Elastoplastic Model for Cemented Soils

This paper presents a model for bonded or cemented soils within the framework of hardening plasticity. The model is based on the concepts that (1) the strength of a cemented soil can be considered to be made up of two components, the usual strength of the soil skeleton and the strength of cementation bonds; and (2) the deformation of the soil is associated with the component of stresses on the soil skeleton (excluding the bonds), as in a reconstituted soil, whereas the cement bonds offer additional resistance at any given strain level. The overall response of the soil under loading can be visualized as two stiffnesses acting in parallel for the given unit strain. Separate stress-strain relations are defined for the two components and they are then combined to give the overall response. The stress-strain relationship for the soil skeleton component is described here using the modified Cam-clay model. A simple model within the elastoplastic framework is proposed for the “cemented” component. The cemented component incorporates strain softening. The input parameters required are minimal, well defined, and easily determined. The model predictions are compared with test data of several soils under drained and undrained triaxial conditions.     

Iodide-Enhanced Electrokinetic Remediation of Mercury-Contaminated Soils

This study investigates using an iodide-enhanced solution at the cathode during electrokinetic treatment to optimize the removal of mercury from soils. The experimental program consisted of testing two types of clayey soils, kaolin, and glacial till, that were initially spiked with 500 mg/kg of Hg(II). Experiments were conducted on each soil type at two voltage gradients (1.0 or 1.5 VDC/cm) to evaluate the effect of the voltage gradient when employing a 0.1 M KI solution. Additional experiments were performed on each soil type to assess the effect of using a higher iodide concentration (0.5 M KI) when using a 1.5 VDC/cm voltage gradient. The tests conducted on the kaolin soil showed that when the 0.1 M KI concentration was employed with the 1.0 VDC/cm voltage gradient, approximately 97% of the mercury was removed, leaving a residual concentration of 16 mg/kg in the soil after treatment. The tests conducted on glacial till indicated that it was beneficial to use the higher (0.5 M KI) iodide concentration and the higher (1.5 VDC/cm) voltage gradient to enhance mercury removal, because, under these conditions, a maximum of 77% of the mercury was removed from the glacial till, leaving a residual concentration of 116 mg/kg in soil after electrokinetic treatment. Compared to kaolin, the lower mercury removal from the glacial till soil is attributed to the more complicated soil composition, such as the presence of carbonates and organic matter, which caused Hg(II) to adsorb to the soil and/or exist as an immobile chemical species.     

Degradation of PCB in different soils by inoculated Alcaligenes xylosoxidans

The degradation of PCB in soils by the biphenyl-utilising strain Alcaligenes xylosoxidans was studied in different soil types. In addition to the congener specificity, significant differences in the degradation of PCB by the strain in the different soil types were observed. Efficiency of degradation was generally better in sterilised soils, but the differences were not as significant as the differences observed between different soil types. These results indicate that the degradation of PCB is probably related not only to the capabilities of the strain employed and quality and amount of competitive species inhabiting the soils, but also to the soil sorption of the PCB congeners. Degradation is faster in the soils containing an intermediate amount of organic carbon with a high portion of total and aromatic carbon in humic acids.     

Some Design Considerations for Embankments on Rate Sensitive Soils

Both the short-term and long-term behavior of reinforced embankments constructed on rate sensitive foundation soils is investigated. Factors such as the rate sensitive properties of the foundation soil, reinforcement stiffness, construction rates, and different foundation soil profiles are considered. The strain rate at which the foundation soils deform during and after embankment construction is examined. For embankments on these soils the analysis indicates that the critical stage with respect to stability occurs during a period of creep and stress relaxation in the foundation soils after construction. The strain rate corresponding to this critical stage controls the operational shear strength of rate sensitive foundation soils and this strain rate falls into a relatively small range of values for the wide range of conditions examined. A technique that allows a conventional undrained limit equilibrium analysis to be modified to allow the design of reinforced embankments over rate sensitive foundation soils is proposed based on the critical stage concept.     

Numerical Modeling of Nonhomogeneous Behavior of Structured Soils during Triaxial Tests

The nonhomogeneous behavior of structured soils during triaxial tests has been studied using a finite element model based on the Structured Cam Clay constitutive model with Biot-type consolidation. The effect of inhomogeneities caused by the end restraint is studied by simulating drained triaxial tests for samples with a height to diameter ratio of 2. It was discovered that with the increase in degree of soil structure with respect to the same soil at the reconstituted state, the inhomogeineities caused by the end restraint will increase. By loading the sample at different strain rates and assuming different hydraulic boundary conditions, inhomogeneities caused by partial drainage were investigated. It was found that if drainage is allowed from all faces of the specimen, fully drained tests can be carried out at strain rates about ten times higher than those required when the drainage is allowed only in the vertical direction at the top and bottom of the specimen, confirming the findings of previous studies. Both end restraint and partial drainage can cause bulging of the triaxial specimen around mid-height. Inhomogeneities due to partial drainage influence the stress–strain behavior during destructuring, a characteristic feature of a structured soil. With an increase in the strain rate, the change in voids ratio during destructuration reduces, but, in contrast, the mean effective stress at which destructuration commences was found to increase. It is shown that the stress–strain behavior of the soil calculated for a triaxial specimen with inhomogeneities, based on global measurements of the triaxial response, does not represent the true constitutive behavior of the soil inside the test specimen. For most soils analyzed, the deviatoric stress based on the global measurements is about 25% less than that for the soil inside the test specimen, when the applied axial strain is about 30%. Therefore it can be concluded that the conventional global measurements of the sample response may not accurately reflect the true stress–strain behavior of a structured soil. This finding has major implications for the interpretation of laboratory triaxial tests on structured soils.     

Experimental Inspiration for Kinematic Hardening Soil Models

Traditional techniques for identifying yielding of soils in the context of classical elastic–plastic soil models are criticized. However, the extended use of such procedures starts to reveal the kinematic nature of the plastic behavior of soils. It is suggested that the experimental determination of stress response envelopes can provide an objective route toward the collection of stress–strain behavior for soils. Stress response envelopes are presented for true triaxial tests on clay and sand: these clearly reveal the kinematic nature of the soil behavior. Response envelopes are presented for different magnitudes of strain probes. As the magnitude of a strain probe increases, the kinematic element of the response decays and the memory for the increasingly distant history is swept out.     

Yield Stress of Super Soft Clays

Super soft clays can be defined as insensitive cohesive soils that have a water content higher than the liquid limit. It is difficult to define and measure the strength of these soils using conventional soil mechanics apparatus. It is proposed that the shear strength be determined using a rotary viscometer and be defined as the shear stress at zero strain (shear strain) rate in this test of viscosity. In this paper a number of potential methods to determine the shear strength or yield stress of super soft clays is considered. The yield stress of four super soft soils, each with varying water contents, have been measured using a rotary viscometer. The results of these tests together with published data are used to develop a relationship between the yield stress and the index properties of super soft clays.     

Plane Strain and Axially Symmetric Consolidation in Unsaturated Soils

A method is presented for the analysis of coupled consolidation in unsaturated soils due to loading under conditions of plane strain as well as axial symmetry. The method is based on the transformation of the governing differential equations by the Fourier transform, when the soil system is deformed under plane strain conditions, or Hankel transform for problems exhibiting axial symmetry. The effect of such transformations is to simplify considerably the solution from a computational point of view. In addition, using these transformations the same differential equations can be used to analyze consolidation under both the above conditions. Results are presented to point out some aspects of the consolidation in unsaturated soils generated by the application of strip as well as circular loads.     

Viscoplastic Cap Model for Soils under High Strain Rate Loading

A viscoplastic cap model of the Perzyna type was developed for simulating high strain rate behaviors of soils. An associative viscous flow rule was used to represent time-dependent soil behaviors. The viscoplastic cap model was validated against experimental data from static and dynamic soil tests. The model was also compared with soil behaviors under creep and stress relaxation with good agreement. However, the model was unable to represent tertiary creep where strain softening became significant. The model was subsequently integrated into LS-DYNA for finite-element simulations of high strain rate behaviors of sandy and clayey soils in explosive tests. The significance of strain rate effect on the soil responses is presented herein. It is concluded that the viscoplastic cap model is adequate for simulations of soil behaviors under high strain rate loading, creep, and stress relaxation, covering a wide range of time-dependent problems.     

Influence of In Situ Factors on Dynamic Response of Piedmont Residual Soils

The in situ chemical and physical weathering of igneous and metamorphic rocks, indentified as the process of formation of Piedmont residual soils, is a fairly well understood phenomenon. However, the effect this weathering has on the physical, mechanical, and dynamic properties of the rock∕soil is not understood fully. This study focuses on the dynamic shear modulus, G, and material damping ratio, D, of this soil formation for low- to mid-level amplitudes of vibration. The paper presents laboratory test results and correlations that demonstrate the effects that the degree of weathering has on these properties for various levels of confining pressure and shear strain amplitude. A total of 12 specimens of Piedmont residual soils from different depths were tested in a Resonant Column (RC) device. The specimens tested were SM and ML soils according to the USCS classification. The low-amplitude shear modulus and damping values were found to be similar to those reported in the literature from laboratory and in situ tests on the same type of soils. It was found that weathering, void ratio, and apparent overconsolidation ratio exert a noticeable influence on the dynamic response as a result of variations in confining pressure. The understanding of these effects will allow for a better prediction of phenomena such as soil amplification, which may result in damage to existing civil infrastructure founded on these soil deposits. The response in free field soil deposits compared with that of soils experiencing added confining stresses due to foundation loading appears to vary significantly in these geologic formations. Threshold strain and the variation of damping, D, with the normalized shear moduli, G∕Gmax, fall within the same range as those recently reported by other authors in similar soils.     

The effect of isosorbide dinitrate following experimental coronary occlusion

A new case, the third in Israel, of subcutaneous sporotrichosis is presented. A pigmentary strain of Sporothrix schenckii was cultured from the unopened and necrotic nodules of the left hand and forearm of an 80-year-old male. Experimental inoculation of the isolated fungus into mice led to the dissemination of the organism in the liver, kidneys and lungs inoculated intraperitoneally, and the development of orchitis with abscess formation in those inoculated intratesticularly. In both groups of mice the causative agent was successfully recovered. Three months of treatment with oral potassium iodide led to the disappearance of the lesions. The source of contamination was found to be the soil adhering to fragments of wood. Two strains of a fungus, morphologically identical to the human S. schenckii, were isolated through the mouse procedure and agar-plating method from soil samples collected in the vicinity of the patient's residence. The soil isolates also proved to be pathogenic in animal inoculation. This is the first isolation of S. schenckii from soils in Israel. The possible relationships between the soil isolates and Ceratocystis stenoceras are discussed.     

Undrained Shear Strength of Granular Soils with Different Particle Gradations

A series of undrained tests were performed on granular soils consisting of sand and gravel with different particle gradations and different relative densities reconstituted in laboratory. Despite large differences in grading, only a small difference was observed in undrained cyclic shear strength or liquefaction strength defined as the cyclic stress causing 5% double amplitude axial strain for specimens having the same relative density. In a good contrast, undrained monotonic shear strength defined at larger strains after undrained cyclic loading was at least eight times larger for well-graded soils than poorly graded sand despite the same relative density. This indicates that devastating failures with large postliquefaction soil strain are less likely to develop in well-graded granular soils compared to poorly graded sands with the same relative density, although they are almost equally liquefiable. However, if gravelly particles of well-graded materials are crushable such as decomposed granite soils, undrained monotonic strengths are considerably small and almost identical to or lower than that of poorly graded sands.     

黑麦草-AMF联合修复铀污染土壤的根际效应

为探究丛枝菌根真菌对植物根际铀的迁移和形态的影响,以铀矿山周边土壤为基础配置多种铀浓度土壤,选取黑麦草作为供试植物,根内球囊霉（Glomus intraradice,Gi）为供试菌株进行盆栽试验。结果显示：黑麦草接种Gi后会促进土壤中的铀向根际和植物根部迁移,铀浓度分布由高到低依次为黑麦草根部、根际土和非根际土;接种Gi改变了根际土中铀的存在形态,黑麦草根际土中的活性态铀占比由32.6%降到30.0%,惰性铀占比由24.9%降至16.3%,潜在活性铀占比由42.5%升至53.7%。接种Gi能促进黑麦草根部对活性态铀的吸收和根际土中惰性态铀向潜在活性态铀的转化。     

Experimental and Modeling Studies of Permanent Strains of Subgrade Soils

Mechanistic-empirical pavement design guide for flexible pavements as per the AASHTO design guide requires characterization of subgrade soils using the resilient modulus (MR) property. This property, however, does not fully account for the plastic or permanent strain or rutting of subgrade soils, which often distress the overlying pavements. Soils such as silts exhibit moderate to high resilient moduli properties but they still undergo large permanent deformations under repeated loading. This explains the fallacy in the current pavement material characterization practice. A comprehensive research study was performed to measure permanent deformation properties of subgrade soils by subjecting various soils under repeated cycles of deviatoric loads. This paper describes test procedure followed and results obtained on three soils including clay, silt, and sandy soils. The influence of compaction moisture content, confining pressure, and deviatoric stresses applied on the measured permanent deformations of all three soils are addressed. A four-parameter permanent strain model formulation as a function of stress states in soils and the number of loading cycles was used to model and analyze the present test results. The model constants of all three soils were first determined and these results were used to explain the effects of various soil properties on permanent deformations of soils. Validation studies were performed to address the adequacy of the formulated model to predict rutting or permanent strains in soils.     

Characterization of Rutting (Permanent Strain) Development of A-2-4 and A-4 Subgrade Soils under the HVS Loading

As part of a national pool funded study 208 on pavement subgrade performance, 12 full-scale test sections (four soil types and three moisture contents) were constructed and tested under the heavy vehicle simulator (HVS) loading. This paper presents the HVS results on two of the four soils tested: AASHTO Class A-2-4 and A-4 soils, respectively. From the results, it was found that the pavement subgrade performance is a function of soil type, moisture content, and applied stress condition. Additionally, this paper also evaluated the current mechanistic-empirical pavement design guide (MEPDG) subgrade rutting (permanent strain) model through comparing with the actual measurements under the HVS loading. It was found that the MEPDG subgrade permanent strain model needs further improvement, and that a single performance model may not be universally applicable to different subgrade soil types. Consequently, a new permanent strain model for each soil type was developed in this paper, based on the HVS results, and that yielded better predictions. With further validation and field calibration, the proposed models offer promising potential to accurately predict rutting behavior of these two soils.     

The significance and trend of hypertension related deaths in urban Sierra Leonean Africans

This study tried to show the contributory role of ions (cations and anions) to great contrast in the goitre prevalence between Bassa and Jos Local Government Areas, both of Plateau State, Nigeria. In pursuance of this, the concentration of cations (Ca++, Fe++, K+, Mg++, Na+, & Zn++) and anions (C1-, F, I-, & NO-3) in soil and drinking water in the two LGAs were determined and their results compared and correlated with the goitre prevalence of these areas. It was observed that both Bassa and Jos LGAs have very low but similar amounts of iodide ions in their soils. Besides, Bassa LGA contained more ions in both soil and drinking water than Jos LGA. In conclusion, the results appear to suggest that the higher ion contents of both soil and drinking water in Bassa LGA exacerbated the coexisting low iodide condition of the LGA, thus resulting in the higher goitre prevalence found in the LGA.     

Analysis of Steady Cone Penetration in Clay

In this paper, a novel finite-element procedure is used to analyze steady cone penetration in soils. Although the procedure is, in principle, applicable to clay and sand with any plasticity model, this paper is only concerned with steady cone penetration in undrained clay. The steady-state finite-element analysis focuses on the total displacements experienced by soil particles at a particular instant in time during the cone penetration test. This is possible because, with the steady-state assumption, the time dependence of stresses and strains can be expressed as a space dependence in the penetration direction. As a result, the finite-element solution of steady cone penetration can be obtained in one step. When compared with the strain path method, the present finite-element procedure offers the following advantages: (1) All equations of soil equilibrium are fully accounted for; (2) cone and shaft roughness can be taken into account in a more rigorous manner and, as a result, the sleeve friction ratio can be properly predicted; and (3) the finite-element procedure can be more easily adapted to analyze cone penetration in dilatant soils.     

Interpretation of Pressuremeter Tests in Sand using Advanced Soil Model

This paper describes a numerical study of drained pressuremeter tests in sand using a one-dimensional finite-element method in conjunction with an advanced soil model MIT-S1, and input parameters corresponding to Toyoura sand. This soil model is capable of describing realistically the transitions in peak shear strength parameters of cohesionless soils that occur due to changes void ratio and confining pressure. The predicted peak shear strengths can be normalized, at least approximately, by introducing a state parameter that references the initial (preshear) void ratio to the value occurring at large strain critical state conditions at the same mean effective stress. The numerical analyses idealize the pressuremeter test as the expansion of a cylindrical cavity and ignore disturbance effects caused by probe insertion. This idealization is relevant to self-boring pressuremeter tests. Results confirm that there is a linear correlation between the in situ (i.e., preshear) state parameter of the soil and the gradient of the log pressure-cavity strain expansion, as first suggested by Yu in 1994 using a much simpler soil model. Indeed, the linear coefficients derived for Toyoura sand differ only slightly from those obtained previously by Yu for six other sands.     

Applications of the PM3 semi-empirical method to the study of triethylenediamine

Charcoal filters impregnated with triethylenediamine (TEDA) are known to be efficient for the collection of volatile methyl iodide, which may be released under a hypothetical loss-of-coolant accident in a nuclear generating station. The structure and thermodynamic stability of the products of the TEDA-methyl iodide reaction have thus been studied using semi-empirical techniques. The reaction of TEDA with two molecules of methyl iodide leads to a quaternization reaction at each of the nitrogens. Moreover, it is shown that substitution of the hydrogens on TEDA with electron-donating groups can lead to enhanced stability of the quaternary ammonium reaction products. The semi-empirical method PM3 (Parametric Method 3) was used as the basis for all calculations. Molecular systems and simulations were constructed using HyperChem 4.5 for Silicon Graphics workstations. Enthalpy determination and geometry optimization were some of the calculations performed on a system.     

Design of Compacted Lateritic Soil Liners and Covers

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.