Soil Specimens Research Articles

Soil Stabilization Using Zein Biopolymer

The characterization and analysis of the cementation properties of novel biopolymer binders in soils are essential for their potential application in geotechnical engineering. This study investigates the cementation effect of a novel zein biopolymer binder on sandy soils. Soil specimens are mixed with various contents of zein biopolymer ranging from 0 to 5%. The mechanical and microscopic characteristics of the treated specimens are evaluated using unconfined compression tests and scanning electron microscopy, respectively, after curing for 3, 7, and 28 days. The results show a consistent increase in compressive strength and elastic modulus of treated soils with increasing curing periods and biopolymer contents. A small amount (1%) of zein biopolymer increases soil strength and elasticity regardless of gradation. Additionally, the bonding force between the soil–zein biopolymer increases linearly with soil uniformity. Therefore, the application of zein biopolymer can be potentially used as a binder for fine- and coarse-grained soils in geotechnical engineering considering its stabilization and sustainability properties.

Geochemical Content of Lead and its Distribution in Soil of Kirkuk City/Northern Iraq

The current study includes determination of the concentrations of lead (Pb) in 18 specimen of Kirkuk city soil (K). Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) technology has been used in the analysis of soil samples in laboratories Acme company in Canada. Results of chemical analysis of samples clarified a rise in average of lead in soil samples (26.11 ppm) compared with international average of soil (10 ppm) and with uncontaminated ones (15 ppm), and rise in its average in surface depth (30.2ppm) compared with the lower depths (17.97ppm), and decreases in its average as compared with local soils in other cities in Iraq. Factor analysis of the geochemical data for the samples above has been conducted and has been shown a presence of affinity and geochemical associations among Pb and both of potassium oxide and phosphorus penta oxide and also some elements such as phosphorus, cadmium, copper and zinc, as well as organic materials. Size analysis of the samples has confirmed that the concentration of Pb increases in the clay fraction in soils, and in a larger quantities than in the silty and sandy fractions. The value of Geoaccumulation index (Igeo) for samples of soil showed that it lies within the medium pollution category to non-pollution. Oxidation - reduction potential and the acidic function have helped to identify the prevailing metallic phase in the soils at the area of study, which is a type of Cerussite.

Predicting the thermal conductivity of unsaturated soils considering wetting behavior: A meso‑scale study

Unsaturated soils are three-phase porous materials that consist of the solid phase, the liquid phase and the gas phase. While accurate predictions to the thermal conductivity of unsaturated soils are crucial for the analysis and design of geothermal systems, the distribution characteristics of the different phases can also significantly affect the thermal performance. In addition, the fact that soils are heterogeneous materials also adds to the challenges in the evaluation of the thermal conductivity of unsaturated soils. In this paper, a methodology is proposed to calculate the thermal conductivity of unsaturated soils. This methodology starts from identifying representative soil parameters based on microscopy images of soil specimens. The meso‑structures that consist of the different phases are then reconstructed in a finite-element model based on the identified characteristics. The Monte-Carlo-based finite-element analyses are then carried out to calculate the thermal conductivity of unsaturated soils while considering the wetting behavior between the solid and liquid phases, which is characterized using the hydrophilia coefficient. After validating the methodology using both the experimental and numerical results reported in the literature, a parametric analysis is conducted. The results indicate that a high quartz content improves the heat transfer, but the quartz content does not affect the heat transfer skeleton. Furthermore, an increase in the solid content and degree of saturation results in an increase in the density of the heat transfer skeleton, which leads to enhanced heat transfer efficiency. A reduction in the hydrophilia coefficient and the formation of liquid-bridges have a similar effect. Last, the effects of wetting are more evident in soils with high porosity and a low degree of saturation.

Modelling of the Torsional Simple Shear Test with Randomized Tresca Model Properties in Midas GTS NX

The dynamic properties of soil obtained from the torsional simple shear test (TOSS) are assumed to be uniform throughout the specimen. For some exceptional soils, this may hold true, but for the most majority of soils that we examine, it is obviously not the case, and this level of non-uniformity depends on the conditions in which the soil was formed. In this paper, we discuss a method of modelling inherently non-uniform soil specimens by representing them with elements that have an elasto-plastic simple Tresca material model with different properties (Elastic young modulus and yield stresses). The combination of properties that can simulate the nonlinear behaviour of the soil is found and calibrated using a model of the TOSS test built in the finite element software Midas GTS NX. Furthermore, the influence of rigid inclusions in the soil is studied and the results show an increase in stiffness with the increasing percentage of inclusion in the soil.

A new sand raining technique to reconstitute large sand specimens

Abstract Sand raining is among the popular techniques used in the laboratory for preparing sand samples. Factors like the deposition intensity (DI) and the falling height (HF) affect the produced relative density (RD) in this technique. Studies showed that the RD increase as the HF increases. This is, however, applicable up to a critical HF beyond which the RD seems unaffected. According to previous experiments, the maximum RD achieved using the sand raining is about (70 ± 5)%. The preparation of samples with higher RD is a prerequisite required in many experimental models. In the present article, a new raining system, which is capable to prepare sand samples with a very high RD and with a fast sand flow, is introduced. The new system was used to examine the relationship between the HF and the RD under different trapped air pressures and using rain nozzles with three different opening diameters. The new system was found appropriate for reconstituting SP-SM with very dense specimens (RD > 99%) with achieving higher DI values and a reduction in preparation time of more than 90% in comparison to the classic raining technique. It is time-saving and very suitable to reconstitute large model soil specimens effectively and quickly.

Temperature effects on the hydraulic properties of unsaturated rooted soils

Soil temperature of vegetated landfill earthen covers varies with time during their service, due to heat released by the degradation of municipal solid waste. In this study, an experimental campaign to capture soil water-retention curve (SWRC) and hydraulic conductivity function (HCF) of unsaturated rooted soils was conducted at different temperatures (25, 45, and 60 °C). Simplified evaporation tests were conducted by subjecting soil specimens to a prolonged drying period at maintained temperature. Based on the responses of matric suction and water content, SWRC and HCF were determined by the instantaneous profile method. It was found that increasing temperature reduced water-retention capacity, due to root shrinkage, thermal expansion of liquid phase, and reduction in forces of capillarity and adsorption. Soil hydraulic conductivity was enhanced by the increase in soil temperature due to reduction of water viscosity and potential preferential flow at root channels induced by root shrinkage. Temperature effects on SWRC and HCF of rooted soils are suction-dependent. A new nonisothermal SWRC model was developed to capture the dual effects of roots and temperature. By using the same set of calibrated parameters, the model demonstrates its ability to predict SWRCs reasonably well within the range of temperature investigated.

Stabilization of Soft Soil by a Sustainable Binder Comprises Ground Granulated Blast Slag (GGBS) and Cement Kiln Dust (CKD)

Due to its significant deficiencies such as low permeability, low bearing and shear strength, and excessive compressibility, soft soil is one of the most problematic types of soil in civil engineering and soil stabilization can be considered a suitable technique for pavements. This study investigates the use of ground granulated blast slag (GGBS) and cement kiln dust (CKD) as stabilizers for soft soil. Thus, this study involves two optimization stages; in the first stage, GGBS was incorporated into 0%, 3%, 6%, 9%, and 12% by the weight of cement to obtain the optimal percentage, which was 6%. Then, the optimal GGBS was blended with CKD in a binary system at 0%, 25%, 50%, 75%, and 100% by the dry weight of the soil. The testing program used in this paper was Atterberg limits with compaction parameters to investigate the physical properties and unconfined compressive strength (USC) at 7 and 28 days to examine the mechanical characteristics. In addition, the microstructures of the soil specimens were tested at 7 and 28 days using scanning electron microscopy (SEM). The findings reveal that the binary system enhanced the physical and mechanical properties of the soft soil. The optimum binder achieved in this study was 6% (25% GGBS and 75% CKD), which generates an increase in strength of about 3.3 times in 7 days, and of 5.5 times in 28 days in comparison to the untreated soil. The enhancement was attributed to the formation of the hydration products as approved by SEM. Consequently, in the case of soft subgrade soils, this technique can increase the pavement’s bearing capacity and performance.

The Sed360 Test for Rapid Sand Particle Size Distribution Determination

Sed360 is a largely automated system for determining image-based particle size distributions (PSDs) of sands. A sedimented soil specimen contained in a 25.4-mm (1-in)-diameter circular acrylic tube sits atop a rotating stage. While the tube rotates, a camera captures an image of the specimen every 4° of rotation. Narrow vertical strips from each image are automatically stitched together to form a complete, unwrapped 360° view of the soil specimen. Image analysis based on a mathematical Haar wavelet transform generates the soil specimen’s PSD. Three sands were tested with the Sed360 and the image-based PSDs are compared to traditional sieving results. As in earlier studies, very good agreement was observed. The Sed360 affords the same benefits of the system’s predecessors (LabSed and FieldSed) over sieving but adds automatic image capture and stitching to create large 360° unwrapped cylinder images of the specimen that are better suited for PSD determination by image analysis. The Sed360 also paves the way for testing a larger range of particle sizes by SedImaging.

Influence of Seawater Erosion on The Strength and Pore Structure of Cement Soil with Ferronickel Slag Powder

To promote the recycling of industrial waste residues in the reinforcement of foundation soil, the anti−seawater erosion of cement soil with ferronickel slag powder in the marine environment was studied. Specifically, this paper employed ferronickel slag powder to partially replace the cement. Then, the apparent morphology, unconfined compressive strength, and nuclear magnetic resonance (NMR) tests were performed on specimens of cement soil with ferronickel slag powder soaked in purified water and seawater. The research results reveal that with the rise in the content of ferronickel slag powder, the erosive effect of seawater on cement soil weakens, while the compressive strength of cement soil increases first and then decreases. With an excessive amount of ferronickel slag powder added to the cement soil, its chemically active effect decreases, leading to a decrease in the strength of the cement soil. When the admixture of ferronickel slag powder in cement soil is 45%, it achieves good performance. The addition of ferronickel slag powder improves the plasticity of cement soil. The higher the content of ferronickel slag powder, the greater the failure strain and residual strength of the cement soil. Microscopic studies indicate that with the increase in the content of ferronickel slag powder, the pores in the cement soil become smaller and smaller, the total pore volume decreases, the continuity of the pore size distribution improves, and the structure becomes more compact, thus enhancing the erosion resistance of cement soil.

Modeling and electromechanical performance of improved smart aggregates using piezoelectric stacks

Smart aggregates (SAs) are often formed by embedding lead zirconate titanate (PZT) patches into concrete or marble blocks. They not only have the advantages of low cost, quick response, high reliability, and long service life, but also possess comprehensive actuating and sensing abilities, and have been widely used in structural health monitoring in the field of civil engineering. However, due to the plate-like geometry of the PZT patch and the limited number of layers, SAs have a relatively short sensing range. To solve this issue, a new type of SA using piezoelectric stacks was developed. Theoretical modeling of this new transducer was established, and prototypes were fabricated. Comparisons between the theoretical predictions and the experimental results are presented, and good agreement can be found. The effects of the key parameters, including the total height of the specimen, the elastic modulus of the cement, the radius of the piezoelectric stack, the thickness of the piezoelectric layer, and the number of piezoelectric layers in the piezoelectric stack, on the electromechanical properties were analyzed, and the guidelines for optimal design were presented. In addition, the improved and the traditional SAs were used to monitor the water content in soil specimens based on the electromechanical impedance technique. The results showed that the improved SAs using piezoelectric stacks are more sensitive than the traditional ones, and have good potential in structural health monitoring in the field of civil engineering.

Double Plane Direct Shear Apparatus for Determination of Adhesion Factor in Clays

Abstract A modified direct shear assembly with two parallel shear planes was designed to enable the simultaneous and independent measurement of cohesive and adhesive resistance; it is named the “double-plane direct shear device.” The three-block specimen box of the device has top and middle blocks filled with soil specimen and the bottom block is made of solid steel. The middle box is laterally displaced while restraining the top and bottom box, leading to concurrent shearing along two parallel shear planes. Results from quick undrained testing of kaolinite at five different consistency indexes (Ic) and three different vertical stresses (σv) are presented. The stress–deformation curves show greater mobilization of adhesive stress than cohesive stress at low deformations at all Ic and σv. The deformation required for the complete mobilization of cohesive and adhesive stresses and their variation with Ic and σv is discussed. A parameter crossover deformation (dco) is defined to identify the region where adhesive stress is greater than cohesive stress, which would be useful in applications where soil stickiness is of concern. The results show that the presence of partial drainage increases the dco, which results in an increased deformation range over which adhesive stress is greater than cohesive stress, thereby increasing the stickiness susceptibility. Furthermore, results show that the adhesion factor (α, defined as the ratio of adhesion to undrained cohesion) always stayed below unity under undrained conditions, whereas under partial drainage conditions, values of α greater than unity were obtained. The study concludes that for the application where soil stickiness is of concern, the determination of α and its usage to analyze stickiness susceptibility should be performed under simulation of appropriate drainage boundary conditions.

Comparing the trend of Vsat similar range of saturated and unsaturated stress state variables

The effect of matric suction on S-wave velocity (Vs) of unsaturated soils has been observed to show different trends from the Vs relationship with effective confining pressure. In some soils, the increase in S-wave velocity per unit stress change in matric suction (ua-uw) is greater than the increase in S-wave velocity per unit stress change in effective confining pressure (σ’3) for saturated and dry soils and vice versa for other soils. In this study, the difference was examined through the stress state variables for unsaturated soils on similar soil samples. Experiments were conducted on sand and kaolin specimens using a triaxial cell modified to include bender elements and a high-air-entry disk for the testing of unsaturated soils. The soil specimens were first fully saturated and Vsat various effective confining pressures were measured. The tests were repeated with similar soil specimens subjected to net confining pressure and matric suction for similar stress range as the previous tests. Data was also collated from the literature. Comparisons were made by plotting on two-dimensional and three-dimensional plots to understand the differences. It was found that soil type and soil fabric play important role in the differences. Soil fabric plays a more important role for compacted soils where soil fabric is affected by the compaction water content.

Field and laboratory measurements of shear wave velocity in unsaturated soils

Shear wave velocity measurements in soil are important for assigning site soil profiles to seismic site classes and for calculating other dynamic soil properties. The seismic cone penetration test (SCPT) is commonly used to determine shear wave velocity profiles in the field. In the laboratory, bender elements provide an easy means to measure shear wave velocity of soil specimens from discrete depths. In this study, shear wave velocity measurements obtained from unsaturated soil profiles in the field and on field samples in the laboratory under similar stress conditions were analyzed and compared. Additionally, the influence of seasonal changes on the behavior of shear wave velocity was investigated. Comparisons of shear wave velocities from the field and laboratory were favorable for similar moisture and stress conditions. However, results showed that as the degree of saturation increases and suction decreases the shear wave velocity can decrease significantly.

Effect of fiber length on the consolidation parameters of coir fiber-reinforced soft clay

Coir fibers are natural fibers with high tensile strength and pressure resistance, making them an alternative soil reinforcement material. However, the effect of fiber length on improving soil consolidation properties has yet to be largely explored. Therefore, this study investigated the effect of the length and content of coir fibers on soft soil mechanical behavior through a series of one-dimensional consolidation tests. Fibers of >10 mm to 30 mm and >30 mm to 50 mm lengths were mixed randomly into the soil with varying content, ranging from 0.00% to 1.25% of the total weight of the mixture. The relationship between the effective stress and the void ratio was explored, unveiling that the void ratio of soil specimens reinforced with coir fibers decreased more gradually than those unreinforced. An increase in the fiber content reduced the compression index (Cc) value and enhanced the coefficient of consolidation (Cv) value, with longer fibers producing more significant values due to more excellent interactions between fibers. Fibers of >30 mm-50 mm yielded optimum Cc and Cv values at the fiber contents of 0.50% to 0.75%.

The Investigation of the Mechanical Properties of EICP-Treated Sand Specimens Prepared by a Double-Reservoir Injection System for Uniform Precipitation of Carbonate via Triaxial Tests

Abstract The injection condition of enzymatic-induced carbonate precipitation (EICP) grouting for uniform precipitation and the mechanical properties of EICP-treated soil specimens were investigated in this study. Urease derived from yellow soybeans was used as the catalyst for the precipitation of the carbonate instead of the expensive purified urease commonly used. The uniformity of the calcium carbonate distribution was investigated by measuring the calcium carbonate content at various locations within the EICP-treated soil specimens through the soil column injection tests. The results showed that the uniformity of the calcium carbonate distribution depends on the reservoir system for the storage of the injection solutions and the injection volume that is associated with the colloidal transport of urease. Based on the proposed injection method, the EICP-treated soil specimens were prepared for two soil types and a series of consolidated undrained triaxial compression tests were conducted to investigate the mechanical properties. It was confirmed that the undrained shear behavior of the EICP-treated sand specimens shows more softening behavior. In addition, the use of a high molarity urea-CaCl2 solution resulted in pronounced reinforcing effects on the strength, which included both the peak and residual strength and the stiffness. The effects of the confining pressure and the soil types on the strength and stiffness were also investigated.

A prototype for water content measurement in partially saturated soils

The paper presents the technological set-up and calibration of a system based on impedance spectroscopy for measuring water content in partially saturated soils. The technique adopted is relatively recent in geotechnical practice; it is used herein to characterize the electrical response of a soil specimen among two conducting electrodes upon application of an alternate voltage and the measurement of the current intensity resulting across the specimen, for frequency values in the range [500 Hz – 50 kHz]. The complex impedance of the soil specimen is due to both resistance, i.e. opposition to current, and reactance, i.e. tendency of the system to yield and retrieve energy, and it depends on the specimen water content. An on-purpose experimental plan has been conceived and is presented herein, aimed at building a calibration function for deriving the water content in pyroclastic soils from the impedance measurements. Preliminary results reveal an adequate level of repeatability of the measurements and suggest the existence of a monotonic correlation between the impedance modulus and the gravimetric water content.

Pore scale investigation of unsaturated granular soil behaviour by means ofin situCT experiments

With continuing evolution of imaging techniques from medical applications and materials science, non-destructive imaging experiments have also become an important method to investigate soil specimens. Amongst other methods, computed tomography (CT) has developed to a tool to visualise and better understand the microstructure of different soils based on 3D image data. Furthermore, the acquisition of a temporal series of CT images allows to study processes in soils on the microscale, e. g., during mechanical loading. In order to study the hydraulic and mechanical behaviour of unsaturated granular soils, we combine different custom-built miniaturised experimental set-ups with geomechanics background with computed tomography, yielding so-calledin situCT experiments. By means of image reconstruction and further image analysis based on segmented CT images acquired during different hydraulic and mechanical experiments, we study the drainage and imbibition process as well as the shear process of unsaturated sand and glass bead specimens on the pore or grain scale. The analysis of data on the microscopic level, including the phase distribution, interfacial areas, contact lines as well as radii of curvature of capillary menisci, allows to obtain insights into the macroscopic water retention behaviour and shear behaviour of granular soils.

Interpretation of constant suction direct shear test

Constant suction direct shear test enables the understanding of the failure mechanism in rainfallinduced landslides. It can be conducted using a conventional direct shear apparatus with some modifications. The constant suction direct shear test is carried out in two stages. In the first stage, the unsaturated soil specimen is consolidated to the target net normal stress and matric suction then sheared in the second stage. Matric suction is usually controlled using the axis-translation principle. It is commonly observed that the shear stress of an unsaturated soil sheared in the direct shear shows a strain-hardening behaviour at large displacements making the determination of the failure stress difficult. Hence, the objective of this study is to critically examine the constant suction direct shear tests and the analysis of the test results to obtain the shear strength parameters for unsaturated soils. Constant suction direct shear test data were collated from the literature. It was found that the interpretation of the direct shear test has two inconsistencies: (1) taking failure shear stress at arbitrary displacement strain or limit, dependent on the size of the direct shear apparatus, and (2) correcting only shear stress for contact area. The effect of these two consequences on the interpretation of the direct shear test range from negligible to significant. The study shows that arbitrary determination of failure shear stress can be resolved by plotting the direct shear test results using a stresspath plot. The effects of area correction are shown to be almost negligible for small horizontal displacements of less than 2 mm for both square and circular shear boxes. A more consistent interpretation of the constant suction direct shear test is demonstrated where both these inconsistencies are considered.

Post-Foundation Studies Using Integrated Geophysical and Geotechnical Methods at New Agbor Road, Uromi, Edo State, Nigeria

Globally, the incessant failure of buildings has drastically led to an increase in the loss of lives and properties, posing lots of concerns about the causes of these devastating effects. This research evaluates the immediate and remote causes of probable foundation failure on some buildings at Ohunyon Street, Uromi, Edo State, using integrated geophysical and geotechnical methods. By optimizing the measured field, calculating the apparent resistivity data, and interpreting the generated electrical resistivity tomography by using the SAS 1000 terrameter and RES2DINV software, a variation in soil resistivity and type was established. The geotechnical method required performing Atterberg limit-index studies on the gathered soil specimens in the region as well as geological laboratory grain size analyses. The pole-dipole results showed two weak zones and one moderately competent zone, whereas the dipole-dipole results revealed three primary layers: topsoil (sandy clay), clayey loam, and silty loam. The results also revealed regular clay permeation within the loam at depths ranging from 0.9 to 1.9 m, indicating yearly wetness, volumetric expansion, shrinkage, and uneven ground settlement. The geotechnical survey results provided useful information on both the textural soil test and the Casagrande soil analysis. All of the results were highly correlated, providing pertinent information regarding the factors responsible for the buildings’ failure and recommending that the foundations of these buildings be reinforced by piling to depths of 2 m (6.6 ft) below the ground surface in order to prevent future failures. This work has distinctly shown how integrated geophysical and geotechnical methodologies can potentially be used to evaluate subsoil competency.

An Experimental Investigation on the Effect of Calcium Chloride As Dust Suppressant on the Strength of Unpaved Road

The quality of the gravel used in road construction has a profound positive impact on roadservice life. The potential use of calcium chloride as a dust control agent and material for stabilizing the base of unpaved roads has been researched.However, the quality of the gravel may be impacted if calcium chloride isintroduced as a dust suppressant into it.The main aim of this researchis to examine the increase in strength of soil specimens treated with calcium chloride and to evaluate how different proportions of calcium chloride as a dust suppressant and base stabilizer affect the California Bearing Ratio value of the soil samples. Mixtures of natural gravel and gravel with varying amounts of calcium chloride were analyzed for their Atterberg limits, grading, maximum dry density, CBR properties, and optimum moisture content.The changes in the characteristics of the gravel -calcium chloride mixtures were analyzed. It was found that the particle size distribution and Atterberg limits remained largely unchanged. However, the optimum moisture content (OMC) decreased from 9.2% to 7.6%, 7.4%, and 7.2% withcalcium chlorideaddedat percentages of2 percent, 3 percent,and4 percent per volumeof dry soil, respectively.Observation of the mixture revealed an increase in the maximum dry density (MDD) as the ratios of calcium chloride were altered.The maximum dry density significantlyincreasedfrom 2.15 Mg/m3to 2.31 Mg/m3, 2.35Mg/m3, and 2.36Mg/m3, respectively. Along with this, the California Bearing Ratio (CBR) demonstrated an improvement of 25% to 29%, 32%, and 36% at 95% compaction with an increase in the ratios of calcium chloride.The increase in dry density can be explained by the improved bonding between particles and the reduction of air voids. This increase in dry density, in turn, positively influences the California Bearing Ratio by transforming soil structure from a dispersed state to a flocculated state.It can be inferred from the results that calcium chloride has the potential to function as a stabilizer for unpaved roads.The findings of this study are expected to reduced life cycle costs for unpaved roads, provide insights for the best approach to materials analysis for unpaved roads, and contribute to environmental benefits by minimizingdust emissions into the atmosphere and reducing the release of chemicals into nature.