Exploration and decision-making in geotechnical engineering – a case study

ABSTRACT

The paper presents methodologies for exploration planning under uncertain conditions based on virtual exploration and Bayesian updating. The process starts with site characterization using existing information to produce geologic profiles. Initial distributions of cost and time are obtained with a Bayesian network model that optimizes the construction strategy for particular geologic conditions. This is followed by the unique step to determine with a “virtual exploration” if additional exploration (e.g. borings) is warranted, and if so, where it should be best done. All this is then applied to the planned Abu Dhabi subway tunnels providing the transportation planners with necessary information for planning and design.     

Antibiotic Resistance and Plasmid Profiles of Vibrio Isolates from Cultured Silver Sea Bream, Sparus sarba

A total of 51 potential pathogenic vibrios were isolated from moribund silver sea bream (Sparus sarba) collected from fish farms in Hong Kong. Using the API 20E system and the scheme of Alsina and Blanch (1994), 7 species were identified from all isolates. These species were Vibrio alginolyticus (24 strains), Vibrio vulnificus (12 strains), Vibrio parahaemolyticus (7 strains), Vibrio logei (4 strains), Vibrio pelagius II (2 strains), Vibrio fluvialis (1 strain) and Vibrio meditterranei (1 strain). The three dominant species (V. alginolyticus, V. vulnificus and V. parahaemolyticus) were confirmed to be virulent to sea bream by experimental challenge.

All isolates were screened for plasmid DNA by agarose gel electrophoresis and tested for susceptibility to 16 antibiotics by the agar dilution method. Of the 51 isolates examined, all strains were sensitive to ceftriaxone, streptomycin, nalidixic acid and rifampicin, and almost all were sensitive to ceftazidime, netilimicin, chloramphenicol and sulfamethoxazole. Most isolates were resistant to ampicillin (60.8%), cefuroxime (66.7%), amikacin (55%), kanamycin (58.8%) and trimethoprim (76.5%). Fifteen of the 51 isolates harboured 1–4 plasmids, with sizes ranging from 9 to 123 kb. Both the plasmids and the associated antibiotic resistance (ampicillin, cefuroxime and trimethoprim) of 9 isolates could be transferred to a recipient by single-step conjugation. However, the frequencies were very low, ranging from 10⁻¹¹ to 10⁻⁹. The present results indicate that resistance to these antibiotics is chromosomal.     

Occurrence of Somma-Vesuvio fine ashes in the tephrostratigraphic record of Panarea,Aeolian Islands

Ash-rich tephra layers interbedded in the pyroclastic successions of Panarea island (Aeolian archipelago, Southern Italy) have been analyzed and related to their original volcanic sources. One of these tephra layers is particularly important as it can be correlated by its chemical and morphoscopic characteristics to the explosive activity of Somma-Vesuvio. Correlation with the Pomici di Base eruption, that is considered one of the largest explosive events causing the demolition of the Somma stratovolcano, seems the most probable. The occurrence on Panarea island of fine ashes related to this eruption is of great importance for several reasons: 1) it allows to better constrain the time stratigraphy of the Panarea volcano; 2) it provides a useful tool for tephrochronological studies in southern Italy and finally 3) it allows to improve our knowledge on the distribution of the products of the Pomici di Base eruption giving new insights on the dispersion trajectories of fine ashes from plinian plumes. Other exotic tephra layers interbedded in the Panarea pyroclastic successions have also been found. Chemical and sedimentological characteristics of these layers allow their correlation with local vents from the Aeolian Islands thus constraining the late explosive activity of Panarea dome.     

Changing eruptive styles in basaltic explosive volcanism: Examples from Croscat complex scoria cone, Garrotxa Volcanic Field (NE Iberian Peninsula)

The Croscat pyroclastic succession has been analysed to investigate the transition between different eruptive styles in basaltic monogenetic volcanoes, with particular emphasis on the role of phreatomagmatism in triggering Violent Strombolian eruptions. Croscat volcano, an 11 ka basaltic complex scoria cone in the Quaternary Garrotxa Volcanic Field (GVF) shows pyroclastic deposits related both to magmatic and phreatomagmatic explosions.Lithofacies analysis, grain size distribution, chemical composition, glass shard morphologies, vesicularity, bubble-number density and crystallinity of the Croscat pyroclastic succession have been used to characterize the different eruptive styles. Eruptions at Croscat began with fissural Hawaiian-type fountaining that rapidly changed to eruption types transitional between Hawaiian and Strombolian from a central vent. A first phreatomagmatic phase occurred by the interaction between magma and water from a shallow aquifer system at the waning of the Hawaiian- and Strombolian-types stage. A Violent Strombolian explosion then occurred, producing a widespread (8 km²), voluminous tephra blanket. The related deposits are characterized by the presence of wood-shaped, highly vesicular scoriae. Glass-bearing xenoliths (buchites) are also present within the deposit. At the waning of the Violent Strombolian phase a second phreatomagmatic phase occurred, producing a second voluminous deposit dispersed over 8.4 km². The eruption ended with a lava flow emission and consequent breaching of the western-side of the volcano. Our data suggest that the Croscat Violent Strombolian phase was related to the ascent of deeper, crystal-poor, highly vesicular magma under fast decompression rate. Particles and vesicles elongation and brittle failure observed in the wood-shaped clasts indicate that fragmentation during Violent Strombolian phase was enhanced by high strain-rate of the magma within the conduit.     

Environmental features of deep-sea habitats linked to the genetic population structure of a crustacean species in the Mediterranean Sea

The deep-sea habitat, from 200 to 2000 m depth, has long been thought as an ecosystem where biotic and abiotic factors vary very little and consequently species are not disturbed by processes and phenomena which could promote fast evolutionary mechanisms. Unfortunately, biological information relating to deep water is limited, especially regarding the population genetics of species inhabiting the Mediterranean Sea, and general patterns cannot be inferred. In this study we report data on the population genetic structure of Aristeus antennatus , a deep-sea decapod crustacean species which has been widely studied due to its important economic value. We surveyed and examined the variation in a 369-bp fragment of the mtDNA control region from individuals caught by Spanish and Italian trawlers in eight localities. High levels of mitochondrial control region haplotypic diversity (ranging from 0.884 to 0.989) were observed. AMOVA showed a high level of genetic variation, more within than between populations, and a low but significant Φ_ST value was recovered. Minimum spanning network did not separate any haplotype group and haplotype distribution does not mirror the geographic origin of the samples. The absence of population substructuring was also observed with a principal coordinates analysis, which uses an individual-by-individual comparison. These results revealed extensive gene flow among populations. Information on demographic history based on mismatch analysis revealed an unstable population, showing an alternate pattern of growth and decline. Our results indicated that in the western and central Mediterranean basins A. antennatus is a large panmictic population with a fluctuating abundance. The absence of deep-sea barriers and adult migration may prevent the structuring of the species into genetically differentiated populations.     

Evidence of estuarine nursery origin of five coastal fish species along the Portuguese coast through otolith elemental fingerprints

Connectivity is a critical property of marine populations, particularly for species with segregated juvenile and adult habitats. Knowledge of this link is fundamental in understanding population structure and dynamics. Young adults of commercially important fish species Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax were sampled off the Portuguese coast in order to establish preliminary evidence of estuarine nursery origins through otolith elemental fingerprints. Concentrations of Li, Na, Mg, K, Mn, Cu, Zn, Sr, Ba and Pb in the otolith section corresponding to juvenile's nursery life period were determined through laser ablation inductively coupled plasma mass spectrometry. Element: Ca ratios in coastal fish differed significantly amongst collection areas, except for Platichthys flesus, and were compared with the elemental fingerprints previously defined for age 0 juveniles in the main estuarine nurseries of the Portuguese coast. Identification of nursery estuaries was achieved for four of the species. Assigned nursery origins varied amongst species and differences in the spatial scale of fish dispersal were also found. Diplodus vulgaris was not reliably assigned to any of the defined nurseries. Overall, results give evidence of the applicability of estuarine habitat tags in future assessments of estuarine nursery role. Research developments on the links between juvenile and adult habitats should contribute for the integrated management and conservation of nurseries and coastal stocks.     

SⅡ型水合物生成与分解动力学研究

笼型水合物是一种晶体构造物质。笼型晶格由氢键作用连接的水分子组成,通过捕获客体气体分子形成稳定的晶体结构。笼型水合物晶体可在相对较低的压力和较高的温度条件下存储含氢气体并稳定存在,这一特性让使用固体载体安全储藏并运输含氢气体成为可能。Florusse等发现通过添加第2种客体分子四氢呋喃（THF）可使含氢水合物在室温下以5Mpa的压力稳定存在,并且通过自然分解即可提取气体,不发生其他化学反应,环保节能。