A multi‐mechanism constitutive model for plastic adaption under cyclic loading     

Claudio di Prisco  Giuseppe Mortara 《国际地质力学数值与分析法杂志》2013,37(18):3071-3086

As is well known, granular soils under cyclic loading dissipate a large amount of energy and accumulate large irreversible strains. Usually, with time, this second effect reduces and the accumulation rate decreases with the number of cycles until obtaining a sort of ideal stationary cyclic state at which ratcheting disappears. In this paper, only this ideal state is taken into consideration and simulated by means of a multi‐mechanism constitutive model for plastic adaptation. For this purpose, the concept of cycle is discussed, many different categories of cyclic stress/strain paths are considered and some theoretical issues concerning both the flow and the strain‐hardening rules are tackled. Even though the paper focuses on soil behaviour, the conclusions can be extended to all materials exhibiting ratcheting due to volumetric behaviour.Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Short-term effects of gamma ray bursts on oceanic photosynthesis     

Liuba Peñate  Osmel Martín  Rolando Cárdenas  Susana Agustí 《Astrophysics and Space Science》2010,330(2):211-217

We continue our previous work on the potential short-term influence of a gamma ray bursts on Earth’s biosphere, focusing on the only important short-term effect on life: the ultraviolet flash which occurs as a result of the retransmission of the γ radiation through the atmosphere. Thus, in this work we calculate the ultraviolet irradiances penetrating the first hundred meters of the water column, for Jerlov’s ocean water types I, II and III. Then we estimate the UV flash potential for photosynthesis inhibition in the whole photic zone, showing that it can be important in the first tens of meters of the water column.  相似文献   

Passive margin evolution and its controls on natural gas leakage in the southern Orange Basin,blocks 3/4, offshore South Africa     

Gesa Kuhlmann  Selwyn Adams  Curnell Campher  David van der Spuy  Rolando di Primio  Brian Horsfield 《Marine and Petroleum Geology》2010,27(4):973-992

Using a 2D seismic dataset that covers part of the southern Orange Basin offshore South Africa, we reconstructed the geological evolution of the basin. This evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post-rift succession since the Early Cretaceous. The Cretaceous succession has been subdivided into five seismic units. The highest sedimentation rates occur within the Barremian/Aptian (unit C1) and the Turonian/Coniacian (unit C3). Two Cenozoic units (T1 and T2) have been distinguished. These show a sudden decrease in sedimentation rate for the whole of the Cenozoic. Three phases of gravitational tectonics, with two Late Cretaceous phases of mass movement in the northern study area and Cenozoic slumping in the southern study area, have been related to sedimentation rates, sea-level changes, paleoenvironmental evolution and regional tectonics. The occurrence of natural gas leakage follows a coast-parallel distribution within the study area. In the near shore part at water depths shallower than 400 m, massive gas chimneys penetrate through the sediment layers and reach the (near-) surface. Within an intermediate narrow band, between 300 and <500 m water depth, the gas migrates more diffusely through sub-vertical faulted Cretaceous sediments, while in the outer part of the basin, through the Cretaceous and Cenozoic gravitational wedges, only very few signs of gas accumulation and migration can be seen along the faults. A conceptual model has been established with the Aptian source rock generating gas in the outer part of the basin. This source rock underlies the Cenozoic wedge in the south and the thick Cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column. This thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments, but moves buoyancy driven up-dip along stratigraphic layers, to escape through the sediments to the sea-floor in the inner shelf area.  相似文献   

Structural cutting of a region showing various compound tectonic deformations (example of Bouficha–Grombalia region)     

Houcem Mzali  Hédi Zouari 《Arabian Journal of Geosciences》2012,5(6):1399-1409

Bouficha–Grombalia region shows complex tectonic deformations and is affected by faults and folds of different geometry. A structural study has allowed to determine that Bouficha–Grombalia region is affected by significant faults of EW, NE-SW and NW-SE directions. These faults divide Bouficha–Grombalia region into several compartments. We distinguish three important structures whose first is in the SW which corresponds to Zaghouan–Bouficha trough. The second structure is situated in the NE, which corresponds to the Grombalia trough. The third structure occupies a central position; it consists in the Bouficha–Grombalia high structure. The last structure is composed by three blocks. Each block is characterised by particular folds geometry. These structures were outlined at least from middle Miocene, and they have undergone the effect of subsequent compressive tectonic events which have led to folds building above or counter the pre-existing NE-SW faults.  相似文献   

Charcoal and pollen analyses and vegetation reconstruction of the Alpine foreland in West Hungary     

Katalin Náfrádi  Pál Sümegi  Tünde T?r?csik 《Central European Journal of Geosciences》2012,4(4):592-602

In the area of archaeological excavations that were performed prior to the construction of Main Road No. 86 in Vas County (West Hungary) in the Alpine foreland new geoarchaeological analyses have been conducted. We used anthracology and pollen analyses to reconstruct the former vegetation cover at the study site. Charcoal data provide site-related information about the local woodland composition, management and human impact, while pollen data provide information on the arboreal and non-arboreal vegetation on a regional or local scale. Adequate samples for anthracological analyses derive from the Bronze Age, Iron Age, Imperial and Migration Periods and Middle-Ages archaeological objects. The core for pollen analyses originates from alluvial sediments of the Borzó Creek and covers the late Pleistocene and the Holocene until the Medieval Period. Charcoal analyses show the dominance of Quercus trees in the vicinity of the human settlements that might indicate a strong human selection, or the fragmentation of samples. Pollen analyses indicate thermophilous vegetation from the beginning of the Holocene, with increasing values of Fagus and Carpinus. Pollens of cereals indicate human activity, which is also demonstrated by the presence of pollen from Juglans and Vitis in the Iron Age sequence. Extensive forest clearance occurred in the Late Iron Age and the Imperial Period.  相似文献   

A distinct element method numerical investigation of compaction processes in highly porous cemented granular materials   总被引：1，自引：0，他引：1  

G. Dattola  C. di Prisco  I. Redaelli  S. Utili 《国际地质力学数值与分析法杂志》2014,38(11):1101-1130

In this paper, the results of an oedometric numerical test campaign, performed by means of a 3D Discrete Element Code on idealised cemented granular cylindrical specimens, are illustrated. The idealised microstructure taken into account is characterised by the following: (i) rigid grains bonded to one another; (ii) a high void ratio; and (iii) two different families of voids: the micro and the macro‐voids. The compaction process developing within the specimens, as well as the localization along tabular zones of pure compressive deformation (compaction banding) that in some cases takes place, are discussed. The influence on the evolution of this peculiar strain localization process of many microstructural/numerical parameters like material porosity, macro‐void size, the constitutive relationship adopted for the bonds and the bond damage rate is analysed. Tests for different values of porosity were run. Below a certain porosity threshold value, the onset of mixed modes of localisation was detected whereas the increase in the macro‐void size is observed to favour the onset of instability. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Numerical modeling and mechanical analysis of an innovative soil anchoring system     

Claudio di Prisco  Federico Pisanò 《Acta Geotechnica》2014,9(6):1013-1028

In this paper, the pull-out performance of an innovative system for soil anchoring is mechanically interpreted on the basis of a preliminary finite element investigation. The system consists of a tie rod equipped with thick steel sockets, extruding into the soil to increase the overall pull-out bearing capacity. The effectiveness of the anchorage is shown to be mainly due to the steel sockets, producing two correlated strength mechanisms: a direct one, associated with the shear/flexural strength of the sockets themselves; and an indirect one, in the form of a remarkable increase in the normal confinement on the tie rod and hence in the mobilizable shear stresses. The numerical results are finally exploited to conceive a simplified mechanical model for the interpretation/prediction of the pull-out anchor performance.  相似文献   

Geotechnical Characteristics of Volcanic Soils Taken from Recent Eruptions     

Rolando P. Orense  Andrew Zapanta Jr.  Akinori Hata  Ikuo Towhata 《Geotechnical and Geological Engineering》2006,24(1):129-161

Recent volcanic eruptions at Mt. Unzen (Japan) in 1990 and Mt. Pinatubo (Philippines) in 1991 produced voluminous amounts of ash and sediments which inundated widespread areas. In later rehabilitation and reconstruction, it is practical and economical to use these freshly deposited sediments as materials for foundations and embankments. However, the geotechnical properties of young volcanic products have not been fully investigated. Accordingly, we investigated the geotechnical characteristics of volcanic soils associated with three recent eruptions, namely, the Unzen and Izu-Oshima eruptions of 1990 and 1986, respectively, in Japan and the Pinatubo eruption of 1991 in the Philippines. We specifically investigated index properties, permeability and compaction characteristics, and strength and deformation behavior in drained conditions. Additionally, we examined the dynamic properties and liquefaction characteristics of samples taken from Mt. Pinatubo. The results showed that the geotechnical characteristics of the deposits generally varied with the sampling sites. Depending on the location, either upstream or downstream from a volcano, the preferential sizing due to alluvial deposition affects engineering properties of the deposits. For example, volcanic sediments upstream from Mt. Pinatubo have high compressibility and low cyclic strength, whereas those taken downstream show dilative tendencies and high liquefaction strength.  相似文献   

Computation of hyperⁿgeometric functions for gravitationally radiating binary stars     

V. Pierro  I. M. Pinto  A. D. A. M. Spallicci di F. 《Monthly notices of the Royal Astronomical Society》2002,334(4):855-858

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Redshift-space limits of bound structures     

Rolando Dünner  reas Reisenegger  rés Meza †  Pablo A. Araya  Hernán Quintana 《Monthly notices of the Royal Astronomical Society》2007,376(4):1577-1587

An exponentially expanding Universe, possibly governed by a cosmological constant, forces gravitationally bound structures to become more and more isolated, eventually becoming causally disconnected from each other and forming so-called 'island universes'. This new scenario reformulates the question about which will be the largest structures that will remain gravitationally bound, together with requiring a systematic tool that can be used to recognize the limits and mass of these structures from observational data, namely redshift surveys of galaxies. Here we present a method, based on the spherical collapse model and N -body simulations, by which we can estimate the limits of bound structures as observed in redshift space. The method is based on a theoretical criterion presented in a previous paper that determines the mean density contrast that a spherical shell must have in order to be marginally bound to the massive structure within it. Understanding the kinematics of the system, we translated the real-space limiting conditions of this 'critical' shell to redshift space, producing a projected velocity envelope that only depends on the density profile of the structure. From it we created a redshift-space version of the density contrast that we called 'density estimator', which can be calibrated from N -body simulations for a reasonable projected velocity envelope template, and used to estimate the limits and mass of a structure only from its redshift-space coordinates.  相似文献