Mechanical Behavior Of Soil Research Articles

Sample dimension effect on cement-stabilized sandy soil mechanical behavior

Stabilized soil with cement has been a widely used solution in geotechnical projects and requires the molding of numerous specimens to investigate their properties in destructive tests, restraining the reuse for other analysis. Also, distinct sample dimension has been utilized in the research without taking this effect into account. Recognizing these needs, the height and diameter (H/D) ratio effect on cement-stabilized soil mechanical behavior was assessed in the present work. Using sandy soil, Unconfined Compression Strength (UCS), Indirect Tensile Strength (ITS) and Ultrasonic Pulse Velocity tests were performed varying the curing period (7 and 28 days), cement type (I and III) and content (6, 7, 8, 9 and 10%), based on conventional (127 x 100 mm) and reduced dimension (105 x 50 mm) specimens. All variables, individually and combined, affected the compression and tensile strengths of the mixtures, resulting in greater gains for the ones molded with type III cement in reduced dimension, at 28 days of curing. The dimension as an influential variable was statistically established using the variance analysis (ANOVA) at a significance level (α) of 0.05, in which reduced dimension showed an average superior resistance of 21.3%. Mixtures molded with H/D ≥ 2 demonstrated strong correlation (R2 = 0.93), pointing to the possibility of ITS prevision through the P-wave velocity nondestructive tests.

Influence of Lateral Multistage Unloading Intensity on Mechanical Properties of Reconstituted Coastal Soils Containing Silty Particles

The unclear understanding of the mechanical behavior of soil under unloading conditions is a significant reason for the frequent occurrence of accidents and difficulties in the deformation control of foundation pit engineering in coastal areas. This paper discusses the effect of multistage unloading intensity on the mechanical properties of reconstituted coastal soils containing silty particles through a series of laboratory tests, namely, the CU triaxial, bender-element, and permeability tests. Results indicate that, with an increase in unloading intensity, the shear strength and stiffness parameters decrease, while permeability slightly increases. The effect of unloading intensity on the mechanical properties of silt and mucky silty clay is more pronounced. Additional consideration should be given to the effect of a single excavation depth on the mechanical properties of fine-grained soil in foundation pit engineering in order to ensure the stability of the surrounding soil and the safety of adjacent structures.

Hydro-mechanical behavior of two clayey soils in presence of household waste leachates

BACKGROUND AND OBJECTIVESIn landfills, containment is provided by natural or artificial clayey materials known for their low permeability and for their pollutant retention capacity. However, the properties of these media are modified by leachates, whose migration they are supposed to limit. This study aims to reconsider the criteria for choosing suitable materials to make a bottom liner through both their long term hydraulic and mechanical performances.METHODSTwo fine materials sampled in Burkina Faso (West Africa) have been characterized in order to compare their hydro-mechanical behavior in the presence of household waste leachates. The first material is classified as an inorganic clay of low to medium plasticity according to Casagrande plasticity diagram, it is mainly kaolinitic with some traces amounts of smectites. The second one is classified clayey sand of low to medium plasticity, the predominant mineral clay being kaolinite. Hydro-mechanical tests were performed on both sampled materials to judge the sealing properties of these materials, as well as the characteristics of deformation and rupture which have an important effect to ensure the durability of a bottom liner. All these tests were performed first with distilled water then with leachates as interstitial fluids in order to understand the modification of the hydro-mechanical properties of the clayey soils.FINDINGSLeachate contamination always alters hydraulic properties of the materials. However, between the two soils, the most clayey and the most impervious (soils from Nouna) undergo the deeper weathering. Indeed, hydraulic conductivity of these soils in contact with a synthetic leachate increases from 1.71x10-10 to 1.51x10-9 m/s. In contrast to soils from Boudry, these soils also undergo very significant settlements over the long term with compressibility indexes varying from 0.164 to 0.225. For both soils, the shear strength increases showing that, from this point view, the leachate work in the sense of of the bottom liner stability. For soils from Nouna, the effective cohesion increases from 3 to 21 kPa with a slight decrease of friction angle; for soils from Boudry a slight increase of cohesion is noticed while friction angle increases from 34 to 37°.CONCLUSIONThis comparative study is of practical use to environmental geotechnics professionals because it shows that the choice in designing a bottom liner must be a compromise between long term hydraulic and mechanical behaviors of soils. It is also important to know the nature of the flows to contain in order to ensure the durability of the structure.

Simulation of mechanical behavior of carbonate gravel with hybrid PSO–SVR algorithm

Large-scale testing is one of the common methods used to study the mechanical behavior of carbonate gravels. However, due to the huge workload of larger-scale tests and a dimensional limitation of laboratory specimens, there are only a limited number of large-scale tests, and the mechanical behavior of carbonate gravels is not fully understood. In this study, a hybrid algorithm combining two techniques of artificial intelligence – particle swarm optimization and the support vector regression technique – are used to simulate soil behavior using on a dataset obtained from large-scale direct tests of carbonate gravels. Three types of single-output models have been developed, results show that the models developed by the proposed hybrid algorithm are highly accurate. In addition, one of the models used is to predict the shear strength of carbonate gravel under different normal stress. The results show that when the normal stress is larger than 600 kPa, the nonlinear shear strength model is more suitable for carbonate gravel with high particle breakage. Modeling the mechanical behavior of soil with artificial intelligence is thus a useful method to evaluate the mechanical properties of gravel economically and conveniently.

Meso and macroscale mechanical behaviors of soil–rock mixtures

Meso and macroscale mechanical behaviors of soil–rock mixtures

Mechanical Consequence Observation and Microscopic Visualization of Internal Erosion Using Developed Plane Strain Erosion Apparatus

Abstract Internal erosion has been frequently reported and has caused failures and instabilities of geotechnical structures. A plane strain erosion apparatus is developed in this study to allow the subsequent conduction of drained compression test after seepage test and the microscopic observation of particle movement through a transparent window. A drained compression test preceded by a seepage test is performed on specimens containing the same initial fines contents to investigate the mechanical consequence impacts of seepage-induced internal erosion. Experimental results reveal that, compared with uneroded soils, internally eroded soils show a larger secant stiffness at a small strain level (∼1 %). At medium strain level (∼15 %), the soils with erosion show smaller deviator stress comparing with soils without erosion. The analysis of images recorded by the microscope proves that the fines contacted with coarse particles possibly transferring the load are distinct between the soils with and without internal erosion at both small and medium strain levels during the drained compression test, which indicates that the soil fabric could affect the mechanical behaviors of soils subjected to internal erosion. Our designed equipment and microscopic observation could throw some light on the research of internal erosion from the view of particle scale.

New Method for Internal Pore-Water Pressure Measurements

Abstract The triaxial test is the most common procedure performed in a geotechnical laboratory to investigate the mechanical behavior of soils. However, often only global pore-water pressure (pwp) is measured at the bottom of specimen during conventional triaxial tests, which cannot detect the variation in internal pwp values to represent the true effective stress path adjacent to the failure surface. Here, a modified triaxial testing apparatus capable of measuring internal pwp within the soil using a filterless rigid piezometer (FRP) is outlined. To validate the effectiveness and capability of this novel test method, a series of consolidated undrained tests were conducted on saturated loose and dense sand. The FRP measurements provide a reliable pwp response, especially at pressures above 400 kPa where the FRPs have a faster response than the base transducer. Moreover, the internal pwp measured by FRPs during the initiation of shearing in loose sand can capture the rapid development of excess pwp before liquefaction or failure. The results also show that there are increases of 25 % in average peak strength of the loose specimen and 8 % in average residual strength of the dense specimen with internal pwp measurement, respectively, compared with only global pwp measurement because of the FRP installation. However, FRP installation appears to have no apparent effect on average peak strength of the dense specimen and average residual strength of the loose specimen. The new triaxial testing method can be applied to study the response and distribution of pwp at specific zones within the soil.

Investigation of the mechanical behavior of salinized agricultural soils using unsaturated triaxial tests and a constitutive framework

The salinization of agricultural soil is a common issue of concern. However, the coupling relationship between soil chemical properties and mechanical behavior has been largely ignored. A constant water content triaxial test was conducted by controlling suction on unsaturated agricultural soils collected from paddy fields. The soil samples were diluted with different salt solutions (a distilled water, a sodium chloride (NaCl) solution and a calcium chloride (CaCl2) solution) to investigate the influence of salinity on the mechanical behavior of soils. The pore water pressure of silt loam was significantly influenced by the pore water salinity, while the pore water pressure of silty clay was significantly influenced by the net normal stress. The results showed that the salt type and concentration significantly affected the cohesion value of silt loam. An empirical constitutive model that incorporated osmotic suction was presented in this paper to explain and quantify the effect of pore water salinity on the shear strength of silt loam. Osmotic suction was considered an independent stress variable in the constitutive model, unlike the salt type and concentration. The Barcelona unsaturated constitutive model explained how the pore water salinity affected the mechanical behavior of agricultural silt loam. With an increase in the osmotic suction in silt loam, the yield surface expanded to both sides of the original ellipses, resulting in an increase in cohesion. The constitutive framework considering osmotic suction provides an improved prediction of the mechanical behavior of agricultural soil under natural conditions subjected to salinization/desalinization. This framework can be implemented in a stabilization plan when the soil and salt are involved in agricultural activities.

Effects of drying-wetting cycles on the salinity and the mechanical behavior of sebkha soils. A case study from Ain M'Lila, Algeria

Sebkha soils are defined as problem soils located in arid, semi-arid, and coastal areas. Generally, they are fine soil, composed of silt, sand, and clay, which are cemented by different salts (e.g., halite, gypsum, and calcite). In nature, sebkha saline soils are exposed to different drying and wetting (D-W) cycles. However, these cycles have a significant effect on the mechanical behavior of these soils. This study aims to characterize the chemical, mineralogical, and geotechnical properties of sebkha soil using an experimental approach. We focus on the effects of D-W cycles on the unconfined compressive strength (UCS) and salinity of sebkha soils from Ain M'Lila, Algeria. In addition, these D-W cycles were applied to the samples dried in the open air to achieve the targeted water content (water content values of 7%, 11.4%, and 13%). The results obtained show that the UCS increases with decrease in water content and decreases with an increase in the number of D-W cycles. In addition, these cycles affect the salinity of the sebkha soil. Indeed, a significant decrease in soil salinity was recorded with an increase in the number of D-W cycles. Finally, a relationship was found between the salinity of the soil and UCS. The latter decreases with a decrease in soil salinity; this relationship becomes very significant for low water content values of 7% or less.

Improving mechanical behaviour of collapsible soils by grouting clay nanoparticles

The primary geotechnical concern of collapsible soils such as loess is their hydromechanical instability. Upon wetting, metastable aggregates disintegrate, leading soil to collapse under the applied load or self-weight. In situ chemical stabilisation, such as grouting, is a favoured option to improve soil mechanical behaviour; however, the low permeability of loess limits the application of permeation grouting in such deposits. Here a new approach is presented based on the injection of dilute suspensions of montmorillonite clay nanoparticles to improve mechanical behaviour of low permeable loess. In addition to clay, the grouting behaviour of an ordinary cement material was evaluated as a typically favoured soil stabiliser. Reconstituted specimens were also prepared by mixing dry clay or cement particles with soil at similar contents and curing time to compare with the grouting method. SEM images were also taken from the cured samples to visualize the soil fabric. Results revealed that clay suspensions feature a high-mobility in the soil medium as well as a remarkable performance in reducing the collapse potential due to: (1) clay effective particle size (∼0.25μm) that facilitates its mobility in soil, and (2) formation of evaporation-driven solid bridges that reinforce the interparticle bonds during post grouting drying. Results encourage the application of clay nanoparticles over cement for an economical and eco-friendly grouting approach to improve the mechanical behaviour of low permeable collapsible soils.

Role of industrial based precursors in the stabilization of weak soils with geopolymer – A review

The performance and durability of any building component do not only depend on the quality of construction material used but is also defined by the ground condition beneath the structural foundation. Soil properties are difficult to predict and change depending on the soil profile location. Expansive soils, sulfur-rich soils, and hydrocarbon-contaminated soils are considered the most vulnerable due to their sudden shrink-swell assets, pollutants, and complex clay mineral contents. Soil untreated for engineering applications has never been recommended. Numerous geotechnical techniques and natural or man-made additives are available to improve the engineering performance of these soils. But most of those techniques are obsolete due to poor performance. To elucidate this, in recent years, the geopolymer has been introduced in the form of an alkaline activated solution as an alteration to the conservative methods of soil stabilization. It was also hoped that using geopolymer in soil stabilisation would reduce resource exploitation and pollution and improve expansive soil engineering performance. This review examined whether strengthening poorly stabilised soil can improve engineering performance while minimising environmental impacts. The objective of the review was to analyse whether they could be accomplished by accumulating different industrial precursor additives or activators with an alkaline activated solution for soil mechanical behaviour improvement.

Remediation Trend of Engineering Behavior of Wastewater Contaminated Clay Using Iron Nano Oxide: Experimental Studies

Soil polluted with urban wastewater due to defect of wastewater disposal and leakage from wastewater channels is a common type of pollution in urban areas which in addition to environmental damage, has significant effects on soil engineering parameters. In present study, effects of municipal wastewater on mechanical behavior of soil and clay microstructure was studied, and then effects of iron oxide nanoparticles on remediation trend of contaminated soil was investigated. To achieve this, unconfined compressive strength (UCS), collapse and SEM analysis tests were performed on contaminated samples containing 20%, 60% and 100% wastewater at 1, 3 and 5 months and also on contaminated soil remidiated with 0.5-4% Iron nano oxide. Results showed that wastewater reduces shear strength of clay and this decreasing trend increases with increasing percentage and contamination duration. UCS of soil contaminated with 100% wastewater decreased by 49% after 5 months of contamination. Also, wastewater in the soil caused to soil collapse after 5 months . SEM images showed the clay structure became clotted after contamination and soil pores increased compared to natural soil. Improvement phase results showed that by addition of Iron nano oxide to contaminated soil, shear strength significantly increased, and optimal percentage of Iron nano oxide was 3% in which UCS increased by 105.2%. By increasing the percentage of Iron nanoxide, intensity of collapse index of contaminated soil decreases. Best case senario, final strain of soil decreases by 43.4% compared to contaminated soil. Therefore, utilizing Iron nanooxide is recommended to improve engineering behavior of contaminated clay.

Scott William Sloan 1954–2019

Scott Sloan (1954–2019) was a leader of academic engineering in Australia and beyond, as evidenced by his numerous professional accolades and important research achievements, which have had significant impact on his chosen profession of geotechnical engineering. Educated in Australia and the United Kingdom, he returned to Australia in 1984 and developed a large and active research group at the University of Newcastle, and tackled a wide range of important problems in civil and mining engineering. These include the development of computational methods to predict the mechanical behaviour of soil and rock masses, and his pioneering methods to predict the collapse states of structures made of, on, and in, earth materials, allowing engineers to design cheaper and safer civil infrastructure around the globe. Sloan established long-standing international collaborations and was awarded many honours for his research achievements. He was also a keen and skilful fisherman and a more than competent blues guitar player.

Mechanical behaviour of bimodal kaolin clay with aggregates

Soil structure has been recognised as a key feature in the understanding of soil’s mechanical behaviour, and research efforts have been made trying to relate them. However, the main difficulties encountered are that numerous factors can simultaneously affect the mechanical behaviour of soils. Among these factors, the presence of aggregates is decisive for the fabric configuration of bimodal soils. The aim of this paper is to evaluate the effect of aggregates on the mechanical behaviour of bimodal soils with no mineralogical variability. For this purpose, aggregates of Kaolin Clay were obtained by compaction at high stresses and bimodal samples with different aggregates content were produced. All samples were subjected to unidimensional consolidation and direct shear tests. Results showed that the increase in aggregates content and the presence of macro-pores affected compressibility, decreasing pre-consolidation stresses and altering compressibility coefficients. The increase in interaction between aggregates generated an increase in friction angles in samples with aggregates, which also impacted their volumetric behaviour during shearing. Thus, the present work contributes to a better understanding of the mechanical behaviour of bimodal soils influenced exclusively by the presence of aggregates.

Influence of Soil Particle Size on the Engineering Properties and Microstructure of a Red Clay

Particle size exerts a significant influence on the mechanical behavior of soil. However, insufficient research has been carried out on red clay formations, which are widespread in some Chinese provinces. Here, using unconfined compressive strength (UCS) tests, wetting–drying (WD) tests, and low-temperature nitrogen adsorption tests, we examined the relationship between the particle size and a number of mechanical and microstructural characteristics of a red clay outcropping at a construction site in China. Our results suggest that, depending on the surface area, porosity, particle size, and dry density, the failure mechanism in UCS tests will be different. That is, as the particle size increases, the failure mode of soil changes from split failure into shear failure. In addition, as the dry density increases, the UCS of the soil sample is significantly improved, and its total porosity and fractal dimension decrease. We also evaluated a dependence on particle size and the number of WD cycles on the distribution and size of cracks in WD tests. We conclude by suggesting that particle size, dry density, and WD behavior should all be taken into account in roadbed designs in red clay formations.

Effect of root orientation on the strength characteristics of loess in drained and undrained triaxial tests

Ecological engineering measures are gaining popularity in the control of mountain hazards, particularly in shallow landslides, in which plant roots improve the shear strength of shallow soil. To measure such improvement, a series of drained and undrained triaxial tests were performed to investigate the role of Cunninghamia R. Br roots in loess soil mechanical behavior collected from Longchi Forest Center, southwest China. The specimens were prepared by distributing roots in four (4) distinct spatial orientations types, i.e., Horizontal, Vertical, Horizontal-Vertical (grid), and Randomly mixed in the soil. All specimens were first fully saturated and subsequently sheared in compression tests under drained and undrained conditions. The test results are evaluated in terms of monotonic stress-strain behavior, volume change, development of excess pore water pressure, and critical state behavior. The results showed that the addition of roots increased the soil shear strength, provides additional resistance to volumetric deformations and increased the positive excess pore water pressure as compared to plain loess soil. The results also revealed that the mechanical response of the soil-root composite depends on the type of root orientation. The shear strength improved highest with horizontal-vertical (grid) root orientation in both drained and undrained conditions among four root orientations. In contrast, the horizontal root orientation showed the least shear strength improvement. Additionally, for the same root orientation type, the shear strength improvement was more pronounced in undrained conditions compared to drained conditions. The plain and soil-root composite shear strength parameters showed that the addition of roots increased the cohesion with little effect on the mobilized angle of friction in both drained and undrained conditions. The findings of this research will provide a strong baseline for developing a predictive constitutive model for soil–root composite.

Modelling the behaviour of unsaturated non-active clays in saline environment

The chemical composition of pore fluid and matric suction rule the mechanical behaviour of soils. In case of clays, their fabric changes in line with those variables. Since both the increase in matric suction and salinity cause a transition from an open to a close microstructure of low and medium activity clayey materials, a unique framework could tackle problems where salinity and saturation changes are expected.This paper presents a simple elasto-plastic model capable of reproducing the behaviour of unsaturated clayey soils in saline environments. Changes in the pore fluid composition are addressed through the use of osmotic suction as a variable. The proposed model extends the Barcelona Basic Model for partially saturated soils to consider the effect of osmotic suction.The model, implemented in the Thebes code, is calibrated for Boom Clay. The reproduced tests include mechanical loading at different matric and osmotic suctions in oedometric conditions, as well as more complex chemo-mechanical stress paths. Despite the simplicity of the formulation, the agreement between the experimental results and the simulations is encouraging. It seems that the modelling approach addresses the most important features of partially saturated soils with saline pore fluid which are slightly or moderately expansive.

Clays Are Not Created Equal: How Clay Mineral Type Affects Soil Parameterization

AbstractClay minerals dominate the soil colloidal fraction and its specific surface area. Differences among clay mineral types significantly influence their effects on soil hydrological and mechanical behavior. Presently, the soil clay content is used to parameterize soil hydraulic and mechanical properties (SHMP) for land surface models while disregarding the type of clay mineral. This undifferentiated use of clay leads to inconsistent parameterization, particularly between tropical and temperate soils, as shown herein. We capitalize on recent global maps of clay minerals that exhibit strong climatic and spatial segregation of active and inactive clays to consider spatially resolved clay mineral types in SHMP estimation. Clay mineral‐informed pedotransfer functions and machine learning algorithms trained with datasets including different clay types and soil structure formation processes improve SHMP representation regionally with broad implications for hydrological and geomechanical Earth surface processes.

Influence of drainage and root biomass on soil mechanical behavior in triaxial tests

Influence of drainage and root biomass on soil mechanical behavior in triaxial tests

Pet fiber reinforced sand performance under triaxial and plate load tests

Annually, large amounts of waste Polyethylene Terephthalate (PET) bottles are discarded worldwide, although their properties can be useful in engineering works, such as soil improvement. Thus, the influence of PET fibers on sandy soil mechanical behavior was assessed in the present work. Consolidated-drained triaxial tests were performed using a 0.5% addition of 1.4 (SF-1) and 3.3 dtex fibers (SF-2). Afterward, plate load and slopes tests in the laboratory scale model were carried out for the most effective fiber. Overall, the inclusion of both fibers improved the stress-strain behavior, evident by greater absorbed strain energy in the reinforced soil. The insertion of 1.4 dtex PET fibers enhanced the internal friction angle of the soil from 31.9º to 44.3º, while a 29.7º value was obtained from 3.3 dtex fibers. Also, a cohesion intercept portion was identified in both composites, corresponding to 22.5 and 58.7 kPa for SF-1 and SF-2, respectively. The PET reinforcement reduced both vertical and horizontal deformation and altered the soil failure mechanism. The settlement reduction in fiber-reinforced sand is stress magnitude dependent, decreasing about 81% for stresses above 300 kPa, in which settlement of 125.3 mm from unreinforced sand was reduced to 23.6 mm by fiber insertion at 400 kPa. At the maximum comparable settlement, a 375.7% enhancement was seen in the bearing capacity, increasing from 240 kPa to 1141.6 kPa. In addition to a better understanding of soil-PET mixture, the results contribute to encouraging sustainable applications in engineering, such as embankment, shallow foundation, and retaining wall layers.