Kinematics of shear bands

Shear bands appear at limit states of soil bodies. They are analysed as thin zones of localised deformation that takes place as simple (i.e. dilatant) shear. It can be observed, however, that shear bands are discontinuous and also may be “reflected” at rigid boundaries. These phenomena appear as incompatible with the assumed shear deformation. The analysis in this paper reveals the kinematics of such “incompatibilities” in terms of continuous deformation fields.     

Directional dependence of site effects observed near a basin edge at Aegion,Greece

We study site effects using 520 weak motion earthquake records from a vertical array in Aegion, Greece. The array is inside a basin, has four stations in soil, and one in bedrock (178 m depth). The site is marked by high seismicity and complex surface geology. We first use the records to establish the downhole accelerometer orientations and their evolution with time. Then we estimate site effects using empirical spectral ratios with and without a reference site (standard and horizontal-to-vertical spectral ratio). We find significant site amplification which cannot be accounted for by 1D model predictions, along with a significant difference in the amplification level between the two horizontal components. These are indications of 2D effects, namely surface waves generated at the basin edge. The difference in amplification between the horizontal components is maximised when these are rotated with respect to the orientation of the basin edge. The strongest amplification takes place in the direction parallel to the basin edge (SH, or out-of-plane motion), and is up to 2 times higher than in the perpendicular direction (SV, or in-plane motion). This directional effect on the amplification is corroborated by numerical 2D modelling using incident SH and SV waves, with the former possibly generating strong Love waves. In the records, the directionality is clear for windows containing the largest amplitudes of the records (S waves and strong surface waves), while it tends to vanish for coda-wave windows. This directionality is also observed when using response spectral ratios rather than Fourier ratios. We compute soil-to-rock amplification factors for peak ground acceleration (PGA) and find it is significantly higher than what is predicted by current design codes. We attribute this difference to the basin edge amplification, linear soil behaviour, and to the inability of simple scalar values like PGA to describe complex amplification effects. Finally, we analyse the earthquake records at a surface station near the slope crest and do not observe significant topographic amplification.     

The influence of pumping parameters in fluid‐driven fractures in weak porous formations

In this work, we investigate the main pumping parameters that influence a fluid‐driven fracture in cohesive poroelastic and poroelastoplastic weak formations. These parameters include the fluid viscosity and the injection rate. The first parameter dominates in the mapping of the propagation regimes from toughness to viscosity, whereas the second parameter controls the storage to leak‐off dominated regime through diffusion. The fracture is driven in weak permeable porous formation by injecting an incompressible viscous fluid at the fracture inlet assuming that the fracture propagates under plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory. Pore fluid movement in the porous formation is based on the Darcy law. The coupling follows the Biot theory, whereas the irreversible rock deformation is modeled with the Mohr–Coulomb yield criterion with associative flow rule. Fracture propagation criterion is based on the cohesive zone approach. Leak‐off is also considered. The investigation is performed numerically with the FEM to obtain the fracture opening, length, and propagation pressure versus time. We demonstrate that pumping parameters influence the fracture geometry and fluid pressures in weak formations through the viscous fluid flow and the diffusion process that create back stresses and large plastic zones as the fracture propagates. It is also shown that the product of the propagation velocity and fluid viscosity, µv that appears in the scaling controls the magnitude of the plastic zones and influences the net pressure and fracture geometry. These findings may explain partially the discrepancies in net pressures between field measurements and conventional model predictions for the case of weak porous formation. Copyright © 2014 John Wiley & Sons, Ltd.     

Catchment-wide estimate of single storm interrill soil erosion using an aggregate instability index: a model based on geographic information systems

The main objective of this paper is to estimate interrill erosion after rainfall in the basin of Mourganis river (442?km²; Kalabaka province, Trikala prefecture, Thessaly, Greece). For the estimation of the interrill erosion, the method of Valmis et al. (1988) was used, in combination with Nearing et al. (1989). Input data of the algorithm include the slope angle of the ground surface, the rainfall, the ground cover type, the height of canopy, and the instability of ground of the study area. The spatial data were processed by standard GIS software. Soil samples were collected in the field to calibrate the model. The results comprise soil erosion maps for two specific rainfall scenarios. The first rainfall scenario refers to the most extreme rainfall in this catchment that happened on the 7/21/1959 with 48?mm/h. The second scenario is closer to average as the intensity rainfall is 3.54?mm/h. The total mass of eroded material ranges from 0.048?t/ha (assuming mean rainfall intensity) up to 3.5?t/ha (for the extreme scenario). We note that the western part of the Mourgani basin exhibits higher erosion than the eastern part.     

Shear strength behaviour of polypropylene fibre reinforced cohesive soils

Soil reinforcement through the inclusion of oriented or randomly distributed discrete elements such as fibres has recently attracted increasing attention in geotechnical engineering. Therefore, the purpose of this paper is to investigate the influence of certain parameters (the strength properties of the fibre, the relative size of the fibres and grains, and the rate of shear) on the shear strength of polypropylene fibre reinforced cohesive soils. A series of consolidated drained or undrained direct shear tests were conducted on unreinforced and reinforced sandy silt and silty clay specimens. Two types of polypropylene fibres with different mechanical indices were used. The fibre content was varied between 0.3% and 1.1% by weight of dry soil. The test results revealed that the inclusion of fibres in soil significantly increases the shear strength. The attainment of the high shear strength is attributed to the micromechanisms involved in the fibre/soil interactions as studied through scanning electron micrographs. The results also showed that the reinforcement effect was more pronounced under undrained shearing conditions. An important outcome from the current work is that, from the data obtained, the strength of the reinforced soil composites is not practically affected by the fibre mechanical indices.     

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 use of the deposit-refund framework in port reception facilities charging systems

The European Union set in place Directive 2000/59/EC with the aim of substantially reducing discharges of ship-generated waste into the sea by improving the availability and use of port reception facilities. According to the Directive, port administrations shall ensure that the cost recovery system must aim to discourage ships from discharging their waste into the sea, while simultaneously placing the burden of costs on ships, in line with the "polluter pays principle". The present paper examines the extent to which the deposit-refund framework could be used in charging systems of port reception facilities. This has been realized through a case study involving a Greek port. Specifically, the charging system proposed here seems to approach quite close to the primary target, i.e. to a charging system that motivates ships to act more environmentally responsible manner regarding their waste, without significantly affecting their total cost nor the competitiveness of the port.     

Modelling the lithospheric rheology control on the Cretaceous rifting in West Antarctica

Small‐scale analogue models were used to investigate the process of Cretaceous orthogonal extension in the West Antarctic Rift System. The models considered the transition from the East Antarctic Craton to a weaker lithosphere, and the results support previous hypotheses about the strong control exerted by lateral variations in lithospheric structures on the process of extension. Strain was mostly accommodated at the boundary between the two types of lithosphere, with a relative uplift of the cratonic block which remained essentially undeformed. Conversely, the weaker lithosphere showed wide‐rifting style geometry, locally associated with core complex‐like structures. In agreement with the natural prototype, this tectonic scenario led to a long‐lasting extension without continental break‐up, and to the absence of relevant surface magmatism.     

Simplified estimation of seismic risk for reinforced concrete buildings with consideration of corrosion over time

Throughout the world, buildings are reaching the end of their design life and develop new pathologies that decrease their structural capacity. Usually the ageing process is neglected in seismic design or seismic risk assessment but may become important for older structures, especially, if they are intended to be in service even after they exceed their design life. Thus, a simplified methodology for seismic performance evaluation with consideration of performance degradation over time is presented, based on an extension of the SAC/FEMA probabilistic framework for estimating mean annual frequencies of limit state exceedance. This is applied to an example of an older three-storey asymmetric reinforced concrete building, in which corrosion has just started to propagate. The seismic performance of the structure is assessed at several successive times and the instantaneous and overall seismic risk is estimated for the near collapse limit state. The structural capacity in terms of the maximum base shear and the maximum roof displacement is shown to decrease over time. Consequently, the time-averaged mean annual frequency of violating the near-collapse limit state increases for the corroded building by about 10% in comparison to the typical case where corrosion is neglected. However, it can be magnified by almost 40% if the near-collapse limit state is related to a brittle shear failure, since corrosion significantly affects transverse reinforcement, raising important questions on the seismic safety of the existing building stock.