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Microbially induced calcium carbonate precipitation (MICP) is a biomediated ground improvement technology that uses ureolytic bacteria to precipitate calcium carbonate minerals to improve the strength and stiffness of soils. MICP can be mediated by either augmented non-native or stimulated indigenous microorganisms, resulting in biocemented soils and generated aqueous ammonium (NH4+) byproducts. Although the process has been extensively investigated, the fate and transport of generated NH4+ byproducts has posed an environmental challenge and to date, their associated environmental impacts have remained poorly understood. In an effort to better quantify process impacts, a large-scale experiment was conducted involving three 3.7 m long soil columns, wherein three different ureolytic biocementation treatment approaches were employed. A life cycle sustainability assessment (LCSA) was performed to compare the environmental impacts and costs of these different MICP treatment approaches as well as evaluate the potential environmental benefits of NH4+ byproduct removal using post-treatment rinsing. The objective of this paper is to present the results of the LCSA study. LCSA results suggest that when treatments are consistent with those performed in this study, stimulation can be more sustainable than augmentation, and the use of lower ureolytic rates can further reduce process environmental impacts by achieving greater spatial uniformity and extent of biocementation. The LCSA outcomes also illustrate tension between the environmental benefits afforded by NH4+ byproduct removal and the life cycle impacts and costs associated with this removal. For the specific testing conditions, the injection of 1.8 pore volumes of rinse solutions to remove generated NH4+ byproducts following biocementation was found to minimize environmental impacts; however, further refinement of such approaches will likely result from future field-scale applications. [ABSTRACT FROM AUTHOR]

Modern innovations increasingly prioritize eco-friendliness, aiming to pave the way for a sustainable future. The field of civil engineering is no exception to this approach, and, in fact, it is associated with almost every sustainable development goal framed by the United Nations. Therefore, the sector has a pivotal role in achieving these goals. One such innovation is exploring the possibilities of using nature-friendly materials in different applications. Biopolymers are substances that are produced either by the chemical synthesis of natural materials or by the biosynthesizing activities of microorganisms. Microbial-derived biopolymers are known for their non-toxic and nature-friendly characteristics. However, their applications are mostly restricted to the field of biotechnology and not fully explored in civil engineering. This article reviews various microbial-derived biopolymers, focusing on the types available on the market, their source and properties, and more importantly, their wide range of applications in the civil engineering field. Additionally, the article explores the prospects for future research and the potential for the practical implementation of these techniques in the pursuit of a sustainable future. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitation (MICP) has been shown to improve geotechnical properties of soil in many laboratory-scale tests. Field deployment of this technology requires large volumes of suspended bacterial inoculum media, and geotechnical engineers are still seeking a low-cost and quick method for upscaling applications. In this paper, we propose a four-step inoculation method to culture Sporoscarcina pasteurii for implementation of MICP in a prototypical dune in the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory of Oregon State University. The four-step inoculation method nonsterilely cultured the bacteria to 42 L in a common microbiology lab and scaled it up to 73 L in the field. The values of optical density at a wavelength of 600 nm (OD600) were obtained to determine the specific growth rate. Two different types of agar plates were evaluated for contamination and cell counting of the bacterial solutions. Shear-wave velocity of the treated dune was continuously measured by pairs of bender elements to monitor the treatment process. The average specific growth rates of the 42- and 73-L bacterial solutions were 5.11×10−3 and 1.27×10−3 min−1 , which were quite high compared with previous studies. The plate results indicated that the four-step inoculation method provided 108 cells/mL of bacterial solution with unobserved contamination. The increase in shear-wave velocity suggested the development of biocementation within sand particle contacts of the dune, demonstrating the effectiveness of the inoculation method. The results suggest that the four-step inoculation process discussed in this paper provides a large amount of bacterial solution for field-scale application of MICP. [ABSTRACT FROM AUTHOR]

This paper presents a case study in which wet and top feed vibro replacement stone columns are used to support a 20-m-high fuel tank built on loose to medium sand deposits. The design considerations, installations, applications, field tests, correlations, and subsequent three-dimensional finite element analyses are presented. The soil profile of the case study comprised approximately 8 to 12 m thick loose to medium-dense silty sand layers with a high groundwater table. The 1-m-diameter stone columns were installed in a triangular pattern with a spacing of 2.1 m. The improvement depths were 8, 11, and 12 m. After construction was completed, quality assurance of the stone column installation was performed via various field tests. Based on the hydro test results, the improved ground could carry an allowable bearing capacity of 200 kPa transferred from the 20-m-high fuel tank and exhibited a maximum settlement of less than 50 mm, which met the design criteria of this project. Owing to reasonable quality control during stone column installation, the tilt of the tank caused by the nonuniformity of the improved sands was less than 10 mm. The enhanced strength ratio of the surrounding sands was 2 the densification effect. Furthermore, three-dimensional finite element simulations were performed. The results were consistent with the field measurements, verifying the effectiveness of the ground improvement technique. This case study demonstrates the practical application and benefits of vibro-replacement stone columns in enhancing bearing capacity, minimizing settlement, and improving overall foundation stability in challenging geotechnical environments, contributing to future engineering practices for similar projects. [ABSTRACT FROM AUTHOR]

The paper focuses on the potential use of industrial wastes, which are fly ash (FA) and cement kiln dust (CKD), to stabilize expansive soils like black cotton (BC) soil for construction purposes. Although many soil stabilization methods exist, the placement of columns consisting of industrial wastes has yet to be tested. Knowing the pozzolanic action and mechanism between the waste product and the soil, this method of placing the industrial waste as a remedy should be trialled. Therefore, this paper proposes and investigates the placement of FA-CKD columns into the soil via a series of laboratory experiments using myriad mixtures and combinations of placement of such columns. The effect of molding water content and curing time on the BC soil’s consolidation and strength behavior was also assessed here. Through the experiments, it is found that the optimum mixture of FA-CKD for the columns is at 90–10%, respectively. This column mixture has been evidenced to improve the unconfined compressive strength of the soil significantly, where its performance improves with curing time. The highest strength improvement can be found at optimum moisture content, followed by wet of optimum and dry of optimum, respectively. By placing the columns in the soil with 4.5D spacing, better consolidation behavior with a reduced swelling potential of BC soil can be found. Based on the above findings, using FA-CKD columns can improve the BC soil’s engineering behavior, contributing to waste-to-wealth and sustainable soil stabilization approaches. [ABSTRACT FROM AUTHOR]

Enzyme induced carbonate precipitation (EICP) is an emerging sustainable technology in the field of geotechnical engineering. It involves the application of urease, a plant-based urease enzyme which mediates the precipitation of calcium carbonate (CaCO3) via hydrolysis of urea. This results in biocementation and subsequent improvement of the strength of the soil. In purview of this developing bio-stabilization technique, Life cycle assessment (LCA) can be used as a promising tool for incorporating sustainability metrics to evaluate the environmental impacts related to EICP technique and assist in policy and decision making. In this present study, an attributional LCA is conducted to investigate and quantify the various environmental impacts associated with EICP concentrations as proposed by various researchers. The environmental impact indicators taken into consideration are global warming potential (GWP), eutrophication potential (EP), energy use potential (EUP) and freshwater ecotoxicity potential (FWP). The results revealed that chemical constituents of EICP i.e., urea (51.25–74.53%) and non-fat milk powder (52.82–87.11%) are the dominant contributors to GWP (max: 2146.95 kg CO2 eq). Urea also contributes to EUP in the range between 69.58 and 92.6% (max: 14,279 MJ). However, NH4Cl, the by-product (NH4Cl) of EICP process, a water pollutant, is the major contributor to EP (max: 326.44 kg N eq) and FWP (max: 289.25 kg 1,4-DCB eq). This indicates that more focus should be bestowed on EP and FWP to better characterize and quantify the associated ecosystem response due to over-utilization of the chemicals, for any EICP stabilization technique. Thus, this analysis considers the aspect of sustainability inground modification technique, aiding the advancement of EICP research. [ABSTRACT FROM AUTHOR]

In a consequence of climate change’s adverse effects, Malaysia’s road infrastructure faces significant challenges, particularly during both dry and rainy seasons, which weaken the natural bonds of the laterite soil. This research, therefore, outlines a laboratory study aimed at assessing the impact of cement stabilisation on the compressibility characteristics of laterite soil, subject to both saturated and unsaturated conditions. This study reveals that a 6% cement dosage is optimal for stabilising the laterite soil, proving the minimum 7-day strength requirement of 800 kPa, as specified by the Malaysia Public Works Department (MPWD) for stabilised subgrade material in low-volume roads. Consequently, the research involved conducting saturated tests (utilising a conventional oedometer) on soil specimens stabilised with 3%, 6%, 9%, and 12% cement dosages. Meanwhile, only the 6% cement-stabilised soil is used in unsaturated tests with a modified suction-controlled oedometer. The findings of this study highlighted that cement-stabilised laterite soil exhibits significantly lower compressibility in comparison to unstabilised laterite soil. Furthermore, the unsaturated oedometer test demonstrated that soil’s compressibility is notably decreased at higher suction levels (drying conditions) compared to lower suction levels (wetting conditions). In summary, this research contributes valuable insights, emphasising the potential of cement as an effective soil stabiliser by reducing soil settlement and enhancing the durability of Malaysia’s roads in response to climate-related challenges. [ABSTRACT FROM AUTHOR]

The demand for sustainable ground improvement methods is rising as urban development expands into areas with challenging soil conditions. Traditional approaches, mostly reliant on cement and lime, contribute significantly to anthropogenic greenhouse gas emissions. Researchers, therefore, are constantly searching for new environmentally friendly stabilization methods to improve the engineering properties of soils. One alternative material used for this purpose is gypsum in its hydrated and dehydrated (hemihydrate/anhydrate) states. Not only can natural gypsum be used for ground improvement but also industrial waste and by-products (e.g. used or waste plasterboard, phosphogypsum, flue gas desulfurization gypsum, titanium dioxide production gypsum by-product) can be recycled, and used. Successful application of these materials could lower the carbon footprint of the construction industries (by reducing the consumption of cement and lime) as well as other industries (by recycling their waste and by-products). However, using gypsum presents challenges due to its moderate water solubility, the formation of swelling clay minerals under certain conditions, and the tendency of dehydrated gypsum to swell upon exposure to water, to name a few. Furthermore, the mechanisms leading to the improved behavior of the gypsum-treated soils are complicated, which has resulted in some seemingly contradictory results reported in the literature. This study presents a systematic and extensive review of the observed behavior of gypsum-treated soils and the different mechanisms causing the observed behavior. The research gaps and the required future steps to address these gaps have been identified and reported. A summary of the effect of gypsum treatment on the mechanical and engineering properties of soils, including unconfined compressive strength (UCS), California Bearing Ratio (CBR), swell potential, Atterberg limits, optimum moisture content (OMC), maximum dry density (MDD), durability, and environmental effects has also been presented.

In this research, experimental studies and numerical analyses were carried out to investigate how the usage of geotextile and geopolymer coated geotextile as a hybrid method changes the uplift behavior of the screw piles in cohesionless soil. In this context, traditional pile behavior, the effect of different number of helixes and embedment depths on screw piles, the mechanism of geotextile and the effects of geopolymer coating process were investigated. In addition, experimental studies were modeled by using Plaxis 3D and parametric studies were carried out after verification between the results of experimental study and numerical analysis. In the numerical analysis, a segmented helix model consisting of four 90-degree slices was developed instead of the planar helixes commonly used in the literature. For further investigation of the effectiveness of hybrid method, parameters such as improvement ratios and breakout factors were calculated. When the results obtained within the scope of the study were evaluated, the geopolymer coating process increased the bearing capacity of the geotextile by 24 % at 27 % less elongation. It was also seen that uncoated and geopolymer coated geotextile increased the screw pile performance in terms of improvement ratios by 294 % and 364 %, respectively.

Stone columns have garnered significant interest in geotechnical engineering as an effective ground improvement technique for enhancing the load-bearing capacity and mitigating settlement issues in soft soils. This study presents a comprehensive bibliometric analysis of scholarly literature on stone columns, utilizing data from the Web of Science database spanning from 1975 to 2023. The analysis aims to provide insights into publication trends, influential journals, key research institutions and authors, geographical distributions, and emerging themes in this domain. Through a systematic data curation process, 505 relevant publications were analyzed using Excel and VOSviewer software. The findings reveal a notable emphasis on geosynthetic encasements, load-settlement behavior, and soft soil reinforcement, with China being a major contributor. Over the past 48 years, the research has evolved from static loading to dynamic loading, sustainable structures, and artificial intelligence applications, as evidenced by the highly cited publications. This study maps the development, current state, and potential future directions of stone column research, serving as a valuable resource for researchers and practitioners in geotechnical engineering.

Urease enzymes from plants are directly utilised in enzyme-induced calcite precipitation (EICP) to catalyse calcium carbonate (CaCO3) precipitation between soil particles to improve their strength and stiffness. EICP does not require microbial culture and may be applicable for finer soils with their smaller size. However, most studies on EICP utilise purified urease enzymes, which are often rare, expensive and limited to food-grade beans or seeds, making the technique less cost-effective. To find alternative and cheaper sources, crude urease extracts from diverse plant species, particularly weeds and Australian native plants, were obtained, identified and characterised using a series of in vitro experiments. All selected plant species contain a considerable amount of urease enzyme, exhibiting different urease activity and calcium carbonate precipitation. EICP treatment by different crude extracts showed different levels of hydraulic conductivity, unconfined compressive strength (UCS), wind and raindrop erosion resistance. However, the crude extract from an Australian weed, matured paddy melon seeds (M-PMS), had the highest specific activity of 8997 U/mg and was further used for EICP treatment of six different soil types. The UCS of treated soils was influenced by the soil types. For similar calcium carbonate content, the strength and stiffness of the EICP-treated specimens were significantly influenced by the confining stress and degree of saturation in undrained triaxial conditions. Also, the mass loss, strength and average calcium carbonate decreased with increasing cycles of wetting–drying, freezing–thawing and elevated temperature. When compared with purified urease enzyme, M-PMS produced comparable strength and durability resistance in the treated samples. [ABSTRACT FROM AUTHOR]

Microbial- or enzyme-induced calcium carbonate (CaCO3) precipitation (MICP and EICP) are relatively new ground improvement techniques. In this study, the mechanical behaviour of biotreated (MICP/EICP) and untreated sands was investigated in light of the critical state soil mechanics framework using a series of direct simple shear (DSS) tests. A wide range of calcium carbonate content (CC), initial void ratio after consolidation (e0) and effective initial normal stress ( σ ′ N 0 ) was considered. The biotreated specimens showed improved shear strength and dilative tendency compared to untreated specimens with similar initial states. The ultimate state (US) for the biotreated sand shifted towards a smaller void ratio (e) than the value of e at the critical state of untreated sand at the same σ′N in e–log σ′N space. Compared to untreated sand, a significantly larger US stress ratio was achieved for the biotreated sand, particularly at high CC and low σ ′ N 0 . The characteristic features of undrained behaviour, such as instability stress ratio, stress ratio at phase transformation and flow potential showed good relationships with modified initial state parameter, void ratio after biotreatment and CC. The bonding ratio, (τ/σ′N)bond, was used to quantify the interparticle bonding. The peak value of (τ/σ′N)bond for the biotreated sand was significantly larger than zero, particularly at high CC and low σ ′ N 0 , while the peak (τ/σ′N)bond for the untreated sand was negligible. It was also observed that the mobilisation and degradation of calcium carbonate bonds in biotreated sand during DSS shearing are influenced by both CC and σ ′ N 0 . [ABSTRACT FROM AUTHOR]

When using jet grouting for soil stabilisation, effects of the installation process need to be evaluated. This could be particularly important for applications in challenging ground conditions and low initial ground stability. This study investigates such effects in soft marine clays using numerical finite-element (FE) simulations for both flat and sloping terrains. Additionally, an analytical solution using the modified Hagen–Poiseuille equation was developed to (a) assess the pressure induced by the grout at any installed depth and (b) illustrate the importance of maintaining a proper amount of return flow to avoid build-up of excessive pressures in the ground during the jet-grouting process. Combining the analytical and the FE simulations, jet-grouting induced soil displacements, were determined. For flat terrain, the area affected by jet grouting was approximately three to four times the column radius. By contrast, for the studied slope (inclination of 1 : 3), the influenced area increased to about ten times the column radius. The obtained displacement magnitude was also considerably larger for sloping terrain than for flat terrain. The reported findings relate to jet grouting in marine clays (which is not the normal application of this technology) and cannot be extrapolated to other soils. [ABSTRACT FROM AUTHOR]

The soil arching effect is the key mechanism for load transfer in pile-supported reinforced road (runway) foundations. To investigate the formation and evolution process of soil arching effect in the whole process of embankment filling and soft soil foundation consolidation, a three-dimensional hydro-mechanical coupled numerical model of pre-fabricated high-strength concrete (PHC) pile-reinforced soft soil runway foundation was established based on the foundation treatment project in Pudong Airport. The laws of variation of soil settlement, pore water pressure and pile soil stress were analysed, and the influence of pile spacing was considered. These data from both numerical simulation and field test indicate the soil arching effect in the foundation reinforced by PHC piles and preliminarily reveal the evolution of soil arching in the process of embankment filling and soft soil foundation consolidation. The preliminary results encourage the authors to continue this research to investigate the evolution of soil arching under aircraft dynamic loads through adding a more suitable constitutive model or subroutine in this numerical model. [ABSTRACT FROM AUTHOR]

Preloading using either vacuum or fill surcharge is an effective method for the treatment of very soft saturated clay. The preloading will reduce the water content and increase the shear strength of soil. However, when the soil to be treated is very soft, it is difficult to take soil samples for laboratory tests or carry out in situ tests to determine the soil properties including shear strength. Therefore, there is a need to develop an analytical method to estimate the shear strength during preloading. In this paper, a simple correlation among settlement, water content and undrained shear strength using critical state theory is proposed for saturated soil under one-dimensional loading condition to allow the undrained shear strength variation of the soil to be estimated during preloading without testing. Laboratory model test and field monitoring data are used to verify the validity of this method and the proposed correlation is effective to be used as rough estimations on the undrained shear strength of soft clay. [ABSTRACT FROM AUTHOR]