Soil Fabric Research Articles

Influence of Initial Anisotropy, Stress Path and Principal Stress Rotation on Monotonic Behavior of Clean and Mixed Sands

It is widely accepted that soil behavior is complicated taking into account soil anisotropy owing to the fact that this phenomenon arises from oriented soil fabric or structure forged in the deposition stage. In this study, a review of major findings of authors’ previous studies are presented with the main focus on soil anisotropy using extensive experimental results incuding Triaxial (TXT), Simple Shear (SSA), and Hollow Cylinder (HCA) apparatus. Effects of initial anisotropy, fabric evolution, stress path, principal stress rotation and intermediate stress state are evaluated for a crushed silica sand. In addition, the effects of Portland cement content and granulated rubber contents on anisotropic behavior of the sand are investigated. Bender elments are mounted on triaxial specimens both in vertical and horizontal directions to measure the shear wave velocity and hence maximum shear modulus at the end of consolidation as well as during shearing up to large strains at critical state condition, as an index of evaluating the fabric evolution. The effects of principal stress rotation and stress paths reveals the crucial role of soil anisotropy on the behavior of clean sand. However, adding either cement or granulated rubber to the sand has considerably decreased anisotropy.

Cyclic resistance of saturated silt under wave-induced non-proportional loading

The significance and complexity of cyclic behavior of saturated silt under non-proportional loading are still of great concern in practice, due to the highly inherent anisotropy of soil fabric. This paper presents an experimental investigation conducted in an automated hollow cylinder apparatus into the undrained anisotropy and cyclic resistance of a saturated marine silt under wave-induced non-proportional loading, which is replicated by simultaneous changeover in magnitudes and directions of the principal stress. Special attention is paid to the influence of cyclic shear mode and stress path, characterized by the cyclic stress ratio (CSR) and the ratio (δ) of the amplitude of deviatoric stress components (i.e. deviator stress and torsional shear stress), on the pore pressure response and deformation characteristics. The cyclic stress path is not a negligible factor for the cyclic resistance of saturated silt in the non-proportional loading, but had significant impact. The CSR can not properly characterize the resistance of silt to cyclic shearing, involving continuous rotation of the principal stress. This observation is considered to be directly associated with the soil fabric anisotropy. Remarkably, for all loading patterns investigated, the pore pressure ratio ru is uniquely correlated with the generalized shear strain γg, rather than to the CSR. Consequently, a closed-form expression is proposed to relate γg and ru, which can be used to predict the onset of failure as well as the pore pressure at a specific strain. By using the equivalent cyclic stress ratio (ESR) to characterize the cyclic undrained resistance of saturated marine silt (in terms of the number of cycles required to failure, NL), a virtually unique correlation between ESR and NL can be established for all the non-proportional loading investigated.

DEM modelling to assess internal stability of gap-graded assemblies of spherical particles under various relative densities, fine contents and gap ratios

It is believed that the relative density (Dr) can affect the internal stability of the gap-graded soils and hence the erosion of their fine particles (i.e. susceptibility to suffusion). This paper investigates the influence of Dr on the contribution of fine particles to soil fabric. A new procedure is proposed to produce samples with target Dr using the discrete element method (DEM). DEM simulations were carried out using spherical particles. Particulate scale analysis of variation of stress reduction factor (αDEM), the evolution of contact type and fine particle coordination number (Zfine) with Dr reveals how Dr affects packing stability. The results show that packings with a fine content of 35% and the gap ratio in a range of 4–7 are in the transitional zone in which they are unstable initially and become internally stable as Dr increases. The behaviour of gap-graded soil in the transitional zone is governed by fine-coarse contacts, but fine-fine contacts dominate the behaviour when soil becomes internally stable. Both αDEM and Zfine are reliable parameters in determining internal stability of gap-graded soils. Finally, the correlation between the results and macro-scale matrix phase diagrams confirms the validity of micro-scale information to describe the underlying phenomenon.

A generalized water retention model with soil fabric evolution

This paper introduces a novel soil–water retention curve model that considers two different mechanisms of water retention – namely capillarity and adsorption – and their evolution with soil fabric along a generalized stress path. The model is formulated based on a new developed framework, which is justified against experimental evidence and incorporates the following developments: (i) the characteristics of the capillary and adsorption water retention curves are identified, and an ad-hoc water retention model is developed for each mechanism; (ii) the capillary and adsorption water retention curves are related to the experimentally determinable water retention curve thanks to a newly defined parameter named “contribution factor”, which changes with the evolution of the fabric. The proposed model is an elastoplastic water retention model and it allows to describe satisfactorily the water retention capacity of different soils. All simulation results support the statement that the adsorptive mechanism plays a crucial rule in the high suction range while capillarity is important in the low suction range. Moreover, it is shown that the developed capillary water retention curve allows to easily compute, at any state of the soil, a suitable capillary degree of saturation; the latter, adopted within the generalized effective stress concept, makes it possible to interpret shear strength data under different saturation conditions properly.

Influence of Bleach Activators in Removing Different Soils from Cotton Fabric

The influence of adding Sodium Perborate Tetrahydrate (NaPB) and tetraacetylethylenediamine (TAED) on the efficiency of removing soils from cotton fabric was evaluated in the study. NaPB as inorganic peroxide and TAED as a bleach activator were added to a commercial washing powder agent. Four standard soils applied on cotton fabric (EMPA standard soiled fabrics) were used in the study, i.e. 101 – carbon black/olive oil, 114 – red wine, 116 – blood/ milk/ink and 160 – chocolate. The washing of fabrics was conducted in accordance with the SIST EN ISO 105-C06 standard at 40, 60 and 90 °C in Launder-Ometer apparatus. The washing efficiency was evaluated by determining the CIE L* colour coordinates of the unwashed and washed fabric samples, and the difference in ΔL* colour coordinates among them. The results showed that NaPB and TAED improve the efficiency of washing for two standard soils, have no effect on one, and deteriorate the washing results of one standard soil.

Spatial distributions of ozonolysis products from human surfaces in ventilated rooms.

Ozone has adverse effects on human health. Skin oil on the human surface acts as an ozone sink indoors, producing oxidation products that can cause skin and respiratory irritations. Concentrations of ozone and oxidation products near human surfaces, including the breathing zone, can be modulated by indoor ventilation modes and human surface conditions. The objective of this study is to examine concentrations and spatial heterogeneity of ozone and ozonolysis products under representative ranges of indoor ventilation, clothing, and breathing conditions. Using computational fluid dynamics (CFD) simulation in conjunction with a chemical kinetic model, details of ozone reactions with the human surface and subsequent chemical reactions are examined. The results show that primary ozonolysis products are concentrated near the soiled clothing, while the secondary products are relatively well distributed throughout the room. Increasing indoor air mixing enhances the ozone deposition to the human surface, thereby resulting in higher emission rates of oxidation products in the room. Soiled clothing consumes more ozone than clean clothing and accordingly produces~65% more primary products and ~15% more secondary products. The results also reveal that unsaturated hydrocarbons from the human breath, such as isoprene, contribute to only ~0.5% of ozone removal compared to ozone deposition to the human surface.

Experimental investigation of both the disturbed and undisturbed granitic saprolite soil

Granitic saprolites are abundant in many regions around the world and they are widely employed in various engineering projects. Behavior of such kinds of soils is not sufficiently understood and our knowledge about the fundamental behavior of saprolites is to a far less extent than the sedimentary soils. Owing to the limited knowledge, many problems occurred in the engineering applications that used saprolites as a construction material. This study presents results of a set of conventional drained and undrained triaxial compression shearing tests on the granitic saprolites in both the disturbed and undisturbed conditions. This study showed that the soil fabric was the paramount factor governing on the soil stress–strain response rather than the soil bonds. Under the drained shearing condition, the undisturbed soil revealed a strain-softening behavior with a dilative response at the low consolidation stress level, while a contractive response was present at the high consolidation stress levels. However, the disturbed soil showed a strain-hardening behavior with a contractive response, regardless of the consolidation stress levels during the drained shearing. The undrained response was complicated, as the soil showed both the contractive and dilative responses with phase transformation points, regardless of the soil condition (i.e., disturbed or undisturbed) and the consolidation stress levels. The bond effect of the intact soil persisted during the consolidation stage; however, its effect did not extend to the large strain-controlled shearing stage, where the tangential stiffness suddenly decreased at the axial strain of 1.5%.

Enhanced Strength Properties of Dredged Marine Sediments Using Electrokinetic Stabilization Method

Nearshore’s facilities are often require frequent and regular maintenance dredging in maintaining appropriate water depths and enlarging the access channel and turning basin. A large amount of sediment was spawned from the dredging work. The dredged marine sediments (DMS) are not apt to be used in construction activities because of its poor geophysical properties. The purpose of this research is to study the improvement in moisture content and strength of DMS by using electrokinetic (EK) method. DMS are classified as a high plasticity silt (MH) with 240.74 % of its natural water content. Stainless steel plate was invoked as the electrode, while distilled water (DW), citric acid (CA) and calcium chloride (CaCl2) were applied as the stabilizing agents. The aforementioned stabilizers are electrically injected into the DMS which causing flow of the solutions through the pores in DMS under 50 V/m of applied direct current (DC). The results of treated DMS are presented in moisture content, undrained shear strength and SEM-EDX analysis. The EK treated DMS shows it increases in strength in the dry zone area after the 14 days treatment. The dry zone area was created near the anode and wet zone was made near the cathode. The application of calcium ions in the treatment had increased the strength and alters the pattern of the soil fabric. Largely, EK has significantly improved the quality of DMS even though the strength increase observed was not homogeneous throughout the specimen.

Experimental study on the effect of fine contents on internal erosion in natural soil deposits

Seepage-induced internal erosion is observed in both artificially engineered fill structures and natural soil deposits. Fine content is of great significance for the fabric of soil. This paper aimed to determine the critical fine contents of natural soil deposits beyond which the internal stability of the mix was distinctly altered and illustrate the internal erodibility from the viewpoint of fabric. To this end, a fixed-wall permeameter capable of accurately detecting the critical hydraulic gradient of erosion initiation and collecting the cumulative eroded soil mass at a constant inflow rate was developed. Silty clay particles and sandy gravel particles extracted from original soil were employed to reconstitute specimens with fine contents ranging from 0 to 100%. Porosity measurement, seepage testing, and direct shear testing were conducted on remolded samples. Companion control specimens were tested under different flow rates to verify the applicability of the experimental device. The results indicate that according to critical fine content, the fabric of the soil samples with different fine contents could be split into coarse-particle-supported structure (CPSS), fine-particle-supported structure (FPSS), and transitional coarse–fine-particle-supported structure (TCFP). The newly developed experimental device provides a feasible methodology to investigate the internal erodibility of natural soil deposits. Different fabrics correspond to disparate shear strengths and distinct erosion characteristics, including the critical hydraulic gradient of erosion initiation, cumulative eroded soil mass, and average hydraulic conductivity. For coarse-particle-supported structure specimens, the coarse particles predominantly govern the mechanical and hydromechanical properties. An increase in fine content within pores formed by coarse particles could increase shear strength and reduce susceptibility to internal erosion. The mechanical and hydromechanical properties of FPSS specimens were basically controlled by fine particles. Coarse particles suspended in a fine matrix could somewhat increase the soil’s shear strength and reduce internal erodibility. TCFP specimens were most vulnerable to internal erosion in terms of minimum critical hydraulic shear stress and maximum cumulative eroded soil mass. It is essential to expand the scope of research to cover the transitional coarse–fine-grain-supported structure instead of remaining limited to the coarse-grain-supported structure.

Experimental Investigation on Small-Strain Stiffness of Marine Silty Sand

The significance of small-strain stiffness (Gmax) of saturated composite soils are still of great concern in practice, due to the complex influence of fines on soil fabric. This paper presents an experimental investigation conducted through comprehensive bender element tests on Gmax of marine silty sand. Special attention is paid to the influence of initial effective confining pressure ( σ c 0 ′ ), global void ratio (e) and fines content (FC) on Gmax of a marine silty sand. The results indicate that under otherwise similar conditions, Gmax decreases with decreasing e or FC, but decreases with increasing FC. In addition, the reduction rate of Gmax with e increasing is not sensitive to σ c 0 ′ , but obviously sensitive to changes in FC. The equivalent skeleton void ratio (e*) is introduced as an alternative state index for silty sand with various FC, based on the concept of binary packing material. Remarkably, the Hardin model is modified with the new state index e*, allowing unified characterization of Gmax values for silty sand with various FC, e, and σ c 0 ′ . Independent test data for different silty sand published in the literature calibrate the applicability of this proposed model.

Volume change and compressive strength of an alluvial soil stabilized with butyl acrylate and styrene

The volume change and uniaxial compressive strength of an alluvial soil stabilized with co-polymer of Butyl Acrylate and Styrene (CBAS) are presented in this paper. CBAS has low viscosity improving its adsorption into the soil microstructure and its ionic structure helps the formation of electrostatic bonding within the clay fabric. CBAS can be applied with ease by directly mixing or spraying onto soils, which potentially makes it favorable for use in compacted fills. Treatment of soil specimens with CBAS indicated significant improvement in the shrinkage and compressibility characteristics with just a percentage addition of 5% by dry mass of soil. On the other hand, obtaining an improvement in the swelling behaviour required at least a 10% addition of CBAS. The secondary compression rate and the uniaxial compressive strength are improved significantly even at very low percentages of treatment. Microstructural changes in the soil fabric are observed with the use of scanning electron microscopy, which indicated that CBAS-soil interaction can be achieved effectively by wet mixing.

A unified soil thermal conductivity model based on artificial neural network

An accurate prediction of thermal conductivity (k) of unsaturated soils is a challenging problem in geothermal applications because k is affected by various factors such as soil fabric, water content, dry density, soil mineralogy and type. This study proposes a unified soil thermal conductivity model to consider these influence factors based on a screened artificial neural network (ANN) approach. Two hundred and fifty-seven (257) thermal conductivity measurements of unsaturated soils were first collected from the literature to compile a database. The ANN approach constrained with model complexity optimization and monotonicity control was then utilized to overcome the potential sample insufficiency problem in order to establish reliable correlations between k (represented by an empirical coefficient) and its influence factors including dry density (ρd), porosity (n), saturation degree (Sr), quartz content (mq), sand content (ms) and clay content (mc). Using this approach, some easy-to-use ANN-based contours for predicting k were developed to guide engineering practice. Results revealed that ANN-based predictions of k by the developed model matched experimental data with enhanced accuracy as compared with some benchmarking thermal conductivity models. The model can rationally consider the effects of multiple influence factors and their coupling effects on k in a quantitative and systematical way.

"The Ring".

Bob had not heeded our advice to remove the gold band from the left third finger. For him, it was a symbol so strong and powerful that the thought of taking that away from Jackie was just unbearable. She had already lost too much to dementia: her affable personality, her independence, her memories, and her language. Still, we were pragmatists, it would be lost. We had been through this before. Surely such an important valuable should be kept at home for safe keeping and not remain with Jackie on the dementia unit. Bob smiled at us, his blue eyes twinkling, stating: “It has been on her finger since she was 19. It needs to stay with her so that she will know I carry her in my heart forever. She will know if I take it off.” Jackie adjusted poorly. First, leaving the unit unaccompanied, setting off a massive search. Then came the refusal of care, the hitting and slapping when frightened, the pacing and looking for her beloved husband. Arms flew in protest to the most seemingly benign requests, like changing soiled clothes. Soon the fragile skin on the arm was open from these protests and the break in its integrity led to an infection. The swelling of her hand would commence in the next 48 hours, making the ring little more than a tourniquet. We had indeed been right. Trying to mitigate our indignity, we called Bob to tell him it would now have to come off. He relented, knowing that it might be causing her physical pain at this juncture. Ring removal is not something that they teach in all internal medicine residencies, and it was certainly not something I learned in medical school. Yet, as a geriatrician, I had performed this task many times. Ironically, the rings that proved to be the most stubborn and hard to remove were not those that had more sentimental value or those that depicted a stronger bond with a life partner, but those that had been less expensive. The cheaper versions held steel shanks in the core, making extraction much more difficult than those made of pure gold. The ring snapped with two revolutions of the cutter, a sure sign that the ring had been as pure in gold as Bob's heart had been all 50 years of marriage. We removed it rather unceremoniously, not fathoming the full meaning of the act and the impact on Bob or our resident. Bob held it for a moment and turned it over in his hand, caressing the band that still bore the date and his initial message to his bride. Tears spilling over in his eyes, he choked “I love you.” As a clinician, I have witnessed patients with advanced dementia having moments of intense clarity before, but I was not prepared for Jackie to stop resisting the attempt to bandage her arm, look at Bob, and return the “I love you” back. We all desperately needed that. For the nurse and me, that moment was a stark reminder of why Bob had struggled so much to allow us to take off the ring. At some point during the endless set of tasks that needed to be done to care for a person with advanced dementia, we had shifted to a point of pragmatism that partially belied our ability to be compassionate and understanding. Her words helped us remember to nurture that again. For Bob, he left knowing that his beloved returned his feelings through the maelstrom of her disease. For Jackie, it provided seconds of respite from what must be a frightening world with complex, inconstruable signals through which the only thing that can permeate is love.

Investigation of the parallel gradation method based on the response of track-bed materials under cyclic loadings

Abstract Ballast/fines mixture is often found in railway substructure and the overall behaviour of tracks is strongly dependent on the mechanical behaviour of this mixture. Since directly testing such mixture with large grains is limited with common laboratory equipment, the consideration of a model material at smaller size is advisable. Parallel gradation method is widely used for this purpose. This study assesses the validity of this method in the case of ballast/fines mixture. Large-scale cyclic triaxial tests were carried out on the ballast/fines mixture at six volumetric coarse grain contents. The results obtained were analysed, together with those obtained previously from small-scale triaxial tests on a microballast/fines mixture whose microballast grain size distribution was determined by applying the parallel gradation method. The cyclic parameters (permanent strain and resilient modulus) were obtained for the two types of mixture. Results show that for all mixtures two distinct soil fabrics can be identified according to the variations of permanent strain and resilient modulus with the volumetric content of coarse grains fv: a fine-fine contact structure for fv ≤ 20% and a grain-grain contact structure for fv ≥ 35%. In the case of fine-fine contact structure, the permanent strains and resilient modulus values of the ballast specimens are consistent with those of the microballast specimens, evidencing the validity of the parallel gradation method. In the case of grain-grain contact structure, the permanent strains and resilient modulus values are found to coincide globally at the two scales, also justifying the validity of the parallel gradation method, the slight differences between the two scales being attributed to the irregular grain sliding and the distribution of the fines soils.

Fabric evolution of granular soils under multidirectional cyclic loading

Cyclic behavior of granular soils under multidirectional shaking is significantly different from that under unidirectional loading. In this study, a series of undrained simple shear simulations were conducted using a discrete-element method (DEM) under unidirectional and multidirectional loading conditions. Although the excess pore water pressure within a sample cannot reach the initial confining pressure, large shear strains of a similar amplitude still develop in samples under multidirectional loading. The simulation results further illustrate that granular soils have vastly different liquefaction resistance under different loading conditions. Evolution of soil fabric is also quantitatively studied in terms of inter-particle contacts and particle-void distribution. The same “stable state” of soil fabric will be reached under different multidirectional loading paths, which corresponds to that of a post-failure hardening state under unidirectional loading. The DEM study provides a new perspective in terms of microstructure evolution of granular soils under a variety of loading conditions.

Determination of 7 nitrobenzene compounds in soil, glass, and cotton cloth by ultrahigh performance liquid chromatography

An ultrahigh performance liquid chromatographic (UHPLC) method has been developed for detection of 7 nitrobenzene compounds (nitrobenzene, 2-nitrotoluene, 1, 3, 5-trinitrotoluene, 3-nitrotoluene, 3, 4-dinitrotoluene, 2, 6-dinitrotoluene, 2, 4, 6-trinitrotoluene) in soil, glass and cotton cloth. Analytes were extracted twice by acetonitrile. 200 μL of the extract solution was pipetted to a tube with 800 μL water. After filtration by a nylon membrane, the analytes were determined by UHPLC with a phenyl modified column. The linear correlation coefficients of more than 0.99 were achieved. The detection range was examined from 0.05 to 5.0 mg/L. In this method, the limit of detection (LOD) of 0.5 mg/kg was obtained. Recoveries in spiked samples were more than 87.8%, and the relative standard deviations were less than 8.5%. This method is simple, and of good recovery, allowing the detection of nitrobenzene compounds in soil, glass and cotton cloth.

A statistical inference of hydraulic shear and clogging in internally unstable soils

Water-retaining earth structures often experience cyclic hydraulic flow patterns, which are believed to alter the soil fabric. Gap-graded soils are identified to be internally unstable. These soils exhibit a change in their hydraulic conductivity when the critical hydraulic gradient is exceeded. The changes beyond the critical hydraulic gradient, however, are yet to be understood. This research study examines the unsteady nature of clogging and unclogging process in saturated gap-graded soils subjected to hydraulic pulses. A set of 60 min flow (suffusion) tests was conducted using a positive displacement pump to subject a cylindrical specimen to controlled hydraulic flow pulses. The global hydraulic gradient across the specimen was continuously monitored. The grain-size distribution of the soil was re-evaluated after the test. The hydraulic shear stresses induced by the flow pulses were estimated numerically and normalised over the maximum value. Similar trends of the hydraulic conductivity and the applied flow rates do not hold when the duration of the flow pulse is increased. A simple procedure based on statistical inference is proposed to visualise the temporal variation of the clogging and unclogging process subjected to the frequency and the phase shift parameters of the flow pulse.

Soil Fabric and Anisotropy as Observed Using Bender Elements during Consolidation

AbstractThis study examined the effects of soil minerals on soil anisotropy and determined the amount of changes in anisotropy during the consolidation process of soils. Soil fabric and anisotropy ...

Behaviour of cement-stabilised silty sands subjected to harsh environmental conditions

This work evaluated the effect of three distinct amounts of fines, Portland cement and dry unit weights on the accumulated loss of mass (ALM), maximum shear modulus at small strains (G0) and tensile strength (qt) of stabilised sands subjected to wetting–drying cycles. Tensile strength test results showed that addition of fines to sand stabilised with cement increased its tensile strength, irrespective of the dry unit weight (γd) and cement content in the mixture. Increasing the amount of fines in compacted cement-stabilised silty sand specimens subjected to wetting–drying cycles reduced the ALM and increased the G0 and qt of the mixtures. This may be due to the fact that specimens with larger amounts of fines have more contact points among the particles, which provides better opportunities for the cement to develop more efficient bonds within the soil fabric, thus improving its mechanical performance. An increase in the cement content and γd of the compacted cement-stabilised silty sand specimens reduced their ALM and increased G0 after each one of the 12 wetting–drying cycles. The G0 and qt of cement-stabilised silty sand specimens with fines increased up to the sixth cycle, remaining practically constant after that, when these specimens were subjected to wetting–drying cycles.

The morphology and elemental variation for contaminated clay soil using Energy Dispersive X-Ray Spectrometry

It is known that the stabilization of normal soils with chemical substances will gradually affect their properties like shape, size and soil particles arrangement. The current study concerns with artificially contaminated clayey soils immobilized by fly ash waste materials and quicklime (CaO). In this research, the time-dependent factor changes the morphology of stabilized – contaminated soil. Energy Dispersive X-ray Spectrometry is performed to further examine components on the clay particles’ surface. The results showed that with an increase in hardening time, morphology analyses by FESEM shows a transformation of soil fabric due to the effect of chemical treatment, and due to the production of cementitious pozzolanic compounds (CSH and CASH). However, with the presence of contamination, it can notice a transformation in the fabric of clay particles towards a more flaky nature at the early curing time due to precipitation of heavy metals as hydroxide or sulphates on the surface of particles. Regarding the EDAX analysis, the Al:Si ratio for cement - fly ash treated clayey soil decreases over time. This is attributed to the increased release of alumina from the mineral of clay structure. However, an increasing Ca:Si ratio is observed, especially after 100 days related to the formation of the portlandite compound from cement hydration over time. While, it is detected variation in these ratios with respect to contaminated soil with time.