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Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Expansive soils are extremely problematic in transportation projects, and significant research has been done into examining the effect of moisture content changes and index properties on the swelling of soils. However, little has been reported on the effect of soil structure, or fabric, on swelling. The purpose of this study is to examine the effect of the soil fabric on swelling while, at the same time, validating a new set-up for a centrifuge testing program developed over the course of the project to allow for testing of undisturbed specimens. Testing to examine fabric was performed using two methods at the same effective stress, the conventional swelling test, ASTM D4546, and a new double infiltration approach in a centrifuge, on specimens of the Cook Mountain clay which were either compacted in the testing set-up or trimmed into cutting rings from soil compacted via ASTM D698, the Standard Proctor test. Specimens were compacted either dry of optimum to create a flocculated soil structure or wet of optimum to create a dispersed soil structure. Specimens were tested at their as-compacted moisture content or at a moisture conditioned moisture content to remove the effect of the initial moisture content. The results show that soils with a dispersed structure tended to swell more, over a longer time frame, and with a higher amount of secondary swelling in relation to soils with a flocculated structure when tested using the same initial moisture content. The strong influence of the initial moisture content on swelling was also verified. Further, soil specimens prepared at a comparatively high dry density for a given fabric and initial moisture content were found to swell more than soils prepared at a comparatively low dry density. The new centrifuge set-up, involving submerged specimens, was validated and was found to produce similar swelling results as those obtained from the ASTM D4546 tests. In addition, the new centrifuge approach was found to be more expeditious and results in less secondary swelling than the conventional ASTM approach. / text

One-dimensional swelling tests were conducted on seven undisturbed and remoulded heavily-overconsolidated clays and indurated mudstones. The samples cover a wide range of properties in terms of geological age, mineralogy, plasticity and diagenetic bonds. It is found that swelling proceeds faster than is predicted by Terzaghi's theory of swelling at low overconsolidation ratios (OCR), but it is slower at high OCR values, probably due to the prominence of secondary swelling. The results show that swelling is of a progressive nature, regardless of plasticity and diagenetic bonds. The coefficient of swelling decreases and the ratio of secondary to primary swelling increases with increasing OCR. At high OCR's, the former drops by more than an order of magnitude below the coefficient of consolidation; the latter can be as high as 0.6 within a log-cycle of time. Progressive softening and failure phenomena in mudrocks are considered to be due to the combined effects of progressive swelling and breakdown of diagenetic bonds. Swelling pressure is found to be indicative of in situ stress conditions. The average swelling index generally increases with pre-consolidation pressure in remoulded samples. Three types of diagenetic bonds are postulated: carbonate cements, viscous-adsorbed-water-type, and mechanical adhesion. Bonds tend to decrease the swelling index and so increase the coefficient of swelling. The fabric of the samples is far different from that assumed in the double-layer theory, which can qualitatively predict the physico-chemical forces involved in swelling. Dead volume, in which the double-layer force cannot operate, is shown to be large. The results of tests using n-decane as pore fluid to suppress osmotic swelling indicates that mechanical swelling is more than 50 to 60 per cent of total swelling in the samples. Both mechanical and total swelling indices are linearly correlated with liquid limit among remoulded samples, except for the Fuller's Earth clay which contains at least 65 per cent smectite (expandable clay).

Thesis (D.E.)--University of Adelaide, 1991. / Includes bibliographical references.

Hydrogels are polymeric materials with chemically, physically or topologically crosslinked networks which have a capacity to absorb and retain water. They have been frequently used for many medical applications because of their useful physical properties such as oxygen permeability and excellent compatibility with living tissue and blood. The long term goal of this research is to develop a hydrogel system for potential use in reconstructive and plastic surgeries such as the closure of cleft palate defects and syndactyly (congenitally fused fingers or toes) repair. The medical requirements for such systems are not only a high degree of swelling, but also slow swelling rate, preferred direction of swelling (anisotropic swelling), appropriate mechanical strength, in addition to being biocompatible. A large degree of swelling would limit the number of surgical procedures required thereby reducing the cost and risk of surgery. A slow swelling rate can avoid tissue necrosis and help tissue growth during the tissue expansion process. Anisotropic swelling is required for specific surgical applications such as cleft palate repairs. Known to be biocompatible hydrogel systems, of a neutral gel system consisting of N-vinyl-2-pyrrolidinone (VP) and 2-hydroxyethyl methacrylate (HEMA) copolymers and an ionizable gel system of VP and acrylic acid (AA) copolymers were prepared using thermal and controlled UV-initiated polymerization. Using these VP/HEMA and VP/AA gel systems, various approaches to control their degree and rate of swelling were studied as a function of key controllable parameters. Their mechanical properties and structural characteristics determining their swelling behavior and mechanical properties also were investigated. Through these studies, how to control the key parameters that affect such swelling behavior was understood in addition to optimizing the gel systems for large degree of swelling, slow swelling rate, and mechanical integrity. Investigations into a number of methods to control the swelling rate were also undertaken for different VP/HEMA based gel systems. Multilayers of alternating gels and elastomer films (polybutadiene (PB) or polydimethylsiloxane (PDMS)) as well as gels encapsulated with the elastomer films were prepared. In addition, gels were prepared with inclusion of either silver nanoparticles or methacrylates with increasing the length of hydrophobic groups for the studies of swelling rate. In this work, two novel methods to control swelling direction (anisotropic swelling) of hydrogels were investigated. One method induces anisotropic swelling through structural gradients within the VP/HEMA gels synthesized by UV polymerization using gradient photomasks. A more promising method used stress induced anisotropic swelling for compressed VP/AA gels. The morphology-gradient VP/HEMA hydrogel system did not show large scale anisotropic swelling. However, the compressed VP/AA gels produced significant anisotropic swelling due to the controlled anisotropy of network morphology. A systematic study as a function of compression temperature, stain and strain rate was performed to derive an understanding of the anisotropic swelling behavior. These compressed gel systems produced not only a large degree of swelling and slow swelling rates but also high anisotropic swelling and proper mechanical stiffness of hydrogels. These materials are believed to be ideal candidates for tissue or skin expansion.

The present thesis is composed of two parts. The first part presents the chemo-mechanical effect on the volumetric and shearing behaviour of saturated soil as a continuum. The second part presents the chemo-mechanical effect on the shearing behaviour of a discontinuity. Following Gajo and Loret, 2003, saturated soil is considered as a two-phase deformable porous medium, namely solid and fluid phase consisting of different species. There are clay particles, adsorbed water and ion in the solid phase. The fluid phase includes pore water and salt which may diffuse through the porous medium. In addition, water may be exchanged between solid and fluid phases while the mass of clay particles and ions in the solid phase remains constant. Thus, the balance equations are momentum balance, the mass balance of pore water and salt in the fluid phase, the mass balance of absorbed water. A two-dimensional element is proposed to approximate the solution of the balance equations which has been implemented in a user-defined subroutine (UEL) of the commercial code ABAQUS. This element has taken into account the 2D displacement of the soil skeleton, multidimensional flow of water, osmotic effect, advection and diffusion of salt. A new hyperelastic law is presented by extending the chemo-mechanical model proposed by Loret et al., 2002. The innovative aspects of the proposed model are the following: 1) both the tangent shear stiffness and bulk stiffness depend on the applied stress state and pore water solution, 2) the anisotropy of fabric tensor is introduced in the elasticity law. Moreover, the yield function has been modified to obtain smaller peak strength for highly overconsolidated samples to have better agreement with experimental results. The proposed 2D model is validated with experimental results on natural bentonite (a very active clay) and the soil extracted from low activity clay of Costa della Gaveta slope in Southern Italy. The swelling and swelling pressure of these two types of soil have been computed and compared with the experimental data to show the accuracy and reliability of the proposed model. Furthermore, the effects of elastic anisotropy are investigated on the soil behaviour such as swelling, swelling pressure, stress paths and horizontal stress. Furthermore, a simplified analysis has been performed to show the effect of swelling pressure on slope stability. In the second part, a contact element is proposed to account for the flow of water and diffusion of salt in addition to displacement in the simulation of interface behaviour. This element has been implemented in a user-defined subroutine (UEL) of ABAQUS. Moreover, a nonlinear elasticity law is proposed in which traction in the contact region has been taken into account. The Mohr-Columb yield criterion is used for the plastic regime in which it is assumed that the friction angle is a function of salt concentration and displacement rate based on the experimental data. Some preliminary results are shown for the flux of salt and water through the element. In addition, the effects of salt concentration and displacement rate are presented on the shearing behaviour of the contact element.

Theoretical models are used in support of the I2S-LWR (Integral Inherently Safe LWR) project for a direct comparison of fuel swelling and fission gas bubble formation between U₃Si₂ and UO₂ fuels. Uranium silicide is evaluated using a model developed by Dr. J. Rest with the fuel in a amorphous state. The uranium dioxide is examined with two separate models developed using a number of papers. One model calculates the swelling behavior with a fixed grain radius while the second incorporates grain growth into the model. Uranium silicide rapidly becomes amorphous under irradiation. The different mechanisms controlling the swelling of the fuels are introduced including the knee point caused by the amorphous state for the U₃Si₂. The outputs of each model are used to compare the fuels.

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