scholarly journals Capillary Barriers during Rainfall Events in Pyroclastic Deposits of the Vesuvian Area

Geosciences ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 274
Author(s):  
Ciro Sepe ◽  
Domenico Calcaterra ◽  
Manuela Cecconi ◽  
Diego Di Martire ◽  
Lucia Pappalardo ◽  
...  
Keyword(s):  
Element Model ◽  
Degree Of Saturation ◽  
Capillary Barrier ◽  
Pyroclastic Deposits ◽  
Rainfall Events ◽  
Soil Layers ◽  
Barrier Formation ◽  
Capillary Barriers ◽  
Grain Size Distributions ◽  
Different Grain Size

In the present paper, the capillary barrier formation at the interface between soil layers, which is characterized by textural discontinuities, has been analyzed. This mechanism has been investigated by means of a finite element model of a two-layer soil stratification. The two considered formations, belonging to the pyroclastic succession of the “Pomici di Base” Plinian eruption (22 ka, Santacroce et al., 2008) of the Somma–Vesuvius volcano, are affected by shallow instability phenomena likely caused by progressive saturation during the rainfall events. This mechanism could be compatible with the formation of capillary barriers at the interface between layers of different grain size distributions during infiltration. One-dimensional infiltration into the stratified soil was parametrically simulated considering rainfall events of increasing intensity and duration. The variations in the suction and degree of saturation over time allowed for the evaluation of stability variations in the layers, which were assumed as part of stratified unsaturated infinite slopes.

Geotextiles to Mitigate Frost Effects in Soils: A Critical Review

1996 ◽  
Vol 1534 (1) ◽  
pp. 5-11
Author(s):  
Karen S. Henry
Keyword(s):  
Field Trials ◽  
Frost Heave ◽  
Laboratory Research ◽  
Capillary Barrier ◽  
Subgrade Soil ◽  
Capillary Barriers ◽  
Geotechnical Structures ◽  
Barrier Performance ◽  
Base Course ◽  
Selection Of

The use of geotextiles to mitigate frost effects in soils has been studied, but few techniques have been developed. Guidelines developed for the placement of granular capillary barriers are presented to serve as preliminary guidelines for geotextile capillary barriers. Laboratory research shows that pore size distribution, wettability, and, for some geotextiles, thickness influence capillary barrier performance in a given soil. Geotextiles that easily wet do not reduce frost heave and may even exacerbate it. On the basis of the literature reviewed, guidance for selection of geotextile capillary barriers in field trials is given. If geotextiles function as capillary barriers during freezing and reinforce or separate and filter the subgrade at the base course interface during thaw, then the potential exists for their use in a combination of functions to reduce frost-related damage in geotechnical structures. It was found that properly designed geotextiles have the potential to reduce frost heave by functioning as capillary barriers, they can be filters for capillary barriers, and they can provide reinforcement or separation or filtration (or all of these) of the subgrade soil to reduce thaw-related damage.

scholarly journals X-ray extinction from interstellar dust

2019 ◽  
Vol 629 ◽  
pp. A78 ◽  
Author(s):  
E. Costantini ◽  
S. T. Zeegers ◽  
D. Rogantini ◽  
C. P. de Vries ◽  
A. G. G. M. Tielens ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Simulated Data ◽  
X Ray ◽  
Cosmic Abundance ◽  
Grain Size Distributions ◽  
Edge Features ◽  
Different Grain Size ◽  
Near Future

Aims. We present a study on the prospects of observing carbon, sulfur, and other lower abundance elements (namely Al, Ca, Ti, and Ni) present in the interstellar medium using future X-ray instruments. We focus in particular on the detection and characterization of interstellar dust along the lines of sight. Methods. We compared the simulated data with different sets of dust aggregates, either obtained from past literature or measured by us using the SOLEIL-LUCIA synchrotron beamline. Extinction by interstellar grains induces modulations of a given photolelectric edge, which can be in principle traced back to the chemistry of the absorbing grains. We simulated data of instruments with characteristics of resolution and sensitivity of the current Athena, XRISM, and Arcus concepts. Results. In the relatively near future, the depletion and abundances of the elements under study will be determined with confidence. In the case of carbon and sulfur, the characterization of the chemistry of the absorbing dust will be also determined, depending on the dominant compound. For aluminum and calcium, despite the large depletion in the interstellar medium and the prominent dust absorption, in many cases the edge feature may not be changing significantly with the change of chemistry in the Al- or Ca-bearing compounds. The exinction signature of large grains may be detected and modeled, allowing a test on different grain size distributions for these elements. The low cosmic abundance of Ti and Ni will not allow us a detailed study of the edge features.

scholarly journals Two Different Grain Size Distributions within the Protoplanetary Disk around HD 142527 Revealed by ALMA Polarization Observation

2018 ◽  
Vol 864 (1) ◽  
pp. 81 ◽  
Author(s):  
Satoshi Ohashi ◽  
Akimasa Kataoka ◽  
Hiroshi Nagai ◽  
Munetake Momose ◽  
Takayuki Muto ◽  
...  
Keyword(s):  
Grain Size ◽  
Protoplanetary Disk ◽  
Size Distributions ◽  
Polarization Observation ◽  
Grain Size Distributions ◽  
Different Grain Size

On the Physico-Chemical Basis for the Capillary Barrier Effect

1988 ◽  
Vol 19 (5) ◽  
pp. 281-292 ◽  
Author(s):  
Anders Rasmuson ◽  
Jan-Christer Eriksson
Keyword(s):  
Water Infiltration ◽  
Hazardous Wastes ◽  
Barrier Effect ◽  
Capillary Barrier ◽  
Simple Estimate ◽  
Soil Layers ◽  
Chemical Basis ◽  
Water Influx ◽  
Physico Chemical ◽  
Coarse Soil

The capillary barrier concept, using fine and coarse soil layers to reduce water infiltration into piles of hazardous wastes, is investigated theoretically. A detailed account of the hydrological and physico-chemical basis for the phenomenon is given. It is established that the capillary barrier will, in practice, only function if the fine layer remains somewhat unsaturated, i.e. the upper menisci exist and no ponding over the fine layer occurs. Accordingly, water reaching the fine layer must be transported laterally within this layer. The pressure conditions are dependent on the length of the interface, the slope of the interface, the thickness of the fine layer, the type of soil in the fine layer, the water influx at the surface, and the total volume of water infiltrated during an infiltration event. A simple estimate shows that the capillary barrier concept is feasible only for small heaps with steep interfacial slopes.

The in situ density and shearing resistance of the Hampshire Basin Plateau Gravels

1991 ◽  
Vol 7 (1) ◽  
pp. 415-422 ◽  
Author(s):  
M. E. Barton ◽  
G. J. Evans ◽  
S. B. Haji Yusof ◽  
Ho Wai Kin
Keyword(s):  
Dry Density ◽  
Sandy Gravel ◽  
Direct Shear Tests ◽  
Fluvial Terraces ◽  
Shearing Resistance ◽  
Replacement Technique ◽  
Grain Size Distributions ◽  
Different Grain Size ◽  
Best Fit

AbstractOne of the principal Quaternary deposits in Central Southern England are extensive spreads of sandy fine to coarse, mainly flint gravels: those at the higher elevations being referred to as “Plateau” Gravels to distinguish them from the “Valley” Gravels. The most widely accepted view of the origin of the Plateau Gravels is that they represent fluvial terraces deposited under periglacial conditions. Although they have provided excellent conditions for foundations, their actual in-situ density and shear strength characteristics were virtually unknown. To remedy this deficiency, a series of in-situ density tests using the sand replacement technique and direct shear tests using 300 mm square samples have been carried out.Samples of sandy gravel from Highcliffe were compacted by hand tamping to minimise particle breakdown and tested in a saturated condition with a dry density approximately 97% of the in-situ value. The results show a curved failure envelope which in the usual form of power law notation gives a best fit result of:- τ = 1.475 σn ′ 0-955 Over the range of normal Stresses from 80 to 370 kPa used in the tests, this corresponds to secant φ′ values from 51°. to 48°. Tests carried out on dry samples gave φ′ values up to 4° higher. Tests on other samples with different grain size distributions show that the shearing resistance increases with the percentage gravel (as opposed to sand) content. These results have been combined with published work on other well graded, mainly flint gravels to give a preliminary quantitative evaluation of the influence of percentage gravel content on shearing resistance.

scholarly journals Pityusa Patera, Mars: Structural analyses suggest a mega-caldera above a magma chamber at the crust-mantle interface

Geology ◽  
2021 ◽  
Author(s):  
Hannes Bernhardt ◽  
David A. Williams
Keyword(s):  
Finite Element ◽  
Solar System ◽  
Finite Element Model ◽  
Magma Chamber ◽  
Element Model ◽  
Mantle Material ◽  
Pyroclastic Deposits ◽  
Caldera Floor ◽  
Prime Target ◽  
Central Plug

Pityusa Patera is the southernmost of four paterae in the 1.2 × 106 km2 wrinkle-ridged plains-dominated Malea Planum region of Mars. Based on their texture, morphology, and uniqueness to Pityusa Patera, we interpret layered, folded massifs as pyroclastic deposits emplaced during patera formation as a collapse caldera. Such deposits would not be expected in a previously suggested scenario of patera formation by subsidence from lithospheric loading. Our structural measurements and modeling indicate that the folding and high relief of the massifs resulted from ~1.3%–6.9% of shortening, which we show to be a reasonable value for a central plug sagging down into an assumed piston-type caldera. According to a previously published axisymmetric finite-element model, the extent of shortening structures on a caldera floor relative to its total diameter is controlled by the roof depth of the collapsed magma chamber beneath it, which would imply Pityusa Patera formed above a chamber at 57.5–69 km depth. We interpret this value to indicate a magma chamber at the crust-mantle interface, which is in agreement with crust-penetrating ring fractures and mantle flows expected from the formation of the Hellas basin. As such, the folded massifs in Pityusa Patera, which are partially superposed by ca. 3.8 Ga wrinkle-ridged plains, should consist of primordial mantle material, a theory that might be assessed by future hyperspectral observations. In conclusion, we do not favor a formation by load-induced lithospheric subsidence but suggest Pityusa Patera to be one of the oldest extant volcanic landforms on Mars and one of the largest calderas in the solar system, which makes the folded, likely mantle-derived deposits on its floor a prime target for future exploration.

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