1,721,053 research outputs found
Ottimizzazione della depurazione elettrocinetica (EKR) da metalli pesanti
No full textTesi di dottorato in Ingegneria Civile ed Ambientale sulla depurazione elettrocinetica dei terreni inquinati con metalli pesant
Ambient seismic noise as an interesting indirect cue for the Cerithidea decollata migrations
Full text linkPresence or absence of water, food availability, capability of avoiding predation, and body temperature are con- stantly changing according to the tidal excursion. In fact, more than the diurnal light-dark variation, tide is shaping the whole intertidal animal life. Therefore, physiological and behavioural systems exist to reduce the stress that the intertidal fauna may face during the unsuitable tidal phase. Cerithidea decollata is a common western Indian Ocean mangrove gastropod. It feeds on the ground at low tide, and climbs the trees two/three hours before the water arrival to avoid submersion. In spite of the irregular East African tidal pattern, it also regularly settles on trunks roughly 40 cm above the maximum level of the incoming tide. Migrations usually take place about twice a day unless at Neap Tide, when snails may remain on the dry ground. Past experiments showed that a biological clock cannot account for water level foreseeing, nor direct visual cues or chemical information from the water itself or from previous migrations have been detected. On the other hand, tidal gravity variations can be felt by the snails. Moreover, other indirect cues could be hypothesize related to a) the oceanic waves reaching the coast and the barrier reef (seismic noise), or b) the changes in ground resistivity (self potential) caused by the sea water moving close. To verify these hypotheses, an integrated geophysical survey (single-station seismic noise and self potential survey) was carried out at Mida Creek (Kenya) to characterize the local seismic wavefield in terms of its amplitude and to measure the temporal variations of the electric potential field. Final goal was to verify whether a correlation exists between the time evolution of these phenomena and the snail movements. Here we present the first results of the seismic noise measurements. Data were acquired by means of a single station all-in-one 3-directional 24-bit digital tromometer equipped with 4.5 Hz geophones. The acquisition run for 11 days (29th June, 2013 - 9th July, 2013). We assumed that the tide transgressions/regressions generate pressure fluctuations on the ground, that are locally transformed into microseismic waves at seafloor propagating inland. Therefore, we evaluated a possible correlation, in terms of decision to climb up or not, between the seismic signals amplitude fluctuations and the snails’ movements. To do so we performed: a) the analysis of the trend of the LF (0.1-2 Hz) and HF (2-60 Hz) seismic noise amplitudes, and b) the comparison of the seismic signals with the height of tide, the number of animals that climbed to the safety level, and the height that they reached during each tide cycle. The study showed an interesting similarity between the time evolution (mean value) of the LF amplitude trend and the animals’ movements. Even thought additional data should be collected to improve the results, it is the first time that a consistent physical cue other than the obvious but discarded ones (visual and chemical), has been identified that could potentially be detected by the snails as well as by other intertidal organisms
Portable low-cost measurement system development for self-potential (SP) monitoring in severe environmental conditions
No full textIn the field of environmental sciences self-potential (SP) data are generally considered as promising and reliable to investigate subsurface properties, especially for their ease of acquisition and simplicity in making qualitative interpretations. Self-potential is a passive method consisting in the measurement of the electric potential at a set of measurements stations. SP anomalies usually indicate the presence of a source of current in the ground due to subsurface disturbances. In order to fulfill such requirements we developed a measurement setup with the main advantages of being portable, low cost, rugged, sufficiently accurate and optimized for low power consumption
Effectiveness evaluation of flood defence structures in different geomorphological contexts
Full text linkThe flood risk in different geomorphological contexts of two less developed countries are investigated in order to evaluate the efficacy of the existing flood defence structures. In particular, a recent floodplain crossed by a wide meandering river and a narrow mountain valley flowed by creek with a torrential regime have been chosen for such analysis in North Albania and central Mexico, respectively. Both areas have been affected by disastrous floods in past years with considerable damages to properties and people. Some safety countermeasures have been performed over time, even if in a non-systematic way. For this reason, the current inclination to flood risk was assessed by means of a freeware software designed to perform one-dimensional (1D) hydraulic modelling for a full network of natural and anthropic channels (HEC-RAS software by Hydrologic Engineering Center River Analysis System). This new analyses take into account: i) the natural morphological variability along the river path, ii) the anthropic interventions on the fluvial dynamics, iii) the landscape appearance after the soil exploitation in the past years, and iv) all the changes induced by an exceeded informal urbanization. The reconstruction of the river and bordering areas geometric data was carried out according to the physical characteristics of the local environment: a bathymetric survey and near-river DGPS acquisitions for the open spaces of the Albanian floodplain, and traditional topographic methods for the highly vegetated Mexican valley. In both cases, the results show that the existing works are, on their own, poorly efficient in containing the predictable floods. Albanians levees seem underdimensioned, while the channelling works are too narrow to contain large amounts of water and solid transport as typical of the Mexican study area. Evidently, a new territorial planning is required in these areas, and some projects are now in place. However, it would be desirable that local authorities were profitably inspired by the criticalities here mentioned
Integrated electromagnetic methods for archaeological prospection and stability assessment of anthropogenic mounds: insights into the English Cemetery in Florence
Full text linkThe archaeological interest in anthropogenic mounds as historical products of human occupation generally con- cerns the understanding of their stratigraphic sequence and the discovery of buried structures. Nevertheless, a further key element relies on the assessment of their stability. This is particularly crucial when the conservation history induced relevant alteration of the former configuration, and a potential collapse might cause damages to heritage and actual risk for public safety.
To respond to such dual diagnostic need, we propose an integration approach based on Very Low Frequency Elec- tromagnetic (VLF-EM) qualitative method and 2D-Electrical Resistivity Tomography (2D-ERT), to make the best out of these two techniques in light of their frequencies/bandwidth and methods of soil investigation (15-30 kHz and DC, respectively).
We present here the results from the experiments performed on one of the test sites selected to validate the pro- posed methodology, i.e. the Protestant Cemetery (the so-called “English Cemetery”) in Florence, Italy, which is a demonstrative example of a huge sample of anthropogenic mounds within urban and rural environments.
Located on a topographic relief, the cemetery testifies a long history since Roman times, as proved by historical documentation and the ceramic findings still now discovered on the (sub-)surface. Converted into a cemetery in 1827, the mound appeared as an anomalous outcrop adjacent to the town walls, prior to the final arrangement and reshaping due to the urban renewal of Florence in 1877, which definitely transformed it into a raised graveyard surrounded by boulevards.
A campaign of VLF-EM and ERT measurements was performed to ascertain the presence of a buried part of the ancient eastern wall and identify the key areas of concern for the stability. High values of resistivity were clearly detected and mapped by means of 2D-ERT along the AA’ array intercepting the hypothesized location of the buried wall. This measure was cross-validated with the corresponding VLF-EM anomaly profiles, thereby retrieving reli- able geophysical evidences suggesting the presence of buried remains.
To correlate the effects of inner structures and soil properties with the stability condition of the mound, crack pattern survey was carried out over the wall containing the mound, jointly to an inspection of the cavities and the interspaces between the exterior masonry surfaces and the rear terrain. The spatial distribution of the opened cracks allowed the actual threat for the stability of the mound to be assessed also in relation to the current positions of the cypresses, periodically replanted for landscape reasons. Interesting insights were obtained by mapping the inclina- tion and tilt direction of the gravestones and funerary monuments, as superficial indicators of ground subsidence and soil compaction/collapse at the top of the mound.
The benefits achieved for site management and tombstones maintenance have encouraged the exportation of this approach (highly adaptable to include also GPR and seismic methods) to other case studies, and open to a sustain- able implementation for the investigation of funerary mounds, such as the Etruscan burial mounds
A way forward to enhance the coping capacity of communities threatened by floods: The Dajç experience (Northern Albania)
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Residual slope stability in low order streams of angangueo mining area (Michoacán, Mexico) after the 2010 debris flows
No full textMexico, largely a tropical mountainous region, is continually subjected to natural hazards like landslides induced by heavy rainfalls. At the end of January 2010, two cold fronts and low-pressure storms moved over the State of Michoacán (central Mexico) and in February the town of Angangueo, in the eastern sector of the Monarch Butterfly Biosphere Reserve, was devastated by a huge muddy debris flow. The in situ observations after the event showed that considerable material was removed from the countryside surrounding the urban area. In this framework two low order streams were indicated as the main suppliers of granular material to the Angangueo River: Melon and Catingón creeks. To evaluate the residual risk and slope stability along these two torrential watercourses, specific investigations were carried out. A GIS-based map of the most relevant hazardous features was performed at high level of detail by means of targeted field surveys that distinguished natural and anthropogenic elements like: (i) riverbanks and slopes with new signs of instability and already collapsed areas; (ii) large accumulations of debris and plant remains in channels and slopes; (iii) deposits of mining waste and abandoned mining areas; (iv) hydraulic works along the riverbeds and (v) cultural elements potentially at risk. In both circumstances, a generalized criticality emerged; moreover, all the riverbanks along the Catingón creek are almost still under unstable conditions, whereas Melon creek has precarious riverbanks only for about 1/3 of the considered slopes. In both cases, the depth of their rupture surfaces seems directly related to the different geotechnical properties of existing materials with some influence from gradients
Laboratory scale electrokinetic remediation and geophysical monitoring of metal-contaminated marine sediments
Full text linkElectrokinetic remediation is an emerging technology that can be used to remove contaminants from soils and sediments. This technique relies on the application of a low-intensity electric field to extract heavy metals, radionuclides and some organic compounds. When the electric field is applied three main transport processes occur in the porous medium: electromigration, electroosmosis and electrophoresis.
Monitoring of electrokinetic processes in laboratory and field is usually conducted by means of point measure- ments and by collecting samples from discrete locations. Geophysical methods can be very effective in obtaining high spatial and temporal resolution mapping for an adequate control of the electrokinetic processes.
This study investigates the suitability of electrokinetic remediation for extracting heavy metals from dredged marine sediments and the possibility of using geophysical methods to monitor the remediation process. Among the geophysical methods, the spectral induced polarization technique was selected because of its capability to provide valuable information about the physico-chemical characteristics of the porous medium.
Electrokinetic remediation experiments in laboratory scale were made under different operating conditions, obtained by varying the strength of the applied electric field and the type of conditioning agent used at the electrode compartments in each experiment. Tap water, 0.1M citric acid and 0.1M ethylenediamine tetraacetic acid (EDTA) solutions were used respectively as processing fluids. Metal removal was relevant when EDTA was used as conditioning agent and the electric potential was increased, as these two factors promoted the electroosmotic flow which is considered to be the key transport mechanism. The removal efficiencies ranged from 9.5% to 27% depending on the contaminant concerned. These percentages are likely to be raised by a further increase of the applied electric field.
Furthermore, spectral induced polarization measurements were performed on the sediments before and after the treatment in order to correlate the measured electrical parameters with the geochemical processes occurring during electrokinetic remediation. A linear relationship was found between chargeability and pH. This result opens the door to the use of spectral induced polarization method to monitor electrokinetic processes in the field
ARCHAELOGICAL WALLS IN PIAZZALE DONATELLO (FIRENZE, ITALY) DETECTED BY USING VLF-EM AND ERT SURVEY
No full textAtti di congress
Elettrodi lineari per tecnica depurativa da metalli pesanti tramite elettrocinesi (DEK): problema in via di risoluzione
No full textAtti di convegn
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