1,720,973 research outputs found
Assessment of the seismic risk associated with small earth dams: a simplified approach
Full text linkSmall earth dams are characterized by a reduced height of the retaining structure and by a limited reservoir volume of water. They are often located along slopes close to populated areas, therefore the risk associated with their potential rupture could be considerable. Also for this reason, the evaluation of their seismic vulnerability is of paramount importance for Civil Protection purposes. In addition, the usual lack of technical information represents a significant further challenge. In this regards, a simplified methodology based on a reduced number of parameters was required for vulnerability assessment studies. A simplified procedure was developed to systematically classify a large number of small earth dams. The proposed methodology is based on the compilation of data-sheets that lead to a preliminary classification of structures in terms of their associated seismic risk. The application of this procedure to about a hundred earth dams in the Piedmont region allowed
identifying the most critical structures, which require a priority in the planning of further investigations and analyses
Evolving fabric and its impact on the shearing behaviour of a compacted clayey silt exposed to drying-wetting cycles
No full textThe fabric and the hydro-mechanical behaviour of compacted clayey silt samples were investigated before and after drying-wetting cycles. Drying-wetting cycles changed the soil fabric by increasing the macro-porosity, while the total void ratio remained almost constant. The cycled samples were more compressible than the original ones and experienced a smaller decrease of suction during shearing at constant water content. The higher compressibility is associated to a more evident reduction of macroporosity.
The smaller suction decrease is reproduced with a double structure water retention model accounting for changes in macro-porosity during shearing. Cycled samples mobilised higher strength and showed a higher dilatancy than original samples sheared at the same initial total stress and suction; furthermore, dilatancy increased with suction for both fabrics. The Li and Dafalias stress-dilatancy relationship, formulated in terms of a macro-structural Bishop stress and accounting for a suction dependency, allowed reproducing the experimental results accurately
Erratum: Dynamic behavior of shallow founded historic towers: Validation of simplified approaches for seismic analyses (International Journal of Geotechnical Engineering 9:1 (13-29) DOI: 10.1179/1939787914Y.0000000066)
No full textA Simplified Methodology for the Assessment of the Seismic Risk Associated with Small Earth Dams
No full textPreliminary investigation on the water retention behaviour of cement bentonite mixtures
Full text linkCement bentonite mixtures are often used to build slurry walls for the containment of both aqueous and non aqueous pollutants, due to their quite low hydraulic conductivity and relatively high ductility and strength. Although their hydro-mechanical behaviour in saturated conditions has been studied in the past, a part of the slurry wall is expected to rest above the groundwater level. The hydraulic characterization in unsaturated conditions is then particularly relevant to evaluate the performance of the barrier, especially when it is aimed at containing non aqueous pollutant liquids which are lighter than water (LNAPL). These non wetting fluids rest above the water table and their penetration is possible just if the barrier is unsaturated. This paper presents some preliminary results of a laboratory characterization of the water retention behaviour of three different cement bentonite mixtures. The mixtures, prepared at cement - bentonite mass ratios ranging from 4:1 to 6:1, were immersed in water and cured for 28 days. Their water retention behaviour was then determined along drying and wetting paths through different techniques, namely axis translation, filter paper and vapour equilibrium. In the high suction range, the water content - suction relationship was found to be independent of cement-bentonite ratio. In the low suction range, the water content at a given suction was found to decrease for increasing cement bentonite ratios
A preliminary investigation on the mechanical behaviour of a stiff Italian clay in the context of hydrogen storage
Full text linkThe large-scale use of renewable energy sources is closely linked to the ability to store excess energy generated
during periods of overproduction for use when demand is at a peak. Storing green energy is therefore a key
component in the move towards a carbon-neutral economy. Underground hydrogen storage in depleted oil and
gas reservoirs may provide an efficient long-term solution. Cyclic injection and production of hydrogen alter the
chemo-hydro-mechanical conditions of the reservoir and caprocks, and possible geomechanical consequences of
such alterations must be preliminarily assessed for safe storage operations. This study aims at exploring the
possible effects of cyclic mechanical loads, such as those that might be induced by hydrogen storage and production, on the mechanical behaviour of a clayey caprock. A series of triaxial tests, both monotonic and cyclic,
were carried out on undisturbed samples of a stiff Italian clay cored from a caprock formation overlying a hydrocarbon reservoir. The results show that the material response is characterized by the distinctive stress-strain
behaviour of stiff clays, with a rather high fragility, which was found to be highly dependent on the loading
strain rate. During laboratory experiments conducted at frequencies larger than in situ ones, cyclic loading under
stress control causes a gradual degradation of the material structure leading to the formation of a clear shear
band followed by a reduction in shear strength. Eventually, failure occurs as the peak shear strength approaches
the applied load. The progressive destructuration also implies a reduction in P- and S-wave propagation velocities and a significant change in the signal shape, which is therefore a promising parameter for monitoring the
material degradation process
Monitoring drying and wetting of a cement bentonite mixture with Electrical Resistivity Tomography
Full text linkCement bentonite slurry cutoff walls are used to encapsulate pollutants within contaminated areas, so avoiding their spreading in the environment. In both temperate and arid climates, at shallow depths, slurry walls are exposed to interaction with the atmosphere and thus to relative humidity values which might induce desaturation and significant shrinkage. This note presents the main results of a study aimed at investigating the impact of drying processes on the integrity and the hydraulic performance of cement bentonite slurry walls. Cement bentonite samples were cured under water for different times (1 months, 2 months and 4 months) and then dried naturally by exposing them to the laboratory environment (T = 21 °C, relative humidity approximately 38%). Once dried, the bottom of the samples was placed in contact with a thin layer of water to induce wetting. The distribution of the electrical conductivity within these samples was evaluated through Electrical Resistivity Tomography measurements, and electrical conductivity maps were converted then into maps of water contents on basis of a phenomenological relationship. The reconstructed water contents compared very well to the measured ones. Drying induced a limited cracking of the samples, which might affect to some extent the hydraulic performance of the barriers
Laboratory characterization of the chemo-hydro-mechanical behaviour of chemically sensitive clays
No full textThis paper focuses on the chemo-hydro-mechanical behaviour of active soils, with special reference to the effects of pore water salinity on the volumetric and shear strength behaviour. Fundamental coupled processes governing transport of solvent and solute in active materials are briefly recalled, together with a model for the volumetric behaviour at the macroscopic scale based on the evaluation of the electrical interaction between clay particles and ions in the pore water at the particle level. Experimental procedures for the laboratory characterization of active soils are then discussed in light of these models and of other well-known phenomenological evidences. Both modified and conventional experimental apparatus can be used in the geotechnical characterization: interpretation of test results requires anyway referring to models accounting for the chemo-mechanical coupling. Experimental data discussed in the paper proceed from tests on bentonites used for waste containment and from tests on a natural illitic-smectitic soil from a marly clay formation in the Langhe area
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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