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Ground settlement resulting from consolidation may lead to tilted buildings, cracks in the pavement, damage to underground utilities, etc. Therefore, it is crucial to understand the consolidation behaviors (including primary consolidation and secondary compression) of the soil of the subgrade. There is a large amount of soft clay deposited in Nanjing, located in the Yangtze River Basin. The consolidation behavior of Nanjing soft clay can significantly affect foundation design and the cost of construction. In this study, experimental measurements of the consolidation behavior of Nanjing soft clay were conducted, and parameters (such as pre-consolidation pressure, secondary consolidation index and secondary consolidation ratio) related to consolidation were assessed. The concept of simulated over-consolidation ratio (OCRs) was proposed, and the close relationship between primary consolidation and secondary compression settlement and the OCRs of Nanjing clay was investigated. [ABSTRACT FROM AUTHOR]

The mechanical properties of agricultural materials influence not only the loads occurring inside agricultural silos, but also the design of several types of post-harvest machinery. The loads generated by these materials inside silos can be predicted with silo calculation methodologies from their mechanical properties. It has been known for many years that these properties are highly dependent on the moisture content of the material. However, to date, there are not many studies focused on its determination. The goal of this research is the determination of the internal friction angle, apparent cohesion, angle of dilatancy and apparent specific weight of maize when different moisture contents are applied. The equipment used for this study consisted mainly of direct shear and oedometer assay apparatus. The maize samples used were moistened using a climatic chamber. Moisture contents applied to maize samples ranged from 9.3% to 17.4%. Results similar to those provided by other authors were obtained for the internal friction angle, apparent cohesion and apparent specific weight. On the other hand, the values obtained for the dilatancy angle of maize as a function of moisture content could not be compared because nothing has been published so far. The values obtained for this parameter overlap with those published for this material under ambient conditions. In addition, for the samples tested, these results did not allow confirming the existence of a direct relationship between the dilatancy angle and the moisture content. Finally, the increase in moisture content led to an increase in apparent specific weight, which differed from that published in the literature. The values provided here can be used for the optimization of storage and handling structures for granular agricultural materials. [ABSTRACT FROM AUTHOR]

In some countries lacking sodium bentonite (NaB), polymer-modified calcium bentonite (CaB) has attracted attention for its application in sand-bentonite slurry trench cutoff walls to control groundwater contamination. Thus, this study used polyanionic cellulose (PAC), an environmentally friendly hydrophilic polymer, to modify CaB. The hydraulic and consolidation properties of cutoff-wall materials (including bentonite cake and backfill) containing CaB or modified CaB with 4% PAC (dry mass ratio, 4%PAC-CaB) under various stress conditions, CaCl2 solution concentrations, and bentonite contents were investigated through a series of experiments, including modified fluid loss, slump, Atterberg limit, oedometer, and rigid-wall hydraulic conductivity tests. The results show that the 4%PAC-CaB cake had better salt resistance and impermeability than CaB and NaB cakes under different stress and salt concentration conditions, and sand-4%PAC-CaB backfill had a significantly higher liquid limit, ideal water content, and compression index, and a lower coefficient of consolidation and permeability than sand-CaB backfill with the same bentonite content. More importantly, the addition of 4% PAC had a more significant effect on decreasing the permeability of the sand-CaB backfill than increasing the CaB content. Overall, 4%PAC-CaB is a promising modified CaB that can replace NaB for the construction of cutoff walls with excellent impermeability. [ABSTRACT FROM AUTHOR]

In this study, a Unified Soil Improvement Technique (USIT) that consists of prewetting, calcium lignosulphonate lime piles, fabric, and soil nail was applied to an expansive soil specimen to both accelerate the process and increase the effect of these techniques. 19 boreholes that had 0.45 cm diameter and 1.9 cm height were opened into an expansive soil specimen in an oedometer ring. Then, these boreholes were filled with a calcium lignosulphonate-water mixture prepared in a liquid form during the prewetting process. Thereafter, these boreholes were filled with a mixture including calcium lignosulphonate, water, and lime. Finally, a fabric was laid down over this specimen and seven pieces of soil nails were used for connecting the fabric and the lime piles. To sum up, the swelling potential of expansive soil specimens under 7 kPa decreased from 43.95 % to 1.58 % after 28 day curing period. The CBR swell of the USIT specimens, which waited in the humid room for 90 days, was measured as 1.14% under 7 kPa surcharge pressure and was measured as 0.4% under 25 kPa surcharge pressure. The significant changes in the swell potential values suggest that the Unified Soil Improvement Technique’s performance is better than calcium lignosulphonate-added lime piles in the improvement of expansive clays. [ABSTRACT FROM AUTHOR]

This study examines the combined impact of pre-test curing and soaking periods on the soil's resistance to collapse those results from treating gypseous sand with varying amounts of nanoclay. The soil comes from the Iraqi city of Najaf. The soil sample is mainly sand. The nanoclay named "Montmorillonite K10" is used, and it is non-toxic. The tests are performed with a computerized Oedometer. The collapse potential is estimated according to a single Oedometer test (SOT), where the specimens are initially dry and then soaked under a stress level of 200 kPa. Four data sets related to the percentages of 0, 3, 6, and 12% nanoclay are used. Each data set comprises three groups of pre-tests for curing duration and different soaking durations. All experiments have a constant initial dry density of 1.64 g/cm3, water moisture of 3%, and gypsum content of 29%. The findings of this study show that the collapse potential (CP) of natural soil specimens decreases as the pre-test curing time increases. Generally, there is a decrease in CP due to adding the nanoclay and 6% of the nanoclay exhibited the highest reduction in CP. Also, there is an increase in the pre-test curing for the nanoclay-treated soil specimens, which leads to an increase in the CP related to the no-curing state. [ABSTRACT FROM AUTHOR]

Index properties such as liquid limit, plasticity index, shrinkage index, colloidal content, and free swell index (FSI) are used to identify and classify the nature of soil expansivity. However, for these tests either powdered or remoulded soils are used for testing and do not reflect the field placement conditions and soil structure. Hence, the present article proposes a new Desiccated State Free Swell (DSFS) index to encompass the field placement conditions and soil structure. In this method, the small compacted soil specimens are subjected to two-stage process – desiccation followed by swell measurement. The compacted or undisturbed soil specimens are placed in 100 ml glass measuring jars and allowed to swell in distilled water, similar to the FSI test. The percentage increase in the volume of the desiccated soil specimens is measured, and the same is used for the classification of degree of soil expansion. A total of 21 soils covering a wide range of plasticity characteristics and swell potentials were used for the present study. Based on the DSFS test results, a new classification chart is proposed for the prediction of the degree of soil expansion. The experimental findings revealed that the soil expansion predicted using the DSFS method is superior to the conventional indirect methods and matches well with the oedometer swell potentials. [ABSTRACT FROM AUTHOR]

Volcanic soil is often used as fill material in road embankment construction in Java island-Indonesia. An understanding of the engineering properties of compacted volcanic soils is needed, especially during the preliminary design phase and during the detailed design phase of the road embankment. Carrying out a field compaction trial test will significantly assist in the design of the compaction process of the road embankment construction. Selecting the correct number of passes from the compactor and the engineering properties of compacted volcanic soils can be obtained from field compaction trial tests. Constrained modulus is one of the engineering properties that can indicate the stiffness of the fill material used in a road embankment. This study aims to determine the constrained modulus of compacted volcanic soil and compare it to the number of passes of a compactor from the field compaction trial test. The volcanic soil used in this study is classified as pumiceous tuff, which is derived from older volcanic rocks. The highest value of the oedometer modulus of compacted volcanic soils is 10.38 MPa which comes from eight (8) times passes of smooth drum roller conducted on field compaction trial test. [ABSTRACT FROM AUTHOR]

The interaction between fine and sand grains has been studied by several researchers to evaluate the liquefaction phenomenon. However, the fine fraction effect on the compressibility behavior is less studied and requires more attention. A laboratory program was conducted to evaluate the effect of both non-plastic fines (silt) and plastic fine (clay) on the compressibility behavior of Chlef sand. The results show that the global void ratio (e) decreases with the increase of the fine content from 0 to 30% and then increases from 30 to 40% of the fine fraction for both mixtures (sand–silt and sand–clay). Inversely, the intergranular void ratio (es) increases with the increase in the fine fraction. Moreover, increasing the fine percentage in the sand leads to an increase in the compressibility index (CC) and the granular compressibility index (Cc-s). Our results indicate that the transition fine content depends on the stress level, the maximum void ratio (emax) calculated on the basis of some hypoplastic parameters model (granular hardness hs and exponent n), and the nature of the fine content (clay or silt). Finally, the gradation parameters (D10, D50, and Cu) have a significant effect on compressibility behavior. [ABSTRACT FROM AUTHOR]

This study proposes a novel method for assessing the evolution of relative density and shear wave velocity that vary with depth and effective stress in non-compacted embankment layers. Embedded soil stiffness measurement devices were used to monitor the shear waves at each stage of filling at the test site, and comprehensive laboratory compaction tests were conducted using a floating ring oedometer cell to reproduce real field conditions with minimal friction. Assuming a constant soil unit weight γ with 7% water content, the effective stress σ' is proportional to depth z (i.e., σ' = γ·z). Field test results were compared with the shear wave velocity relationships determined in laboratory tests for four samples of differing relative density (30%, 50%, 70%, and 90%), indicating that the relative density at the bottom of the embankment varied between 15% and 48%. However, the constant soil unit weight applied in this study can underestimate the relative density of the embankment, causing a prediction error if the self-weight compaction of the embankment is not minute. Therefore, this study provides guidelines based on a physics-inspired and data-based approach and anticipates the relative density and shear wave velocity analyzed in the context of depth in non-compacted embankment layers. The physics-based data analyses suggested in this study can be used in first-order estimations to assess the relative density and shear wave velocity evolution in non-compacted embankment layers. • A method for estimating the relative density of non-compacted embankment layers was studied. • A device was developed to monitor the shear waves of a non-compacted embankment. • A simple comparison between field and lab tests was conducted. • The model-based approach effectively estimated the relative density of embankment layers. [ABSTRACT FROM AUTHOR]

This paper revisits the issue of a potential substitutions of the Hoek-Brown failure model by the standard Mohr-Coulomb model in the stability analysis of rock masses. The derivation of equivalent shear strength parameters of the Mohr-Coulomb proposed by Hoek et al. [1] is addressed with emphases on the suitable range of stresses for which the equivalence of the two failure criteria applies. To that end, a simple numerical analysis of the oedometric test is carried out. It is seen that a correct choice of the upper limit of the minimum compressive principal stress is crucial for the Mohr-Coulomb model to provide predictions comparable to the Hoek-Brown model. This issue is addressed next in the light of the solution of slope stability problem. All the presented results were derived with the help of the GEO5 FEM finite element software [2]. [ABSTRACT FROM AUTHOR]

Soil collapse is a major geotechnical problem that causes architectural and structural damage to buildings and engineering infrastructure. Losses due to soil collapsibility have an economical aspect and the study of these soils is very important due to the large occurrence of collapsible soils around the world. In this research, conventional oedometer tests and suction-controlled oedometer tests were conducted to study the benefit of compaction as a method of improving the behavior of a lateritic soil that is particularly susceptible to collapse after soaking. The results offer practical information to minimize problems arising from collapsible soils. The soil water content before the sample is inundated affected the soil collapsible behavior. Soil specimens less dense when compacted at the dry side of the compaction curve exhibited volume variation under loading less than 4% and collapse deformations up to about 11% when exposed to flooding, while soil specimens compacted at optimum moisture content showed volume variation under loading around 10% and a maximum collapse deformation by about 6%. The collapse deformations changed significantly with inundation stress for the soil compacted especially for stresses above 100 kPa. The collapse deformations were almost insignificant when the lateritic soil had a relative compaction of 90% with values almost always less than or equal to 2%, proving that the compaction process is a soil improvement technique that can significantly reduce the collapse induced by inundation. [ABSTRACT FROM AUTHOR]

In this paper, the deformation properties of sand, reinforced with carpet waste, are investigated by carrying out a set of large-scale oedometer tests under different overburden pressures. The oedometer apparatus employed in this study has been equipped with vertical and lateral pressure cells, which allow the value of the soil's coefficient of lateral pressure at rest, to be determined as well as its compressibility. Carpet waste was added to sand at weight percentages of 0, 5, 10 and 15%. Results were indicative of a reduction in the coefficient of lateral pressure at rest, K0 with the increase in carpet content of the mixtures. The reduction in the value of K0 amounted to 10% at a carpet content of 15%. The compressibility properties of the mixtures were evaluated as well, by recording one-dimensional displacement in the samples. Results demonstrated an increase in the coefficient of volume change with the increase in carpet content, particularly for lower levels of overburden pressure. Predictive models were developed based on the multi-linear regression (MLR) procedure to predict the coefficient of lateral pressure at rest and coefficient of volume change for the sand–carpet mixtures normalized to the values of sand. [ABSTRACT FROM AUTHOR]

The creep behavior of soft clays is essential in evaluating the long-term deformation of foundations. Because this behavior of naturally deposited clays is very complex as a result of their structures, loading history, and physicochemical processes, in addition to the heavy workload and high cost for the sampling procedure of natural soft clays, oedometer creep tests were usually conducted on reconstituted clays, aiming to establish the fundamental work for the elastic-viscoplastic modeling (EVP) and the creep prediction of natural soft clays. In this study, based on a series of one-dimensional creep tests of reconstituted soft clays, the relationship between the creep coefficient (Cα) and the vertical effective stress (σ′ v) and that between Cα and the ratio of vertical effective stress to preyielding stress (σ′ v /σ′y ) are presented in semilogarithmic planes. The results suggest that the Cα value increases with the vertical effective stress prior to reaching the threshold stress (~2.17σ′y), and then Cα gradually decreases after it. The results (Cα vs. compression index Cc) show that the statistical Cα/Cc value of reconstituted clays ranges from 0.015 to 0.05, which is more than that of natural soft clays (0.03-0.05). This suggests that the reconstitution process is beneficial to restrain the creep of soils. Furthermore, it was found that the Cα/Cc value of reconstituted clays linearly decreased with the void ratio when vertical effective stress exceeded the threshold stress (~2.17σ′y). Based on the data of this study and data from previous studies, a prediction equation for Cα after the threshold stress is proposed, showing that Cα is a function of the void ratio and the void ratio at the liquid limit. [ABSTRACT FROM AUTHOR]

Abstract In this paper, through micromechanical analyses, the microstructural responses of kaolinite samples subjected to 1-D consolidation were quantitatively analyzed. Using a tailor-made, 3D-printed oedometer in preparing samples subjected to different loading levels, the applied loading was maintained during the freezing process of the sample in order to preserve the fabric associations for the subsequent characterizations using Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscopy (SEM). At least 3000 particles were identified in each sample to provide representative data for the micromechanical analyses. Besides, the voids and solids (particles and aggregates) were separated using proper binary images; the voids of the irregular shapes were further described using an equivalent ellipse. With the boundary established between the intra- and inter-aggregate pores based on the MIP results, the quantitative SEM analyses further revealed that the inter-aggregate pores exhibit a significantly large area fraction and therefore dominate the deformation responses. Fabric tensors were used to further quantify the directional behavior of the voids and particles. In addition, to provide complementary information and to further understand the associated deformation mechanism, the shape evolution of the inter-aggregate pores was examined, also based on the SEM images. All the findings further describe the compression process of the inter-aggregate pores during the collapse of the card-house structure formed by the aggregates. As the vertical stress increases, the card-house structure is gradually compressed; hence, the enclosed inter-aggregate pores that are initially elongated vertically are compressed into a rounder shape. For those pores which are initially aligned horizontally, they are further compressed and become more elongated in the horizontal direction. Ultimately, the inter-aggregate pores gradually align in the horizontal direction, and the associated pore shape becomes flattened. The particles that form the aggregates also unavoidably follow the same trend, to also align in the horizontal direction. Highlights • The microstructural responses of kaolinite are quantitatively analyzed. • Load-preserved, high quality kaolinite samples are prepared for analysis. • Fabric tensors are used to quantify the direction distribution of fabrics. • The shape evolution of inter-aggregate pores is examined. [ABSTRACT FROM AUTHOR]

With the objective to study the effect of viscous property on the mechanical behaviour of structured clays, a series of compression and consolidation-undrained shear tests in different loading rates, using oedometer and triaxial instruments respectively, were carried out on undisturbed samples of clays. The compression curves in different load incremental ratios shows that the load incremental ratio has an effect on structural yield stresses, while it has little influence on compression indices of clays. The stress-strain-pore pressure curves show that shear strength increases, while pore water pressure decreases with increasing shear strain rate, and the critical state stress ratio is constant in reasonable shear strain rate range. When the shear strain rate exceeds the boundary of shear strain rate, the pore water pressure drops sharply and the failure mode changes from plastic failure to brittle failure. The test results illustrate that loading rate has an effect on the structural yield stress and shear strength, while it has little influence on compression index and critical state stress ratio of structured clays. [ABSTRACT FROM AUTHOR]

Biochar has been shown to have multiple, positive benefits on soil physico‐chemical and biological properties. However, mechanical behaviour of biochar‐amended soils has been given relatively less attention. Therefore, in this study, we aimed to describe these properties of soil freshly amended with Miscanthus biochar in the context of compaction mitigation through a comprehensive laboratory study. In particular, for the first time, we evaluated the short‐term loading and unloading responses of replicated biochar‐amended soils using a modified oedometer, using different rates of application of biochar (2, 6 and 10% w/w, dry weight basis), in two types of soil (humus‐free loam and field loam) prepared at two different (10 and 22% w/w) soil moisture contents. From the experiment, dry density (ρd), void ratio (e), compression index (Cc) and relaxation ratio (R) were derived and statistically analysed. The addition of biochar was shown to reduce ρd, while e increased with the amount of added biochar. The addition of biochar increased Cc and R. The effect of soil moisture content and soil types was also found to be statistically significant on the above parameters. However, field studies are needed to understand the long‐term mechanical behaviour of biochar‐amended soils and further studies are required to examine the performance of different biochar types and soil types. [ABSTRACT FROM AUTHOR]

Abstract Lithium Metatitanate (Li 2 TiO 3 or LMT) and Lithium Orthiosilicate (Li 4 SiO 4 or LOS) are the prominent among the suitable candidate materials for breeders. Robust design of the breeder blankets requires a thorough understanding of the thermo-mechanical response of the breeder materials at different loading conditions. In this context, the material characterization plays a vital role. Solid breeder concept of various member nations comprises of pebbles in steel container. Determination of effective properties of the pebble beds helps in understanding and formulation of constitutive relations for such granular systems. In order to develop simulation tools to understand the complex thermo-mechanical response of the breeder units, the properties of the material should be known. Hence, the objective of this work is to characterize crush load of Li 2 TiO 3 pebbles and investigate the thermo-mechanical response of the pebble beds. The study involves determining the crush load of individual pebbles and pebble-bed elastic modulus. Uniaxial oedometric tests are performed to investigate the influence of temperature on the effective elastic modulus of the pebble beds. [ABSTRACT FROM AUTHOR]

A new methodology was developed to perform computer simulations of crushable rockfill particles using the discrete element method. Rockfill was modelled using a clump logic, responsible for providing a statistical and spatial variability in the strength and shape of the particles. Clumps have a major advantage of severely decreasing the number of contact equations to be solved in the model, resulting in less computer time. A series of single-particle crushing tests and an oedometer test were simulated using crushable particles and were in agreement with experimental data. A comprehensive study of the brittle failure of single-particle crushing tests is presented. [ABSTRACT FROM AUTHOR]

Of late, various constitutive models have been proposed in the literature for the purpose of capturing the various complex physical mechanisms governing the creep behavior of soft soil. However, the more complex the model, the greater the number of associated uncertain parameters it has, and the less robustness it is. In this study, the Bayesian model class selection approach is applied to select the most plausible/suitable model describing the creep behavior of soft soil using laboratory measurements. In total, one elastic plastic (EP) model and eight elastic viscoplastic (EVP) models are investigated. To assess the performance of the different models in the prediction of creep behavior of soft soils, Bayesian model class selection is respectively performed using the oedometer test data from the intact samples of Vanttila clay and reconstituted samples of Hong Kong Marine Clay collected from the literature. All unknown model parameters are identified simultaneously by adopting the transitional Markov Chain Monte Carlo (TMCMC) method, and their uncertainty is quantified through the obtained posterior probability density functions (PDFs). The result shows that the proposed method is an excellent candidate for identifying the most plausible model and its associated parameters for different kinds of soft soils. The approach also provides uncertainty evaluation of the model prediction based on the given data. [ABSTRACT FROM AUTHOR]

Loess soils are characterized by metastable microstructure, high porosity and water-sensitivity. These soils have always been problematic soils and attracted attention from researchers all over the world. In the present study, three loess soils extracted at various depths from the Loess Plateau of China, i.e. Malan (Q3), upper Lishi (Q22) and lower Lishi (Q21) loess soils, were studied. Single oedometer-collapse tests were performed on intact loess specimens to investigate the collapse behavior of three loess soils. The microstructure and chemical composition of each loess before and after collapse test were characterized using scanning electron microscopy (i.e. SEM) and energy dispersive spectroscopy (i.e. EDS) techniques. The microstructural evolution due to wetting collapse was interpreted qualitatively and quantitatively in terms of the pore morphology properties. The results suggest that: ① the collapse potential of each loess may rise again after a round of rise and drop, which could be failure of the new-developed stable structure under quite high vertical pressure. It implies that loess may collapse even if it has collapsed. ② Q3, Q22 and Q21 loess have different types of microstructure, namely, granule, aggregate and matrix type of microstructure, respectively. ③ The microstructural evolution due to loading and wetting is observed from a granule type to an aggregate type and finally to a matrix type of structure. The variations in distributions of pore morphology properties indicate that collapse leads to a transformation of large-sized pores into small-sized pores, re-orientation and remolding of soil pores due to particle rearrangement. ④ A porous structure is essential for loess collapse; however, the non-water-stability of bonding agents promotes the occurrence of collapse under the coupling effect of loading and wetting. [ABSTRACT FROM AUTHOR]

Given a political context in which energy and environmental stakes have become increasingly dominant, road engineering practices have favoured saving energy and protecting the environment. Among these practices, the use of cold mixes treated with bitumen emulsion has proven to be a suitable technique. Cold mix design, as well as the design of pavements including cold mix asphalt (CMA) layers, is highly empirical and based on local skills and tend to limit the development of this environmentally-friendly pavement technique. In the case of CMA, no mechanical behaviour law has been established to take into account its evolutive behaviour. The paper is set in three parts. The CMA model is presented in Part I. The second part of the paper illustrates the numerical response of the model on a compressive sinusoidal load. The last part presents some first simulations of the cyclic oedometer laboratory tests. By comparing then to the numerical simulations, they show the relevance of the model to account for the CMA behaviour. [ABSTRACT FROM AUTHOR]

This paper evaluates the degree of uniformity achieved in clay beds prepared for model tests using slurry consolidation method. Clay Specimens were prepared in a cylindrical tank split into five horizontal rings of equal height. This set-up facilitated the sampling of clay for quality checks viz., oedometer tests, gradation analyses, vane shear strength and water content determination in horizontal and vertical directions throughout the specimen. The results from the study show that while the spatial variation of water contents conforms to the acceptance criterion, the same is not true for that of undrained shear strength which is the main parameter of interest for model tests. It is proposed, therefore, to make the acceptance criterion for water content stricter by the factor bs, which is the characteristic of the soil type, depicting slope of the linear function of water content, w, versus undrained shear strength, su, on log-log scale. Oedometer tests showed the reduction of consolidation pressure with depth, which indicates the loss of applied pressure while being transmitted to the lower layers. Gradation analyses suggested no particle segregation in the consolidated specimen. The relation between water content and consolidation pressure was utilised to plot pressure distribution contours throughout the specimen. The uniformity in the specimen was also compared with that prepared through centrifuge consolidation. [ABSTRACT FROM AUTHOR]

A"transitional" mode of soil behaviour implies that dense and loose samples do not converge towards the same volumes within the strains and stresses applied by simple oedometer and triaxial tests. As this behaviour involves soils with different gradings and mineralogies (e.g. gap graded, well graded and/or mixed mineralogies), identifying the factors responsible is difficult. Nevertheless, it has been previously speculated that strong forms of fabric that are difficult to break down as strains and stresses are applied, might be the common cause. This paper aims at investigating some elements of fabric at the microscale of transitional soils. A gap graded and two well graded mixtures with large amounts of non-plastic fines were investigated by oedometer and triaxial tests. As it would be difficult to identify experimentally many commonly used elements of fabric in these soils, e.g. the contact network, mercury intrusion porosimetry was used as a first step to characterise the evolution of pore size distributions (PSDs) of dense and loose samples undergoing the same stress paths, using the PSDs as a proxy of fabric. Multi-directional bender element testing was performed to confirm the isotropy of the elastic stiffness, from which it might be inferred that the fabric is also isotropic. Statistical parameters of the PSDs were calculated, the changes of which were related to the evolution of macroscale void ratios. The robust fabrics causing lack of convergence were characterised by a complex evolution of the PSDs, the initial differences of which could not be erased during conventional testing. This work also provided a simple method to examine the fabric of particularly well graded or gap graded materials, for which other techniques, such as CT or SEM, could not reveal the multi-scale nature of the fabric. [ABSTRACT FROM AUTHOR]

Pressure on land use has caused great site development along the coastal area of south western Nigeria. However, research works for the purpose of evaluating appropriate depths of foundations in the area were without cognizance of engineering challenges that may ensue as a result of the organic content, and associated factors of the soils. This paper evaluates the compositional effects of the soils on foundation materials, and a phenomenological model of compressibility of fines during design and construction of problem-free foundations in the area. Thirty (30) disturbed soils were analysed for moisture content, grain size distribution, consistency limits, chloride, pH and sulphate, while the oedometer consolidation test was carried out on another 30 undisturbed soils. The stratigraphic sequence in the profile comprises medium dense to coarse grained silty clayey sand to 16.80 m depth, below loose grey organic silty clayey sand from the surface. Results show in most cases, that the foundation soils contain insignificant percentages (0.95–5.8%) of organic solids. Moisture content (44–70 % ), chloride (74.9 ppm), sulphate (420 ppm) ions concentration and pH (8.96) could enhance the corrosive potential of the soils. It is recommended that Portland cement concrete will be suitable in the environment. Foundation settlement with respect to surface area (0.028≤ m v  ≤ 0.434m 2 MN −1 at 200 kNm −2 ; 0.038 m v  ≤ 0.776m 2 MN −1 at 400 kNm −2 ; 0.038≤ m v  ≤ 0.879m 2 MN −1 at 800 kNm −2 ) ranges from low to medium compressibility with respect to consolidation pressure. Therefore, footings load need be spread over the soils, and foundation design need be based on site-specific soil information. [ABSTRACT FROM AUTHOR]

Although extensive research has been performed on the mechanical properties of cement-stabilized clays, quite a few attempts have been made on the compression behavior of remolded cement-admixed clays. The results from oedometer tests have been discussed to investigate the compressibility of remolded cement-admixed clays, taking into consideration cement amount and curing time. The findings show that the difference in shape and position of compression curves is attributed to cement amount and curing time. Most compression index (Cc) values of remolded cement-admixed clays are greater than those of untreated clay due to the presence of remolded yield stress σ′yrthat is closely related to initial water content and clay fabric. Based on the obtained test data, the relationships ofCcvs.e0,Ccvs.w0,Ccvs.e1,Ccvs.eyr, and σ′yrvs.eyrare preliminarily discussed and quantitatively established. Especially, an important divergence of void indexIvat effective stress σ′vless than remolded yield stress σ′yrcan be observed at different cement amounts and curing durations. Being independent on cement amount, curing time, and initial state of soil, an excellent convergence occurs at stress σ′vgreater than yield stress σ′yr. The normalized compression curves ofIvvs. σ′vat σ′v > σ′ycan be expressed by a unique line that agrees well with intrinsic compression line (ICL) and extended ICL. [ABSTRACT FROM AUTHOR]

Cement bentonite (CB) barriers are self-supporting, low permeability, structures used to retard groundwater flow and as such strength and hydraulic conductivity parameters are often stipulated when developing the mixtures. This paper reports an investigation into the deformation and compression behaviour of a CB containing ground granulated blastfurnace slag using the unconfined compressive strength apparatus, triaxial (undrained, unconsolidated) and oedometer. Samples were also exposed to drying and rewetting to investigate possible response to changes in environmental conditions. Cracking was observed prior to peak stress suggesting that the hydraulic conductivity of a barrier may be adversely affected before the shear strength is reached in undrained conditions. The compression response of CB indicates the presence of a threshold stress; once exceeded the magnitude of settlements are significantly greater than those encountered below this threshold. If a barrier experiences localised changes in loading conditions then there is the potential for damage from induced differential settlements; thus it is recommended that the threshold stress should also be considered at the design stage in addition to strength and hydraulic conductivity requirements. The response of the material exposed to drying-rewetting was unexpected and requires further investigation to determine how a barrier will respond to changing environmental conditions. [ABSTRACT FROM AUTHOR]

The sand compaction pile (SCP) method can be applied to soft marine clay ground that is a reinforcement of composite ground consisting of compacted sand piles and surrounding clay. The application of SCP method in the immersed tunnel of Hong Kong-Zhuhai-Macao Bridge verify SCP method is a robust solution to limit the total settlement and differential longitudinal settlement and to promote smooth transition from immersed tunnel to artificial island. The SCP method has significant settlement reduction effect on marine clay. The SCPs can also function as a drainage path to accelerate the consolidation process in marine clay. It is also found that the consolidation rate of SCP-improved ground is delayed compared with that predicted program which is most probably because of the soil disturbance effect during the installation of SCPs. [ABSTRACT FROM AUTHOR]

A test embankment was established on the soft Ballina clay and practising engineers and academics were invited to make predictions of the behaviour of the embankment. Comprehensive geotechnical investigations were performed and the testing data were provided to the predictors. This paper presents Class A and Class C predictions made by the authors for the embankment. In Class A prediction, the soft clay was modelled as a single homogeneous layer. The Class A prediction showed good agreement with measurements for settlement, but not for pore pressure and lateral ground movement. Class C prediction divided the soft clay into two layers based on the information of ground investigation, and achieved better predictions for settlement, pore pressure and lateral movement. Finite element analysis using Plaxis 2D was carried out for the prediction, and Soft Soil Creep model was used for the soft clay. Consolidation parameters were assessed by statistical analysis of the oedometer test data. Sensitivity studies were performed to investigate the influence of parameters on the analysis results. Results of the predictions and sensitivity studies are discussed in the paper. [ABSTRACT FROM AUTHOR]

The creep degradation is a common phenomenon for soft structured clays. In this paper, the creep degradation behavior for soft structured clays is first studied by combining intrinsic creep behavior and the structure indicator. A creep-implicit model and a creep-explicit model corresponding to a stress-based and a creep-based structure indicators are developed, respectively, under one-dimensional condition. Parameters determination for both models is straightforward from oedometer tests. Coupled with consolidation theory, both models are used to simulate oedometer tests with different structural levels and load durations on three clays. The predictive ability of the two models on creep behavior, creep degradation behavior and evolution of structure indicator is analyzed. The relationship between the two structure indicators is discussed based on experimental results. The comparison between experimental and numerical results demonstrates that both models can accurately describe the creep degradation behavior of soft structured clay under one-dimensional loading. [ABSTRACT FROM AUTHOR]

This work studies the effect of the curing time on the creep behaviour of a stabilised soft soil, using volumetric and deviatoric creep laws associated with constitutive models. Results of unconfined compressive strength tests for several curing times are used to define the time evolution of the mechanical and creep properties. The models/creep laws are validated by oedometer and triaxial creep tests, for 28 and 90 days of curing. The long-term behaviour of an embankment built on a soft soil reinforced with deep mixing columns shows that the effect of curing time decreases the settlement and increases the improvement factor. [ABSTRACT FROM AUTHOR]

The compressibility characteristics of Singapore marine clay in reconstituted and undisturbed states were studied using oedometer, constant rate of strain, Rowe cell, and isotropic consolidation tests. The intrinsic compression curve of the reconstituted clay was found to be similar to that proposed earlier with some minor deviations at low vertical stresses of less than 100 kPa. The field and laboratory compression behaviors were found to be similar, hence the laboratory curve could be used as a reference for interpreting the field behavior. Factors affecting the measurements of compression index and yield stress were discussed. As the coefficient of lateral earth pressure at the top upper clay was close to 1, the compression curves of vertically and horizontally trimmed samples were almost similar. The yield stress was mainly controlled by the strain rate; i.e., the higher strain rate resulted in the higher yield stress. Constrained modulus as derived from cone penetration tests and flat dilatometer tests were also examined and compared with laboratory test results. The in situ tests showed the decrease in constrained modulus with depth and generally the dilatometer test was found to register a higher modulus value. [ABSTRACT FROM AUTHOR]

Dredged marine soils (DMS) can be reused as fill materials for land reclamation project other than dump back to the open sea. However, in Malaysia, dredged marine soils were considered as a geowaste because of it has poor engineering properties. In the present study, dredged marine soils were excavated from the dredging works near the jetty of Kuala Perlis, Malaysia. To investigate the settlement reduction of DMS, a sand-mixed was used in this study and these results were compared with natural DMS (without sand). Oedometer test were conducted to calculate the consolidation properties of DMS and k-value can be obtained from the test. The test results showed that the dissipation of water from soils occurs faster in the sand-mixed compare to the control sample (without sand) due to the drainage path that have been reduced (two-way drainage). [ABSTRACT FROM AUTHOR]

In this article, the potential of a binder developed by admixing fly ash and ground granulated blast furnace slag (GGBS) to stabilise expansive soils is evaluated. Laboratory tests included determination of free swell index, swell potential and swelling pressure tests of the soil/binder mixtures at different mixing ratio. The test results showed decrease in the swelling behaviour of the soil with increase in binder content. The percent swell–time relationship was observed to fit the hyperbolic curves enabling us to predict the ultimate percent swell from few initial test results. Addition of 1% of lime to the binder showed further improvement in reducing swelling. A good linear relationship is established between percent oedometer swell and modified free swell index (MFSI) for soil/binder mixtures without lime but the same has not been observed in the presence of lime. The compressibility characteristics of the soil/binder mixtures reduced nominally with increase in binder content but in the presence of lime, the compressibility reduced significantly. Binder used in this study has been found to be effective and economic to stabilise expansive soils with lesser amount of chemical additives such as lime. [ABSTRACT FROM AUTHOR]

Accurate modeling of the time-dependent behavior of geomaterials is of great importance in a number of engineering structures interacting with soft, highly compressible clay layers or with organic clays and peats. In this work, a uniaxial constitutive model, based on Perzyna's overstress theory and directly extendible to multiaxial stress conditions, is formulated and validated. The proposed constitutive approach essentially has three innovative aspects. The first concerns the implementation of two viscoplastic mechanisms within Perzyna's theory in order to distinguish between short-term (quasi-instantaneous) and long-term plastic responses. Similarly, elastic response is simulated by combining an instantaneous and a long-term viscous deformation mechanism. The second innovative aspect concerns the use of a bespoke logarithmic law for viscous effects, which has never been used before to simulate delayed soil behavior (as far as the authors are aware). The third concerns the model's extensive validation by simulating a number of different laboratory test results, including conventional and unconventional oedometer tests with small and large load increments/decrements and wide and narrow loading/unloading cycles, constant rates of stress and strain tests, and oedometer tests performed in a Rowe consolidation cell with measurement of pore pressure dissipation. [ABSTRACT FROM AUTHOR]

This paper presents a numerical scheme for a solid–fluid coupled discrete-element method (DEM) that takes into consideration solid deformation and pore pressure generation and dissipation. Analytical solutions of conventional soil mechanics examples obtained by oedometer testing are used to quantitatively validate the proposed algorithm. The numerical results show good agreement with the analytical solutions. The proposed method advances the current capability of solid–fluid coupled DEM analysis to simulate the mechanical behavior of saturated granular materials. [ABSTRACT FROM AUTHOR]

This paper examines the ability of volumetric and deviatoric creep laws associated with constitutive models to simulate the creep behaviour of a soft soil in its natural state or chemically stabilised state. Initially, the models/laws are validated by oedometer and triaxial creep tests, for the stabilised and unstabilised soils. Finally, the long-term behaviour of an embankment built on a soft soil reinforced with deep mixing columns is predicted based on the properties for a curing time of 28 days. The results show that the creep phenomenon should be considered in a long-term analysis of deep mixing columns. [ABSTRACT FROM AUTHOR]

The compression behavior of structured soils after virgin yielding is highly nonlinear and cannot be captured by a single line in the e--ln(p') space. The slope of the compression curve of structured soils changes gradually as the structure of the soil crashes and reaches to the slope of the same soil in the remolded state. When the initial and final values are known, the disturbed state concept can be used to describe the compression behavior of structured soils. In this study, the state of the structured soil at the beginning of virgin yielding was considered as initially intact, and its state after full destruction was considered as fully adjusted. The compression index of the soil at any particular state between these two states was described using a state function based on the experimental results. A compression model with a variable slope of the compression curve was developed using the distributed state concept. The proposed model was implemented in the modified Cam-clay model and verified using data available in the literature for oedometer and triaxial tests on structured soils. Comparison with the experimental results of triaxial shearing tests showed that the proposedmodel was able to describe the behavior of specimens with low overconsolidation ratiosmore accurately. [ABSTRACT FROM AUTHOR]

One of the essential inputs in settlement prediction models is the soil modulus, which may be obtained from laboratory tests or estimated from in situ measurements. The total uncertainty in predicting the confined modulus of a sandy soil is quantified with data from side-by-side in situ testing using the standard penetration test, the static cone penetration test, the light dynamic probing and the laboratory oedometer test. To estimate transformation errors, correlations are proposed between in situ and laboratory data. The results indicate that similar magnitudes of total uncertainties are associated with the in situ methods, which are approximately twice as high as those from the direct oedometer method. The quantified uncertainties are an important input for reliability-based designs of foundations under similar soil conditions. [ABSTRACT FROM AUTHOR]

Riverbank filtration (RBF) systems are often used to treat surface water near rivers. The effectiveness of such systems depends heavily on the properties of the riverbank material that is used for filtering and treating the water. To improve the system's treatment efficiency, modifications may be conducted to the riverbank soil. Altering the properties of the soil might, however, affect the stability of the riverbank. In this study, soil and water samples near Lake Chini were collected and characterized. Filtration test was conducted to evaluate the efficiency of the soil in treating the water. The soil was modified by mixing it with powdered activated carbon (PAC) at varying percentage of 5 and 10%. In addition, compressibility test was carried out using a standard oedometer. Test results indicated that the soil alone was insufficient to treat the water to drinking water quality standards. Modification with activated carbon improved the water quality from Class II to Class I. However, compressibility test revealed that there were some changes to the pressure - void ratio relationship, indicating that the alteration of soil properties with the addition of activated carbon filters might affect the stability of the riverbank. [ABSTRACT FROM AUTHOR]

The GMZ bentonite/additive mixtures have been proposed as the buffer/backfill media for the high-level radioactive waste geological disposal in China. In this study, two types of mixtures were prepared by mixing variable amounts of crushed granite powder or quartz sand (a range of 10% to 50% by dry mass of aggregate addition) with pure GMZ bentonite. To investigate the volumetric deformation characteristics of the bentonite/additive mixtures under coupled hydro-mechanical conditions, sequential oedometer tests comprising four phases were carried out, including preliminary compression, swelling under constant vertical stress, re-compression, and unloading-rebounding. Experimental results indicate that the volumetric deformation characteristics of the mixture largely depend on the initial condition, additive content and type. The evolutions of compression index and swelling index are governed by the degree of saturation and the state of soil matrix during different loading phases. During the compression phase, the soil compressibility relates to the formation of additive skeletal structure, while the rebound behavior during the unloading phase is determined by the competing mechanical and physico-chemical effects. The correlation between swelling index and bentonite dry density is not unique and dependent on the nature of the additive. The impact of additive properties on the volumetric behavior is further confirmed through tracking swelling indicators including final swelling strain and swelling pressure. This study provides an improved fundamental understanding of the mechanical behavior of GMZ bentonite/additive mixture under coupled conditions and optimizes their engineering applications for nuclear waste disposal. [ABSTRACT FROM AUTHOR]

This paper proposes a constitutive model to describe the isotropic compression response of unsaturated, compacted clay under undrained conditions over a wide range of mean stresses. The total stress-based model captures the impacts of the initial degree of saturation on the apparent preconsolidation stress and the slope of the compression curve up to the point of pressurized saturation. The points of pressurized saturation for specimens with different initial degrees of saturation were predicted using a modified form of a pore-pressure analysis from the literature. The compression response for pressure-saturated specimens was dominated by the pore water, although dissolved air and soil structure may play a role for some soils. The model was calibrated using results from a series of compression tests on compacted clay specimens having initial degrees of saturation ranging from 0.6 to 1.0 and the same initial void ratio. The model was found to provide a good match to the experimental data for mean stresses up to 160 MPa, in particular due to the improvements in the analysis from the literature to evaluate the points of pressurized saturation. [ABSTRACT FROM AUTHOR]

The time-dependent stress-strain behavior of clayey soil is a great concern for predicting long-term settlement especially for large-scale land reclamation projects. In this paper, long-term time-dependent behavior of Hong Kong Marine Deposits (HKMD) under the loading stage and unloading stage is investigated by multi-staged loading oedometer test. Special emphasis has been given to study creep and swelling behavior. It is found that the clayey soil demonstrates the creep behavior during the loading stage, whereas it shows the swelling behavior during the unloading stage. The analysis of the creep behavior shows that there exists a linear trend between creep strain and time (in log-scale) within a certain period, whereas a nonlinear relationship in a long term view. Similar result is found for the swelling behavior. A nonlinear function is found to be suitable to predict the long-term creep and swelling behavior. The creep strain limit and swelling strain limit can be obtained if the nonlinear function is adopted to fit the experimental data. In addition, a new modified Elastic Visco-Plastic model considering Swelling (EVPS model) is proposed and presented, which considers the nonlinear creep and swelling behavior. In this modified EVPS model, the final creep and swelling equilibrium stress-strain state can also be obtained when the time is infinite. [ABSTRACT FROM AUTHOR]

The compression index, swelling index and preconsolidation stress values are essential for reliable settlement calculations. However, it is a challenge to obtain representative parameters for very soft, organic, high-plasticity clays, which are often found in the Jacarepaguá Lowlands, Rio de Janeiro, Brazil. In recent decades, several geotechnical correlations have been proposed for estimating the parameters to check oedometer test data. The compression index can be estimated based on simple laboratory index tests and the preconsolidation stress can be found by means of piezocone and vane tests. In this paper, data from 24 different investigation clusters located in the region are analysed. Undisturbed samples were collected from 20 different locations; 67 piezocone tests and 48 vane tests were carried out, which resulted in a comprehensive data bank. Then correlations were developed and compared with a number of equations to assess their reliability. Special emphasis was given to correlations between the compression index and soil water content, and also between the preconsolidation stress and the corrected cone resistance and shoulder pore pressure measured in the piezocone tests. [ABSTRACT FROM AUTHOR]

Evaluation of the volume change behavior of expansive soils under controlled suction and boundary conditions is important for the proper design of different geotechnical systems. Osmotic technique was used by several researchers for suction controlled testing of expansive soil specimens. This technique involves circulating polyethylene glycol solution (PEG) over a semi-permeable membrane underlying a test specimen. Different suction controlled testing apparatuses incorporating osmotic techniques were developed included triaxial and oedometric testing conditions to simulate different boundary conditions. This paper describes a series of calibration performed on suction controlled modified oedometer and triaxial equipment used for testing expansive soil. The modified oedometer, developed by the authors, comprises of thin-wall oedometer ring instrumented with strain gauges to measure the lateral stresses evolving during the test. The first part of this paper introduces the errors that arise during osmotic suction testing, concerning the device flexibility and PEG solution losses. The second part of the paper highlights the calibration procedure for estimating lateral stresses in modified oedometer from instrumented strain gauges as well as introduces a correction for the temperature fluctuation. Finally, the effect of triaxial cell flexibility on the volume change measured during osmotic suction controlled testing as well as temperature effect on volume change measurements were evaluated and correction procedures were introduced. [ABSTRACT FROM AUTHOR]