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91.
David Washington Daniel Rodriguez Vincent Ogunro 《Geotechnical and Geological Engineering》2011,29(1):13-17
The monitoring operation of an older impoundment (such as dams and waste barrier materials) during the service life of the
structure cannot be overemphasized. Since older infrastructures seem to be more susceptible to piping and seepage failure,
their construction design should be analyzed and monitored at places where a potential problem could occur. Once an impoundment
is constructed without adequate filters layers and foundation treatments, then the prevention of piping or seepage may require
an effective approach to constructing a cut-off wall to prevent eventual failure. In order to identify and understand theses
failure modes, it is important to identify the physical parameters of the impoundment system, such as the zones of various
soil gradations, the compaction of these zones, the hydraulic conductivity, the compatibility of the soil formations within
and beneath the core or liner, as well as the cohesive and dispersive properties of soils at various location within the structure.
Once these parameters are known and quantified, an adequate assessment of the structure’s susceptibility to piping or contaminant
transport can be established. This type of an analysis will enable the proper design of a cut-off wall and predetermine the
effectiveness of its long-term performance. The Vermont Waterbury Dam (built in 1938) is example of seepage related problem
that implemented a cut-off wall design to prevent piping paths from undermining the structure. In this case, some forensic
sampling had to be performed and the parameters of the soils as just mentioned were key factors in determining the wall design.
In this paper, the Waterbury dam rehabilitation is investigated as case studies, in order to better understand how older designs
and poor construction of impoundments can lead to piping condition in dams as well as failures in waste barrier systems. The
Secant Cut-off wall (constructed at Waterbury Dam) is mentioned as a corrective measure taken for this dam and there is a
brief discussion as to how this construction rehabilitation technique can be applied to waste barrier impoundments. 相似文献
92.
D. A. Holdsworth Rupa Vuthaluru Iain M. Reid Robert A. Vincent 《Journal of Atmospheric and Solar》2002,64(18)
The differential absorption experiment (DAE) was first proposed in the 1950s for the estimation of mesospheric and lower thermospheric electron density using MF/HF radars. The technique was used extensively until the late 1970s, when interest in the technique declined, due to experimental limitations and questions regarding the assumptions of the technique. This paper describes the application of the DAE within the online observations of the Buckland Park MF (BPMF) radar. The experimental limitations of the technique for the BPMF radar are discussed, with particular attention paid to effects of complex gain differences between receiving channels used to decompose the linearly received signals into circular components. Hourly and monthly averaged midday DAE electron densities are presented, revealing good agreement with IRI model estimates. Monthly averaged midnight DAE electron densities are also presented, revealing good qualitative agreement with the IRI model estimates. 相似文献
93.
94.
Since both lining structure and rock mass exhibit delayed behaviour, tunnel equilibrium conditions evolve with time. After
discussing existing work done on different aspects of long-term tunnel behaviour, the aim of this paper is to “understand”
the influence of rock mass and lining degradations on the long-term stability conditions of the tunnel by means of the convergence–confinement
method. In order to represent the effects of degradation on tunnel long-term conditions, specific degradation models are selected
according to the disorders identified during principal inspections of road tunnels in Switzerland. By simulating the reduction
of the mechanical properties of both the rock mass and the lining or by using creep models, it is possible to assess the influence
of the main degradation processes on tunnel stability. The results are interpreted in terms of tunnel safety factor. The presented
approach for the determination of the long-term behaviour of tunnels, although valid for simple tunnel geometry and field
stress conditions, allows to roughly estimate the influence of significant degradation processes that affect the rock mass
and the supporting structure. Though this approach results in some simplification, it may be generalised and adopted with
more refined numerical analyses for improving the assessment of tunnel long-term conditions. 相似文献
95.
J. Perbos P. Escudier F. Parisot G. Zaouche P. Vincent Y. Menard F. Manon G. Kunstmann D. Royer L. -L. Fu 《Marine Geodesy》2003,26(3):147-157
On 7 December 2001, Jason-1 was successfully launched by a Boeing Delta II rocket from the Vandenberg Air Force Base, California. The Jason-1 satellite will maintain the high accuracy altimeter service provided since 1992 by TOPEX/Poseidon (T/P), ensuring the continuity in observing and monitoring the Ocean Dynamics (intraseasonal to interannual changes, mean sea level, tides, etc.). Despite one-fourth the mass and power, the Jason-1 system has been designed to have basically the same performance as T/P, measuring sea surface topography at a centimetric level. This new CNES/NASA mission also provides near real-time data for sea state and ocean forecast. The first two months of the Jason-1 mission have been dedicated to the assessment of the overall system. The goals of this assessment phase were:
1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES);
2. To verify that platform performance requirements are met with respect to Jason-1 requirements;
3. To verify that payload instruments performance requirements evaluated at instrument level are met;
4. To assess the performance of the Jason-1 Ground System.
This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products. 相似文献
1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES);
2. To verify that platform performance requirements are met with respect to Jason-1 requirements;
3. To verify that payload instruments performance requirements evaluated at instrument level are met;
4. To assess the performance of the Jason-1 Ground System.
This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products. 相似文献
96.
Vincent Mannings 《Astrophysics and Space Science》1995,224(1-2):185-188
Studies of circumstellar dust and gas in pre-main-sequence systems are in part motivated by a desire to probe possible sites of future or on-going planet formation and, should accretion onto young stars be taking place, to determine whether the observed remnants of embryonic envelopes might yet contribute significantly to the final masses of stars as they evolve towards the main sequence. New 0.35- to 1.3-mm flux measurements have been made for 13 intermediate-mass pre-MS systems in order to estimate total dust+gas masses and to investigate the spatial distribution of circumstellar material. At least two sources may be dominated by compact circumstellar disks; emission from extended envelopes appears to be important for the majority of sources. HD 163296 is an unusual object and warrants further examination. 相似文献
97.
Michael E. ZOLENSKY Andrei V. IVANOV S. Vincent YANG David W. MITTLEFEHLDT Kazumasa OHSUMI 《Meteoritics & planetary science》1996,31(4):484-493
Abstract Kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises. Many Kaidun clasts have been intensely altered by aqueous fluids, as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate- and phyllo-silicate-filled veins. In this report, we describe an unusual CM lithology containing many mineralogical features not previously reported from any meteorite, including pyrrhotite, with exclusive needlelike morphologies and thick mantles of phyllosilicate, and complex aggregates of phyllosilicate, melanite garnet, crosscut by pentlandite veins. The latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 °C, which is significantly higher than that attained during secondary processing from other known CM material. 相似文献
98.
99.
This paper presents a novel dynamical model to analyze the long‐term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion‐dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down‐the‐hole percussive drilling as well as top‐hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite‐dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low‐size down‐the‐hole percussive system, follow. The period‐1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
100.
Sources and history of heavy metal contamination and sediment deposition in Tivoli South Bay, Hudson River, New York 总被引:1,自引:0,他引:1
Gaboury Benoit Edward X. Wang William C. Nieder Michael Levandowsky Vincent T. Breslin 《Estuaries and Coasts》1999,22(2):167-178
Persistent inorganic constitutents preserved in sediments of aquatic ecosystems record temporal variability of biogeochemical
functioning and anthropogenic impacts.210Pb and137Cs dating techniques were used to study the past variations of heavy metals (Pb, Cu, and Zn) and accumulation rates of sediments
for Tivoli South Bay, in the Hudson River National Estuarine Research Reserve ecosystem. South Bay, a tidal freshwater embayment
of the Hudson, may play an important role in the sediment dynamics of this important river. The measured sedimentation rate
range of 0.59 to 2.92 cm yr−1 suggests that rapid accumulation occurred during the time period represented by the length of the cores (approximately the
past 50 yr). Direct measurements of sediment exchange with the Hudson River reveal high variability in the sediment flux from
one tidal cycle to the next. Net exchange does not seem to be adequate to explain sediment accumulation rates in the bay as
measured by210Pb and137Cs. The difference may be supplied from upland streams or the Hudson River during storm events. Concentrations of the metals
Pb, Cu and Zn were found to be well correlated with each other within individual cores at five of six sites tested. This suggests
a common proximate source for the three metals at a specific site. The evidence is consistent with mixing in some environmental
compartment before delivery to the bay. While metals self-correlate within individual cores, absolute concentrations, depth
distribution patterns, and ratios of the metals to each other vary among the cores collected at different locations within
the bay. Organic matter, Fe content, and particle size distribution of sediments do not account for the intercore variations
in metal concentration. It is likely that cores collected from different sites may have derived metals from different sources,
such as watershed streams and tidal exchange with the Hudson River. 相似文献