Strength Of Sand Research Articles

Assessment of the Composition Effect of a Bio-Cementation Solution on the Efficiency of Microbially Induced Calcite Precipitation Processes in Loose Sandy Soil.

Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H2NCONH2, C6H10CaO6, CaCl2, MgCl2). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated.

Particle size effect on unconfined compressive strength of biotreated sand

The great variations in mechanical properties of biotreated specimens have been reported due partially to the wide range of particle size, while research on the particle size effect in biotreated sand remains limited. In this study, we conducted specifically-designed unconfined compressive tests on biotreated sand to investigate the particle size effect with two types of sands, calcareous sand (CCS) and glass bead sand (GBS) of five different particle sizes. Experimental results indicate that unconfined compressive strength (UCS) of specimens increases significantly as cementation level increases, and UCS of biotreated CCS specimens is apparently higher than that of GBS specimens at the same cementation level. A power law decrease in UCS is observed with increasing particle size, which was characterized with an empirical equation by adapting Frossard's size effect equation. SEM photos suggest that the coating CaCO3 in the specimens with small particles contributes considerably and the size effect on UCS is attributed to the reduction of this kind of contribution with increasing particle size.

Fixed-axis shear characteristics of marine coral sand under various consolidation conditions

Coral sand is commonly used to construct ports and other types of infrastructure in coral reefs, where soil elements within slopes and embankments are usually under anisotropic stress because anisotropy is inherent to coral sand. In this study, marine coral sand was subjected to undrained fixed-axis shear tests using a cyclic hollow-cylinder shear apparatus, and the results indicate that the undrained response of such sand is influenced significantly by the initial orientation angle of the major principal stress (α0) and the monotonic loading direction angle (αm). In all cases, the excess pore water pressure (ue) of the coral sand tended to increase and then decrease with increasing generalized shear strain (γg), implying that such sand exhibits shear shrinkage and then shear expansion under monotonic loading. Another finding was that in the case of isotropic consolidation, the phase-transition strength (SPT) and phase-transition internal friction angle (φPT′) of the marine coral sand tended to decrease and then increase with increasing αm, while those in the case of anisotropic consolidation were always maximum in the α0 direction. There is a linear relationship between the SPT of marine coral sand and a dimensionless parameter β, where β−1 varies cosinusoidally with α0 and αm.

A Simplified Model for Shear Behavior of Mortar Using Biomimetic Carbonate Precipitation.

As a common molecule in biomineralization, L-aspartic acid (L-Asp) has been proven to be able to induce in vitro CaCO3 precipitation, but its application in sand reinforcement has never been studied. In this study, L-Asp was employed in sand reinforcement for the first time through the newly developed biomimetic carbonate precipitation (BCP) technique. Specimens with different number of BCP spray cycles were prepared, and a series of direct shear tests were conducted to investigate the impact of spray number on shear strength, critical displacement, and residual strength. Then a simplified power model for shear stress-displacement behavior was established and calibrated with the measured data. The results show that BCP can significantly improve the shear strength of sand. As the number of spray cycles increases, both the shear strength and residual strength increase, while the critical displacement decreases. Such variations can be described with two sigmoid models and a linear model, respectively. The simplified power model performs well in most cases, especially at higher spray numbers. This study is expected to provide a practical model for the shear behavior of BCP-treated mortar.

Experimental Study of Sulfate Erosion Resistance of Cementitious Sand with Waste Glass Powder

In order to save natural resources and protect the natural environment, the relevant performance of waste glass powder as a building material must be enhanced. In general, volcanic ash activity is enhanced through grinding the glass powder particles to a specific degree of fineness, thereby improving the overall strength of cementitious sand. Our current need is to study the effects of replacing standard sand with glass powder of varying particle size and dosage range on its resistance to sulfate erosion as well as the corresponding mechanisms. To further examine the durability properties of glass powder cementitious sand, this study uses glass powder of 100–200 mesh and 200–500 mesh to create cementitious sand samples, replacing 10% and 15% of standard sand with equal volume. After curing for 28 days in a standard curing room, the samples are submerged in tap water and a 5% concentration of sodium sulfate solution for 30, 60, 90, 120, and 150 days. Subsequently, the mass loss rate, flexural strength, and compressive strength are measured to reflect the sulfate erosion resistance of the cementitious sand samples containing glass powder. The findings indicate that the flexural and compressive strengths of cementitious sand with waste glass powder experience a swift decline in strength during the pre-erosion stage and a slow decline or even an increase in strength during the post-erosion stage as erosion age progresses. As the glass powder dosage increases, there is a noticeable decrease in the flexural and compressive strengths, in which the doping of 200–500 mesh doped with 15% of glass powder has the worst effect on the resistance to sulfate erosion. As the particle size increases, both flexural and compressive strengths significantly improve, suggesting that sulfate erosion properties are gradually enhanced. The primary reason for this phenomenon is that when glass powder substitutes fine aggregate, the activity develops more slowly in the initial stage, primarily filling the pores and cracks. However, the activity increases rapidly later, more fully integrating with the cement mortar in sodium hydroxide’s hydration product to create dense hydrated calcium silicate crystals. This enhances the overall strength of the sample, filling the pore structure within the system, and is more conducive to resisting the erosion effect of sulfate ions on the sample.

Study on dynamic strength and liquefaction mechanism of silt soil in Castor earthquake prone areas under different consolidation ratios

Under the Castor earthquake, there is a risk of liquefaction instability of saturated tailings, and the evolution of dynamic pore pressure can indirectly reflect its instability process. Before applying dynamic loads, the static stress state of soil is one of the main factors affecting the development of soil dynamic strength and dynamic pore pressure, and there are significant differences in soil dynamic strength under different consolidation ratios. This paper conducted dynamic triaxial tests on saturated tailings silt with different consolidation ratios, and analyzed the dynamic strength variation and liquefaction mechanism of the samples using the discrete element method (PFC3D). The results showed that 1) as the Kc′ gradually increased, and there was a critical consolidation ratio Kc′ during the development of the dynamic strength of the sample. The specific value of Kc′ was related to the properties and stress state of saturated sand. The Kc′ in this research was about 1.9. When Kc < 1.9, dynamic strength was increased with the increase in Kc; when Kc > 1.9, dynamic strength was decreased with the Kc. 2) Under the impact of cyclic load, when samples were normally consolidated (Kc =1), the pore water pressure would tend to be equal to the confining pressure to cause soil liquefaction. In the case of eccentric consolidation (Kc > 1), the pore water pressure would be less than the confining pressure, thus, the soil liquefaction would not be induced, and the pore pressure value would decrease with the increase of consolidation ratio. This paper provides engineering guidance value for the study of dynamic strength and liquefaction mechanism of tailings sand and silt in Castor earthquake prone areas under different consolidation ratios.

Evaluating the Influence of Sand Particle Morphology on Shear Strength: A Comparison of Experimental and Machine Learning Approaches

Particulate materials, such as sandy soil, are everywhere in nature and form the basis for many engineering applications. The aim of this research is to investigate the particle shape, size, and gradation of sandy soil and how they relate to shear strength, which is an essential characteristic that impacts soil stability and mechanical behaviour. This will be achieved by employing a combination of experimental methodology, which includes the use of a microscope direct shear apparatus, and machine learning techniques, namely multiple linear regression and random forest regression. The experimental findings reveal that angular-shaped sand particles enhance the shear strength characteristics compared to spherical, rounded ones. Similarly, coarser sand particles improve these characteristics compared to finer sand particles, as do well-graded particles when compared to poorly graded ones. The machine learning findings show the validity of both models in predicting shear strength when compared to the experimental results, showing high accuracy. The models are designed to predict shear strength of sand considering six input features: mean particle size, uniformity coefficient, curvature coefficient, dry density, normal stress, and particle regularity. The most important features from both models were identified. In addition, an empirical equation for calculating shear strength was developed through multiple linear regression analysis using the six features.

Dosage method for unconfined strength and fatigue life of fiber-reinforced cement-treated sand

Fiber-reinforcement has been reported as an effective and cost-attractive technique to improve the mechanical behavior of cemented soils. However, the dosage methodologies for these mixtures are still limited, especially regarding dynamic loading. The objective of this research was to analyze the dynamic response and strength behavior of fiber-reinforced cement-treated sand. In this sense, fatigue life, unconfined compressive strength, and split tensile strength tests were conducted. Results indicated that the mechanical behavior of the soil-cement mixtures was governed by fiber content, cement content and void ratio. The presence of fibers, the increase in cement content and the decrease in void ratio improved the overall mechanical behavior of all specimens. The porosity/cement content index resulted in a viable dosage method to predict both the monotonic and cyclic behavior of the mixtures. Lastly, the statistical analysis of variance corroborated the experimentally observed findings.

Micro- and nano- bentonite to improve the strength of clayey sand as a nano soil-improvement technique

Nano-additives results in the formation of nano-cementation (NC). This process is recently used to improve the durability of various building materials. NC used to improve the strength of untreated soil materials, also known as nano soil-improvement (NSI). In few years, the role of nano-additives in various types of soils were developed. In this research, the role of micro- and nano- size of bentonite as soil stabilizer was evaluated as first few research to improve geotechnical properties of soils. Nano-additives prepared by micro- and nano- sizes of bentonite were blend with four formulations. These formulations of micro- and nano- additives at concentrations of 0, 1, 2, and 3%, namely 0% Micro-Bentonite, 1% Micro-Bentonite, 2% Micro-Bentonite, 3% Micro-Bentonite, 0% Nano-Bentonite, 1% Nano-Bentonite, 2% Nano-Bentonite, and 3% Nano-Bentonite, respectively. These formulations of micro- and nano- additives were separately added to soil. Specimens with 3% nano-bentonite showed significant improvement in unconfined compressive strength (UCS) of soil that was more than 2.3-times higher than control specimen in 7-d curing time. Also the performance of micro-bentonite resulted in improvement in UCS of soil that was more than 1.1-times higher than control specimen at 7-d curing time. The secant modulus at 50% of peak stress (E50) of the samples treated with micro- and nano- additives increased in comparison to untreated specimens. Further, X-ray fluorescence (XRF), scanning electron microscopy, and X-ray diffraction analyses characterized micro- and nano- structures of soil specimens, and showed the performance of nano-additives in improving strength of soils. Results show that nano-bentonite as a type of nano-additives is an effective means of increasing the strength of soils. This research shows the significant of nano-bentonite in soil improvement, as a NSI technique.

Cementation anisotropy associated with microbially induced calcium-carbonate precipitation and its treatment effect on calcareous and quartz sands

Microbially induced calcium-carbonate precipitation (MICP) can help cement sand particles together and has emerged as a promising alternative to traditional ground-improvement treatments for granular soils. Owing to precipitation and absorption in different directions, MICP leads to anisotropic cementation. This study was aimed at examining the mechanism of cementation anisotropy and its treatment effect on two commonly used granular soils in geotechnical engineering: quartz sand and calcareous sand. A novel MICP technique was used to prepare bio-cemented sand specimens with different anisotropic patterns of cementation. Microscopic detection techniques were applied to examine the microstructure of the produced MICP cementation. The cementation in the vertical and horizontal directions was different, owing to gravity. The granular surface properties affected the content, morphology, and cement force of the bio-cements produced by MICP treatment. The results of unconfined compression strength experiments confirmed the occurrence of cementation anisotropy and its substantial effects on the stiffness, strength, and fracture patterns of MICP-treated quartz sand and calcareous sand. These findings can help to clarify the formation mechanism of bio-cements and promote the optimised application of MICP for the treatment of granular soils.

Mechanical Properties of Eolian Sand Solidified by Microbially Induced Calcium Carbonate Precipitation (MICP)

Eolian sand is widely distributed in desert areas, and can easily trigger sandstorms under the combined effects of wind and thermal conditions. In this paper, an eolian sand solidification test via microbially induced calcium carbonate (CaCO3) precipitation (MICP) was conducted to explore prospective applications of MICP in the field of dust prevention and sand fixation. A bacterial growth test and a MICP mineralization reaction test were performed based on the response surface method and an orthogonal experiment. Based on eolian sand solidification test, the effects of cementation number and dry density on the permeability and strength characteristics of solidified eolian sand, as well as the content of CaCO3 generated were analyzed. The results showed that the bacteria grew best at a temperature of 35 °C, a pH of 9, and a shaking frequency of 170 rpm. Both urease activity and bacterial concentration increased as the temperature and pH increased but showed a trend of rising before falling as the shaking grew faster. The optimal conditions for MICP mineralization were a bacterial concentration of OD600=1.5, a consolidating fluid concentration of 1 mol/L, a reaction time of 16 h, a pH of 9, and a temperature of 25 °C. The permeability coefficient of solidified eolian sand decreased as the dry density and the number of cementations increased, whereas the CaCO3 content increased with the number of cementations. As the number of cementations increased, the unconfined compressive strength (UCS) of eolian sand initially rose before stabilizing and then increasing again. The CaCO3 content had a positive relationship with UCS, which with the correlation coefficient reached 0.80.

Experimental Study on Strength and Liquefaction Characteristics of Sand under Dynamic Loading

To investigate the influence of moisture content, density, and loading frequency on the dynamic strength and liquefaction characteristics of sandy soil, a series of vibration triaxial tests were designed and conducted. The tests were divided into incremental loading tests and cyclic loading failure tests. The results of the incremental loading tests indicated that the shear modulus decreases with increasing moisture content and density, while it increases with increasing loading frequency. The damping ratio of unsaturated samples showed no significant correlation with moisture content, whereas samples with a density above 50% exhibited an increasing trend in damping ratio with increasing density. The damping characteristics of the sandy soil were found to be related to the loading frequency, exhibiting the characteristics of viscous damping. The results of the cyclic loading tests revealed that the dynamic failure mode of the sand soil is the ultimate equilibrium failure mode. Increasing moisture content and decreasing density make the samples more susceptible to failure. During the process of cyclic loading leading to dynamic failure, the shear modulus of unsaturated samples remains constant, while the shear modulus of saturated samples gradually decreases. The damping ratio of saturated soil is significantly higher than that of unsaturated soil. During the process of cyclic loading leading to dynamic failure, the damping ratio of saturated soil shows no apparent correlation with loading frequency, but it decreases with increasing density.

Effect of Particle Breakage and Interlocking on Strength and Dilatancy Characteristics of Calcareous Sands

Studies show that the shear strength of angular-shaped calcareous sand is mainly affected by dilatancy, interparticle locking, and particle breakage. In the present study, a series of consolidated-drained triaxial compression tests on calcareous sands are carried out to investigate the strength impacts of dilatancy, interparticle locking, and particle breakage. It is found that as the stress level increases, the friction angle difference reflecting the effect of the particle breakage increases. In contrast, the friction angle difference reflecting the interparticle locking and dilatancy effect decreases gradually. Moreover, the critical stress ratio of the high-angled calcareous sands decreases, which may be attributed to particle breakage. The obtained results demonstrate that when the stress level exceeds a certain value, the critical stress ratio remains constant. Then the correlation between the particle breakage, interparticle locking, and dilatancy effects in the shear strength is studied. Finally, based on the performed analysis on energy dissipation in calcareous sands, a dilatancy model is proposed that covers the particle breakage effect. The performed analyses demonstrate that the proposed model can accurately explain the experimental data.

Hydrate dissociation and mechanical properties of hydrate-bearing sediments under local thermal stimulation conditions

Considering the interaction between hydrate dissociation and the mechanical properties of hydrate-bearing sediment (HBS) facilitates a deep understanding of the relationship between hydrate extraction efficiency and reservoir stability during hydrate exploitation. In this study, a series of tests were carried out to study the effects of hydrate dissociation under local thermal stimulation and the mechanical properties of HBS by using the plane strain shear test apparatus. The characteristics of the local maximum shear strain and volumetric strain were also investigated using the particle tracking velocimetry (PTV) method. The results show that the tested water-saturated host sands have the same heat transfer characteristics under local thermal stimulation, despite having different particle size distributions and mineral compositions. The temperature transfer inside the HBS was slower than that of the host sand sample, and the temperature distribution of the HBS after hydrate dissociation was the same as that of the host sand sample. HBS under an axial loading force higher than that of the peak strength of the host sand would fail after hydrate dissociation. Additionally, even partial dissociation of the hydrate can lead to catastrophic failure of HBS under this condition.

Machine Learning-Based Prediction of Unconfined Compressive Strength of Sands Treated by Microbially-Induced Calcite Precipitation (MICP): A Gradient Boosting Approach and Correlation Analysis

The current study applies a soft-computing approach based on the gradient boosting method to predict the unconfined compressive strength (UCS) of sands treated with microbially-induced calcite precipitation (MICP). A 10-fold cross-validation method and hyperparameter tuning are performed to find the optimal architecture of the gradient boosting algorithm. A total of 402 data of unconfined compression tests performed on biocemented sands are utilized in this study. The dataset includes eight input parameters: median sand particle size, uniformity coefficient of sand, initial void ratio, calcium chloride concentration, urea concentration, urease activity, optical density of bacteria, and calcite content. The finding demonstrates that the gradient boosting method outperformed five commonly used machine learning algorithms (artificial neural networks, random forests, k-nearest neighbors, support vector regression, and decision trees) in predicting the UCS of biocemented sands. Using the gradient boosting, the predicted UCS has a strong correlation with the actual values (R2 = 0.95). Moreover, a series of correlation and feature importance analyses are carried out over the dataset. The relationships between unconfined compressive strength, calcite content, and initial void ratio are discussed within the article. Furthermore, some guidelines are provided for assessing the effect of environmental factors on the UCS of biocemented sands. For further study, the limitations of this study regarding the insufficiency of data for correlation and environmental modification are addressed.

Effects of incorporating large quantities of nickel slag with various particle sizes on the strength and pore structure of cement-based materials

Firstly, nickel slag sand with a concentrated particle size distribution in the range of 2.36–0.60 mm was used to replace the mechanism sand in the ratio of 0%, 25%, 30%, 50%, 70% and 100%. Second, partial particle size substitution was used to partially replace nickel slag sand with particle sizes of 2.36–1.18 mm and 1.18–0.60 mm in proportions of 0%, 30%, 50%, 60%, 70% and 100%, respectively, to optimize particle gradation of mixed sand. Cement mortar specimens were prepared using different mixed sands composed of the above two substitution methods and at a water-cement ratio of 0.5. Then, the effects of nickel slag sand with varying substitution methods on the strength and pore structure of cement-based materials were investigated by mechanical tests, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Standard sand was also used as an experimental control group. The experimental results revealed that the maximum flexural and compressive strength of nickel slag sand using a full-size substitution group corresponded to an optimal dosage of 30%, while the optimal dosage of nickel-slag sand using a specific-size substitution group was 60%. The water absorption of the two particle sizes replaced the specimens decreased and then increased with the inclusion of nickel slag sand. The results showed a consistent trend with the variations in electrical resistivity and total porosity of MIP. From the SEM photographic results of the SS, MS, NF30 and NP60 specimens, the cement paste can be more tightly wrapped around the round spherical nickel slag particles. NF30 and NP60 specimens showed a denser internal structure, multi-dimensional hydration products and a lack of pores and microcracks, which is fully consistent with experimental results of mechanical properties and microstructures.

Numerical investigation of pull-out capacity and failure mechanism of suction anchors with mooring line in sand

Suction anchor is a widely used anchorage foundation in taut or catenary mooring systems to fix floating structures. This paper aims to investigate the pull-out capacity and failure mechanism of suction anchors in sand using the finite element method which models the attached mooring line on the anchor padeye. The advanced critical state elastoplastic constitutive model SIMSAND is utilized which can well simulate the state-dependent peak strength and stress-dilatancy behavior of sand, and its accuracy and effectiveness are validated with centrifuge test results. A series of systematical parametric studies are then carried out to explore the effects of the mooring line, aspect ratio, padeye position and loading angle on the pull-out capacity and failure mechanism of the suction anchor. Based on the numerical results and those obtained in other researchers’ work, the optimal padeye position and the normalized V–H envelopes are explicitly discussed. Finally, a calculation framework is put forward for predicting the inclined pull-out capacity of suction anchor in sand considering the mooring line effect.

Influence of size and concentration of carbonate biomineral on biocementation and bioclogging for mitigating soil degradation

Microbially induced carbonate precipitation (MICP) is a promising technique to enhance the geotechnical properties of geomaterial either by strengthening via biocementation or reducing the hydraulic conductivity via bioclogging. This rate of modification mainly depends on the amount, and nature of biomineral precipitated and it is influenced by various environmental, chemical, and microbial factors. Given this, the present study aims to investigate the effect of biochemical conditions such as concentration of biomass and chemical reagents on the amount and nature of biomineral and its impact on the strength and permeability of biomodified sand. For this, the two microbes i.e., Sporosarcina pasteurii and isolated Proteus species at three different initial concentrations and chemical reagents by varying 0.1–1 molar of urea and calcium were considered. The amount and microstructural behavior of biomineral in different biochemical conditions concluded that the governing mechanism differs for both biocementation and bioclogging under identical MICP treatment. The strength enhancement or biocementation is dependent on the size of the biomineral precipitated whereas the reduction in permeability or bioclogging is mainly dominated by the amount of biomineral. The optimum value of biochemical conditions i.e., 108 cells/ml of biomass and 0.25 M concentration of cementation reagents was chosen to further evaluate the effect of equal MICP treatment on the biocementation and bioclogging of sands having different grain sizes. The study infers that not the absolute size of the biomineral but the relative size of soil grain and biomineral influence the linkage between the soil particles and hence affect the strength of biomodified soil.

Microscopic Properties and Splitting Tensile Strength of Fiber-Modified Cement-Stabilized Aeolian Sand

Microscopic Properties and Splitting Tensile Strength of Fiber-Modified Cement-Stabilized Aeolian Sand

Strength mechanism and electrochemical characterization of cement-bonded calcareous sand in different water environments

Cement-bonded calcareous sand (C-BCS) can effectively enhance the strength of calcareous sand, which is widely in infrastructure construction on islands in the South China Sea, and can fulfil the engineering requirements of island pavement subbase. However, the enhancement mechanisms and meso-generalized structural characteristics of C-BCS under different water environments and cement dosages are unclear. In this study, we consider the unconfined compressive strength as an evaluation index to quantify the degree of hydration reaction, change of hydration products, and meso-generalized structure of C-BCS in freshwater and seawater. We performed analyses using electrochemical impedance spectroscopy, X-ray diffraction, and scanning electron microscopy. The results demonstrate that C-BCS can satisfy the strength requirements of highway and airport runway subbases with 10% and 15% cement admixture, respectively. Furthermore, the corrosion deterioration phenomenon occurs and spreads in C-BCS in seawater. The internal hydration process of C-BCS can be continuously monitored using the electrochemical impedance spectroscopy test, and a correlation between the electrochemical and mechanical parameters at different ages is proposed. The meso-generalized structure inside the C-BCS can be densified by the bridging and pore filling effects of hydration products on calcareous sand particles, thereby improving the strength of calcareous sand. Additionally, we provide a concrete mechanistic explanation underlying the forming strength of C-BCS, and an optimized design approach of C-BCS considering several complex engineering properties.