Advance in the penetrometer test formulation to estimate allowable pressure in granular soils

In this paper, we present a modification of the existing mathematical formulation used to obtain the allowable bearing pressure from dynamic penetration tests in order to extend its applicability to the design of shallow foundations. The conventional relationships adopted to obtain the allowable bearing pressure from penetrometer tests have a discontinuous gradient, and they are limited to a depth less than the footing width. The aim of this work was to find a relationship that permits the estimation of this pressure in cohesionless soils, from the results of dynamic probing super heavy tests, through a single non-piecewise and continuous relationship that remains valid up to depths several times the footing width. This equation was applied as part of the geomechanical characterization survey undertaken for the construction of an elevated helipad in the centre of the Iberian Peninsula. The survey results were considered satisfactory, and the construction was completed without structural problems.     

Structural evolution within the Luning–Fencemaker fold-thrust belt, Nevada: progression from back-arc basin closure to intra-arc shortening

The Luning–Fencemaker fold-thrust belt (LFTB) of central Nevada reflects major Mesozoic shortening in the western US Cordillera, and involved contractional deformation in Triassic and lower Jurassic back-arc basinal strata. Structural analyses in the Santa Rosa Range, in the northern LFTB, provide new insight into the evolution of this belt. Four phases of deformation are recognized in the Santa Rosa Range. D₁ involved tight to isoclinal folding, cleavage development under low-grade metamorphic conditions, and reverse faulting. This deformation phase reflects NW–SE shortening of 55–70% in the Early and/or Middle Jurassic. D₂ structures are similar in orientation to D₁ but involved much less overall strain and are well developed only to the southeast. D₂ appears to be related to thrusting along the eastern margin of the LFTB in the Middle and/or Late Jurassic. D₃ deformation reflects very minor shortening (<5%) in a subvertical direction, and is tentatively interpreted to reflect stresses generated during initial intrusion of mid-Cretaceous plutons in the area. D₄ deformation demonstrably occurred synchronously with emplacement of Cretaceous granitoids dated at 102 Ma (U–Pb zircon) based on syntectonic relations between D₄ structures and thermal metamorphism associated with intrusion, and an upgrade in D₄ strain in the thermally softened metamorphic aureoles of the intrusions. This last phase of deformation reflects minor regional NE–SW shortening, coupled with localized strain associated with pluton emplacement.Formation of the LFTB structural province was accomplished during the D₁ and D₂ phases of deformation, and most shortening occurred during the D₁ event. This Jurassic deformation led to structural closure of the back-arc basin by top-to-the-SE tectonic transport and development of a largely ductile fold-thrust belt. Subsequent deformation (D₃ and D₄) is >50 m.y. younger and unrelated to development of the LFTB. The younger deformation reflects a combination of minor regional shortening, interpreted to be related to the Cretaceous Sevier orogeny, plus localized shortening related to emplacement of Cretaceous intrusions.     

Palaeomagnetism,age, and geochemistry of the Denchai Basalt,northern Thailand

The Denchai Basalt of northern Thailand is part of a large continental alkalic basaltic province extending through Thailand into Laos, Kampuchea, and Vietnam. It covers an area of about 70 km² and consists of seven flows, all with reversed magnetic polarity. The uppermost flow has yielded an age of 5.64 ± 0.28 Ma by the K-Ar method. During the igneous activity, magmas were apparently erupted from only one vent area, but changed in chemical composition from “hawaiite” (transitional to continental tholeiite) to true hawaiite and then to basanite. The basanite is the probable source of gem-quality zircon and sapphire mined from placer deposits associated with the basalts.     

Biogeochemistry and bacteriology of ferrous iron oxidation in geothermal habitats

A survey of hot, acid springs in Yellowstone Park has shown that high concentrations of ferrous and ferric iron are often present. Total ionic iron concentrations in different springs ranged from less than 1 ppm to greater than 200 ppm, and up to 50% of the ionic iron was in the ferrous form. Some of these springs also have high concentrations of reduced sulfur species (S^2? and S⁰). Significant populations of the bacterium Sulfolobus, acidocaldarius, an autotrophic organism able to live and oxidize sulfur compounds at low pH and high temperature, were present in most of these springs. The role of this organism in the oxidation of ferrous iron was investigated by incubating natural samples of water and assaying for disappearance of ferrous iron. Controls in which bacterial activity was inhibited by addition of 10% NaCl were also run. Bacterial oxidation of ferrous iron occurred in most but not all of the spring waters. The temperature optimum for oxidation varied from spring to spring, but significant oxidation occurred at temperatures of 80–85°C, but not at 90°C. Thus, 85–90°C is the upper temperature at which bacterial iron oxidation occurs; a similar upper limit has previously been reported for sulfur oxidation in the same kinds of springs. The steady-state concentrations of ferrous and ferric iron are determined by the rate at which these ions move into the spring pools with the ground water (flow rate), by the rate at which ferric iron is reduced to the ferrous state by sulfide, and by the rate of bacterial oxidation. The bacterial oxidation rate is faster than the flow rate, so that the rate of reduction of ferric iron is probably the rate-controlling reaction. In several springs, no decrease in ferrous iron occurred, even though high bacterial populations were present. It was shown that in these springs, ferrous iron oxidation occurred but the ferric iron formed was reduced back to the ferrous state again. These springs were all high in suspended sediment and the reductant was shown to be present in the sediment. X-ray diffraction revealed that the sediment contained three major ingredients, elemental sulfur, natroalunite, and quartz. Chemical analyses showed a small amount of sulfide, too little to reduce the ferric iron. Elemental sulfur itself did not reduce ferric iron but when elemental sulfur was removed from the sediment by CS₂ extraction, the activity of the sediment was abolished. It is hypothesized that the sulfide present in the sediment (possibly bound to natroalunite) reacts with elemental sulfur to form a reductant for ferric iron. The results show that bacteria can have a profound influence on the ferrous/ferric ratios of geothermal systems, but that temperature and mineral composition of the water may significantly influence the overall result.     

Palaeozoic radiometric age provinces in the Andean basement,latitudes 25°–30°S

More than fifty new K-Ar age determinations are reported for mineral separates and whole-rock samples from igneous and metamorphic basement rocks of northwestern Argentina and contiguous Chile between 25° and 30°S. The age data define three thermal events, occurring in the late Ordovician-Silurian (400–450 m.y.), mid-Carboniferous (310–340 m.y.) and Permian (225–270 m.y.), and confirm deductions of previous workers that the crystalline basement rocks of the Pampean Ranges of northwestern Argentina are not of Precambrian age, but rather evolved predominantly during the Palaeozoic. The proposed radiometric age provinces and the inferred orogenic history of the area are compared with those for the rest of South America, and it is confirmed that, by the late Ordovician, the focus of major orogenic activity in South America was located along the present western and southern margins of the craton, and tended to migrate westwards during the Palaeozoic.     

Recent environmental changes in Laguna Mar Chiquita (central Argentina): a sedimentary model for a highly variable saline lake

Abstract Laguna Mar Chiquita, a highly variable closed saline lake located in the Pampean plains of central Argentina, is presently the largest saline lake in South America (≈ 6000 km²). Recent variations in its hydrological budget have produced dry and wet intervals that resulted in distinctive lake level fluctuations. Results of a multiproxy study of a set of sedimentary cores indicate that the system has clearly recorded these hydrological variations from the end of the Little Ice Age (≈ ad 1770) to the present. Sedimentological and geochemical data combined with a robust chronology based on ²¹⁰Pb profiles and historical data provide the framework for a sedimentary model of a lacustrine basin with highly variable water depth and salinity. Lake level drops and concurrent increases in salinity promoted the development of gypsum–calcite–halite layers and a marked decrease in primary productivity. The deposits of these dry stages are evaporite‐bearing sediments with a low organic matter content. Conversely, highstands are recorded as diatomaceous organic matter‐rich muds. Average bulk sediment accumulation rose from 0·22 g cm^?2 year^?1 in lowstands to 0·32 g cm^?2 year^?1 during highstands. These results show that Laguna Mar Chiquita is a good sensor of high‐ and low‐frequency changes in the recent hydrological budget and, therefore, document climatic changes at middle latitudes in south‐eastern South America. Dry conditions were mostly dominant until the last quarter of the twentieth century, when a humid interval without precedent during the last 240 years of the lake's recorded history started. Thus, it is an ideal system to model sedimentary and geochemical response to environmental changes in a saline lacustrine basin.     

Assessment of the stability of H/V spectral ratios from ambient noise and comparison with earthquake data in the Cologne area (Germany)

Situated in an active tectonic region the highly industrialised Cologne area (Germany) suffers from moderate-sized earthquakes. Our contribution to the mitigation of earthquake risk includes a microzonation study using ambient seismic noise and earthquake recordings from two field campaigns. An analysis of these data using the horizontal-to-vertical (H/V) as well as the classical spectral ratio (CSR) technique led to the following observations and conclusions: (1) The spatial variation in the thickness of the sedimentary cover is reliably retrieved using the fundamental resonance frequency estimated from the peak in the (H/V) ratio of ambient noise. (2) This fundamental resonance frequency is stable in time, but the amplitude of the peak (the amplification factor) is not. (3) The relative amplification variation of the H/V ratio in the area should therefore be checked systematically with repeated measurements before drawing conclusions about its significance. (4) The analysis of the H/V ratio of ambient noise provides the lower frequency bound, above which amplification may occur. (5) The shapes of the spectral ratios obtained by the different methods are generally in good agreement. However, the analysis of earthquake data shows that significant amplification of ground motion may also occur at frequencies higher than the fundamental one even when thick sediments are present.     

Mercury exposure through fish consumption in the urban area of Alta Floresta in the Amazon Basin

This work addresses the mercury exposure scenarios through fish consumption in the urban area of Alta Floresta, by comparing the different patterns of mercury exposure from fish ingestion for different population groups. This study was based on field surveys that could provide background information, such as the characteristics of Hg sources, characteristics of local and regional environment, Hg concentrations in different media, and the characterization of the local urban population. The urban area of Alta Floresta is one of the most important gold-trading centers in Amazonia, where approximately 1 ton of gold has been commercialized monthly. The general adult urban population is exposed to low-level mercury concentration via fish consumption with an average daily intake of 0.2 μg/kg (b.w.) and an estimated hazard quotient of 0.7. However, the fishermen families present an average daily intake of 2.2 μg/kg (b.w.) and a hazard quotient of 8.6. The children of fishermen families between 5 and 14 years old are the main risk group for Hg exposure via fish ingestion. Based on the uncertainty analysis, the Hg fish concentrations and the fish ingestion rate were found to be the main parameters affecting the variability of the model outputs.     

Life cycle and population structure of the polychaeteFicopomatus enigmaticus (Serpulidae) in Mar Chiquita coastal lagoon,Argentina

Ficopomatus enigmaticus, a polychaete inhabiting the subtidal zone in the Mar Chiquita coastal lagoon, builds reef-like aggregates that facilitate silt accumulation. To describe the life cycle, samples were take monthly from September 1984 to September 1985. In contrast with other polychaetes, it has two oocyte generations per year; maturation of the oocytes takes approximately 4 mo. Temperature level and day length regime do not appear as environmental signals to the onset of oogenesis, although they possibly affect oogenesis growth. Two periods of spawning and recruitment were observed in November–December and April–May, when water temperature is above 18°C. Hermaphroditic individuals were not found. Sex ratio was male-biased in all months, significantly in November, February, and August (p<0.001). Monthly size-frequency distributions show distinct year-classes with early (November–December) and late (April–May) recruitment. Early recruited cohorts have two spawning periods during a 24-mo lifespan. Late cohorts have one spawning period during their 20-mo lifespan. The life cycle of this species can be summarized as follows: annual iteroparous—1 to 2 batches of small eggs per female during each lifespan, free spawning, planktotrophic larvae, sedentary suspension-feeder worms.