# Browsing by Subject "Consolidation"

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Item Compressibility and permeability of Gulf of Mexico mudrocks, resedimented and in-situ(2014-05) Betts, William Salter; Flemings, Peter Barry, 1960-Show more Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior.Show more Item Compression and permeability behavior of natural mudstones(2011-12) Schneider, Julia, 1981-; Flemings, Peter Barry, 1960-; Mohrig, David; Cardenas, Meinhard B.; Day-Stirrat, Ruarri J.; Germaine, John T.Show more Mudstones compose nearly 70% of the volume of sedimentary basins, yet they are among the least studied of sedimentary rocks. Their low permeability and high compressibility contribute to overpressure around the world. Despite their fundamental importance in geologic processes and as seals for anthropogenic-related storage, a systematic, process-based understanding of the interactions between porosity, compressibility, permeability, and pore-size distribution in mudstones remains elusive. I use sediment mixtures composed of varying proportions of natural mudstone such as Boston Blue Clay or Nankai mudstone and silt-sized silica to study the effect of composition on permeability and compressibility during burial. First, to recreate natural conditions yet remove variability and soil disturbance, I resediment all mixtures in the laboratory to a total stress of 100 kPa. Second, in order to describe the systematic variation in permeability and compressibility with clay fraction, I uniaxially consolidate the resedimented samples to an effective stress equivalent to about 2 km of burial under hydrostatic conditions. Scanning electron microscope images provide insights on microstructure. My experiments illuminate the controls on mudstone permeability and compressibility. At a given porosity, vertical permeability increases by an order of magnitude for clay contents ranging from 59% to 34% by mass whereas compressibility reduces by half at a given vertical effective stress. I show that the pore structure can be described by a dual-porosity system, where one rock fraction is dominated by silt where large pores are present and the majority of flow occurs and the other fraction is dominated by clay where limited flow occurs. I use this concept to develop a coupled compressibility-permeability model in order to predict porosity, permeability, compressibility, and coefficient of consolidation. These results have fundamental implications for a range of problems in mudstones. They can be applied to carbon sequestration, hydrocarbon trapping, basin modeling, overpressure distribution and geometry as well as morphology of thrust belts, and an understanding of gas-shale behavior.Show more Item The effect of expanded shale lightweight aggregates on the hydraulic drainage properties of clays(2013-05) Mechleb, Ghadi; Gilbert, Robert B. (Robert Bruce), 1965-Show more Fine grained soils, in particular clays of high plasticity, are known to have very low values of hydraulic conductivity. This low permeability causes several problems related to vegetation growth and stormwater runoff. One way to improve the permeability of clay soils is by using coarse aggregates as a fill material. Recently, Expanded Shale has been widely applied as an amendment to improve drainage properties of clayey soils. However, limited effort has been made to quantify the effect of Expanded Shale on the hydraulic conductivity or on the volume change of fine grained soils. Specifically, the field and laboratory tests required to quantify the amounts of Expanded Shale to be mixed with clays to obtain desired hydraulic conductivity values have not been conducted. This paper presents the results of a series of laboratory fixed-wall permeameter tests conducted on naturally occurring clay deposits in the Austin area with different plasticity. The testing program comprised of clay samples with different quantities of Expanded Shale aggregates by volume, ranging between 0 and 50%, and compacted at two different compaction efforts (60% and 100% of the standard Proctor compaction effort). The laboratory test results indicate that the hydraulic conductivity of the three soils increases by at least an order of magnitude when the Expanded Shale is mixed in quantities between 25 to 30% by volume depending on the compaction effort. Expanded Shale amended samples also showed lower swelling potential with increasing amendment quantities. Moreover, when the clay with the higher plasticity was mixed with 25% Expanded Shale, the compression and recompression ratios decreased by 25% and 15% respectively.Show more Item Finite Element Formulations for Moving Boundaries, Material Interfaces, and Postprocessing, With Applications to Heat Transfer and Consolidation in Porous Media(1988-05) MacKinnon, Robert James; Carey, Graham F.; Sepehrnoori, KamyShow more The research described here concerns finite element modeling of problems involving moving boundaries and different material types, together with postprocessing and superconvergence behavior. An example from geomechanics corresponding to underground coal gasification is included to demonstrate the moving grid and moving boundary technique. A new treatment for material interface elements is introduced as part of this formulation. In test calculations this treatment is shown to be superior to previous material averaging strategies. The postprocessing analysis and superconvergence theory is based on an entirely new approach which extensively uses Taylor series analysis and leads to some novel results in finite element modeling. These include new flux and stress postprocessing formulas, and new solution enhancement strategies. Some of these ideas are promising for treatment of other classes of problems such as those in reservoir engineering involving different material types and multiphase flow.Show more Item Geotechnical properties, one-dimensional consolidation behavior and liquefaction susceptibility of the glaciolacustrine clay samples from the Oso landslide(2019-05-20) Mert, Ahmet Ali; Gilbert, Robert B. (Robert Bruce), 1965-Show more Involving a wide range of ground movements, such as rock falls, deep slope failures, and shallow flows of debris, landslides may cause damage to property, injury, and death. Such a landslide occurred in Washington state, near Oso, in 2014. Synthesized available literature on identical soil material was used for the investigation. On the two samples, S1 and D5 from the event site, plasticity tests and one-dimensional consolidation testing were performed. Main objectives were to compare the volume of the 2014 debris run-out with the volume of the colluvium at the toe of the slope prior to the 2014 slide, to estimate the properties of the colluvium, to explore hypotheses about how the strength of the colluvium reduced enough for it to flow like a liquid, and to provide guidance for future projects to identify the possibility of a large run-out like this event. To achieve these objectives, a literature review and an experimental program comprised compiling all the available information about the 2014 debris flow, conducting supplementary laboratory testing on remolded samples from the slope, summarizing the synthesized available literature on the mechanisms of the 2014 debris flow, and investigating hypotheses to explain the Oso debris flow. Provided the conducted test results and the obtained available data from the literature, two conclusions may be drawn: 1. The debris flow volume included more than only colluvium, with previously in-place materials behind it, 2. It is hard to explain whether the debris flowed like a liquid based on the critical state line, liquidity indices, or undrained remolded shear strengths obtained.Show more Item Modeling of pore pressure propagation and dissipation in compressible porous media(2017-05) Hachem, Hussein A.; El Mohtar, Chadi Said; Gilbert, Robert B. (Robert Bruce), 1965-Show more This research is a study of the different phenomena associated with the propagation of pore water pressure in high plasticity clays. Specifically, it addresses the pore pressure response in areas subjected to sudden increases in pore water pressure at their top boundary. The main applications of this research would be the study of pore pressure responses in grouted piezometers and the pore pressure buildup in areas with rainfall-induced landslides failures. This phenomenon of pore pressure diffusion is coupled with Terzaghi’s theory of consolidation. For that purpose, an analysis of pulse tests (consisting of measuring pore pressure response with time due to increases in pore water pressure boundary conditions) conducted by previous researchers is performed. In conjunction with the pulse tests, modified consolidation tests are also executed. The coefficients of diffusion affecting the pore pressure response in each of these cases are then evaluated. In addition, an analytical model is developed to mathematically describe the pore pressure response in clays under pressure pulses. The derivation of the differential equation describing this response makes use of Darcy’s theory of flow in porous media, where a difference in gradients causes a difference in flow patterns. The derived equation is then compared to Terzaghi’s equation of consolidation. This couples model shows that a sudden pulse of pressure causes a slower pore pressure response than the one caused by an increase of total stress. The role that pore pressure diffusion and consolidation simultaneously contribute are studied in a modified CRS consolidation setup. The mathematical modeling of these processes together is compared to the experimental results. Due to these two processes working together, at no particular point in time is there an increase of pressure at any depth in the soil that matches the initial increase of pressure application. The research also mentions the limitations of applying the derived equations. These limitations are inherently related to the simplifying assumptions presented in the theory, as well as to the complexity of porous media. Future follow-up research is also suggested.Show more