A hypoplastic macroelement for single vertical piles in sand subject to three-dimensional loading conditions

This paper presents a novel macroelement for single vertical piles in sand developed within the hypo-plasticity theory, where the incremental nonlinear constitutive equations are defined in terms of generalized forces, displacements and rotations. Inspired from the macroelement for shallow foundations of Salciarini and Tamagnini (Acta Geotech, 4(3):163–176, 2009), the new element adopts the “intergranular displacement” mutuated from Niemunis and Herle (Mech Cohes Frict Mater, 2:279–299, 1997) to reproduce the behavior under cyclic loading. Analytical and numerical strategies are provided to calibrate the macroelement’s parameters. Comparisons with experimental results show the performance of the macroelement that while being simple and computational fast is suitable for finite element calculations and engineering design.     

The implication of transfer faults in foreland basin evolution: application on Pindos foreland basin,West Peloponnesus,Greece

Pindos foreland basin in west Peloponnesus (Tritea, Hrisovitsi and Finikounda sub‐basins) during Late Eocene to Early Oligocene was an underfilled foreland basin. The basin's geometry was affected by the presence of internal thrusting and transfer faults, causing changes in depth and width. Due to internal thrusting, the foreland basin changed through time from a uniform to non‐uniform configuration, whereas transfer faults have an intensive impact on depositional environments within the basin. Internal thrusting (Gavrovo, internal and middle Ionian thrusts) activated synchronously with the major Pindos Thrust, creating intrabasinal highs that influenced palaeocurrent directions. The transfer faults cross‐cut the intrabasinal highs and produced low relief areas that act as pathways for sediment distribution. The sediments are thicker and sandstone‐rich on the downthrown sides of the transfer faults. In these areas, sandstone reservoirs could be produced. Such tectonically active areas constitute promise for oil and gas reservoirs and traps.     

Geophysical investigation of tumuli by means of surface 3D Electrical Resistivity Tomography

Tumuli are artificially erected small hills that cover monumental tombs or graves. In this work, the surface three-dimensional (3D) Electrical Resistivity Tomography (ERT) method, composed of dense parallel two-dimensional (2D) tomographies, was used to investigate the properties of the tumuli filling material and to resolve buried archaeological structures inside the tumuli.The effectiveness of the method was investigated by numerical modeling and through 3D inversion of synthetic apparent resistivity data. A resistivity model that simulates the inhomogeneous tumulus material and the tombs that are buried inside the tumulus was assumed. The Dipole–Dipole (DD), Pole–Dipole (PD), Pole–Pole (PP), Gradient (GRAD), Midpoint-Potential-Referred (MPR) and Schlumberger Reciprocal (SCR) arrays, which are suitable for multichannel resistivity instruments, were tested. The tumulus topography (pyramid or capsized cup) was incorporated into the inversion procedure through a distorted finite element mesh. The inversion procedure was based on a smoothness constrained Gauss–Newton algorithm in which the Active Constraint Balancing (ACB) method was also applied in order to enhance the least-squares resolving power and stability.Synthetic modeling showed that the different tumulus layers and the horizontal contact of the artificial tumulus material with the natural background soil were reconstructed by all of the tested electrode arrays. Generally, PD and the GRAD arrays comprise the optimum choices to investigate the subsurface properties of a tumulus and locate buried tombs. The MPR model was inferior to the GRAD model, while the DD, PP and SCR models had the poorest resolution. It was also shown that the inversion models are practically independent from the survey direction and the topography shape of the tumulus.The real field data collected employing the PD array along a small tumulus from the archaeological site of Vergina in northern Greece enhanced the synthetic modeling results. The inversion model outlined a number of archaeological structures that exhibit a high possibility to correlate with graves. Overall, this work signifies that the surface 3D ERT method can provide a valuable tool in the non-destructive archaeological exploration of tumuli.     

Factors Affecting the Settlement Estimation of Stone Column Reinforced Soils

The ground improvement technique of stone columns has been effectively used over the last decades in order to accelerate the consolidation rate of soft soils by providing a drainage path, reduce foundation settlements, improve the bearing capacity of the soil, and limit the risk of liquefaction due to seismic activity. Because of the time consumption of a three dimensional (3D) calculation, most stone column projects are presently studied by axisymmetric finite element computations. Otherwise, it is the analytical method of Priebe that is commonly used to predict the final settlements of a single stone column and the corresponding settlement reduction factor. Both methods, axisymmetric finite element analysis and Priebe’s analytical method make use of the axisymmetric theory of unit cell. The main objective of this study is to examine and compare the three dimensional response of stone column reinforced soils with the axisymmetric analysis results. A proposed analytical method, governed by the failure mechanism of a cylindrical cone is also presented. The comparison between these different approaches is studied and evaluated in conjunction with in situ measurements. It is proved that the beneficial effect of this ground improvement technique, especially on the foundation soil with the lower strength characteristics, is more pronounced. Also, it is concluded that due to unit cell theory, the settlement reduction factor is usually under predicted and the failure of the composite system is impossible, even under high applied pressures. The proposed analytical method of the cylindrical cone failure mechanism is proved to be in good agreement with the 3D results.     

Interactive visual analytics of hydrodynamic flux for the coastal zone

Researchers wish to study the potential impact of sea level rise from climate change, and visual analytic tools can allow scientists to visually examine and explore different possible scenarios from simulation runs. In particular, hydrodynamic flux is calculated to understand the net movement of water; but typically this calculation is tedious and is not easily achieved with traditional visualization and analytic tools. We present a visual analytic method that incorporates a transect profiler and flux calculator. The analytic software is incorporated into our visual analytics tool Vinca, and generates multiple transects, which can be visualized and analysed in several alternative visualizations; users can choose specific transects to compare against real-world data; users can explore how flux changes within a domain. In addition, we report how ocean scientists have used our tool to display multiple-view views of their data and analyse hydrodynamic flux for the coastal zone.     

Chemical composition of wet deposition in a Mediterranean site Athens,Greece related to the origin of air masses

The goal of this study is to determine the chemical composition of rain, in the wider region of Athens, Greece for the time period 1st September 2001 to 31st August 2002. Two model automatic rain samplers were installed in the Meteorological Station of Laboratory of Climatology (latitude: 37° 58′ N, longitude: 23° 47′ E) inside the Athens University Campus and in a site at Heraklio Attica, a northern suburb of Athens (latitude: 38° 03′ N, longitude: 23° 45′ E). The concentrations (μeq l⁻¹) of the major cations (H⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and anions (Cl⁻, , και ), as well as pH and conductivity of rain in 39 total samples were determined. The figures of pH range from 6.4 to 8.4 and conductivity from 8 to 207 μS cm⁻¹. The analysis showed that Ca²⁺ ions are abundant within all examined samples, while and present the highest concentrations from the anions. In order to find out the origin of the air masses, the air mass back trajectories were calculated. Five sectors of the origin of air masses were revealed: the North, the South, the Local, the West and the East sector. Multivariate methods included Factor Analysis and Discriminant Analysis were applied to the examined ion concentrations and three main factors were extracted, which discriminated the ions according to their origin. The first group of ions is interpreted as the result of the anthropogenic activity, the second group represents the acidity–alkalinity independently of their source and the third one the marine influence.     

The first photometric analysis of the near-contact binary star V370 Cygni

The first complete CCD light curves of the eclipsing binary system V370 Cygni have been obtained in the B, V, R and I filters during 5 consecutive nights in 2005 at Kryoneri Observatory, Greece. These curves were analyzed with the Wilson–Devinney program in order to determine the geometrical and physical parameters of the system. The analysis indicates a semi-detached configuration and a mildly evolved state of the system.      

Near-contact binaries among short-period Algols: the case of BF Velorum with a pulsating component

A photometric analysis of the short-period Algol eclipsing binary system BF Velorum based for the first time on complete BVRI CCD light curves is presented. The new photometric solution obtained with the Wilson-Devinney program reveals that BF Vel is a near-contact semi-detached system with its secondary component filling its Roche lobe. Moreover, we discovered pulsations of one member of the binary system, the analysis of which shows main frequencies of 44.9386 and 33.6731 cycles/day. Absolute elements of the system were calculated, and the evolutionary status of its members was estimated.      

A study of weather types at Athens and Thessaloniki and their relationship to circulation types for the cold-wet period, part II: discriminant analysis

A discriminant analysis is applied in order to determine the relationships between circulation types in the middle troposphere and prevailing weather types over two major Greek cities, Athens and Thessaloniki. In order to describe the synoptic conditions, an automatic classification scheme for the Greek region is used. For each circulation type identified (14 in total), several meteorological parameters at the 500 hPa level are calculated such as geopotential heights and their anomalies, temperature and relative vorticity. Weather group-types that reflect the conditions at the surface, were previously defined using a two-step cluster analysis. These types result from a combination of five meteorological parameters—maximum temperature, precipitation amount, relative humidity, wind velocity and sunshine duration. The study period is 43 years long (1958–2000) and is restricted to the cold and wet period of the year, from December until March. For Athens, six weather types are developed, whereas for Thessaloniki five are produced. By means of a stepwise discriminant analysis (DA) model, the most important variables from the 500 hPa level are found and are used to generate the necessary functions that can discriminate weather types over the two stations. The aim of the present study is first to discriminate weather types effectively and to identify the most important discriminating variables, and second, to connect these weather types to elements of the prevailing synoptic pattern, through mathematical functions provided by DA. The results of the evaluation of the aforementioned procedure are considered to be very satisfactory.