^40Ar／^39Ar Fast Neutron Activation Ages of Quartz from the Jinman Vein Copper Dposit in Western Yunnan and Their Significance

Quartz samples collected from the Jinman vein copper deposit in the Lanping Basin of western Yunnan were determined by⁴⁰Ar/³⁹Ar fast neutron activation techniques, and the spectra are characterized as being saddle-shaped. The samples yielded a plateau age of 58.05 ± 0.54 Ma, a minimum appearance age of 56.76 ±0.81 Ma and an isochron age of 54.30 ± 0.15 Ma, the three ages being close to each other, indicating that the ages of the quartz samples so far determined are true and reliable. The plateau age represents the time of formation of Cu-bearing quartz veins, which is corresponding to Early Himalayan. This age is also consistent with the time at which a tectonically thermal event (60 Ma) took place within the Lanping Basin, Yunnan Province. In consideration of the fact that copper ore and other ore types in the vast area of western Yunnan are concentrated mainly in the Early Himalayan strata, the authors believe that there must have existed some indispensable key factors leading to metallogenesis on a large scale during the Early Himalayan period in western Yunnan and also constraining in union the formation of ore deposits there.     

A scanning electron microscope study of the effects of dynamic recrystallization on lattice preferred orientation in olivine

Effects of dynamic recrystallization on lattice preferred orientation (LPO) in olivine were investigated through the combination of two SEM-based techniques, electron backscattered diffraction (EBSD) technique for crystallographic orientation measurement and backscattered electron imaging (BEI) for dislocation observation. Samples are experimentally deformed olivine aggregates in simple shear geometry. In the sample deformed at T=1473 K and high stresses (480 MPa), only incipient dynamic recrystallization is observed along grain-boundaries. Orientations of these small recrystallized grains are more random than that of relict grains, suggesting an important role of grain-boundary sliding at this stage of recrystallization. In the sample deformed at T=1573 K and low stress (160 MPa), dynamic recrystallization is nearly complete and the LPO is characterized by two [100] peaks. One peak is located at the orientation subparallel to the shear direction and is dominated by grains with high Schmid factor. The other occurs at high angles to the shear direction and is due to the contribution from grains with low Schmid factor. Grains with high Schmid factor tend to have higher dislocation densities than those with low Schmid factor. Based on these observations, we identify two mechanisms by which dynamic recrystallization affects LPO: (1) enhancement of grain-boundary sliding due to grain-size reduction, leading to the modification of LPO caused by the relaxation of constraint for deformation; (2) grain-boundary migration by which grains with lower dislocation densities grow at the expense of grains with higher dislocation densities. Based on the deformation mechanism maps and stress versus recrystallized grain-size relation, we suggest that the first mechanism always plays an important role whereas the second mechanism has an important effect only under limited conditions.     

A three-dimensional parametric study of the use of soil nails for stabilising tunnel faces

Applying an effective nailing system at a tunnel heading, not only improves the stability of the tunnel heading and limits deformation at the tunnel face, but it also reduces volume loss during excavation and hence reduces ground surface settlement. The effectiveness of a soil nail system is affected by many factors such as the diameter and stiffness of the nails. In this paper, a systematic parametric study was conducted to study the axial rigidity of a nail, E_nA_n, for improving the stability of tunnel headings and reducing ground movements in stiff clay. The parametric study involved a series of three-dimensional elasto-plastic coupled-consolidation finite element analyses. The stability of the tunnel face is improved with increasing E_nA_n. For a given nail density applied at the tunnel face, an optimum axial rigidity of the nail (E_nA_n)_opt can be identified. The efficiency of the nailing system diminishes when (E_nA_n)_opt is reached. The use of a soil nailing system reduces the magnitude of stress relief at the tunnel heading during excavation. Thus, this reduction of stress relief minimises the amount of soil yielding and excess pore water pressure generated in the soil around the tunnel heading.     

Hydraulic Characteristics of Rough Fractures in Linear Flow under Normal and Shear Load

Summary A hydro-mechanical testing system, which is capable of measuring both the flow rates and the normal and shear displacement of a rock fracture, was built to investigate the hydraulic behaviour of rough tension fractures. Laboratory hydraulic tests in linear flow were conducted on rough rock fractures, artificially created using a splitter under various normal and shear loading. Prior to the tests, aperture distributions were determined by measuring the topography of upper and lower fracture surfaces using a laser profilometer. Experimental variograms of the initial aperture distributions were classified into four groups of geostatistical model, though the overall experimental variograms could be well fitted to the exponential model. The permeability of the rough rock fractures decayed exponentially with respect to the normal stress increase up to 5 MPa. Hydraulic behaviours during monotonic shear loading were significantly affected by the dilation occurring until the shear stress reached the peak strength. With the further dilation, the permeability of the rough fracture specimens increased more. However, beyond shear displacement of about 7 to 8 mm, permeability gradually reached a maximum threshold value. The combined effects of both asperity degradation and gouge production, which prohibited the subsequent enlargement of mean fracture aperture, mainly caused this phenomenon. Permeability changes during cyclic shear loading showed somewhat irregular variations, especially after the first shear loading cycle, due to the complex interaction from asperity degradations and production of gouge materials. The relation between hydraulic and mechanical apertures was analyzed to investigate the valid range of mechanical apertures to be applied to the cubic law. Received June 12, 2001; accepted February 26, 2002 Published online September 2, 2002     

Landslide risk assessment and management: an overview

Landslides can result in enormous casualties and huge economic losses in mountainous regions. In order to mitigate landslide hazard effectively, new methodologies are required to develop a better understanding of landslide hazard and to make rational decisions on the allocation of funds for management of landslide risk. Recent advances in risk analysis and risk assessment are beginning to provide systematic and rigorous processes to enhance slope management. In recent years, risk analysis and assessment has become an important tool in addressing uncertainty inherent in landslide hazards.This article reviews recent advances in landslide risk assessment and management, and discusses the applicability of a variety of approaches to assessing landslide risk. Firstly, a framework for landslide risk assessment and management by which landslide risk can be reduced is proposed. This is followed by a critical review of the current state of research on assessing the probability of landsliding, runout behavior, and vulnerability. Effective management strategies for reducing economic and social losses due to landslides are described. Problems in landslide risk assessment and management are also examined.     

Structural relaxation in the MnCO3–CaCO3 solid solution: a Mn K-edge EXAFS study

Mn K-edge EXAFS spectroscopy of solid-solution samples encompassing the complete MnCO₃–CaCO₃ series shows that first-shell Mn–O distances deviate little from the 2.19-Å distance observed in pure MnCO₃. Very slight lengthening is observed only in the limiting case of dilute Mn(II) calcite solid solutions, where the Mn–O distance is 2.21 Å. The observed nearly complete structural relaxation and the composition independence of the Mn–O distance are consistent with the Pauling model behavior of solid solutions, and agree with previous studies showing a high degree of relaxation around hetero-sized substituents in the calcite structure. Strain occurs through bond bending, which is facilitated by the exclusively corner-sharing topology of calcite. Observed distances from Mn to more distant neighbors show significant variation across the solid-solution series that resembles Vegard's law-type behavior but reflects averaging. The high degree of relaxation suggests modest enthalpies of mixing in the solution, consistent with calorimetric studies.     

Principal axes of m-DOF structures PartⅠ:Static loading

This paper is the first in a two-part series that discusses the principal axes of M-DOF structures subjected to static and dynamic loads. The primary purpose of this series is to understand the magnitude of the dynamic response of structures to enable better design of structures and control modification devices/systems. Under idealized design conditions, the structural responses are obtained by using single direction input ground motions in the direction of the intended control devices/systems,and by assuming that the responses of the structure is decoupleable in three mutually perpendicular directions. This standard practice has been applied to both new and retrofitted structures using various seismic protective systems. Very limited information is available on the effects of neglecting the impact of directional couplings (cross effects - of which torsion is a component) of the dynamic response of structures. In order to quantify such effects, it is necessary to examine the principal axes of structures under both static and dynamic loading.This first paper deals with quantitative definitions of principal axes and "cross effects" of three-dimensional structures under static load by using linear algebra. It shows theoretically that, for three-dimensional structures, such principal axes rarely exist. Under static loading conditions, the cross effect is typically small and negligible from the viewpoint of engineering applications. However, it provides the theoretical base for subsequent quantification of the response couplings under dynamic loads, which is reported in part Ⅱ of this series.     

Experimental validation of the wavefield transform of electromagnetic fields

The wavefield transform is a mathematical technique for transforming low-frequency electromagnetic (EM) signals to a non-diffusive wave domain. The ray approximation is valid in the transform space and this makes traveltime tomography for 3D mapping of the electrical conductivity distribution in the subsurface possible. The transform, however, imposes stringent frequency bandwidth and signal-to-noise ratio requirements on the data. Here we discuss a laboratory scale experiment designed to collect transform quality EM data, and to demonstrate the practical feasibility of transforming these data to the wavefield domain.
We have used the scalable nature of EM fields to design a time-domain experiment using graphite blocks to simulate realistic field conditions while leaving the time scale undisturbed. The spatial dimensions have been scaled down by a factor of a thousand by scaling conductivity up by a factor of a million. The graphite blocks have two holes drilled into them to carry out cross-well and borehole-to-surface experiments. Steel sheets have been inserted between the blocks to simulate a conductive layer.
Our experiments show that accurate EM data can be recorded on a laboratory scale model even when the scaling of some features, such as drill-hole diameters, is not maintained. More importantly, the time-domain EM data recorded in cross-well and surface-to-borehole modes can be usefully and accurately transformed to the wavefield domain. The observed wavefield propagation delay is proportional to the direct distance between the transmitter and receiver in a homogeneous medium. In a layered medium, data accuracy is reduced and, hence, our results are not so conclusive. On the basis of the experimental results we conclude that the wavefield transform could constitute a valid approach to the interpretation of accurate, undistorted time-domain data if further improvement in the transform can be realized.     

Use of Chemotaxonomy To Study the Influence of Benzalkonium Chloride on Bacterial Populations in Biodegradation Testing

Contradictory results are reported for the behaviour of quaternary ammonium compounds (QACs) in sewage treatment plants (STPs). QACs may sorb onto activated sludge. Only little information is available with respect to effects of QACs against bacteria in STPs. Only 5 to 15 % of bacteria present in sewage sludge can be detected by means of culture dependent microbiological methods. The shift of the bacterial populations due to effects of test compounds have not been studied up to now with culture independent methods. The microbial populations shift was studied in situ using culture independent chemotaxonomy profiling ubiquinones and polyamines. Additionally, toxic effects of QACs against bacteria present in the test vessels of the Zahn‐Wellens test (OECD 302 B) were assessed with a toxicity control in the test. The ubiquinone profiles representing changes in Gram‐negative populations mainly showed that the activated sludge was affected only in test vessels containing benzalkonium chloride. According to chemotaxonomy Acinetobacter or/and some members of Pseudomonas spp. have been selected by benzalkonium chloride after some adaptation period (8 to 12 days).     

Sediment yield and storage variations in the Négron River catchment (south western Parisian Basin,France) during the Holocene period

In the Négron River catchment area (162 km²), surface‐sediment stores are composed of periglacial calcareous ‘grèze’ (5 × 10⁶ t) and loess (21 × 10⁶ t), and Holocene alluvium (12·6 × 10⁶ t), peat (0·6 × 10⁶ t) and colluvium (18·5 × 10⁶ t). Seventy‐five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0·6 t km^?2 a^?1) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7·0 t km^?2 a^?1 from alluvium stores and 7·6 t km^?2 a^?1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18·7 t km^?2 a^?1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub‐basin to another (3·9 to 24·5 t km^?2 a^?1) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps (‘rideaux’). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one‐third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment. Copyright © 2002 John Wiley & Sons, Ltd.