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We study the mineralogical changes suffered by specimens of natural miocene red and green continental sandstones (from Pozuelos Formation and Tiomayo Formation) cropping out in the Argentine Puna that increase their bulk magnetic susceptibility and change color when thermally treated. We hypothesize that on heating siderite, which is present in small quantities as cement in the studied sandstones, would oxidize and decompose into maghemite and/or magnetite. Subsequent heating to higher temperatures sometimes would bring about the conversion of maghemite and/or magnetite to hematite. Mössbauer spectroscopy proved to be a very valuable tool for the determination of the presence of siderite in small amounts in the studied samples. The present results show that further work is needed in order to fully understand the mineralogical changes suffered by continental sandstones during heating. The characterization of such changes occurred during laboratory routines is relevant, since they can help to better understand natural processes. 相似文献
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A multidirectional semi‐analytical method for analysis of laterally loaded pile groups in multi‐layered elastic strata 
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下载免费PDF全文 A semi‐analytical method for calculating the response of single piles and pile groups subjected to lateral loading is developed in this paper. Displacements anywhere in the soil domain are tied to the displacements of the piles through decay functions. The principle of virtual work and the calculus of variations are used to derive the governing differential equations that describe the response of the piles and soil. The eigenvalue method and the finite difference technique are used to solve the system of coupled differential equations for the piles and soil, respectively. The proposed method takes into account the soil surface displacement along and perpendicular to the loading direction and produces displacement fields that are very close to those produced by the finite element method but at lower computational effort. Compared with the previous method that considered only the soil displacement along the loading direction, accounting for the multi‐directional soil displacement field produces responses for the piles and soil that are closer to those approximated by the finite element method. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Umashankar Balunaini Sungmin Yoon Monica Prezzi Rodrigo Salgado 《Geotechnical and Geological Engineering》2014,32(2):505-523
Use of tire shred–soil mixtures as backfill materials in mechanically stabilized earth walls has several advantages over other backfill materials: (1) good drainage, (2) high shear strength, and (3) low compacted unit weight. This paper presents the results of laboratory pullout tests performed on uniaxial geogrid embedded in tire shred–sand mixtures. The effects of tire shred size, tire shred–sand mixing ratio and confining pressure on the interaction between the geogrid and tire shred–sand mixtures are evaluated. Three sizes of tire shreds are considered: tire chips (with 9.5 mm nominal size), tire shreds 50-to-100 mm long and tire shreds 100-to-200 mm in length, with mixing ratios of 0, 12, 25 and 100 % of tire shreds in the mixtures (by weight). Based on compaction testing of a number of mixtures, the optimal mixing proportion of tire shreds and sand was found to lie between 25/75 and 30/70 (by weight of tire shred and sand); this is equivalent to approximately 40/60 and 50/50, respectively, by volume of tire shreds and sand. The pullout resistance of a geogrid embedded in tire shred–sand mixtures is significantly higher than that of the same geogrid embedded in tire shreds only. The size of the tire shreds has negligible effect on the pullout resistance of a geogrid embedded in mixtures prepared with either low (12/88 mix) or high (100/0 mix) tire shred content. However, when the 25/75 mixture is used, greater geogrid pullout resistance was obtained for the geogrid embedded in tire chip–sand mixtures than in tire shred–sand mixtures. 相似文献
4.
This paper shows the results of a ground magnetic survey carried out to study solid waste landfills. The area located southward of Gualeguaychú town was chosen as a pilot case. This zone was selected considering the available knowledge about the cessation of operations, and the interest of the local authorities in verifying the existence of anomalies indicative of possible dangerous pollutants. The total magnetic field was measured along six profiles, and the corresponding anomalies were calculated. The profiles were modelled in 2.5 D, and along them Eulers deconvolution was used to estimate the depth to the sources. The first and the second derivatives of the residual magnetic field were calculated, in order to sharpen the anomalies. Our interpretation suggests that the characteristics of the modelled bodies and the magnitudes of the detected anomalies do not indicate the presence of drums in the sanitary infill. 相似文献
5.
The Chaco foreland basin was initiated during the late Oligocene as a result of thrusting in the Eastern Cordillera in response to Nazca–South America plate convergence. Foreland basins are the result of the flexural isostatic response of an elastic plate to orogenic and/or thrust sheet loading. We carried out flexural modelling along a W–E profile (21.4°S) to investigate Chaco foreland basin development using new information on ages of foreland basin strata, elastic and sedimentary thicknesses and structural histories. It was possible to reproduce present-day elevation, gravity anomaly, Moho depth, elastic thicknesses, foreland sedimentary thicknesses and the basin geometry. Our model predicted the basin geometry and sedimentary thicknesses for different evolutionary stages. Measured thicknesses and previously proposed depozones were compared with our predictions. Our results shed more light on the Chaco foreland basin evolution and suggest that an apparent decrease in elastic thickness beneath the Eastern Cordillera and the Interandean Zone could have occurred between 14 and 6 Ma. 相似文献
6.
In this work, we consider historical earthquakes registered in Chile (from 1900 up to 2010) with epicenters located between 19 and 40°S latitude, in order to evaluate the probabilities of the occurrence of strong earthquakes along Chile in the near future. Applying Gumbel??s technique of first asymptotic distribution, Wemelsfelder??s theory and Gutenberg?CRichter relationship, we estimate that during the next decade strong earthquakes with Richter magnitudes larger than 8.7?C8.9 could occur along Chile. According to our analysis, probabilities for the occurrence of such a strong earthquake range between 64 and 46% respectively. Particularly in the very well known ??seismic gap?? of Arica, a convergence motion between Nazca and South American plates of 77?C78?mm/year represents more than 10?m of displacement accumulated since the last big interplate subduction earthquake in this area over 134?years ago. Therefore, this area already has the potential for an earthquake of magnitude >8. 相似文献
7.
Ganju Eshan Kılıç Mustafa Prezzi Monica Salgado Rodrigo Parab Niranjan Chen Wayne 《Acta Geotechnica》2021,16(11):3489-3516
Acta Geotechnica - This paper presents the results and analyses of uniaxial compression experiments performed on three silica sands. The sands have comparable particle-size distributions, but their... 相似文献
8.
M.J. Orgeira L.N. Castro G.A. Goldmann C.B. Prezzi E. Sileo D.R. Vega C. Franzosi R.D. Acevedo O. Martínez J. Rabassa J.F. Ponce O.R. Tófalo 《地学前缘(英文版)》2017,8(1):137-149
The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m2/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere. 相似文献
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In this paper, the effect of soil disturbance caused by installation of prefabricated vertical drains (PVDs) on the rate of
consolidation is studied by two-dimensional finite element analysis. A transition zone lying between the highly disturbed
smear and the undisturbed zones is considered in the analysis. The hydraulic conductivity in the transition zone is assumed
to vary linearly from a low value in the smear zone to the original in situ value in the undisturbed zone. The analysis uses
the actual band shape of the PVD and the rectangular shape of the unit cell. A parametric study is carried out to investigate
the effects of the degree of soil disturbance, the size of the smear and the transition zones, the PVD spacing and the mandrel
size and shape. Design guidelines, where the smear and transition zones are replaced by an expanded smear zone producing the
same effect, are provided so that existing analytical solutions considering only the smear zone can be used for analysis and
design. A comparison with experimental results shows that consideration of the transition zone is important for correct estimation
of the degree of consolidation. 相似文献