Aportaciones al conocimiento de la evolución paleoclimática y paleoambiental en la Península Ibérica durante los dos ultimos millones de años a partir del estudio de trasvertinos y espeleotemas

En este trabajo se contemplan los resultados principales del Proyecto" Reconstrucción Paleoclimática desde el Pleistoceno Medio a partir de análisis geocronológicos e isotópicos de travertinos españoles" (P. CEC FI2W-CT91-0075 " Paleoclimatological revision of climate evolution in the Western Mediterranean Region, Evaluation of altered scenarios) . Se seleccionaron cuatro áreas de depósitos travertínicos de carácter fluvial (Priego, Río Blanco), lacustre (Río Blanco, Banyoles) y aluvial (Tolox) así como una zona con depósitos espeleotémicos (Karst de la Cueva del Reguerillo). En ellas se obtuvieron datos sobre la evolución del paisaje y del clima, los travertinos y espeleotemas son indicadores de clima cálido s.l. que de forma abreviada son: O Mediante la geomorfología y dataciones (paleomagnetismo, U/Th, Resonancia de espín Resumen electrónico y racemización de aminoácidos), se determinó las historia fluvial de los travertinos de Priego y Río Blanco así como del Karst de la Cueva del Reguerillo donde, además, se dataron un paleosismo y fenómenos de neotectónica. La data más antigua obtenida mediante Resonancia de espín electrónico fue 950ka, mientras que mediante racemización de aminoácidos se dataron depósitos de más de 750ka. Mediante dataciones, sedimentología, análisis de isótopos estables y palinología se determinaron aspectos de la evolución climática de algunas áreas de la Península Ibérica. La correlación entre palinología e isotopía permitió la validación de algunos de los resultados. También se obtuvieron datos cualitativos sobre input hidraúlicos a los sistemas fluviales o kársticos

Experimental and computational modeling of unsaturated soil behavior under true triaxial stress states

Ph.D.Emir Josʹe Macar

Evaluation of swell behaviour of expansive clays from specific moisture capacity

Current swell characterization techniques used to interpret the mechanical volume change occurring during the swelling process are not successful due to lack of inclusion of influential properties. Accurate prediction of swelling behaviour allows us to design more efficiently and with better reliability. This research aims at developing a more comprehensive framework to predict swell potential. Laboratory studies are conducted on five natural expansive soils with different degree of expansiveness. Initial studies include determination of basic soil characterization, swell strains and swell pressures at their compacted state along with their inherent mineralogy. Later, replicate samples were studied for soil water characteristic curves using standard pressure cell apparatus and filter paper techniques. The path traversed by the specimen during swelling process is representative of the soil water characteristic curve of the same specimen. Hence, studies are pursued to understand the relationship between degree of expansiveness and the specific moisture capacity relative to that particular range of suction head. Test results showed that the degree of expansion represented by swelling strain or swelling pressure is proportional to the specific moisture capacity determined during the swelling process

Reconciling soil-water retention properties and shear strength parameters of compacted clayey soils via suction-controlled ring shear testing

A preliminary experimental program has been undertaken to assess suction-controlled peak and residual shear strength properties of a statically compacted, moderate plasticity clayey soil. The experimental program was accomplished in a fully servo/suction-controlled ring shear apparatus, suitable for testing unsaturated soils under large deformations via the axis-translation technique. The test results highlight the important role played by matric suction on residual shear strength behaviour of compacted clayey soils. For the range of net normal stresses and suction states investigated, the increase in peak shear strength with increasing suction was found to be significantly nonlinear for the clayey soil. A distinct correspondence was also observed between the nonlinear nature of peak shear strength envelope, with respect to increasing matric suction, and the soil-water retention curve. The residual failure envelope, however, remains reasonably linear for the range of suction values induced in the present work via axis-translation

Characterization of compacted silty sand via relative humidity-controlled triaxial testing

Rather limited experimental evidence is available of triaxial shear-induced response of unsaturated soils at suction states far beyond residual suction. In this work, a fully automated, relative-humidity (Auto-RH) control unit is adapted to a newly implemented double-walled triaxial cell to test compacted silty sand specimens under consider-ably high total suction states via the vapor-pressure technique. The work is intended to gain critical insight into some of the most essential hydro-mechanical features of densely compacted intermediate geomaterials, such as post-peak softening and strain-induced dilatancy, under suction-controlled monotonic shearing. In general, peak strength is followed by large strain-induced softening until critical state is apparently reached. Strain-softening is observed to be-come considerably more pronounced with increasing total suction. The slope of critical state lines, however, remains virtually constant, regardless of induced total suction, in agreement with critical state-based constitutive frameworks previously postulated for unsaturated soils

Essential features of compacted silty sand behavior via suction-controlled triaxial testing

The main intent of this work was to gain further insight into some of the limitations (and potential) of the Barcelona Basic Model (BBM) in predicting the stress-strain response of compacted unsaturated soils that are prone to post-peak strain-induced softening during suction-controlled shearing. To this aim, a comprehensive series of suc-tion-controlled tests were conducted on statically compacted specimens of silty sand using a recently implemented, servo/suction-controlled, double-walled triaxial apparatus. The brittle and dilatant nature of the test soil, as expected, did not allow for good agreement between the experimental and BBM predicted stress-strain responses of compacted silty sand, since post-peak softening was not adequately captured. BBM simulations, however, held reasonably good during the early shearing stage (up to about 1-2% total shear strain), and at higher values of shear strain, that is, close to critical state condition

Evaluation of Swell Behavior of Expansive Clays from Internal Specific Surface and Pore Size Distribution

The interdependency of microsoil fabric-related properties and swell/shrink behavior of expansive soils needs to be identified to achieve a more thorough and accurate prediction of heave of expansive soils. In a recent research study, two microsize-related properties of a soil—pore size distribution and specific surface area—were identified and examined in an effort to address their synergistic effects on swelling behavior of soils. To study this aspect in detail, eight natural expansive clayey soils from known expansive soil regions were sampled and studied by using two test methods: conventional one-dimensional vertical swell tests and novel three-dimensional volumetric swell strain tests. Microinternal structural details, including pore void distribution, were obtained from mercury intrusion porosimetry (MIP) studies on compacted soil specimens. Specific surface area (SSA) details of the same soils were determined using the chemical ethylene glycol monoethyl ether (EGME) method. Attempts were made to predict macroswell properties, using both pore and surface area properties. Modeling analyses and results showed that the swelling behavior of the clays was dependent on a newly introduced parameter that accounted for both clay mineralogy constituents and internal pore distribution of the soils. The new swell property models showed accurate predictions of measured swell strains of the present soils, depicting the importance of including mineralogy and pore fabric details in a given soil

Unsaturated Shear Strength of Compacted Clayey Soil via Suction-controlled Ring Shear Testing

An experimental program has been undertaken to assess both peak and residual shear strength parameters of statically compacted, moderate plasticity clayey soil under suction-controlled conditions, resulting in a defined set of suction-dependent peak and residual failure envelopes over a relatively wide range of suction states, from 0 to 300 kPa. The experimental program was accomplished in a servo/suction-controlled ring shear apparatus, which is suitable for testing unsaturated soils under large deformations via the axis-translation technique. Test results substantiate the crucial role that has been observed to be played by the imposed matric suction on the residual shear strength of compacted clayey soils. For the range of net normal stress (0-200 kPa) and matric suction (0-300 kPa) states investigated, the increase in either peak or residual shear strength, with increasing matric suction, was found to be manifestly nonlinear. Furthermore, a distinct correspondence was observed between the nonlinearity of the peak shear strength envelope, with respect to increasing matric suction, and the soil-water retention properties of the clayey soil. Results, in general, suggest that a conceptual residual shear strength framework for unsaturated soils, similar to that postulated for peak shear strength, can eventually be formulated as more experimental evidence of this kind is made available