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Particle size gradation is an important parameter for small strain stiffness of sand, and it can also affect the biocementation behavior. In this study, a series of isotropic consolidation tests were performed to study the gradation-dependent small strain shear modulus of a glass sand with light biocementation. Shear wave velocities in multi-directions were measured with bender elements. The test results showed that the small strain shear modulus G0 and stiffness anisotropy decrease and increase with the increase in uniformity coefficient Cu, respectively, for the uncemented sand. When sands were biocemented, the decrement of G0 gradually vanishes with biocementation level, showing that G0 increases with Cu. The development of G0 ratios between the biocemented and the uncemented sands generally experiences four stages. The stiffness anisotropy is also changed with biocementation, showing the decrease in stiffness ratio especially for the unloading stages. The changes of stiffness anisotropy are more explicit for the sands with higher Cu and biocementation level. [ABSTRACT FROM AUTHOR]

Recently, microbial biopolymer-based soil treatment (BPST) has gained attention for its application in environmentally friendly soil stabilization, particularly for enhancing the strength and stability of fine-grained soils. However, the effects of BPST on clay's compressibility (consolidation) and expansion (swelling) behaviors remain unclear. This study used xanthan gum, a microbially produced polysaccharide with anionic charges, to stabilize kaolinite clay. The effect of xanthan gum BPST on the consolidation and swelling behavior of cohesive kaolinite clays was assessed through a series of experimental tests, including one-dimensional consolidation tests with elastic wave measurements, swelling tests, environmental scanning electron microscopy, and unconsolidated-undrained triaxial tests. The formation of xanthan gum hydrogels induces pore-clogging, resulting in a delay in the consolidation process, increased energy dissipation, and compressibility. Furthermore, the interaction between kaolinite and xanthan gum improved the undrained shear strength of kaolinite soils, thereby reducing the consolidation time required for a specific bearing capacity. This study demonstrates the possible application of controlling hydraulic conductivity, seismic stabilization, and rapid surface stabilization. However, additional drainage is necessary for in situ applications. [ABSTRACT FROM AUTHOR]

Granite residual soil is vulnerable to collapse under rainfall-induced erosion. This may in turn lead to the occurrence of landslides or debris flows on slopes. Previous studies on use of microbial-induced carbonate precipitation (MICP) technique for soil stabilization are often conducted on sandy soils and also with rainfall-induced erosion are rarely assessed for a slope treated with MICP. This study investigated the feasibility of using the MICP technique for surface protection of granite residual soil slopes against erosion. The MICP technique was applied to soil samples using the spraying method. Hydraulic conductivity and rainfall erosion tests (using flume) were conducted to assess the coating effects of MICP on granite residual soils. In addition, crust thickness, calcite content and near-surface strength were measured to interpret the results. Tests were repeated to assess any variability in results. Scanning electron microscopy, energy-dispersive spectrometer and X-ray diffraction (XRD) were conducted on treated and untreated samples to interpret the formation of calcite due to MICP. After 7 days of curing, the calcite content increases to 4.3%, whereas mean coating thickness is 4.2 mm. Unconfined compressive strength is increased by 20.3% as compared with the bare soil. MICP treatment reduced the soil hydraulic conductivity and erosion rate by 90.9% and 95.2%, respectively. This was attributed to the bio-cementation process generating a surface coating on granite residual soils, leading to a reduction in pore throats, as observed in the obtained micrographs. Compared to the bare soil, the runoff rate in the MICP-treated soil was increased by 39.4% on average. However, the erosion is found to reduce significantly in MICP-treated soil. Based on ANOVA analysis, it could be concluded that the rainfall intensity found to be a significant factor affecting the erosion rate of granite residual soil slopes. [ABSTRACT FROM AUTHOR]

Biocementation based on the microbially induced carbonate precipitation (MICP) process can be used as a soil improvement method to improve the mechanical strength of granular soils. In this study, triaxial consolidated drained (CD) tests and constant shear drained (CSD) tests were carried out to evaluate the applicability of MICP as a method to mitigate suffusion and improve the internal stability of silty sands under seepage conditions. The CD test results demonstrated that biocementation is efficient in terms of strength improvement and deformation control of silty sand. The shear strength and the slope of failure line in p'-q plane increased with the number of treatment cycles at various levels of soil density. The CSD tests simulated the concurrent seepage-constant shear drained conditions that can trigger suffusion and instability of slopes. Results showed that the stress ratio q/p' and the hydraulic gradient at which the biocemented samples became unstable were higher than those of the untreated samples, which suggests that biocementation can effectively improve the stability of soils under concurrent seepage-constant shear drained conditions. Additionally, the biocemented samples also have stronger resistance against suffusion compared with untreated samples showing lower amount of eroded fine particles. Suffusion resistance improved with the number of treatment cycles and soil density. [ABSTRACT FROM AUTHOR]

Biocement based on a Microbially Induced Calcite Precipitation (MICP) process has emerged to be a promising alternative to cement for soil improvement. A two-phase injection method is commonly used for the MICP treatment of granular soil. However, the samples treated using this method may not be uniform. Recently, an acidified one-phase-low-pH injection method was developed using HCl as a buffer. This method could improve the uniformity of the MICP treatment to a certain extent. However, the distance in which the soil could be treated uniformly is still limited. This paper presents a CH3COOH-buffered one-phase-low-pH method which could improve the uniformity of biocement treatment considerably compared with the one-phase-low-pH method based on HCl. The key feature of this method is to create a much longer lag duration; thus, the biocementation process can be delayed and allow the all-in-one solution to be distributed more uniformly in soil within the lag duration. The uniformity of MICP-treated 1-m and 2-m sand columns was evaluated by comparing the unconfined compressive strengths and the calcium carbonate contents measured at different locations along the sand columns. The test results show that the proposed method is much more effective in improving the uniformity of the MICP treatment though a significant increase in the lag duration, given the other conditions the same. [ABSTRACT FROM AUTHOR]

In the last decade, biopolymers have been used as organic soil binders in ground improvement and earthen construction material modification. Although biopolymer-treated soils have substantially enhanced mechanical strength, the deformation characteristics under external loads and material durability (e.g. biodeterioration due to microbial activity) have not yet been fully understood, which limits the in situ practical application of the biopolymer-based soil treatment technology. This study investigated the efficiency of combined carrageenan and casein in strengthening a clayey soil with the biodeterioration consideration. Both mechanical tests (e.g. unconfined compressive strength and one-dimensional consolidation) and biological tests (e.g. high throughput sequencing and rating of mould growth) were conducted. Results indicated that the usage of the carrageenan–casein mixture induced a higher soil compressive strength compared with either carrageen or casein, due to the formation of a three-dimensional gel network. In addition, carrageenan–casein mixture and casein decreased the compressibility of the clayey soil, which might be attributed to the casein's peculiarity of self-associating into micelles, leading to minimal interactions with water molecules. Carrageenan, due to its affinity for water, increased the soil compressibility. Under the impact of microbial activity, the biopolymer-treated soils underwent deterioration in both surface appearance (i.e. coloured stains and patches caused by mould growth) and compressive strength. A linear relationship was proposed, in which a reduction in compressive strength by approximately 11% is expected while the rating of mould growth is increased by one in a five-rating system. The current research demonstrates that the soil reinforcement with combined carrageenan and casein is able to improve both soil strength and deformation behaviours. It is also suggested to take into account the biodeterioration considerations in the design and implementation of biopolymer-based soil reinforcement practices. [ABSTRACT FROM AUTHOR]

A coupled bio-chemo-hydro-mechanical model (BCHM) is developed to investigate the permeability reduction and stiffness improvement in soil by microbially induced calcite precipitation (MICP). Specifically, in our model based on the geometric method a link between the micro- and macroscopic features is generated. This allows the model to capture the macroscopic material property changes caused by variations in the microstructure during MICP. The developed model was calibrated and validated with the experimental data from different literature sources. Besides, the model was applied in a scenario simulation to predict the hydro-mechanical response of MICP-soil under continuous biochemical, hydraulic and mechanical treatments. Our modelling study indicates that for a reasonable prediction of the permeability reduction and stiffness improvement by MICP in both space and time, the coupled BCHM processes and the influences from the microstructural aspects should be considered. Due to its capability to capture the dynamic BCHM interactions in flexible settings, this model could potentially be adopted as a designing tool for real MICP applications. [ABSTRACT FROM AUTHOR]

Microbial induced calcite precipitation (MICP), a bio-cementation process, can be adopted to improve the engineering properties of granular soils. Bio-stimulation, via directly enriching indigenous ureolytic bacteria, is a sustainable and economical approach to achieve MICP. In this study, batch solution experiment was firstly conducted to investigate the biochemical aspects of the bio-stimulated MICP process in coral sands. Three different enrichment media were compared. The statistical analysis was performed to reveal statistically significant factors that influence ureolytic activity, pH value, and viable cell number. Then, the unconfined compression and rainfall-induced erosion tests were conducted to investigate the strength and erosion-resistance of bio-stimulated MICP treated coral sands. The experimental results demonstrate that the enrichment duration, initial urea concentration, and enrichment type are major influencing factors of the ureolytic activity. It is found in this study that yeast-extract-based enrichment media with 170 mM initial urea concentration and enriched for 72 h could achieve the best bio-stimulated MICP treatment efficiency. In addition, higher initial urea concentration in the enrichment medium could yield higher ureolytic activity, which could consequently result in higher cementation content and thus larger UCS and better resistance to rainfall-induced erosion. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) has been extensively studied for soil improvement in geotechnical engineering. The quantity and size of calcium carbonate crystals affect the strength of MICP-treated soil. In this study, microfluidic chip experiments and soil column experiments were conducted to optimize MICP treatment protocols for effective strength enhancement of MICP-treated sandy soils. The microscale experiments reveal that, due to Ostwald ripening, longer injection intervals allow crystals to dissolve and reprecipitate into larger crystals regardless of the concentration of cementation solution. Even though a cementation solution input rate of 0.042 mol/l/h is sufficient to maintain a high chemical transformation efficiency, a further reduction in the input rate by about four times resulted in an increase in the size of crystals produced by the end of treatment from about 40 to 60 μm. These findings were applied in soil column experiments. Results showed that significantly larger crystals and higher soil strength were achieved when the normalized rate of cementation solution injection was reduced from 0.042 to 0.021 mol/l/h. Crystal size and soil strength increased slightly more when the normalized input rate was further reduced from 0.021 to 0.010 mol/l/h. This study demonstrates how data from microscale microfluidic experiments that examine the effects of injection intervals and concentration of cementation solution on the properties of calcium carbonate crystals can be used to optimize MICP treatment in macroscale sand soil column experiments for effective strength enhancement. [ABSTRACT FROM AUTHOR]

Utilization of bacterial biofilms and extracellular polymeric substances (EPS) for engineered bioclogging has recently garnered increasing attention in various geotechnical practices, such as leakage sealing in water-front structures, soil erosion protection, earthquake-induced liquefaction mitigation, and hydraulic barrier installation. However, the long-term durability is still questioned as to how long the biofilm-associated bioclogging would last as the biofilms readily degrade in nutrient-poor conditions. Therefore, we explore the feasibility of using fine clay particles to enhance the durability of biofilm-induced bioclogging. A series of column experiments were performed to compare the clogging durability of bentonite-associated biofilms against that of biofilms only. The results confirmed that a continuous feed of nutrients to the model bacteria, Bacillus subtilis, stimulated biofilm formation and caused a ~ 99% reduction in hydraulic conductivity of sands. However, nutrient-poor fluid flow caused instantaneous sloughing of biofilms and removal of bioclogging. By contrast, bioclogging associated with bentonite–biofilm aggregates demonstrated enhanced durability against shear detachment by fluid flows in a starved condition. EPS analysis and SEM imaging revealed that bentonite particles in the introduced suspension formed aggregates with biofilms by coating and being embedded within biofilms. This study suggests that the exploitation of bentonite–biofilm aggregations can remarkably enhance bioclogging durability in nutrient-poor conditions. This coupled clay–biofilm clogging approach is expected to provide benefits in developing a strategy for engineered bioclogging in geotechnical practices. [ABSTRACT FROM AUTHOR]

In this paper, we study analytically the three-dimensional (3D) stress–strain relationships at the elastic stage with regard to the anisotropic granular materials composed of regularly arranged bonded ellipsoidal particles by the micro-structural mechanics approach, where the macroscopic elastic constants are expressed in closed form with respect to the microscopic parameters. The bonded ellipsoidal particle assembly is first equivalent to a 3D lattice network composed of lattice beams with different contact properties. Based on the principle of energy balance, the macroscopic elastic stress–strain relationships for the equivalent micropolar continuum are obtained by analysing the unit cells of the lattice beam system. Using the proposed closed-form expressions of the anisotropic elastic constants, the elastic moduli, Poisson's ratios, Cauchy and Cosserat shear moduli and bending moduli can be expressed as functions of the microscopic parameters pertaining to the particle shape, size and contact properties. The elastic moduli and Poisson's ratios from closed-form expressions for regular particle arrangement and modified expressions for irregular particle arrangement are noted to be in agreement with the results obtained using distinct element method (DEM). The results suggest that the regularly arranged ellipsoid particle assembly shows a typical 3D orthotropic feature, and the elastic constants change significantly as the anisotropy of particle increases. [ABSTRACT FROM AUTHOR]

Soil improvement techniques have been developed experimentally and empirically from various geotechnical standpoints based on physical, chemical, and biological findings. The traditional microbiological perspectives consider microbially induced soil cementation as an environment-friendly soil improvement technique. In particular, microbially induced carbonate precipitation (MICP) is recognised as an effective method with applications in real geotechnical problems. Traditionally, highly active species with carbonate-precipitating and their optimum environmental conditions have been identified through laboratory experiments and field surveys. Recently, numerical simulations considering microbial metabolic reactions have been tried for elucidating MICP. However, the mathematical and numerical evaluation of the relationship between bacterial growth and MICP requires further investigation. This study proposed a novel numerical simulation scheme for evaluating the effects of bacterial growth on stress distribution in soil micro- and macro-structure. In particular, this scheme utilised a reaction–diffusion system to determine bacterial growth and MICP in micro-structures. Further, stress and strain distributions in multi-scale structures were evaluated by a homogenisation method. Consequently, the simulation results of the calcium carbonate precipitation were 0.85–4.5 μmol/mm3 at 10.3 h. Evidently, the model values are reasonably consistent with the experimental data. Further, the homogenisation simulations indicated that soil stabilisation could be attributed to the formation of a novel skeleton structure comprising soil particles and calcium carbonate-filled soil pores. [ABSTRACT FROM AUTHOR]

Concentration of cementation solution (CCS) is one of the key factors influencing the cementation effect on soil improvement through the microbially induced carbonate precipitation (MICP) process. To precipitate more calcium carbonate per treatment, a higher CCS is needed. However, the MICP process may be retarded or even terminated with an increase in CCS. This retarding effect can be a major limitation for the MICP-based soil treatment and thus needs to be understood properly. This paper presents a systematic study on the conditions causing retarding and its effect on biocementation. The test results of this study have identified that there is retarding effect of CCS on the MICP process, showing that the calcium conversion efficiency, which represents the amount of calcium that has been converted into calcium carbonate in each treatment, reduces with the increase in CCS, and the concentration of calcium is the control factor. The retarding effect will dominate increasingly when CCS is higher than 1.0 M and the amount of calcium carbonate precipitation will reduce for the given amount and type of bacteria used in this study and become zero with CCS of 2.5 M. For the same calcium carbonate content, the unconfined compressive strength is greater for sand treated using a lower CCS as the contribution to the bonding strength by the calcium carbonate generated under a lower CCS is greater than that under a higher CCS. [ABSTRACT FROM AUTHOR]

Heterogeneity in either chemically or microbiologically induced carbonate-based ground improvement methods is a major obstacle in engineering application. Spectral induced polarization (SIP), an innovative and nondestructive method, which has demonstrated promise in monitoring microbial activity, was used in this study to monitor enzyme induced carbonate precipitation (EICP). The complex conductivities, together with the shear wave velocities (Vs), of an EICP modified sand were monitored using a self-developed spectral induced polarization–bender element column. The mean precipitate size was calculated by relaxation time (τ) and the Schwarz equation. The precipitate contents were calculated by cumulative gamma distribution function on the global polarization magnitude (mn) with R2 = 0.989. The stiffness of the enhanced geomaterial, in terms of Vs, correlates to mn with a cumulative lognormal distribution function with R2 = 0.967. Contact cementation was postulated as the dominant association pattern. The possible mechanism for this may be the formation of eddies and the nucleation of CaCO3 crystals during precipitation. The results suggest that SIP can be used as an effective nondestructive monitoring tool to assess the stiffness of geomaterials. [ABSTRACT FROM AUTHOR]

Microbial carbonate precipitation is expected to play a major role in next-generation soil improvement technologies. To date, research into this method has relied on experimental and/or observational approaches. However, in order to understand the long-term effects of microbial carbonate precipitation and apply these to real environments, it is necessary to employ a predictive approach to determine the future state of the soil when using this soil improvement method. In this work, a mathematical model and numerical simulations based on the reaction–diffusion system for the microbial urea hydrolysis reaction are proposed. These techniques may be used to provide the spatiotemporal precipitation patterns of carbonates between soil particles and the particle surfaces. The simulation results revealed that the characteristic precipitation patterns depend on the diffusion of carbonates caused by the microbial urea hydrolysis reaction, and there was a significant shift in the amount of carbonate from a dissipated state into an equilibrium state. [ABSTRACT FROM AUTHOR]

Biogrouting is a ground improvement technique, which utilizes microorganisms. The numerical simulation of biogrouting is important to ensure efficient operation and to assess the applicability to the target ground. In this study, we compared syringe-scale biogrouting with biogeochemical simulation. Parameters suitable for practical applications were included. The rate constant and half-saturation constant of the reaction rate law in ureolytic bacteria Pararhodobacter sp. strain SO1, obtained from the simulation based on the urease activity test, were 1 × 10−8 mol/mg/s and 0.635 M, respectively. To achieve the same mineral precipitation in measurement and simulation, a setting in which only the calcite precipitated was used. In the sequential simulation of the solidification test, a variation in discharged Ca2+ concentration was reproduced by introducing an "adjustment index", which considers the microbial biomass contributing to the reaction. Moreover, for the re-injection test, in which microbes were injected again to further improve the biogrout strength, the settings were validated by the sequential simulation followed by predictive simulation on different injection dates. The results indicate that by conducting a biogeochemical simulation of calcite precipitation for biogrouting using ureolytic bacteria, the strength of biogrout can be predicted and managed. [ABSTRACT FROM AUTHOR]

A multi-disciplinary approach is adopted in the present work towards investigating bio-cemented geo-materials which extends from sample preparation, to microstructural inspection and mechanical behaviour characterization. We suggest a new way to induce "cell-free" soil bio-cementation along with a comprehensive description of bio-improved mechanical and microstructural properties. We utilize the soil bacterium Sporosarcina Pasteurii in freeze-dried, powder—instead of vegetative—, state and determine overall reaction rates of "cell-free" microbial-induced calcite (CaCO3) precipitation (MICP). We further investigate strength and stiffness parameters of three base geo-materials which are subjected to MICP under identical external bio-treatment conditions. Different trends in the mechanical response under unconfined and drained triaxial compression are obtained for fine-, medium- and coarse-grained sands for similar range of final CaCO3 contents. Pre- and post-yield dilatancy–stress relationships are obtained revealing the contribution of dilatancy in the achievement of peak strength. Medium-grained sand yields higher dilatancy rates and increased peak strength with respect to fine-grained sand. Further, insight into the bio-cemented material's fabric is provided through scanning electron microscopy, time-lapse video microscopy and X-ray micro-computed tomography with subsequent 3D reconstruction of the solid matrix. A qualitative description of the observed precipitation behaviours is coupled with quantified microscopic data referring to the number, sizes, orientations and purity of CaCO3 crystals. Results reveal that MICP adapts differently to the adopted base materials. Crystalline particles are found to grow bigger in the medium-grained base material and yield more homogenous spatial distributions. Finally, a new workflow is suggested to ultimately determine the crucial contact surface between calcite bonds and soil grains through image processing and 3D volume reconstruction. [ABSTRACT FROM AUTHOR]

Biogrouting is a new ground improvement method that has been studied in recent years. This method involves mainly the use of a microbially induced calcite precipitation process to bind soil particles to increase the strength or to fill in the pores of soil or joints of rock for seepage control. There are two major challenges in the use of biogrout for seepage control through rock joints. The first is how to inject the biogrout solutions, and the second is to understand the mechanisms for the formation of calcite under seepage flow. In this paper, a study on the injection of biogrout solution and the formation of precipitates along a circular 1D flow channel is presented. To minimize the influence of flow, a new one-phase injection method to inject bacterial solution and cementation agents simultaneously was adopted in this study. Factors affecting the formation and distribution of precipitates along the flow channel such as flow velocity, flow rate, and aperture of flow channel were investigated. The experimental results indicated that less calcite was precipitated at locations further away from the injection point due to depletion of the reactants' concentrations along the flow path. Using the one-phase injection method, the bacterial activity had a major effect on the accumulation of the calcite on the inner surface of the flow channel. The total calcite precipitated on the surface of the flow channel increased slightly with increasing bacterial activity or flow rate. An equation to predict the distance travelled by the biosolution has been derived based on the testing results. [ABSTRACT FROM AUTHOR]

Soil bio-cementation via microbially induced carbonate precipitation (MICP) has been extensively studied as a promising alternative technique to traditional chemical cementing agents for ground improvement. The multiple-phase injection methods are currently well adopted for MICP treatment, but it is rather complex and requires excessive number of injections. This paper presents a novel one-phase injection method using low-pH all-in-one biocement solution (i.e. a mixture of bacterial culture, urea, and CaCl2). The key feature of this method is that the lag period of the bio-cementation process can be controlled by adjusting the biomass concentration, urease activity, and pH. This process prevents the clogging of bio-flocs formation and thus allows the biocement solution to be well distributed inside the soil matrix before bio-cementation takes effect, allowing a relatively uniform MICP treatment to be achieved. Furthermore, the ammonia gas release would be reduced by more than 90%, which represents a significant improvement in the environmental friendliness of the technology. The new one-phase method is also effective in terms of the mechanical property of MICP-treated soil; an unconfined compressive strength of 2.5 MPa was achieved for sand after six treatments. [ABSTRACT FROM AUTHOR]

Previous studies have shown that biocement, or microbially induced calcite precipitation, can improve the mechanical behaviour of clean sand. However, the behaviour of biocemented sand is affected by several factors. In this paper, triaxial consolidated drained tests and K0 consolidation tests were carried out on sands (Ottawa sand, ASTM graded) with varying biocement treatment passes and relative densities to study the failure and drained stress–strain behaviour and compressibility of biocemented sand. It is found that for loose and medium dense sands, the slight biocement treatment on sand can be as good as or better than the densification treatment in terms of the strength improvement and the deformation control. In the triaxial tests, the shear strength, the slope of failure line in p'-q plane and the peak dilation rate increase with the increase in treatment passes at various levels of relative density. For the loose sand (Dr = 30%), 2-pass biocement treatments (1.0% calcite content) are sufficient to achieve a shear strength, a slope of failure line and a peak dilation rate higher than or similar to that of untreated dense sand (Dr = 90%), and for the medium dense sand (Dr = 50%), 1-pass biocement treatment (0.79% calcite content) is sufficient. In the K0 consolidation tests, the axial strain of the sand decreases with the increasing treatment passes. For medium dense sand (Dr = 50%), 1-pass treatment can control the axial strain to a level similar to that of untreated dense sand (Dr = 90%). The variation of K0 value versus axial strain during K0 consolidation for the biocemented sand shows a different pattern compared with the untreated sand, due to the presence of biocementation effect. Biocemented sand shows a smaller K0 value than the corresponding untreated sand at the final state of the K0 consolidation tests. Scanning electron microscopy was also conducted on the sand samples to investigate the particle-level structure of the biocemented sand and its correlations to the mechanical behaviour. [ABSTRACT FROM AUTHOR]

Microbial biopolymers have recently been introduced as a new material for soil treatment and improvement. Biopolymers provide significant strengthening to soil, even in small quantities (i.e., at 1/10th or less of the required amount of conventional binders, such as cement). In particular, thermo-gelating biopolymers, including agar gum, gellan gum, and xanthan gum, are known to strengthen soils noticeably, even under water-saturated conditions. However, an explicitly detailed examination of the microscopic interactions and strengthening characteristics between gellan gum and soil particles has not yet been performed. In this study, a series of laboratory experiments were performed to evaluate the effect of soil–gellan gum interactions on the strengthening behavior of gellan gum-treated soil mixtures (from sand to clay). The experimental results showed that the strengths of sand–clay mixtures were effectively increased by gellan gum treatment over those of pure sand or clay. The strengthening behavior is attributed to the conglomeration of fine particles as well as to the interconnection of fine and coarse particles, by gellan gum. Gellan gum treatment significantly improved not only inter-particle cohesion but also the friction angle of clay-containing soils. [ABSTRACT FROM AUTHOR]

X-ray computed tomography (CT) has emerged as the most prevalent technique to obtain three-dimensional morphological information of granular geomaterials. A key challenge in using the X-ray CT technique is to faithfully reconstruct particle morphology based on the discretized pixel information of CT images. In this work, a novel framework based on the machine learning technique and the level set method is proposed to segment CT images and reconstruct particles of granular geomaterials. Within this framework, a feature-based machine learning technique termed Trainable Weka Segmentation is utilized for CT image segmentation, i.e., to classify material phases and to segregate particles in contact. This is a fundamentally different approach in that it predicts segmentation results based on a trained classifier model that implicitly includes image features and regression functions. Subsequently, an edge-based level set method is applied to approach an accurate characterization of the particle shape. The proposed framework is applied to reconstruct three-dimensional realistic particle shapes of the Mojave Mars Simulant. Quantitative accuracy analysis shows that the proposed framework exhibits superior performance over the conventional watershed-based method in terms of both the pixel-based classification accuracy and the particle-based segmentation accuracy. Using the reconstructed realistic particles, the particle-size distribution is obtained and validated against experiment sieve analysis. Quantitative morphology analysis is also performed, showing promising potentials of the proposed framework in characterizing granular geomaterials. [ABSTRACT FROM AUTHOR]