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-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.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.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.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-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.Item Effect of Load Path on Mode of Failure at the Brittle-ductile Transition in Well-sorted Aggregates of St. Peter Sand(2010-10-12) Dilci, Gokturk MehmetGranular aggregates of quartz subjected to triaxial compression under constant effective pressures (Pe) undergo macroscopic failure at critical stress states that depend on the effective mean stress. Although the mode of failure and mechanical response vary systematically with mean stress at failure, prefailure loading at subcritical stress states may induce yielding, and subcritical load paths may influence behavior at failure. Here, I investigate how the failure of quartz aggregates at conditions favoring compaction depends on consolidation history and load path in the transitional and ductile deformation regimes in terms of strain localization and microfracture fabric. Three distinct non-standard triaxial compression load paths were employed; the paths involve different preconsolidation of the aggregates at subcritical isotropic stress followed by differential loading with increasing or decreasing confining pressure. Deformed aggregates were injected with epoxy and studied using optical microscopy techniques to determine microscopic damage evolution for the different load paths. Microfracture data show that preconsolidation at subcritical isotropic loads facilitates formation of campaction bands during subsequent triaxial compression in the transitional regime. The preferred orientation of intragranular cracks evolves from near random fabrics for isotropic loading to strongly preferred orientations parallel to the maximum principal compression direction for differential loading, with the strongest preferred orientation within the compaction bands. Aside from the preconsolidation, different load paths have only a minor effect on the mechanical response during macroscopic failure.Item Memory Consolidation in Learning a Bimanual Coordination Skill(2012-07-16) Wang, ChaoyiThe present study was conducted to examine the process of consolidation when learning a difficult bimanual coordination pattern. There are two phenomena associated with the process of consolidation, an enhancement in performance without additional practice and the stabilization observed as resistance to interference from a similar task after acquisition of a novel skill. Both phenomena have been widely examined in sequence skill learning studies. However, few studies have examined the consolidation effect after training of a continuous and rhythmic bimanual coordination pattern. The first goal of this study was to determine if sleep enhances the performance of a minimally trained 1:2 pattern of bimanual coordination in a manner that has been observed with sequencing skills, that is, performance significantly improves after an overnight sleep. A recent study by Buchanan & Wang (in-press) showed that by manipulating the position of a visual-augmented-feedback cursor, either behind or to-the-side of a 1:2 bimanual coordination template, an advantage of the side cursor position was found in the no-feedback retention test after a fifteen-minute break. The second goal was to test whether an overnight sleep may reduce the guidance effect associated with the behind cursor position as reported in Buchanan & Wang (in-press). In the present experiment, the effect of an overnight sleep on learning a 1:2 pattern of bimanual coordination was accessed with six test trials presented immediately (IMM group) or 24 hours (SLEEP group) after 5 minutes of practice. The test trials included three trials with feedback and three trials with feedback removed. For either the IMM or SLEEP group, half of the participants practiced with the behind cursor position and the other half practiced with the side cursor position. The results indicated that the SLEEP group showed an improvement in performance from the acquisition trials to the feedback test trials whereas the IMM group did not. The advantage of the side cursor position at the no-feedback retention test was not evident in the current study. These results are consistent with our two predictions and provide evidence of enhancement in learning a 1:2 pattern bimanual coordination skill.Item Procedural Skill Initiation, Chunks & Execution; Contributions of Offline Consolidation(2013-02-26) Bhatia, Sanjeev RaiIt has been suggested that improvement in the performance of many motor sequence tasks such as playing musical instruments, operating complex machinery or tools, and/or performing a variety of athletic activities results from the learner?s ability to parse the movement into fundamental action primitives called motor chunks. Moreover, it has been suggested that the organization of motor chunks within a sequential behavior can be influenced by consolidation occurring outside the boundary of practice during which reorganization can occur leading to faster sequence production. The present study involved modest practice of a discrete sequence production task (DSPT) followed by subsequent assessment of performance of this task either immediately after the completion of practice or after a 24-hr delay. Of critical interest was the change in performance from the end of training to the test phase in three features of the sequence implementation namely sequence initiation, motor chunk transition, and element execution components. It was anticipated that motor chunk transition would be susceptible to significantly greater offline enhancement in the 24-hr delayed test case. Based on the extant literature it was also expected that sequence initiation and/or execution processes may also be sensitive to offline consolidation. No evidence emerged that supported the proposal that motor chunk transitions revealed additional gains following a longer interval between training and test. It is possible this effect was underestimated because of some imprecision in the manner in which motor chunk transitions were identified. There was clear evidence for offline gains for both sequence initiation and element execution processes. These data are difficult to interpret within the framework of a number of contemporary accounts of sequence production such as the dual-processor model in which sequence production is governed by a cognitive and motor processor.