Evaluation of Engineering and Cement–Stabilization Parameters of Clayey–Sand Mixtures under Soaked Conditions

Clay soils, especially clay soils of high or very high swelling potential often present difficulties in construction operations. However, the engineering properties of these clay soils can be enhanced by the addition of cement, thereby producing an improved construction material. Higher strength loss of cement stabilized clay soils after soaking in water is attributed to water absorbing capacity of the clay fraction (e.g. montmorillonite). Kaolinite and illitic soils are largely inert and resist to water penetration. These clays generally develop satisfactory strengths resulting to low strength reduction [Croft, 1967]. The swelling clays such as bentonite soaked in water, due to environmental conditions, result to volume increase causing macro and micro-fracturing in engineering structures. These fractures accelerate water penetration and consequently cause greater strength loss [Sällfors and Öberg-Högsta, 2002]. The water intrusion during soaking creates swelling and disrupts the cement bonds. The development of internal and external force systems in soil mass, due to soaking conditions, establish the initiation of slaking. Internal force system of a stabilized clayey soil consists of the resultant stresses established by the bonding potential of a cementing agent and the swelling potential of a clay fraction. In an effort to study this influence of soaking conditions and final absorbed water content on the stabilization parameters (cement, compaction, curing time), both unconfined compressive strength and slaking (durability) tests were carried out on two different cement stabilized clayey mixtures consisted of active bentonite, kaolin and sand.     

Changes in the chemistry of shallow groundwater related to the 2008 injection of CO2 at the ZERT field site, Bozeman, Montana

Approximately 300 kg/day of food-grade CO₂ was injected through a perforated pipe placed horizontally 2–2.3 m deep during July 9–August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO₂. As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1–6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO₂ injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO₂ injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO₂ leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO₂ intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0–5.6), alkalinity (400–1,330 mg/l as HCO₃), and electrical conductance (600–1,800 μS/cm) following CO₂ injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90–240 mg/l), Mg (25–70 mg/l), Fe (5–1,200 ppb), and Mn (5–1,400 ppb) following CO₂ injection. These chemical changes could provide early detection of CO₂ leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO₂ injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 ± 2 mg/l, and the variations do not correlate with CO₂ injection. CO₂ injection, however, is responsible for detection of BTEX (e.g. benzene, 0–0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly below the maximum contaminant levels (MCLs). Sequential leaching of core samples is being carried out to investigate the source of metals and other solutes.     

Assessment of extreme weather events on transport networks: case study of the 2007 wildfires in Peloponnesus

This paper deals with the 2007 wildfires that hit Peloponnesus, the southern peninsula of Greece, presenting an overview of the impacts in terms of infrastructural damages and human injuries and losses. Network performance and components’ criticality analyses are used to assess the effects of the fires in vehicular traffic and the overall transport network. The crisis and emergency management of the event are discussed in depth, highlighting potential gaps and possibilities for future improvement. The paper concludes with a presentation of the adaptation measures that succeeded the event in terms of recovery plans, national efforts on fire prevention programs and wildfire management.     

Simulation of polychlorinated biphenyls transport in the vadose zone

Polychlorinated biphenyls (PCBs) are the main constituents of clophen (the liquid of the electric transformers and capacitors) and have been characterized as potential human carcinogens. PCBs can be a hazardous contaminant of soil and groundwater. We used the mathematical model variably saturated 2D flow and transport (VS2DT model) to simulate the transport of PCBs from the soil surface to groundwater for a time period of 30 years. We also used a mathematical model to simulate the colloid-facilitated PCB transport, under saturated flow conditions. The results showed that PCBs dissolved in water cannot be transported to large depths in unsaturated soils, because of their strong sorption onto soil and low solubility in water. For soils with very low or no organic matter content, PCB transport is much faster and the probability of groundwater contamination is much higher. PCBs can partition to colloids originating from dissolved organic matter in groundwater. Colloid-facilitated PCB transport is faster compared to PCB transport in aqueous solution with no colloids present.     

Ground deformation effects from the ~M6 earthquakes (2014–2015) on Cephalonia–Ithaca Islands (Western Greece) deduced by GPS observations

The implications of the earthquakes that took place in the central Ionian Islands in 2014 (Cephalonia, M _w6.1, M _w5.9) and 2015 (Lefkas, M _w6.4) are described based on repeat measurements of the local GPS networks in Cephalonia and Ithaca, and the available continuous GPS stations in the broader area. The Lefkas earthquake occurred on a branch of the Cephalonia Transform Fault, affecting Cephalonia with SE displacements gradually decreasing from north (~100 mm) to south (~10 mm). This earthquake revealed a near N–S dislocation boundary separating Paliki Peninsula in western Cephalonia from the rest of the island, as well as another NW–SE trending fault that separates kinematically the northern and southern parts of Paliki. Strain field calculations during the interseismic period (2014–2015) indicate compression between Ithaca and Cephalonia, while extension appears during the following co-seismic period (2015–2016) including the 2015 Lefkas earthquake. Additional tectonically active zones with differential kinematic characteristics were also identified locally.     

Yield frequency spectra and seismic design of code‐compatible RC structures: an illustrative example

The seismic design of an eight‐story reinforced concrete space frame building is undertaken using a yield frequency spectra (YFS) performance‐based approach. YFS offer a visual representation of the entire range of a system's performance in terms of the mean annual frequency (MAF) of exceeding arbitrary global ductility or displacement levels versus the base shear strength. As such, the YFS framework can establish the required base shear and corresponding first‐mode period to satisfy arbitrary performance objectives for any structure that may be approximated by a single‐degree‐of‐freedom system with given yield displacement and capacity curve shape. For the eight‐story case study building, deformation checking is the governing limit state. A conventional code‐based design was performed using seismic intensities tied to the desired MAF for safety checking. Then, the YFS‐based approach was employed to redesign the resulting structure working backwards from the desired MAF of response (rather than intensity) to estimate an appropriate value of seismic intensity for use within a typical engineering design process. For this high‐seismicity and high‐importance midrise building, a stiffer system with higher base shear strength was thus derived. Moreover, performance assessment via incremental dynamic analysis showed that while the code‐design did not meet the required performance objective, the YFS‐based redesign needed only pushover analysis results to offer a near‐optimal design outcome. The rapid convergence of the method in a single design/analysis iteration emphasized its efficiency and practicability as a design aid for practical application. Copyright © 2017 John Wiley & Sons, Ltd.     

Multi-model multi-analysis ensemble weather forecasting on the grid for the South Eastern Mediterranean Region

Weather forecasting is based on the use of numerical weather prediction (NWP) models that are able to perform the necessary calculations that describe/predict the major atmospheric processes. One common problem in weather forecasting derives from the uncertainty related to the chaotic behaviour of the atmosphere. A solution to that problem is to perform in addition to “deterministic” forecasts, “stochastic” forecasts that provide an estimate of the prediction skill. A computationally feasible approach towards this aim is to perform “ensemble forecasts”. Indeed, in the frame of SEE-GRID-SCI EU funded project a Regional scale Multi-model, Multi-analysis ensemble forecasting system (REFS) was built and ported on the Grid infrastructure. REFS is based on the use of four limited area models (namely BOLAM, MM5, ETA, and NMM) that are run using a multitude of initial and boundary conditions over the Mediterranean. This paper presents the tools and procedures followed for developing this application at a production level.     

Deformation patterns in the southwestern part of the Mediterranean Ridge (South Matapan Trench,Western Greece)

Seismic reflection data and bathymetry analyses, together with geological information, are combined in the present work to identify seabed structural deformation and crustal structure in the Western Mediterranean Ridge (the backstop and the South Matapan Trench). As a first step, we apply bathymetric data and state of art methods of pattern recognition to automatically detect seabed lineaments, which are possibly related to the presence of tectonic structures (faults). The resulting pattern is tied to seismic reflection data, further assisting in the construction of a stratigraphic and structural model for this part of the Mediterranean Ridge. Structural elements and stratigraphic units in the final model are estimated based on: (a) the detected lineaments on the seabed, (b) the distribution of the interval velocities and the presence of velocity inversions, (c) the continuity and the amplitudes of the seismic reflections, the seismic structure of the units and (d) well and stratigraphic data as well as the main tectonic structures from the nearest onshore areas. Seabed morphology in the study area is probably related with the past and recent tectonics movements that result from African and European plates’ convergence. Backthrusts and reverse faults, flower structures and deep normal faults are among the most important extensional/compressional structures interpreted in the study area.