The second International Symposium on the Arctic Research (ISAR-2): Brief overview

The Arctic and the surrounding region of the sub-Arctic represent a key area for the study of global change because the anthropogenic impact, particularly the rate of warming, is projected to be the greatest in any part of the world due to the complicated feedback processes which occur. This Arctic region has undergone very large changes in recent years due to global warming, and accelerated change is predicted. The rapid changes that are occurring in the Arctic, and that have been the topic of the ISAR-1 and ISAR-2 conferences, manifest themselves at a number of scales. The large scales are Arctic-wide changes in key environmental parameters, which are described in a series of papers in this issue. On a more subtle scale we see changes to species and to biological processes in the Arctic. We hope that readers will enjoy the range of papers published in this issue, and will appreciate that phenomena ranging in scale from global radiation balance to clutch size of birds' eggs are actually all related via the central fact of the present-day Arctic, its high rate of warming.     

Study on the physical disintegration characteristics of Subang claystone subjected to a modified slaking index test

Some instability problems were found on natural or engineered slopes mostly lying on Subang claystones. The instability problems included excessive erosion, slumps and rock falls. The field performance surveys of the problems suggested that the claystones physically weather rapidly so that the rock properties they exhibit during excavation often change to properties with a more characteristic of soil. Such a phenomenon is generally known as a slaking process. In order to gain better understanding about the slaking of Subang claystones, a series of experimental laboratory studies were carried out involving a modified slaking index test. Claystone samples used in this study were obtained from their exposures along the Northern West Java area of Indonesia. Petrographic analysis was correspondingly performed to identify mineral and texture/fabric, and in turn, to determine the inherent factors of the rocks which might affect the slaking process. The stssudy results indicated that the claystones were characterized by high to very high slaking properties having a maximum slaking index (I_s) of 57.4% and a mean I_s of 43.8%. Major dispersion slaking on sample surfaces and high cracking in response to excessive swelling were recognized as main slaking modes within the claystones. All samples lose progressively less material through the five wet–dry cycles of a slaking index test, indicating a decelerated slaking rate. It was evident that the main inherent factors controlling the slaking process were expandable clay mineral smectite, non-clay mineral pyrite and soluble mineral calcite. Moreover, a quite important of inherent bonding material and stress release energy in the slaking characteristics of the claystones was revealed by a closure phase of an initial hairline crack during unloading.     

Small diameter tunnel excavation method using slurry pipe-jacking

In order to protect the safety of workers construction, as well as for environmental and cost reasons, efficient small-diameter shallow tunneling methods have recently become increasingly important in regards to outside plant engineering such as for water supplies, electricity, telecommunications and gas. The effects of the above projects in overcrowded urban areas are significant and often result in substantial impact and traffic delays associated with a loss of travel time. Clearly the solution to these utility placement problems, if the full impact of trench excavation is to be avoided, is trench less technology. In particular, for construction work near existing facilities, underground tunnels that are excavated by slurry pipe-jacking are being increasingly employed in order to avoid problems. Slurry pipe-jacking was firmly established as a special method for the non-disruptive construction of the underground pipelines of sewage systems. Pipe-jacking, in its traditional form, has occasionally been used for short railways, roads, rivers, and other projects. Basically the system involves the pushing or thrusting of a drivage machine through concrete pipes ahead of jacks. This method utilizes mud slurry that is formed around the pipes in order to stabilize the surrounding soil. Moreover, in recent years, the rectangular shape of the concrete pipe in using slurry pipe-jacking was introduced due to the effective uses of the space. Based on his reason, the rectangular shape of the concrete pipe is often adopted in Japan. From this point of view, this paper discusses the effect shapes have on the stability of surrounding soil by means of the numerical analysis. Secondly, this paper discusses the performance of the mud slurry around the drivage pipes by means of the two-dimensional Eulerian-Lagragian seepage analysis. Moreover, in slurry pipe-jacking, the performance of the mud slurry plays an important role in the pushing process. Finally, the thrusts in slurry pipe-jacking can be predicted accurately by evaluating the resistance between the mud slurry and the concrete pipes and the resistance between the soil and the pipes in the curved jacking area. This revised version was published online in July 2006 with corrections to the Cover Date.     

An X-ray diffraction study of shock-wave-densified SiO<Subscript>2</Subscript> glasses

 The densification and structural changes in SiO₂ glass compressed up to 43.4 GPa by shock experiments are investigated quantitatively by the X-ray diffraction technique. Direct structural data (average Si–O and Si–Si distances and Si–O–Si angles, coordination number of the Si atom) of these shock-densified SiO₂ glasses have been obtained by analyzing the radial distribution function curves, RDF(r), calculated with X-ray diffraction data. The coordination number of all densified glasses is about 4 and shows almost no pressure variation. The SiO₂ glass has shown density increase of 11% at a shock compression of 26.3 GPa. This density evolution could not be explained by the coordination change. The reduction of the average Si–O–Si angle (144° at 0 GPa to 136° at 26.3 GPa) obtained from RDF(r) data may account for this density increase. This Si–O–Si angle change may be caused by shrinkage of the network structure and the increase of small rings of SiO₄ tetrahedra. For higher shock pressure, a decrease in the Si–O–Si angle to 140° was observed. This is consistent with the decrease in density at 32.0 and 43.2 GPa. This decrease in the Si–O–Si angle and density could be attributed to an annealing effect due to high after-shock residual temperature. This pressure dependence of average Si–O–Si angles in shock-densified SiO₂ glass agrees with the results of our previous Raman spectroscopic study. On the other hand, the pressure variation for the first sharp diffraction peak (FSDP) was analyzed to estimate the evolution of intermediate range structures. It is suggested that the mean d value (d _m ) obtained from the position of FSDP strongly depends on the shock and residual temperature, as well as shock pressure. Received: 29 June 2001 / Accepted: 14 November 2001     

Fluid inclusion studies of the polymetallic hydrothermal ore deposits in bolivia

Homogenization temperature and salinity were determined for fluid inclusions in mostly quartz and partly sphalerite, cassiterite, and barite from the 28 tin-polymetallic ore deposits in Bolivia. Generally, the homogenization temperatures and salinities of these fluid inclusions are comparatively high for ore deposits formed by cassiterite mineralization, such as Morococala and Avicaya in the Oruro district, frequently indicating a temperature higher than 300°C and salinity higher than 20 equiv. wt% NaCl. Particularly, it is quite possible that tin deposits associated with the W-Bi and tourmaline mineralizations such as Viloco and Caracoles have been produced by such high-temperature hypersaline fluid ranging up to 500°C and 56 equiv. wt% NaCl, similar to the porphyry copper type. This feature reveals that the hydrothermal fluid related to the Sn-W-Bi mineralization may be of magmatic origin. Homogenization temperatures for the Pb-Zn deposits with no tin minerals are low, mostly ranging 170°–300°C. At the Avicaya-Bolivar mining area in the Oruro district as well as at the Tasna and Chocaya-Animas mining areas in the Quechisla district temperature gradients consistent with the zonal distributions of ore minerals were confirmed.     

Development of an apparatus to measure groundwater qualities in situ and to sample groundwater using boreholes

 To accurately measure the pH, Eh, EC and temperature of groundwater retrieved from boreholes, a deep groundwater sampling apparatus was developed which provided sensory measurements both in situ and in a flow-through cell at ground level. Under a pressure of 1×10⁶ Pa the in situ accuracy of the apparatus sensor was within the following limits: pH ±0.2, temperature ±0.1°C, Eh ±10 mV, and EC ±2.4%. The measuring and sampling of deep groundwater from a borehole of more than 1000 m in depth was performed continuously for 30 days. Values of pH were the same for the in situ sensor, the flow-through cell sensor and the laboratory measurements of the sampled water. At the beginning of the sampling period, Eh values of the in situ sensor indicated deep groundwater conditions. The apparatus is particularly useful for Eh measurement. Chemical composition and stable isotope ratios indicated that the groundwater sampled from more than 1000 m depth was a connate water with a chemical composition slightly different from seawater of the present time, and the groundwater retrieved from 800 m depth was a meteoric water. Natural radioactive elements are thought to be the origin of the tritium in the groundwater retrieved from the 1000 m depth. Received: 6 August 1996 / Accepted: 22 October 1996     

Rapid and Simple Measurement of H2 Emission from Active Faults Using Compact Sampling Equipments

Smaller equipment has been developed for sampling and measuring H₂ in fault zones. A considerable volume of hydrogen emission, suggesting the presence of fluid paths along fault zones, was detected within a 1‐h simple field procedure at an active fault in Central Japan, the Atotsugawa Fault. The equipment enabled measurements in a thin fault gouge with a thickness of 10 mm; this led to pervasive sampling from small fault zones hosted in harder rocks. A rapid evaluation of the spatio‐temporal heterogeneity of hydrogen emissions along the faults, using the present method, would increase knowledge of fluid circulation around faults.     

Effect of Mine Water on the Stability of Underground Coal Mine Roadways

The basic objectives of mine roadways are to provide sufficient cross sections to accommodate equipment, transport, personnel travel and ventilation. However, many roadways become damaged to the extent of needing maintenance, generally dinting, and in some cases requiring re-ripping. Strata conditions play important effects on stability of roadways and other mining activities. Weak rocks cause excessive roadway closures, and water softens some rocks and worsens the closure problem. Therefore, study on effect of mine water on the stability of underground coal mine roadways is important for underground coal mine development. A scientific discussion on the effect of water on the stability of roadways is given on the basis of results obtained by means of field investigation and laboratory tests. Based on analysis, rock in saturated condition has only between 0.19 to 0.49 of its compressive strength and 0.17 to 0.59 of its tensile strength in dry condition. Among the coal measures rock in research area, water has the most obvious effect on the strength reduction of shale. The slaking behavior of shale has also been the worst among the other. Field investigation of roadway driven in shale shown vertical closure in the wet and dry condition area reached 40–60 and 5–15 cm respectively, in 30 days after the drivage. Among the measures, drainage is considered to be the most economical and simplest method to reduce the water content in the rocks or the rock masses.