Soil Specimens Research Articles

Effect of clay content on the thermal conductivity of unfrozen and frozen sandy soils

Thermal conductivities of five sandy soils subjected to freezing-thawing and drying-wetting cycles were determined. Specimens were prepared at five different clay contents of 0, 5, 10, 15, 20% prior to compaction at the Proctor maximum dry density. Soil specimens were saturated prior to freezing-thawing and drying-wetting experiments. During a freezing-thawing cycle, soil's thermal conductivity and unfrozen water content were measured at different temperatures ranging from -3 °C to 0 °C. During a drying-wetting cycle, soil's thermal conductivity was measured at different water contents. The experimental results were then compared with predictions by two of the most appropriate existing models, namely De Vries's and Johansen's models, in order to provide insights into the effects of clay content on soil thermal conductivity at (saturated and unsaturated) unfrozen and frozen states.

Effects of push–pull injection–suction spacing on sand biocementation treatment

The process of ureolysis-driven biocementation is used to improve granular soils. The precipitation of calcium carbonate (CaCO3) crystals results from the reactions of urease generated by ureolytic bacteria and chemical reagents, which strengthen or bind soil particles together. Using a lab-based scaled physical model, this study investigated the influence of selected spacing intervals (107, 214 and 321 mm) on the effectiveness of biocementation through the injection–suction or ‘push–pull’ approach. Polystyrene moulds were used to create soil specimens. These were then injected with six cycles of treatment solutions at the intervals stated. The compressive strengths and calcium carbonate contents of the biocemented soil specimens were measured after curing. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy and effluent analysis (pH and ammonium measurements) were also performed. The biocemented soil specimens with different spacing intervals obtained compressive strengths of 2.53 ± 1.06 to 4.2 ± 2.3 MPa, while the calcium carbonate contents were from 2.78 ± 0.3 to 11.16 ± 1.5%. The elemental compositions and bonding of calcium carbonate precipitates in the biocemented soil were confirmed by EDS and FTIR spectra, while SEM micrographs revealed chip-like and irregular rhombohedral crystal forms. The results demonstrated that injection spacing had an effect on biocemented soil treated by microbially induced carbonate precipitation.

On the critical particle size of soil with clogging potential in shield tunneling

Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles. However, soil clogging rarely occurs in strata with coarse-grained soils. Theoretically, a critical particle size of soils should exist, below which there is a high risk of soil clogging in shield tunneling. To determine the critical particle size, a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents. It was found that the tangential adhesion strength at the soil–steel interface gradually increased linearly with applied normal pressure. When the particle size of the soil specimen was less than 0.15 mm, the interfacial adhesion force first increased and then decreased as the water content gradually increased; otherwise, the soil specimens did not manifest any interfacial adhesion force. The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force, thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling. The critical particle size of soils causing clogging was determined to be 0.15 mm. Finally, the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.

Laboratory Experiments on Soil Stabilization to Enhance Strength Parameters for Road Pavement

AbstractClay soils can cause significant distress in road construction due to their low strength. Stabilizing such soil improve with binder agents prior to the geotechnical works can significantly its performance and ensure safety and stability of roads while exploitation. This research envisaged the use of five different binders (lime, energy fly ash, bio fly ash, slag, cement) as an additive stabilizing agents to improve the strength parameters of soil as required in engineering industry standards. The variations of strength was assessed using measurements of P-wave velocity of the elastic waves propagating through soil specimens stabilized by different combination of binders. Measurements were performed on 28thday of soil treatment. The best effects of added binders were noted in the following combinations: cement / energy fly ash / bio fly ash (P-waves >3100 m/s), followed by combination lime / energy fly ash / GGBFS (P-waves >2800 m/s) and cement / lime / energy fly ash (P-waves >2700 m/s). Adding lime is effective due to its fixation and chemical bond with particles. The study contributes to the industrial tests on soil strength for constructing roadbed.

Qualitative Assessment of Soil and Sediment Pollution with Some Heavy Metals: A Case Study of Duhok Valley in The Kurdistan Region of Iraq

The current study was conducted on the valley of Duhok and the agricultural lands irrigated from it, where three sites were identified for collecting samples quarterly from soil and sediment using clean plastic bags for the purpose of measuring lead, nickel, cobalt and copper. Pollution load index (PLI), Nemerow pollution index (PIN), Potential Ecological Risk (PER) and Geo-accumulation Index (Igeo) were also calculated according to the internationally approved methods. The results indicated that most of lead, nickel and copper concentrations in soils and sediments exceeded the limits allowed by WHO, reaching annual rates (96.758, 168.746 and 29.88) , (111.25, 219.65 and 48.162) mg.kg-1, respectively. This fluctuation in concentrations was reflected in the values of the studied indicators for both soil and sediment, where 50% and 58% of the studied specimen are of the polluted grade and the remnant are of the non-polluted grade according to the PLI values. So is the case with PIN where 58% of the soil specimen and 41.6% of the sediment samples were of the severe pollution grade, while 25% and 33.3% of the specimen were of the heavy pollution grade and the remnant were slightly pollution grade. The same applies to the results of the PER index values, where 50% and 41.67% of the specimen were from the Medium ecological risk category, and the rest were from the low ecological risk category, likewise for the (Igeo) values, 100% and 96% of the soil and sediment samples were from the Weakly polluted category.

Optimization of electroosmotic flow to enhance the removal of contaminants from low‑permeable soils

Electrokinetic is an effective method for the extraction of contaminants from low-permeable soils. This work examines the influence of Ca+2 ions on the electroosmotic flow and the effect of electric potential, current, and pH variations on the removal of Pb2+, Na+, and Clˉ ions from artificially contaminated soil during vertical electrokinetic experiments. The DC electric field of 1 Vcm−1 was applied across the soil specimen via steel mesh electrodes for 24, 48, and 72 h of the experiment. In this work, the vertical electrokinetic cell was used to avoid the deposition of Na+ and Pb +2 ions near the soil surface after the treatment. making it even less permeable. The results show that the formation of acidic and alkaline environments in soil specimens affects the transport of ionic species by reducing the effect of electromigration and electroosmotic water flow. The enhancement of electroosmosis using Ca+2 ions as an electrolyte increased the extraction efficiency of Pb2+ (i.e., 41%) and Na+ (i.e., 82%) ions instead of the Clˉ (i.e., 69%) ions due to the high electroosmotic flow (i.e., 81 mL) from anode to the cathode. For relatively low electroosmotic flow (i.e., 19 mL), the extraction efficiency of Clˉ ions (i.e., 76%) was higher than that of Pb2+ (i.e., 27%) and Na+ (i.e., 44%) ions. The results demonstrated that the extraction efficiency of ions and energy consumption increased with treatment time and were higher during the first 24 h of the experiments.Graphical Abstract

The frost heave characteristics of a coarse-grained volcanic soil quantified by particle image velocimetry

The increasing use of the seasonally frozen and permafrost regions for civil engineering constructions and the effects of global warming on these regions have stimulated research on the behaviors of frozen soils. In the present study, the frost heave characteristics of a coarse-grained soil with volcanic nature was experimentally investigated. A large soil tank model was established in laboratory for this purpose. The effects of temperature boundary, external water supply, and water transfer type on the frost heave characteristics of the volcanic soil were studied, through a series of frost heave tests. The particle image velocimetry (PIV) technique was used to quantify the full field deformation of the soil specimen. The results suggest that temperature gradient inside the soil specimen is the driving force for the migration of pore water and vapor. The largest increment in water content generally agrees well with the frost penetration depth. The contribution of vapor to the frost heave of the soil specimen is typically small. The applied seeding method, selected subset size, image-object space calibration, and calculation processes ensured accurate PIV results. Discussions regarding the presented experimental investigation and the employment of PIV technique for quantifying frozen soil deformation are summarized. These findings and discussions can provide valuable insights into the frost heave behavior of the studied soil in particular, as well as promote the application of PIV for frozen soil engineering.

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.