The influence of petrography,mineralogy and chemistry on burnability and reactivity of quicklime produced in Twin Shaft Regenerative (TSR) kilns from Neoarchean limestone (Transvaal Supergroup,South Africa)

Mineralogy and Petrology - This study evaluates the influence of chemical, mineralogical and petrographic features of the Neoarchean limestone from the Ouplaas Mine (Griqualand West, South Africa)...     

LIDAR strip adjustment: Application to volcanic areas

DEMs derived from LIDAR data are nowadays largely used for quantitative analyses and modelling in geology and geomorphology. High-quality DEMs are required for the accurate morphometric and volumetric measurement of land features. We propose a rigorous automatic algorithm for correcting systematic errors in LIDAR data in order to assess sub-metric variations in surface morphology over wide areas, such as those associated with landslide, slump, and volcanic deposits. Our procedure does not require a priori knowledge of the surface, such as the presence of known ground control points. Systematic errors are detected on the basis of distortions in the areas of overlap among different strips. Discrepancies between overlapping strips are assessed at a number of chosen computational tie points. At each tie point a local surface is constructed for each strip containing the point. Displacements between different strips are then calculated at each tie point, and minimization of these discrepancies allows the identification of major systematic errors. These errors are identified as a function of the variables that describe the data acquisition system. Significant errors mainly caused by a non-constant misestimation of the roll angle are highlighted and corrected. Comparison of DEMs constructed using first uncorrected and then corrected LIDAR data from different Mt. Etna surveys shows a meaningful improvement in quality: most of the systematic errors are removed and the accuracy of morphometric and volumetric measurements of volcanic features increases. These corrections are particularly important for the following studies of Mt. Etna: calculation of lava flow volume; calculation of erosion and deposition volume of pyroclastic cones; mapping of areas newly covered by volcanic ash; and morphological evolution of a portion of an active lava field over a short time span.     

Quasi‐static and pseudo‐dynamic testing of unbonded post‐tensioned rocking bridge piers with external replaceable dissipaters

It has been well documented that following a major earthquake a substantial percentage of economic loss results from downtime of essential lifelines in and out of major urban centres. This has thus led to an improvement of both performance‐based seismic design philosophies and to the development of cost‐effective seismic structural systems capable of guaranteeing a high level of protection, low structural damage and reduced downtime after a design‐level seismic event. An example of such technology is the development of unbonded post‐tensioned techniques in combination with rocking–dissipating connections. In this contribution, further advances in the development of high‐performance seismic‐resistant bridge piers are achieved through the experimental validation of unbonded post‐tensioned bridge piers with external, fully replaceable, mild steel hysteretic dissipaters. The experimental response of three 1 : 3 scale unbonded, post‐tensioned cantilever bridge piers, subjected to quasi‐static and pseudo‐dynamic loading protocols, are presented and compared with an equivalently reinforced monolithic benchmark. Minimal physical damage is observed for the post‐tensioned systems, which exhibit very stable energy dissipation and re‐centring properties. Furthermore, the external dissipaters can be easily replaced if severely damaged under a major (higher than expected) earthquake event. Thus, negligible residual deformations, limited repair costs and downtime can be achieved for critical lifeline components. Satisfactory analytical–experimental comparisons are also presented as a further confirmation of the reliability of the design procedure and of the modelling techniques. Copyright © 2008 John Wiley & Sons, Ltd.     

Shakemaps uncertainties and their effects in the post-seismic actions for the 2012 Emilia (Italy) earthquakes

The May 20, 2012, Emilia Ml 5.9 earthquake was followed by some major aftershocks, well recorded by a large number of temporary stations that were installed to monitor the sequence. These additional recordings allowed us a thorough testing of the performance of the ShakeMap—a procedure designed to provide rapid information on the experienced ground motion. We found that the shakemaps for the May 29, 2012, Ml 5.8 earthquake, obtained using the permanent stations only, underestimate significantly the ground motion computed with the highest station density, especially for PSA at long periods (T \(=\) 3.0 s). This low-frequency motion is controlled primarily by the surface waves recorded in the Po plain: the observed site effects are likely not accounted properly by the site correction coefficient based on Vs30 as implemented in the ShakeMap procedure. The shakemaps determined during the seismic sequence have been included in an Italian national law that was passed after the 2012 earthquake. According to this law, the factories safety verifications were bound to the comparison between the shakemaps and the design acceleration required by the current national seismic code. We then decide to appraise the impact of the shakemap accuracy on the law provisions. Following the law recommendations, we have estimated the possible errors resulting from the incomplete evaluation of the ground shaking: our results show that, if the complete dataset were available at the time of the law approval, the number of buildings for which the safety check was required would have been significantly smaller.     

Empirical observations and numerical modelling of tides,channel morphology,and vegetative effects on accretion in a restored tidal marsh

Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine-grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high-resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco-geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood-ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In-situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea-level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience. © 2019 John Wiley & Sons, Ltd.     

Dynamic response analysis of nonlinear secondary oscillators to idealised seismic pulses

The paper deals with the seismic response analysis of nonlinear secondary oscillators. Bilinear, sliding and rocking single-degree-of-freedom dynamic systems are analysed as representative of a wide spectrum of secondary structures and nonstructural components. In the first stage, the equations governing their full dynamic interaction with linear multi-degree-of-freedom primary structures are formulated, and then conveniently simplified using primary-secondary two-degree-of-freedom systems and dimensionless coefficients. In the second stage, the cascade approximation is applied, whereby the feedback action of the secondary oscillator on the primary structure is neglected. Owing to the piecewise linearity of the secondary systems being considered, efficient semi-analytical and step-by-step numerical solutions are presented. The semi-analytical solutions allow the direct evaluation of the seismic response under pulse-type ground excitations and are also used to validate step-by-step numerical schemes, which in turn can be used for general-type seismic excitations. In the third stage, a set of decoupling criteria are proposed for the pulse-type base excitations, identifying the conditions under which a cascade analysis is admissible from an engineering standpoint. Finally, the influence and relative dependencies between the input parameters of the ground motion and the primary-secondary assembly are quantified on the response of the secondary systems through nonlinear floor response spectra, and general trends are identified and discussed.     

Recent contamination of mercury in an estuarine environment (Marano lagoon,Northern Adriatic,Italy)

The Marano Lagoon, in the northern Adriatic Sea (Italy), has been affected by mercury (Hg) contamination from industrial and mining activities. It has been estimated that 186,000 kg of Hg were deliberately discharged into the main drainage system (Aussa–Corno River) by a chlor-alkali plant (CAP) from 1940s to 1984. The lagoon has also experienced a secondary long-term Hg input, originated from mining activity in Idrija (Slovenia), due to the supply of fluvial suspended particles carried by the Isonzo River in the Gulf of Trieste. Since local fishing activities are extensively conducted, there is great concern on the risk posed by potentially harmful effects of Hg to the trophic chain.