Browsing by Subject "Swelling"
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Item Characterization of the swelling potential of expansive clays using centrifuge technology(2010-05) Kuhn, Jeffrey Albin; Zornberg, Jorge G.; Gilbert, Robert B.; Scanlon, Bridget R.; Folliard, Kevin J.; DiCarlo, DavidThe characterization of the swell potential of expansive clay is complicated by the fact that traditional swell testing methods require an excessive amount of time for specimens to swell to their maximum heights. As a result, the practicing engineer has typically referred to correlations between swell potential and index properties rather than directly measuring swelling in a laboratory experiment. The purpose of this study is to evaluate an alternate testing method using a geotechnical centrifuge in an attempt to decrease the time required to evaluate the swell potential of expansive clays so that expermientally obtained swelling properties may be obtained within a reasonable time period. This study includes an experimental program involving a series of tests in which compacted clay specimens are flown in a cetrifuge and their heights are monitored as water infiltrates into them.Item Coupled chemo-mechanical processes in reservoir geomechanics(2018-06-15) Shovkun, Igor; Espinoza, David N.; Sharma, Mukul M; Foster, John T; Balhoff, Matthew T; Hesse, Marc EReservoir geomechanics investigates the implications of rock deformation, strain localization, and failure for completion and production of subsurface energy reservoirs. For example, effective hydraulic fracture placement and reservoir pressure management are among the most important applications for maximizing hydrocarbon production. The correct use of these applications requires understanding the interaction of fluid flow and rock deformations. In the past a considerable amount of effort has been made to describe the role of poroelastic and thermal effects in geomechanics. However, a number of chemical processes that commonly occur in reservoir engineering have been disregarded in reservoir geomechanics despite their significant effect on the mechanical behavior of rocks and, therefore, fluid flow. This dissertation focuses on the mechanical effects of two particular chemical processes: gas-desorption from organic-rich rocks and mineral dissolution in carbonate-rich formations. The methods employ a combination of laboratory studies, field data analysis, and numerical simulations at various length scales. The following conclusions are the results of this work: (1) the introduced numerical model for fluid flow with effects of gas sorption and shear-failure-impaired permeability captures the complex permeability evolution during gas production in coal reservoirs; the simulation results also indicate the presence non-negligible sorption stresses in shale reservoirs, (2) mineral dissolution of mineralized fractures, similar to pore pressure depletion or thermal cooling/heating can increase stress anisotropy, which can reactivate critically-oriented natural fractures; in-situ stress chemical manipulation can be used advantageously to enlarge the stimulated reservoir volume, (3) semicircular bending experiments on acidized rock samples show that non-planar fractures follow high porosity regions and large pores, and that fracture toughness correlates well with local porosity. Numerical modeling based on the Phase-Field approach shows that a direct relationship between fracture toughness and porosity permits replicating fracture stress intensity at initiation and non-planar fracture propagation patterns observed in experiments, and (4) numerical simulations based on a novel reactive fluid flow model coupled with geomechanics show that mineral dissolution (i) lower fracture breakdown pressure, (ii) can bridge a transition from a toughness-dominated regime to uncontrolled fracture propagation at constant injection pressures, and (iii) can increase fracture complexity by facilitating propagation of stalled fracture branches. The understanding of these chemo-mechanical coupled processes is critical for safe and effective injection of CO2 and reactive fluids in the subsurface, such as in hydraulic fracturing, deep geothermal energy, and carbon geological sequestration applications.Item Effect of fabric on the swelling of highly plastic clays(2014-05) Armstrong, Christian Philip; Zornberg, Jorge G.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.Item Modelling and simulations of hydrogels with coupled solvent diffusion and large deformation(2014-12) Bouklas, Nikolaos; Huang, Rui, doctor of civil and environmental engineering; Landis, Chad M.Swelling of a polymer gel is a kinetic process coupling mass transport and mechanical deformation. A comparison between a nonlinear theory for polymer gels and the classical theory of linear poroelasticity is presented. It is shown that the two theories are consistent within the linear regime under the condition of a small perturbation from an isotropically swollen state of the gel. The relationships between the material properties in the linear theory and those in the nonlinear theory are established by a linearization procedure. Both linear and nonlinear solutions are presented for swelling kinetics of substrate-constrained and freestanding hydrogel layers. A new procedure is suggested to fit the experimental data with the nonlinear theory. A nonlinear, transient finite element formulation is presented for initial boundary value problems associated with swelling and deformation of hydrogels, based on nonlinear continuum theories for hydrogels with compressible and incompressible constituents. The incompressible instantaneous response of the aggregate imposes a constraint to the finite element discretization in order to satisfy the LBB condition for numerical stability of the mixed method. Three problems of practical interests are considered: constrained swelling, flat-punch indentation, and fracture of hydrogels. Constrained swelling may lead to instantaneous surface instability. Indentation relaxation of hydrogels is simulated beyond the linear regime under plane strain conditions, and is compared with two elastic limits for the instantaneous and equilibrium states. The effects of Poisson’s ratio and loading rate are discussed. On the study of hydrogel fracture, a method for calculating the transient energy release rate for crack growth in hydrogels, based on a modified path-independent J-integral, is presented. The transient energy release rate takes into account the energy dissipation due to diffusion. Numerical simulations are performed for a stationary center crack loaded in mode I, with both immersed and non-immersed chemical boundary conditions. Both sharp crack and blunted notch crack models are analyzed over a wide range of applied remote tensile strains. Comparisons to linear elastic fracture mechanics are presented. A critical condition is proposed for crack growth in hydrogels based on the transient energy release rate. The applicability of this growth condition for simulating concomitant crack propagation and solvent diffusion in hydrogels is discussed.Item Swelling induced deformation and instability of hydrogels(2010-08) Kang, Min Kyoo; Huang, Rui, doctor of civil and environmental engineering; Kyriakides, Stelios; Ravi-Chandar, Krishnaswamy; Landis, Chad M.; Ho, Paul S.A hydrogel consists of a cross-linked polymer network and solvent molecules, capable of large, reversible deformation in response to a variety of external stimuli. In particular, diverse instability patterns have been observed experimentally in swelling hydrogels under mechanical constraints. The present study develops a general theoretical framework based on a variational approach, which leads to a set of governing equations coupling mechanical and chemical equilibrium conditions for swelling deformation of hydrogels, along with proper boundary conditions. A specific material model is employed for analytical and numerical studies, for which the nonlinear constitutive behavior of the hydrogel is derived from a free energy function combining rubber elasticity with a polymer solution theory. A finite element method is then developed and implemented as a user-defined material (UMAT) in the commercial package, ABAQUS. By numerical simulations, the effect of constraint on inhomogeneous swelling of substrate-attached hydrogel lines is elucidated. It is found that crease-like surface instability occurs when the width-to-height aspect ratio of the hydrogel line exceeds a critical value. Next, by considering a hydrogel layer on a rigid substrate, swell-induced surface instability is studied in details. A linear perturbation analysis is performed to predict the critical condition for onset of the surface instability. In contrast to previously suggested critical conditions, the present study predicts a range of critical swelling ratios, from about 2.5 to 3.4, depending on the material properties of the hydrogel system. A stability diagram is constructed with two distinct regions for stable and unstable hydrogels with respect to two dimensionless material parameters. Numerical simulations are presented to show the swelling process, with evolution of initial surface perturbations followed by formation of crease-like surface patterns. Furthermore, with combined swelling and mechanical compression, the stability analysis is extended to predict a general critical condition that unifies the swell-induced surface instability of hydrogels with mechanically induced surface instability of rubbers. The effect of surface tension is found to be critical in suppressing short-wavelength modes of surface instability, while the substrate confinement suppresses long-wavelength modes. With both surface tension and substrate confinement, an intermediate wavelength is selected at a critical swelling ratio for onset of surface instability. Both the critical swelling ratio and the characteristic wavelength depend on the initial thickness of the hydrogel layer as well as other material properties of the hydrogel. It is found that the hydrogel layer becomes increasingly stable as the initial layer thickness decreases. A critical thickness is predicted, below which the hydrogel layer swells homogeneously and remains stable at the equilibrium state. Finally, three-dimensional finite element models are developed to simulate swelling deformation of hydrogel lines. Depending on the aspect ratio of the cross section as well as the material properties of the hydrogel, two types of swell-induced instability patterns are envisaged, i.e., localized surface instability versus global buckling.