing a layer of multi-axial geogrid at the interface of AB and subgrade. The test sections were instrumented to record the distribution of stress and strain at different depths. A single-axle dual wheel truck gear configuration mounted to one of ERDC’s specially designed load carts was used to apply simulated truck traffic to the test sections where each pass of the truck gear was equivalent to 1.51 equivalent single axle loads (ESALs). Instrumentation response data and surface rut depth measurements were analyzed for performance evaluation of each test section. The results showed that the inclusion of geogrid contributed to minimizing the deformation of AB and subgrade. In addition to the experimental studies, numerical studies were performed using 2D Finite-Element (FE) simulation. FE models for geogrid stabilized and control test sections were developed in Plaxis using linear elastic constitutive soil models. The theoretical strain responses from the FE models were compared to the experimental dataset. The numerical results indicated that the stiffness of AB and subgrade is increased with the inclusion of geogrid. However, further numerical studies, incorporating a non-linear soil constitutive model and applying a moving wheel load with a dual tire configuration, are required to enhance the efficiency of the FE models.

Experiments were conducted to evaluate the hydraulic conductivity of non-prehydrated and prehydrated geosynthetic clay liners (GCLs) to coal combustion product (CCP) leachate. One commercially available bentonite-polymer (B-P) GCL with polymer loading of 3.8% (B-P-3.8) and one sodium-bentonite (Na-B) GCL were tested in this study. Hydraulic conductivity tests were conducted with Na-B and B-P-3.8 GCLs to one synthetic CCP leachate directly, which was chemically representative of the CCP leachate with high-ionic (HI) strength (ionic strength = 3179 mM). Comparative tests were conducted with the same GCL specimens prehydated with neutral or alkaline prehydration solutions until hydraulic equilibrium before permeated with HI leachate to determine the beneficial effect of prehydration. Hydraulic conductivity of Na-B GCLs prehydrated with synthetic solutions (pH = 6.8 and pH = 12) to HI leachate were two orders of magnitude lower than that of non-prehydrated Na-B GCL. Hydraulic conductivity of B-P-3.8 GCL permeated directly with HI leachate was 3.0 × 10^–8 m/s. The B-P-3.8 GCL prehydrated with the alkaline solution maintained low-hydraulic conductivity to HI leachate (5.8 × 10^–11 m/s), whereas B-P-3.8 GCL prehydrated with neutral solution yield to a relatively higher hydraulic conductivity (e.g., 4.6 × 10^–10 m/s).

Natural zeolite is a lightweight crystalline mineral that is formed as a tectosilicate aluminosilicate structure. Such structure includes interconnected channels which induce specified properties that may be considered as contradicted when compared to flaky-structured clay. In this study, the influence of incorporating a small quantity of zeolite on the density and plasticity of clay is investigated. Six zeolite percentages (0%, 1%, 3%, 5%, 10%, and 15%) were added by weight to an expansive clayey sample. Then, optimum water content (OMC), maximum dry density (MDD), Atterberg limits, and swelling potential were determined for all blends. Results showed that addition of 15% zeolite to clay decreased the OMC by about 29% and increased the MDD by 7.5%. Addition of 15% zeolite to clay resulted in a decrease in plasticity index and swelling potential by about 14% and 22%, respectively. Scanning electron microscope (SEM) images were also provided to visualize the microstructures.

Moisture-wicking fabrics first appeared in the market more than 20 years ago and have been mostly used for the clothing industry to improve comfort by soaking sweat when they are worn on human body. Extensive research has been conducted in this industry to improve properties and behavior of wicking fabrics. In recent years, wicking fabrics have been increasingly used as wicking geotextiles to remove moisture from soils to mitigate frost heave, poor drainage, and soil expansion problems. This paper provides a comprehensive literature review of the development of wicking fabrics in the clothing industry and the applications of this technology as wicking geotextiles in geotechnical engineering. The review first discusses the basics of wicking fibers including types of polymers, geometries of fibers, fiber-water surface interaction, water transportation in fibers, water evaporation from fibers, fiber-water-soil interaction, and their influence factors, and then summarizes recent research and advances in the use of wicking geotextiles to solve moisture-related problems in geotechnical engineering, especially for roadways.

Bentonite-polymer composite geosynthetic clay liners (BPC-GCLs) are used to line containment systems with leachates that are too aggressive for conventional sodium bentonite (NaB) GCLs to maintain low-hydraulic conductivity. Experimental observations indicate that the hydraulic conductivity of BPC-GCLs is affected by the properties of the polymer, the polymer loading and distribution, and the potential for the polymer to migrate and elute under a hydraulic gradient. In this study, pore-scale computational hydraulic models were developed and employed to simulate the movement of polymer in the intergranular spaces of BPC-GCLs. The model domain consisted of a collection of NaB granules and one or several globules of polymer gel. A pressure gradient was applied from the inlet to the outlet. Polymer viscosity, polymer loading, and the number and location of globules of polymer gel were varied between models. When polymer gel clogs open pores, lower hydraulic conductivity is achieved because flow is directed through fewer channels and more tortuous pathways. Lower viscosity polymer gels are eluted more readily than higher viscosity polymer gels, leading to higher hydraulic conductivity. Polymer loading, location, and distribution also affect hydraulic conductivity. BPC-GCLs with identical polymer loading and different distributions of polymer had hydraulic conductivity differing orders of magnitude. The findings suggest that BPC-GCLs can be engineered to achieve different outcomes by varying the hydrodynamic properties of the polymer, the polymer loading, and the distribution of the polymer in the pore space.

Rainfall induced slope failures are becoming a major threat in unsaturated soil slopes worldwide. Major part of Kerala state in India, especially the hilly regions are covered with residual lateritic soil that are formed under the process of weathering and mineralogical changes in the parent rock. Matric suction within the natural soil slopes contribute to its stability in the unsaturated state as it increases the shear strength. Many rainfall induced slope failures were reported in lateritic soil slopes in Kerala, during monsoon seasons of 2018, 2019, and 2020. An attempt was made to check the feasibility of application of geosynthetic reinforced composites in repairing and reconstructing a failed soil slope by means of resilient reinforced soil structures. The reinforced composites used in the present study was a knitted polypropylene non-woven geotextile, reinforced with high-tenacity polyester yarns in both machine and cross machine directions. The geotechnical characterization of the soil collected from the failed slope was carried out. Soil water characteristic curve of the lateritic soil and geosynthetic water characteristic curve of the hybrid geosynthetics were experimentally determined. Rainfall infiltration analysis was conducted in order to check the resilience or adaptation of the geosynthetics reinforced soil slopes to a changing climate. The stability analysis confirmed that the unreinforced soil slopes fail at the onset of rainfall infiltration whereas reinforced slope with reinforced composites helped in maintaining the integrity of slopes.

Alkali-activated binders (AABs) have been investigated as a promising alternative to traditional cement-based binders for low cost and high strength. AABs hold significant environmental advantages unlike traditional cement used for ground improvement. This study evaluates the feasibility of utilizing AAB along with synthetic fibers to improve the mechanical properties of sand. For the AAB binders used in this study, fly ash (FA), and ground granulated blast furnace slag (GGBFS) formed the precursor. While the sodium hydroxide (NaOH) solution and sodium silicate (Na₂SiO₃) solution were used as the liquid alkaline activators. The mechanical behavior of the produced AAB-treated specimens was evaluated based on their unconfined compressive strength (UCS). AAB-treated specimens with fibers showed an increase in the compressive strength regardless of the fiber content added to the mixture. The AAB-treated soil reinforced with macro synthetic fibers has shown 16% improvement in peak compressive strength by adding 0.1% fiber by weight of dry sand. The addition of fibers to AAB treated specimens has improved the specimen’s ductility by increasing residual compressive strength after reaching the peak compressive strength in the UCS test. Moreover, the ductile behavior was observed by the substantial increase in the calculated absorbed energy during the test. The absorbed energy for AAB treated sand with 0.5% of fiber was calculated to be 214% higher than the case of AAB treated control sand specimens without fiber.

Filamentous fungi in soil branch hyphae through pores, creating an interconnected fiber network, which is known as mycelium. Fungal mycelium can cross-link and entangle soil particles, which alters soil pore structures. Fungi can also secret hydrophobic compounds, changing the water wettability of soils. These fungal traits can affect hydraulic properties of soils. This study investigated the effect of fungi on soil water retention and hydraulic conductivity of the Ottawa 50/70 sand treated by a saprotrophic fungus, Trichoderma virens (commonly existing in soil). Soil water retention curve (SWRC) and hydraulic conductivity tests were performed on fungi-treated and untreated Ottawa 50/70 sand. Water repellency of fungi-treated sand was also assessed by measuring contact angles (between water droplet and fungi on sand specimen) and water drop penetration time (WDPT). When compared to the untreated sand, an approximate 6-fold increase in air entry suction (s_AEV) and 2-fold reduction in hydraulic conductivity were observed in fungi-treated sand after growing fungi for 10 days. Scanning electron microscopy (SEM) imaging was conducted to assess the morphologies of sand matrix treated by fungi.

Mud dauber wasp builds nests using soil for their offspring. Properties of soil materials used for nest construction can have significant effects on reproductive success in mud dauber species. This study aimed to investigate the physical and mechanical properties of the nest soils used by mud daubers. About 131 nests of black and yellow mud daubers, Sceliphron camentarium, were collected from five locations in Louisiana. A series of experiments were performed to characterize their physical (moisture content, density, plasticity, and grain size distribution) and mechanical (penetration resistance) properties. Scanning electron microscopy (SEM) imaging analysis was conducted to assess the morphology of the nest soils. The test results indicate that mud dauber nest soils are well-graded and have high strength, density, and low-moisture content.

Lightweight Cellular Concrete (LCC) (also named as foam concrete or gas concrete) is a special construction material, which typically consists of Portland cement, water, and air voids created by a foam agent. This material has been increasingly used as a backfill material for geotechnical applications in recent years. Researchers and engineers have performed laboratory tests, model tests, and field tests to study its material properties and field performance. To have a better understanding of the LCC properties, this paper summarizes and assesses the material composition (e.g., binder, other ingredients, and foam agent) and the properties (e.g., density, permeability, compressive and shear strengths, modulus of elasticity, thermal conductivity, and fire resistance). This paper also provides a brief review of its geotechnical applications as a backfill material for mechanically stabilized earth walls, foundations, road bases, and void filling. The typical density of LCC ranges from 300 to 800 kg/m³, the thermal conductivity ranges from 0.1 to 0.7 W/mK, and the modulus of elasticity ranges from 1 to 8 GPa. The change of density and air voids has significant effects on the material properties. Compressive and shear strengths of LCC increase and the volume of air voids decreases as the density increases. This paper also documents several case studies of using LCC as a backfill and a base course for geotechnical applications and their field performance.

Geopolymers created from alkali activator and aluminosilicate source material offer a promising alternative to ordinary Portland cement concrete. This study explores geopolymers created from gold mine tailings and probes the connection between microstructure and dissolution. The geopolymers were cured for 7 days in the oven, in either covered or uncovered conditions. The specimens were then immersed in ultrapure water for 7 days and the resulting strength loss and increase in void space were recorded. The uncovered specimens fared better in the dissolution test, but still experienced strength losses of 75% as compared to the intact specimens. The internal surface area of the uncovered specimens increased tenfold, and the void space increased dramatically (especially for pores around 400 nm in diameter). The covered curing only increased these phenomena, with strength losses of up to 90% and an even greater increase in internal surface area and void space. These significant losses are due to the dissolution of the aluminosilicate gel, which leaches out of the specimen and is replaced by additional voids. The phenomenon of geopolymer dissolution in water must be considered in future durability studies and remedied for this class of materials before geopolymers may be used more widely in industry applications.