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51.
Manoj Datta G. Venkatappa Rao Shashi K. Gulhati 《Marine Georesources & Geotechnology》2013,31(4):307-341
Abstract This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes. During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material. Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil. This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified. 相似文献
52.
Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to
heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required
to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of
the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide
are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust
passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important
to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of
slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can
be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta
Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available
worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain.
VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was
delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient
resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the
slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature
correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive
structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out
water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide. 相似文献
53.
We have examined the potential of using a closed-path sensor to accurately measure eddy fluxes of CO2. Five inlet tubeflow configurations were employed in the experimental setup. The fluxes of CO2 were compared against those measured with an open-path sensor. Sampling air through an intake tube causes a loss of flux, due to the attenuation of CO2 density fluctuations. Adjustments need to be made to correct for this loss and to account for density effects due to the simultaneous transfer of heat and water vapor. Theory quantifying these effects is discussed.The raw CO2 flux measured with the closed-path sensor was smaller than that measured with the open-path sensor by about 15% (on average) for the turbulent tubeflow configurations with a short (3 m) intake tube, by 31% for turbulent tubeflow with a longer (6 m) intake tube and by 24% for laminar tubeflow. The difference was, in part, caused by tube attenuation of the CO2 density fluctuations and inadequate sensor time response. The elimination of the flux adjustment for the simultaneous transfer of sensible heat (i.e., the attenuation of ambient temperature fluctuations in the intake tube) generally accounted for the rest of this difference.The raw flux measured with the closed-path sensor was corrected for frequency response and density effects. Except in the case of laminar tubeflow, the corrected closed-path flux agreed consistently with the corrected open-path flux within a few percent (<5%). These results suggest that closed-path sensors, with appropriate corrections, can be used to measure CO2 flux accurately. Recommendations are included on selecting an optimum flow configuration to minimize the effect of sampling air through a tube.Published as Paper No. 9938, Journal Series, Nebraska Agricultural Research Division. 相似文献