This work provides an insight into how the molecular interactions influence macroscale properties of two materials: swelling clay and oil shale. Swelling clays cause enormous damage to infrastructure: buildings, roads, and bridges. Understanding the mechanisms are essential to prevent the detrimental effects and use of these clays for engineering applications. Our group studied the effect of fluid polarity on sodium montmorillonite (Na-MMT) swelling clay mineral using molecular modeling and experiments for bridging the molecular level behavior with the microstructure, swelling pressure, permeability, and compressibility. Various polar fluids (Dielectric Constant 110 to 20) found in landfill leachates are used. Our molecular dynamics (MD) simulations show that the nonbonded interactions of Na-MMT with polar fluids are higher than with low and medium polar fluids. These results are consistent with the results from Fourier transform infrared (FTIR) spectroscopy experiments. The polarity of the fluids and the fluid content influence the interlayer spacing, interlayer modulus, nonbonded interactions, and conformation as well as the shear strength parameters, the angle of internal friction (φ) and cohesion (c). Furthermore, the unconfined compressive strength experiments are used to evaluate the undrained cohesion at various swelling level. The nanomechanical properties, the modulus of elasticity (E) and hardness (H), of the undisturbed dry and saturated Na-MMT at various level of swelling are evaluated using nanoindentation experiments for the first time. The undrained cohesion, modulus of elasticity, and hardness decrease with increase in swelling level. Swelling controls the microstructure of Na-MMT clay, and the clay particles breakdown into smaller sizes with increase in swelling level. The Green River Formation located in the United States is the richest oil shale deposit in the world. Oil shale contains clay minerals, bitumen, and kerogen—a precursor to crude oil. A three-dimensional (3D) kerogen model is built from seven fragments, and the interactions of kerogen with Na-MMT is investigated using MD simulations to understand how the kerogen is bound to the clay mineral. The nonbonded interactions between Na-MMT and kerogen as well as among kerogen fragments are found. This work seeks to develop new methods to extract kerogen economically and efficiently. / Department of Energy (DoE) / Mountain Plains Consortium (MPC) / North Dakota Established Program to Stimulate Competitive Research (ND EPSCoR)

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / n this article, the geotechnical behavior of the reinforced soil is studied through additions of polypropylene fiber and recycled glass powder, this in order to obtain a homogeneously reinforced soil matrix to reduce possible structural failures, differential settlements and increase capacity bearing. The sample used was classified as a clay soil with low plasticity (CL) and with moderately expansive characteristics, based on the values of the Liquid Limit, Plastic Limit and Plasticity Index. The effect of the 1% polypropylene fiber and different amounts of recycled glass powder (0%, 4%, 5%, 6.5%), with respect to dry weight is analyzed in this soil. The purpose of varying the quantity of these materials is to find a trend of the strength parameters and obtain the optimal percentages that provides improvements in geotechnical behavior. Modified Proctor and Direct Shear tests were carried out, this latter to obtain the shear strength parameters of the mixtures and compare them with the clay soil. Finally, the optimal result for soil improvement was the mixture made by 1% polypropylene fiber and 4% glass powder, which achieved an increase of the angle of friction and cohesion.

Compacted soils are frequently used as subgrade for pavements as well as commercial and residential buildings. The stiffness and shear strength properties of compacted soils, which are collectively denoted as Ω in this thesis, fluctuate with moisture content changes that result from the influence of environmental factors such as the evaporation and infiltration. For example, mechanistic pavement design methods require the information of resilient modulus (MR), which is the soil stiffness behavior under cyclic traffic loading, and its variation with respect to the soil moisture content determined from laboratory tests or estimation methods. Significant advances have been made during the last five decades to understand and model the variation of the Ω with respect to soil moisture content and soil suction (s) based on the principles of mechanics of unsaturated soils. There are a variety of models presently available in the literature relating the Ω to the s using different approaches. There are however uncertainties extending these models for predicting Ω - s relationships when they are used for a larger soil suction range. In addition, the good performance of these models are only valid for certain soil types for which they were developed and calibrated. Studies presented in this thesis are directed towards developing a unified methodology for modelling the relationship between the Ω and the s using limited while easy-to-obtain information. However, more emphasis has been focused on the MR - s relationships of pavement subgrade soils considering the need for the application of the mechanistic pavement design methods in Canada. The following studies have been conducted: (i) State-of-the-art review on existing equations in the literature for the MR - s relationships is summarized. A comparison study is followed to discuss the strengths and limitations of these equations; (ii) A unified methodology for modelling the Ω - s relationships is proposed. Experimental data on 25 different soils are used to verify the proposed unified methodology. The investigations are applied on small strain shear modulus, elastic modulus, and peak and critical shear strength. Good predictions are achieved for all of the investigated soils; (iii) Performance of the proposed methodology is examined for the MR - s relationships using experimental data of 11 subgrade soils. Reasonably good predictions are achieved for all of the subgrade soils; (iv) Extensive experimental investigations are conducted on the MR - s relationships for several subgrade soils collected from various regions in Canada. Experimental results suggest non-linear variation in the MR with respect to s, moisture content and the external stress. The measured results are modelled using the proposed methodology with adequate success; (v) Additional experimental investigations are performed to determine the variation of the elastic modulus (E) and unconfined compression strength (qu) with the s and the gravimetric moisture content (w) for several Canadian subgrade soils. An approach, which is developed extending the proposed unified methodology, is used to normalize the measured MR - w, E - w and qu - w relationships. It is shown that the normalized MR - w, E - w and qu - w relationships exhibit remarkable similarity and can be well described using the proposed approach. Such similarity in the normalized Ω - moisture content relationships are also corroborated using the experimental data on several other soils reported in the literature. The proposed unified methodology alleviates the need for the determination of the Ω - s relationships which requires elaborate testing equipment that needs the supervision of trained personnel and is also time-consuming and expensive. In addition, experimental programs in this thesis provide detailed experimental data on the MR, E, qu, and soil-water characteristic curves of Canadian subgrade soils. These data will be helpful for the better understanding of the hydro-mechanical behavior of the Canadian subgrade soils and for the implementation of the mechanistic pavement design method in Canada. The simple tools presented in this thesis are promising and encouraging for implementing the mechanics of unsaturated soils into conventional geotechnical engineering practice.

Thesis (Civ.E)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1981 / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 107-108. / by Robert William Day. / Civ.E

Research is presented which encompasses a study of epoxies based on diglycidyl ether of bisphenol A (DGEBA) cured with 2-ethyl-4-methylimidazole (EMI-24) in the presence of the nonionic surfactant Triton X-100. Interest in this epoxy system is due partially to the potential application as a waterborne replacement for solvent cast epoxies in E-glass laminated printed circuit boards. This research has revealed that the viscoelastic behavior of the cured epoxy is altered when serving as the matrix in a glass composite. The additional constraining and coupling of the E-glass fibers to the segmental motion of the epoxy matrix results in an increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E-glass composite is also sensitive to the surface chemistry of the glass fibers. Model single-ply epoxy/E-glass laminates were constructed in which the glass was pretreated with either 3-aminopropyltriethoxysilane (APS) or 3-glycidoxypropyltrimethoxysilane (GPS) coupling agents. Dynamic mechanical analysis (DMA) was then used to create master curves of the storage modulus (E') in the frequency domain. The frequency range of the master curves and resulting cooperativity plots clearly varied depending on the surface treatment of the glass fibers. It was determined that the surfactant has surprisingly little effect in the observed trends in cooperativity of the composites. However, the changes in cooperativity due to the surface pretreatment of the glass were lessened by the aqueous phase of the waterborne resin. Moisture uptake experiments were also performed on epoxy samples that were filled with spherical glass beads as well as multi-ply laminated composites. No increases in the diffusion constant could be attributed to the surfactant. However, the surfactant did enhance the final equilibrium moisture uptake levels. These equilibrium moisture uptake levels were also sensitive to the surface pretreatment of the E-glass. / Ph. D.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering. / The project report deals with the relationship between the undrained shear strength and the moisture content of Red Berea sand tailings. The tailings were obtained from the Red Berea sand dunes near Richards Bay, Kwa-Zulu Natal, South Africa. The geology of the area consists of Miocene deposits of red clayey sand, classified as Berea Formation. A method for determining stability of a tailings dam for Red Berea sand tailings, was investigated. The general method of using the degree of saturation of the tailings to specify the rate of rise, is not applicable to this type of tailings. It was found that a relationship exists between the undrained shear strength of the tailings, and the moisture content. The moisture content can easily be measured and the undrained shear strength can then be calculated. The calculated undrained shear strength can be used in a total stress analysis to determine a factor of safety against failure. This project report consists of a discussion of the literature, which was used as the basis for the assumptions made, as well as a description of the tests performed to prove the above-mentioned relationship. Test results are given, interpreted and used in an illustrative example of a stability analysis. / Andrew Chakane 2020

No description available.

When a clay soil is sheared, clay particles along the shear plane become aligned in the direction of shear, forming "slickensided" surfaces. Slickensided surfaces are often observed along the sliding plane in field landslides. Because the clay particles along a slickensided surface are already aligned in the direction of shear, the available shear resistance is significantly less than that of the surrounding soil. During an earthquake, ground shaking often causes landslide movement. For existing landslides or repaired landslides that contain slickensided rupture surfaces, it is reasonable to expect that the movement will occur along the existing slickensided surfaces, because they are weaker than the surrounding soil. The amount of movement that occurs is controlled by the dynamic resistance that can be mobilized along the slickensided surfaces. The objective of this study was to investigate, through laboratory strength tests and centrifuge model tests, the shearing resistance that can be mobilized on slickensided rupture surfaces in clay slopes during earthquakes. A method was developed for preparing slickensided rupture surfaces in the laboratory, and a series of ring shear tests, direct shear tests, and triaxial tests was conducted to study the static and cyclic shear resistance of slickensided surfaces. Two dynamic centrifuge tests were also performed to study the dynamic shear behavior of slickensided clay slopes. Newmark's method was used to back-calculate cyclic strengths from the centrifuge data. Test results show that the cyclic shear resistance that can be mobilized along slickensided surfaces is higher than the drained shear resistance that is applicable for static loading conditions. These results, coupled with a review of existing literature, provide justification for using cyclic strengths that are at least 20% larger than the drained residual shear strength for analyses of seismic stability of slickensided clay slopes. This represents a departure from the current state of practice, which is to use the drained residual shear strength as a "first-order approximation of the residual strength friction angle under undrained and rapid loading conditions" (Blake et al., 2002). / Ph. D.

Unlike other thermo-mechanical soil responses, the effects of temperature on residual shear strength of soils are not well understood. Previous studies on temperature effects on residual shear strength show some contradictory findings that might be attributed to the sample's mineralogical composition and the testing procedure. This thesis aims to contribute to the understanding of (1) the temperature effects on the liquid limit of cohesive soils, (2) the impact of testing procedure on temperature-dependent residual friction angle, and (3) temperature effects on residual friction angle of soils. The fall cone tests are used to determine temperature effects on the liquid limit, while a temperature-modified ring shear apparatus is used to evaluate the residual friction angle in this study. To assess the impact of the testing procedure, the temperature is changed to 50°C at three different instants: before consolidation, before preshearing, and after preshearing; the resulting residual friction angles are assessed and compared. The effects of temperature on residual friction angle of soils are also investigated by changing the temperature in the ring shear apparatus to 10°C, 20°C, 40°C, and 50°C before consolidation. The study found that the impacts of temperature on liquid limit is mineralogy dependent. Also, the instant at which temperature change occurs in ring shear tests was found to be insignificant in terms of the residual friction angle. Moreover, the findings of the ring shear experiments suggest that clay mineralogy is important in the study of temperature-dependent residual friction angle of cohesive soils. Antigorite-rich soils may experience up to 50% changes in their residual friction angle, while soils with other clay minerals may experience less than 20% variations over a temperature range from 10 to 50 °C. / Master of Science / The increase in the frequency of landslides was found to be attributed to seasonal variation in temperature and an increase in global temperature due to climate change. To anticipate, mitigate and adapt to this costly natural disaster, understanding soil response to temperature change is an essential step. The residual shear strength of a soil is a parameter used to analyze stability of landslides. The relationship between this residual shear strength and temperature is not well understood. Previous studies on temperature effects on residual shear strength show some contradictory findings that need to be better understood for a more robust assessment of the climate change impacts on the stability of natural and man-made slopes. This thesis represents a first step to fill the knowledge gap in identifying the temperature effects on the residual shear strength of soils so that the impact of climate change and seasonal variation in temperature on slopes can be assessed more rigorously. This study consists of three tasks. The first task is to assess the effects of temperature on liquid limit, a parameter widely used to estimate the residual shear strength. The second task is to investigate the impacts of the testing procedures on residual shear strength, representing three field conditions where temperature change takes place at three different instants: when the soils is consolidating under applied load, after the soil consolidated and before development of a failure plan, and after failure initiated. The last task is to assess the effects of temperature on residual shear strength of soils. From the study, it was found that the effects of temperature on liquid limits and residual shear strength are dependent on the soil's mineralogical composition. It was also found that the instant in which the temperature changes in the testing procedure does not substantially impact the residual friction angle of the soil.

No description available.