Fine-grained Soils Research Articles

Bacteria-Induced Calcite Precipitation for Engineering and Environmental Applications

Numerous engineering and environmental issues can be resolved using the bacterial-induced calcite precipitation (BCP), which has the potential to be environmentally friendly, sustainable, and economical. In BCP, bacterial enzymes used substrates and divalent cations to bind negatively charged ions to the bacterial surface and produce biocementation. Various metabolic pathways involved in the calcite precipitation and ureolysis are the principal bacterial pathways that have been illustrated by most bacteria including Sporosarcina pasteurii, Bacillus subtilis, and Pseudomonas putida. Ammonia is produced by these bacteria, which is toxic and should be eliminated. Therefore, BCP via carbonic anhydrase could be a preferred option because the end-products are not toxic. The growing global requirement of ground improvement boosted the demand for biostabilization because of its numerous benefits, including environmental issues. Dust suppression, remediated soil contaminants, polychlorinated biphenyl calcium ions, and CO2 sequestration, proving that BCP is environmentally friendly and sustainable. Furthermore, for fine-grained soils having pores smaller than 0.5 μm, the enzyme-induced calcite that uses enzymes instead of bacteria is more suitable to stabilize the soil by precipitating the calcite. The use of BCP as binders for soil stability and strengthening, innovative construction materials, subsurface barriers, and impermeable crusts is an emerging field. Calcite precipitated in the pores increases strength more than 20 times, resulting in a significant reduction in compressibility. Similarly, reduced soil permeability to up to 99% broadens its applicability. This review argues that BCP can be induced by multiple approaches, including urease expressing bacteria and carbonic anhydrase expressing bacteria as well as free enzymes.

Prediction of Soil-Water Characteristic Curves of Four Subgrade Materials using a Modified Perera Model

One of the main hydraulic properties of unsaturated soils is the Soil-Water Characteristic Curve (SWCC). It is essential to understand, predict soil water storage and determine the hydraulic and mechanical behaviour of soils. These curves can be obtained by direct and indirect measurements. The measurements to obtain these curves are expensive, delicate to perform and can be really slow for fine soils, so predictive models become necessary. In order to make a numerical model, a couple of identification tests were carried out to obtain the physical properties of each sample among the four subgrade materials collected in the regions of Dakar and Thies (Senegal). The measurement tests of the matric suction were then conducted depending on the nature of the material (fine-grained soil or coarse-grained soil) and allowed to draw the SWCC of each soil. Among numerous predictive models developed for SWCC in the last decades; this study used the Perera model to fit the SWCC of four (04) subgrade materials, which did not give a satisfactory coefficient of correlation (R2 = 58% and a relatively low sum of the squared residuals (SSR)). This leads to modifying the Perera model to better fit the SWCC on the basis of an understanding of the effect of each parameter on the shape of the SWCC. The proposed modified model was validated by checking the adjusted R2, minimizing the SSR in order to approach at most the experimental air entry value. The modified model works pretty well on coarse-grained and fine-grained soils. This modified model of Perera provided a very good correlation R2equal to 99.98, 98.74, 99.64, and 99.73 for the sandy soils (Sebikotane and Keur Mory) and the Marley and Clayey soils of Diamniadio, with a minimal SSR obtained compared to Perera’s and Hernandez model. Doi: 10.28991/CEJ-2023-09-06-03 Full Text: PDF

Recent development on optimization of bio-cementation for soil stabilization and wind erosion control

This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control. Bio-cement is a type of cementitious materials by adopting natural biological processes for geotechnical and construction applications. Bio-cementation is usually achieved through microbially- or enzyme-induced carbonate precipitation (MICP or EICP). The use of soybean urease can be a cost-effective solution for carbonate precipitation and bio-cementation, which is named SICP. The produced calcium carbonate can cement soil particles and bring considerable strength improvement to soils. In this paper, the mechanisms and recent development on the technology optimization are reviewed first. The optimization of bio-cementation involves 1) altering the treatment materials and procedures such as using lysed cells, low pH, the salting-out technique; and 2) using cheap and waste materials for bio-cement treatment and bacterial cultivation. The objectives are to improve treatment uniformity and efficiency, use bio-cement in more scenarios such as fine-grain soils, and reduce costs and environmental impacts, etc. Studies on the mechanical behaviour and wind erosion performances of bio-cemented soil show that the wind erosion resistance can be improved significantly through the bio-cement treatment. In addition, the use of optimized method and additives such as xanthan gum and fibers can further enhance the strength, treatment uniformity or ductility of the bio-cemented soils. Attention should be paid to wind forces with saltating particles which have much stronger destructive effect than pure wind, which should be considered in laboratory tests. Field studies indicate that bio-cement can improve soil surface strength and wind erosion resistances effectively. Besides, local plants can germinate and grow on bio-cemented soil ground with low-concentration treatments.

Mapping the environmental impacts from land subsidence hazard in Pekalongan City and its correlation with the subsurface condition

Land subsidence in Pekalongan city has affected almost the entire municipality for at least ten years. Land subsidence has occurred in almost all Pekalongan city areas at 2-12 cm/year rates. The direct and indirect environmental impacts of land subsidence are enormous. We aim to map the environmental impacts of land subsidence in Pekalongan city and evaluate the severity of the impacts with the subsurface condition of the affected area. We employed site investigation using resistivity and CPTu soundings at representative sites to reveal the subsurface soils and site survey to map the environmental impacts. Resistivity measurements using a Schlumberger array were carried out at 24 sites, along with 12 CPTu measurements up to 30 m deep. Results show that the subsurface condition up to the depth of 30 m consists of alluvial sediment of clay, silt, and organic soils intercalated with lenses of sand. The alluvial sediment in the southern part is dominated by sandy soils and has a higher stiffness with cone resistance of 1-2 MPa and a friction ratio of 50-200 kPa. The subsurface soils in the northern part are dominated by clay, silt, and organic soils with low cone tip resistance of <0.5- 1 MPa, and friction ratio of <0.25-100 kPa. These values indicate that the sandy soils in the southern part are more compact and have higher bearing capacity than the soft, fine-grained soils in the northern area. The visible impacts of land subsidence include flood and inundation, settlement of buildings and roads, and cracks in houses and infrastructure. The severity of impacts worsens from South to North of the city. This condition is related to the subsurface stratification and engineering properties, where lower bearing capacity occurs in the north.

Rate-dependency of residual shear strength of soils: implications for landslide evolution

Shear-rate weakening or strengthening behaviours can effectively control landslide runouts, defining sudden runaway sliding or years-long slow-creep phases. These behaviours are partly controlled by the properties of the basal material. Understanding its stress–strain–time response is crucial in physically-based assessments of landslide dynamics and the associated risk. We investigate the frictional resistance of a calcium bentonite, a kaolin and a quartz sand by means of a conventional ring-shear apparatus under normal stresses representative of landslide shear zones. Results for the fine-grained soils, in line with literature on pure clays, indicate important velocity strengthening, whereas small shear-rate effects were observed in sand. As long as effective stresses remain constant, a velocity strengthening response can exert a feedback that, under certain conditions, counteracts perturbations in boundary conditions and prevents fast runouts on pre-existing shear zones. Accordingly, we argue that specifically testing for shear-rate-dependency and incorporating observed behaviours in model formulations can be beneficial for better predicting landslide fates.

Investigation on the Microstructure, Unconfined Compressive Strength, and Thermal Conductivity of Compacted CDG Soil by MICP Treatment during Curing

As an eco-friendly treatment method, the microbially induced calcite precipitation (MICP) approach has been widely adopted in sand, but its use on compacted fine-grained soils remains scarce. In this study, compacted completely decomposed granite (CDG) soils at both the dry and wet side of the optimum water content (dry- and wet-of-optimum) were treated by the MICP approach, using a bacterial suspension and chemical reagents at fixed concentrations. After various curing periods, the microstructure (by scanning electron microscopy testing), the produced calcium carbonate content, the unconfined compressive strength (UCS), and the thermal conductivity were analyzed through a series of laboratory tests. The testing results indicate that the sample at dry-of-optimum exhibits a flocculated microstructure, while a dispersed microstructure is shown for the sample at wet-of-optimum. The calcium carbonate content increases with the curing period until reaching a stable value at around 6 days’ curing. After 6 days’ curing, the MICP process is relatively static, without significant amounts of calcium carbonate produced. With this treatment, the UCS of the sample is improved, where higher efficiency was observed for the sample at wet-of-optimum conditions. The variation of UCS for the MICP-treated samples with respect to the curing period follows the same trend as that of calcium carbonate content. At dry-of-optimum, the air-solid phases control the heat transfer in the MICP-treated samples with a discontinuous water phase, leading to insignificant effects of the MICP treatment on the thermal conductivity. In contrast, the water-solid phases dominate the heat transfer in the MICP-treated samples at wet-of-optimum, resulting in variation of the thermal conductivity with the curing period similar to that for the calcium carbonate content.

Studi Karakteristik Propertis Tanah di Kecamatan Polen Kabupaten TTS

Knowing soil characteristics is very important for an engineer to ensure the safety of buildings above the ground. Therefore, conducting a soil investigation in the laboratory and field testing The island of Timor, especially in the Polen sub-district, Timor Tengah Selatan district, has fine-grained soil deposits. In the sub-district area, a large dam is being built, namely the Temef Dam and the main road link connecting one city and four regencies on the island of Timor also. This study aims to determine the characteristics of the soil both physically and mechanically through laboratory testing. The results showed that the location in Puna Village was clay of low plasticity, while the Loli Village had high plasticity clay deposits. The higher of soil's plasticity index, the higher the potential for swelling of the soil. The increased swelling potential causes the low shear strength of the soil. Clay with low shear strength cannot support the construction load on it. Therefore, before the construction of the building on it, it is necessary to improve the soil. In addition to its weaknesses, on the other hand, impermeable clay is used in the dam core material, where the location of material extraction is still within reach so that the work becomes economical.

Generalized model for predicting the thermal conductivity of fine-grained soils

As a renewable energy, geothermal is considered as one of the important approaches to mitigate the energy crisis and climate change. The thermal conductivity of soils is a key parameter required in the utilization of geothermal resources, and it plays an important role in engineering, environmental science, earth science, and agriculture. Generally, the existing models that predict the thermal conductivity of soil are limited to specific types of soil and specific conditions. As a result, it is difficult to apply these models to engineering practice. Therefore, a simple, efficient, and generalized model capable of predicting the thermal conductivity of soils is necessary. In this work, a generalized model for calculating the thermal conductivity of fine-grained soils is established. This model considers the initial dry density, initial water content, temperature, and mineral composition. The proposed generalized model is based on a large amount of measured data from different countries and regions. Its validity is verified after being cross-validated with a back-propagation artificial neural network (BP-ANN) model. Compared with two existing models, the proposed model achieves the best thermal conductivity estimation of fine-grained soils. Additionally, it has a wide range of applications, requires only a few parameters, and does not need recalibration.

Prediction of resilient modulus of fine-grained soil for pavement design using KNN, MARS, and random forest techniques

Prediction of resilient modulus of fine-grained soil for pavement design using KNN, MARS, and random forest techniques

Prediction of Pile Setup for Driven Pipe Piles in Fine-Grained Soils Using Gene Expression Programming

Prediction of Pile Setup for Driven Pipe Piles in Fine-Grained Soils Using Gene Expression Programming

Hydraulic conductivity of fine-grained soils subjected to freeze-thaw cycles

This paper presents laboratory data from tests on four fine-grained soils: reconstituted Kaolinite, destructured Bothkennar clay, reconstituted Bothkennar clay, and reconstituted Gault clay. The soil samples were conditioned in an oedometer cell while being subjected to varying numbers of freezing and thawing cycles. The influence of freeze-thaw cycles on key soil parameters, including the hydraulic conductivity, Atterberg limits, compression and swelling index was studied. The experimental results were then compared with the analysis of a previously published database of hydraulic conductivity measurements on fine-grained soils called FG/KSAT-1358. The paper demonstrates that while multiple cycles of freezing and thawing affect some of the studied soil parameters, such as the Atterberg limits and the compression characteristics, the effects on the hydraulic conductivity transformation model parameters, linking the water content ratio to hydraulic conductivity are less apparent. The results are useful for geotechnical and pavement engineers when making assessments of freeze-thaw effects on subgrade materials in cold regions.

Effect of Biochar on Soil-Water Characteristics of Soils: A Pore-Scale Study

The mechanical and hydraulic properties of soils are largely governed by their soil-water characteristics, which are influenced by factors such as pore size distribution (PSD). While biochar is commonly used as an additive to alter soil properties, its effect on PSD and the soil water retention curve (SWRC) at the pore scale remains unclear. This study aims to investigate the impact of biochar on PSD and SWRC in soils of different types. The study utilized nuclear magnetic resonance (NMR) and the filter paper method to obtain the particle size distribution (PSD) curve and soil water retention curve (SWRC) of various types of soils, ranging from fine-grained to coarse-grained, with different amounts of biochar. The results and discussion revealed that the impact of biochar on soil PSD and SWRC varied depending on the soil type and biochar content. In fine-grained soils, the addition of 8% biochar resulted in the greatest decrease in mesopore size and percentage, while in medium-grained soils, 6% biochar had the most significant effect, and in coarse-grained soils, the optimum biochar content was 2%. At low suction states, the addition of 8% and 2% biochar improved the water retention of fine-grained and medium-grained soils, respectively, but had little effect on coarse-grained soils. Overall, the effect of biochar on soil-water characteristics was non-monotonic and depended on the relative sizes of biochar and soil particles. Therefore, selecting the optimum biochar-to-soil ratio requires careful consideration of these factors.

Effect of the Field-Stress State on the Subgrade Resilient Modulus for Pavement Rutting and IRI

The new Mechanistic-Empirical Pavement Design Guide (MEPDG) uses the subgrade resilient modulus (MR) as the key input parameter to represent the subgrade soil behavior for pavement design. The resilient modulus increases with an increase in confining pressure, whereas, for an increase in deviatoric stress, it increases for granular soils and decreases for fine-grained soils. The value of MR is highly stress dependent, with the stress state (i.e., bulk stress) a function of the position of the materials in the pavement structure and applied traffic loading. Applying excessive vertical stress at the top of the subgrade without knowing the appropriate stress state can result in permanent deformation. In situ stress must be calculated so the correct resilient modulus can be determined. To facilitate the implementation of MEPDG, this study develops a methodology to select the appropriate subgrade resilient modulus for predicting rutting and IRI. A comprehensive research methodology was undertaken to study the effect of in situ or undisturbed subgrade MR on pavement performance using the MEPDG. Results show that MR obtained from in situ stress is approximately 1.4 times higher than the MR estimate from NCHRP-285. Thus, the in situ stress significantly affects the calculation of subgrade MR and, subsequently, the use of MR in the predicted rutting, with IRI using the AASHTOWare pavement mechanistic-empirical design. Results also show that the pavement sections were classified as in “Good” and “Fair” conditions for rutting and IRI, respectively, considering in situ MR.

Implementation of an Advanced Constitutive Models for Fine-Grained Soils

Implementation of an Advanced Constitutive Models for Fine-Grained Soils

Fluvial response to Quaternary hydroclimate in eastern Africa: Evidence from Gona, Afar, Ethiopia

The Busidima Formation in the Afar region, Ethiopia, spans the Quaternary and records the cultural evolution of the genus Homo. Yet, the Middle Pleistocene to Holocene fluvial environments in which early humans lived are undersampled in eastern Africa. This paper examines the stratigraphy, geochronology and paleoenvironments of the newly designated Odele Member of the uppermost Busidima Formation (<152 thousand years ago (ka)), which has received little attention despite representing a critical period in the evolution of early Homo sapiens and its migration out of Africa. The Odele Member is 40–50 m thick and is dated using tephrochronology, radiometric, luminescence, and electron spin resonance techniques. The member spans 151 to 7 ka, defined at the base by the widespread Waidedo Vitric Tuff (WAVT, 151 ± 16 ka modeled age and 95.4% credible interval - C.I.). There are two prominent erosional unconformities in the Odele Member, a lower one after the WAVT deposition with a modeled 95.4% C.I. range of 124–97 ka; and an upper one involving widespread alluvial fan incision commencing between 21.7 and 12.9 ka. The uppermost Odele Member also contains black, organic-rich mats, redox features, reed casts, and freshwater gastropods marking wetter conditions during the terminal Pleistocene and Early Holocene. A black, fine-grained relict soil coeval with the Halalalee paleosol bounds the top of the Odele Member and has mollic and vertic properties, weathering since ∼12 ka. These incision events and prominent paleosol development near/at the top of the Busidima Formation document Middle to Late Pleistocene Awash River incision to its present-day course. Paleo-rainfall estimates suggest that the Early Holocene-age Halalalee paleosol weathered under a climate with mean annual rainfall 10–15% higher than today. A compilation of radiocarbon ages from aquatic gastropods, carbonized wood and charcoal from the upper Odele Member shows wetter and possibly more vegetated conditions during late marine isotope stage (MIS) 3 and the African Humid Period (AHP) that are tightly coupled with precession-driven summer insolation maxima. These key findings suggest that periods of incision, aggregation, and landscape stability in the Odele Member have an orbital precession pacing. The Odele Member revises upward the age of the Busidima Formation to 7 ka, showing that it spans into the Holocene and now includes Middle and Later Stone Age archaeological traditions.

A Comprehensive Review of Soil Remolding Toughness Determination and Its Use in the Classification of Fine-Grained Soils

The remolding toughness property of fine-grained soil has not been investigated that much, mainly because it has not lent easily to direct measurement, with soil toughness usually qualitatively described. In practical terms, as the plastic limit wP is approached, tougher soils require greater rolling effort during the wP test, such that plasticity and toughness properties can be used to distinguish those plastic soils having greater deformation resistance for various field applications. This state-of-the-art review paper presents a critical appraisal of soil remolding toughness determination and its limited use, to date, in the classification of fine-grained soils. The recent developments reviewed and critically assessed include mechanical thread rolling for nominal toughness measurement during the wP rolling-out procedure, various extrusion approaches, and proposed correlations between toughness and the plasticity index to liquid limit ratio. From statistical analysis of previously reported toughness–consistency limits data, some new correlations are introduced in the present paper. Soil classification using the traditional Casagrande plasticity chart is not entirely accurate for certain soil types in that one can observe soils that present high toughness (something typical of clay) being incorrectly classified as silt soil. From this perspective, a new toughness chart is introduced to augment (or for use instead of) the Casagrande plasticity chart in obtaining more reliable soil classification. This paper concludes with recommendations on future research efforts for routinely obtaining soil toughness measurements.

Analysis of a landfill cover without geomembrane using varied particle sizes of recycled concrete

Previous studies have demonstrated the effectiveness of a novel three-layer landfill cover system constructed with recycled concrete aggregates (RCAs) without geomembrane in both laboratory and field. However, no systematic investigation has been carried out to optimize the combination of the particle sizes for fine-grained RCAs (FRC) and coarse-grained RCAs (CRC) that can be used for the three-layer landfill cover system. The aim of this paper is to assist engineers in designing the three-layer landfill cover system under a rainfall of 100-year return period in humid climate conditions using an easily controlled soil parameter D 10 of RCAs. The numerical study reveals that when D 10 of FRC increases from 0.05 mm to 0.16 mm, its saturated permeability increases by 10 times. As a result, a larger amount of rainwater infiltrates into the cover system, causing a higher lateral diversion in both the top FRC and middle CRC layers. No further changes in the lateral diversion are observed when the D 10 value of FRC is larger than 0.16 mm. Both the particle sizes of FRC and CRC layers are shown to have a minor influence on the percolation under the extreme rainfall event. This implies that the selection of particle sizes for the FRC and CRC layers can be based on the availability of materials. Although it is well known that the bottom layer of the cover system should be constructed with very fine-grained soils if possible, this study provides an upper limit to the particle size that can be used in the bottom layer ( D 10 not larger than 0.02 mm). With this limit, the three-layer system can still minimize the water percolation to meet the design criterion (30 mm/yr) even under a 100-year return period of rainfall in humid climates.

Stress-Dependent Shear Strength of Resedimented Nile Silty Clay

The variation of clay undrained shear strength with consolidation stresses is of paramount importance to geotechnical engineers. For several decades, the normalized shear strength of clays has been the cornerstone of geotechnical design in many applications, such as staged construction of embankments. Recently, different trends of shear strength dependency on consolidation stresses have emerged indicating nonlinear variation. Resedimentation has been a useful and reliable method to investigate stress dependency by generating lab test specimens of fine-grained soils with a minimum sample to sample variation for benchmark studies. Previous work on resedimented Nile silty clay (RNSC) has shown unique features, such as high sand fraction and contradicting index properties used for soil classification. The shear strength of Nile silty clay (NSC) and the effects of the consolidation stresses are explored through a laboratory program on resedimented samples from material excavated within the Nile River flood plains. A portion of the material was processed using mechanical energy, which exhibited a significant increase in the liquid limit and a larger clay-sized fraction of particles from grain-size distribution tests. The measured engineering parameters are compared with comparable studied soils and established empirical correlations to provide insights on mechanical behaviors of the NSC. NSC is found to have a rapid decrease in the undrained shear strength ratio and a rapid increase in the lateral stress ratio with increasing consolidation stress.

Laboratory Evaluation of the Improvement of Geotechnical Properties of Fine-grained Soil Stabilized with Plastic Bottle Ash

The first principle in construction works is to have resistant land to build a building. Soil improvement is one of the common methods of improving geotechnical properties and increasing the usability of soil materials. One of the ways to improve the properties of the soil and transform the land into a place where construction is possible is to modify the soil by using additives to it. The use of waste as a material to improve the physical properties of the soil has attracted the attention of researchers. Among these wastes, we can mention rubber wastes, which, in addition to the large volume they occupy, will also cause environmental pollution. In this article, the effect of adding plastic bottle ash on the Zetterberg range and paste properties, the California bearing ratio, and the resistance properties of clay mixed with sand has been investigated. The results of the laboratory tests obtained from this research show the improvement of soil properties by adding plastic bottle ash.

Effect of ionic surfactants on the settling behavior of silt

Ionic surfactants are easily adsorbed by silt and clay particles, thus affecting the flocculation characteristics and settling behavior. The settling velocity, typical size, Zeta potential and surface tension of silt flocs were measured in the presence of two different kinds of ionic surfactants. The results indicated that the cetyltrimethylammonium bromide (CTAB, a typical cationic surfactant) can dramatically accelerate the settling of slit particles, while the linear alkylbenzene sulfonate (LAS, a typical anionic surfactant) slightly retarded silt sedimentation to some extent. In still water, the representative settling velocity dramatically increased from 0.36 cm s−1 to 0.43 cm s−1 with the increase of CTAB concentration, which increased by more than 20%. Oppositely, the sedimentation rate decreased from 0.36 cm s−1 to 0.33 cm s−1 with the increase of LAS concentration. In flowing water, as the flow rate increased from 0 to 20 cm s−1 and the ionic surfactant concentration increased from 0 to 10 mg L−1, the sedimentation rate decreased to 57% and 89% in the presence of CTAB and LAS respectively, which was due to an enhanced dispersion of silt particles and a breaking of flocs. The SEM image test shows that the floc particle size increased 1.5 times of the primary particle size under the high CTAB concentration. The flocculation induced by ionic surfactants greatly influences the sediment size as well as the law of settling velocity. The intrinsic influence mechanism was also discussed based on the variations of silt particle properties. This systematic study can be used for further development of flocculation models and particle size distribution of fine-grained soil.