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21.
Eduardo?Bilotta Leonardo?Cascini Vito?Foresta Giuseppe?SorbinowEmail author 《Geotechnical and Geological Engineering》2005,23(4):365-402
Landslides of the flow type involving granular geo-materials frequently result in casualties and damage to property because of the long travel distance and the high velocities that these may attain. This was true for the events that took place in Campania Region (Southern Italy) in May 1998, involving pyroclastic soils originating from explosive activities of the Somma-Vesuvius volcano. Although these phenomena have frequently affected various areas of the Campania region over the last few centuries, there were no useful geological and geotechnical references available in the aftermath of the May 1998 events. For this reason Salerno University, which was involved in the scientific management of the emergency, addressed the issue of acquiring data on the geological, geomorphological and hydrogeological features of the slopes where the landslides had taken place. The information acquired made it possible to set up a slope evolution model that is able to interpret, from a geological point of view, past and more recent landslides that had occurred in the same area. As preliminary geotechnical analyses had already validated the above model, more detailed investigations were performed both on the pore pressure regimen of the covers still in place as well as on the physical and mechanical properties of pyroclastic soils, in saturated and unsaturated conditions. The present paper begins by discussing the data acquired during the .rst phase of the studies and then goes on to illustrate the laboratory results so far obtained with the aid of approximate procedures. These help advance our knowledge of pyroclastic soils within a reasonable time frame, thus improving landslide triggering analysis. 相似文献
22.
Vito Coppola Maria Boni H. Albert Gilg Bozena Strzelska-Smakowska 《Mineralium Deposita》2009,44(5):559-580
The Silesia–Cracow district in Poland has been one of the world’s principal sources of zinc from nonsulfide zinc ore (Polish:
galman). The still remaining nonsulfide ore resources can be estimated at 57 Mt at 5.6% Zn and 1.4% Pb. Nonsulfide mineralization
is mainly hosted by Lower Muschelkalk (Triassic) limestone and is associated with different generations of the hydrothermal
ore-bearing dolomite (OBD I, II, III). A fundamental ore control is believed to have been exerted by the basement faults,
which were repeatedly reactivated during the Alpine tectonic cycle, leading to the formation of horst-and-graben structures: these dislocations may have caused short periods of emersion and the circulation of meteoric waters during the
Cenozoic. Nonsulfide ores show a wide range of morphological characteristics and textures. They occur as earthy masses, crystalline
aggregates, and concretions in cavities. Breccia and replacement textures are also very common. The most important mineral
phases are: smithsonite, Fe–smithsonite, Zn–dolomite, goethite, and Fe–Mn(hydr)oxides. Minor hemimorphite and hydrozincite
have also been detected. Two distinct nonsulfide ore types occur: the predominant red galman and the rare white galman. In the white galman, Fe–smithsonite and Zn–dolomite are particularly abundant. This ore type is commonly considered as a peripheral hydrothermal
alteration product related to the same fluids that precipitated both the OBD II–III and the sulfides. In contrast, a supergene
origin is commonly assumed for the red galman. Evidence of the petrographic and mineralogical difference between white and red galman is also found in stable isotope data. Smithsonite from red galman shows a limited range of δ
13CVPDB values (−10.1 to −11.4‰), and δ
18OVSMOW values (25.3‰ to 28.5‰, mean 26.8 ± 0.3‰). The uniform and low carbon isotope values of red galman smithsonite are unusual for supergene carbonate-hosted deposits and indicate the predominance of a single organic carbon
source. Smithsonite from white galman has a more variable, slightly more positive carbon isotope (−2.9‰ to −7.4‰), but broadly similar oxygen isotope composition
(26.8‰ to 28.9‰). The relationship of the white galman ore with the hydrothermal system responsible for OBD II and sulfide generation is still uncertain. The most important paleoweathering
events took place in both Lower and Upper Silesia during Late Cretaceous up to Paleogene and early Neogene time. During this
period, several short-lasting emersions and intense weathering episodes facilitated the formation of sinkholes in the Triassic
carbonate rocks and the oxidation of sulfide orebodies through percolating meteoric waters. These phenomena may have lasted
until the Middle Miocene. 相似文献
23.
Alessio Nicosia Costanza Di Stefano Vincenzo Palmeri Vincenzo Pampalone Vito Ferro 《水文研究》2021,35(10):e14407
Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) and interrill erosive phenomena. The dye tracer technique to measure surface flow velocity Vs is based on the measurement of the travel time of a tracer needed to cover a known distance. The measured Vs must be corrected to obtain the mean flow velocity V using a factor αv = V/Vs which is generally empirically deduced. The Vs measurement can be influenced by the method applied to time the travel of the dye-tracer and αv can vary in different flow conditions. Experiments were performed by a fixed bed small flume simulating a rill channel for two roughness conditions (sieved soil, gravel). The comparison between a chronometer-based (CB) and video-based (VB) technique to measure Vs was carried out. For each slope-discharge combination, 20 measurements of Vs, characterized by a sample mean Vm, were carried out. For both techniques, the frequency distributions of Vs/Vm resulted independent of slope and discharge. For a given technique, all measurements resulted normally distributed, with a mean equal to one, and featured by a low variability. Therefore, Vm was considered representative of surface flow velocity. Regardless of roughness, the Vm values obtained by the two techniques were very close and characterized by a good measurement precision. The developed analysis on αv highlighted that it is not correlated with Reynolds number for turbulent flow regime. Moreover, αv is correlated neither with the Froude number nor with channel slope. However, the analysis of the empirical frequency distributions of the correction factor demonstrated a slope effect. For each technique (CB, VB)-roughness (soil, gravel) combination, a constant correction factor was statistically representative even if resulted in less accurate V estimations compared to those yielded by the slope-specific correction factor. 相似文献
24.
Costanza Di Stefano Alessio Nicosia Vincenzo Pampalone Vincenzo Palmeri Vito Ferro 《水文研究》2019,33(9):1317-1323
In this paper, a recently deduced flow resistance equation for open channel flow was tested under equilibrium bed‐load transport conditions in a rill. First, the flow resistance equation was deduced applying dimensional analysis and the incomplete self‐similarity condition for the flow velocity distribution. Then, the following steps were carried out for developing the analysis: (a) a relationship (Equation 13 ) between the Γ function of the velocity profile, the rill slope, and the Froude number was calibrated by the available measurements by Jiang et al.; (b) a relationship (Equation 17 ) between the Γ function, the rill slope, the Shields number, and the Froude number was calibrated by the same measurements; and (c) the Darcy–Weisbach friction factor values measured by Jiang et al. were compared with those calculated by the rill flow resistance equation with Γ estimated by Equations 13 and 17 . This last comparison demonstrated that the rill flow resistance equation, in which slope and Shields number, representative of sediment transport effects, are introduced, is characterized by the lowest values of the estimate errors. 相似文献
25.
26.
In this paper, a method to predict the equilibrium bed slope in natural streams based on the incipient motion criterion is proposed. The method is based on the criterion suggested by Gessler to simulate the grain size distribution of the armour coat using the concept of critical shear stress of a sediment mixture. In particular, a different expression of the probability for a single particle size to be part of the armour coat is firstly proposed; then, a simple two‐steps criterion is suggested to estimate the safety factor required by the proposed approach. The method is applied in three different Italian regions (Calabria, Basilicata, and Tuscany) and required several field campaigns involving the survey of 251 stream reaches upstream of grade‐control structures. The area including five Calabrian streams is firstly used to test the suitability of the two‐steps approach. In this area, considering the detailed information about the particle size of bed material, the effect of using a simplified grain size distribution for each torrent is also checked. The method is then applied within the two additional areas (Basilicata and Tuscany) in order to check the geographic influence on the prediction of the stable longitudinal profile. A comparison between measured and estimated values of the equilibrium bed slope showed a good agreement for the Calabrian streams, where the number of the investigated stream reaches is greater, and satisfactory results for the torrents located in Basilicata and Tuscany where the field data set is more limited. The overall results encourage the extension of the proposed method to additional field data and suggest the use of this approach by hydraulic designers in order to stabilize the longitudinal profile of natural streams. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
27.
Roberto Sulpizio Rosanna Bonasia Pierfrancesco Dellino Mauro A. Di Vito Luigi La Volpe Daniela Mele Giovanni Zanchetta Laura Sadori 《Journal of Volcanology and Geothermal Research》2008
Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity. 相似文献
28.
Mauro A. Di Vito Elena Zanella Lucia Gurioli Roberto Lanza Roberto Sulpizio Jim Bishop Evdokia Tema Giuliana Boenzi Elena Laforgia 《Earth and Planetary Science Letters》2009,277(3-4):408-421
Public works in progress in the Campanian plain north of Somma-Vesuvius recently encountered the remains of a prehistoric settlement close to the town of Afragola. Rescue excavations brought to light a Bronze Age village partially destroyed and buried by pyroclastic density currents (PDCs) of the Vesuvian Pomici di Avellino eruption (3.8 14C ka BP) and subsequently sealed by alluvial deposits. Volcanological and rock-magnetic investigations supplemented the excavations.Careful comparison between volcanological and archaeological stratigraphies led to an understanding of the timing of the damage the buildings suffered when they were struck by a series of PDCs. The first engulfed the village, located some 14 km to the north of the inferred vent, and penetrated into the dwellings without causing major damage. The buildings were able to withstand the weak dynamic pressure of the currents and deviate their path, as shown by the magnetic fabric analyses. Some later collapsed under the load of the deposits piled up by successive currents. Stepwise demagnetization of the thermal remanent magnetization (TRM) carried by potsherds embedded in the deposits yields deposition temperatures in the order of 260–320 °C, fully consistent with those derived from pottery and lithic fragments from other distal and proximal sites. The fairly uniform temperature of the deposits is here ascribed to the lack of pervasive air entrainment into the currents. This, in turn, resulted from the lack of major topographical obstacles along the flat plain.The coupling of structural damage and sedimentological analyses indicates that the currents were not destructive in the Afragola area, but TRM data indicate they were still hot enough to cause death or severe injury to humans and animals. The successful escape of the entire population is apparent from the lack of human remains and from thousands of human footprints on the surface of the deposits left by the first PDCs. People were thus able to walk barefoot across the already emplaced deposits and escape the subsequent PDCs. The rapid cooling of the deposits was probably due to both their thinness and heat dissipation due to condensation of water vapour released in the mixture by magma–water interaction. 相似文献
29.
Measuring hydrological connectivity inside a soil by low field nuclear magnetic resonance relaxometry 总被引:1,自引:0,他引:1 下载免费PDF全文
Hydrological connectivity inside the soil is related to the spatial patterns inside the soil (i.e., the structural connectivity). This, in turn, is directly associated with the physical and the chemical processes at a molecular level (i.e., the functional connectivity). Nuclear magnetic resonance (NMR) relaxometry can be successfully applied to reveal both structural and functional components of soil hydrological connectivity. In the present study, the low field NMR relaxometry was applied on water suspended soils sampled at the upstream‐ and downstream‐end of three different length plots. Also the sediments collected from the storage tanks at the end of each plot were water suspended and monitored by NMR relaxometry. The results from the NMR investigations were elaborated by using a mathematical approach in order to quantify both the functional and structural connectivity components. In particular, following integration of the T1 distribution curve, an S‐shaped curve was obtained. It revealed two plateaus corresponding to the shortest (low component) and the longest (high component) intervals of relaxation times, respectively. According to relaxometry theory, the two T1 intervals, associated to the different plateaus, were attributed to micro and macro soil pores, respectively. The two T1 intervals were used to define a functional connectivity index, while the central part of the S‐shaped distribution was used to define a structural connectivity index. Here we provide the physical meaning of the our mathematical approach, thereby revealing that functional connectivity index increases with plot length, as a result of a selective eroded particle transport. Moreover, the relationship structural connectivity index versus plot length resulted quasi‐independent of grainsize distribution, whereas the values of the structural connectivity index for the sediment samples resulted lower than those obtained for the corresponding soils. 相似文献
30.
Stable isotopes were measured in the carbonate and organic matter of palaeosols in the Somma–Vesuvius area, southern Italy in order to test whether they are suitable proxy records for climatic and ecological changes in this area during the past 18000 yr. The ages of the soils span from ca. 18 to ca. 3 kyr BP. Surprisingly, the Last Glacial to Holocene climate transition was not accompanied by significant change in δ18O of pedogenic carbonate. This could be explained by changes in evaporation rate and in isotope fractionation between water and precipitated carbonate with temperature, which counterbalanced the expected change in isotope composition of meteoric water. Because of the rise in temperature and humidity and the progressive increase in tree cover during the Holocene, the Holocene soil carbonates closely reflect the isotopic composition of meteoric water. A cooling of about 2°C after the Avellino eruption (3.8 ka) accounts for a sudden decrease of about 1‰ in δ18O of pedogenic carbonate recorded after this eruption. The δ13C values of organic matter and pedogenic carbonate covary, indicating an effective isotope equilibrium between the organic matter, as the source of CO2, and the pedogenic carbonate. Carbon isotopes suggest prevailing C3 vegetation and negligible mixing with volcanogenic or atmospheric CO2. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献