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261.
Electric imaging and laboratory resistivity testing for geotechnical investigation of Pusan clay deposits 总被引:3,自引:0,他引:3
Large-scale reclamation works for new land development in the Nakdong River plain have been extensively carried out on soft clays. Several geotechnical characteristics of the clays could not be well evaluated, partly due to easy disturbance during drilling and sampling. Consequently, geophysical methods, seen as nondestructive testing tools, have been applied in geotechnical investigation of Pusan clays for the first time. In this study, the 2D electric imaging technique was employed to map the thick soft clay deposits in four reclamation sites. The Pusan clay deposit was very well mapped. Electric resistivity of Pusan clays was measured on over 50 core samples in the laboratory, and then correlated with other geotechnical parameters such as salinity, organic content, water content, plasticity, unit weight and sampling depth. Additionally, electric resistivity of about 20 natural clays collected worldwide was measured and compared to that of the Pusan clays as an initial effort in creating a database of clay electric resistivity to help further application of electric imaging in geotechnical investigation of clayey soils. 相似文献
262.
H.-J. Oh B.-J. Sohn E. A. Smith F. J. Turk Ae-suk Seo H.-S. Chung 《Meteorology and Atmospheric Physics》2002,81(3-4):273-287
Summary ?This study compares and contrasts six infrared-based satellite rain estimation techniques and their validation during a 2-month
period from June 20–August 20, 1998 over the Korean peninsula. Two probability matching techniques (PMM1, PMM2), a look-up
table technique (LUT), a convective-stratiform technique (CST), the Negri-Adler-Wetzel technique (NAWT), and the Arkin technique
(ARKT) are applied to hourly infrared GMS imagery. Retrieved rainrates are compared against one-minute reporting raingage
observations from the dense Automated Weather Station (AWS) network of Korea. The high spatial resolution and fine temporal
resolution of the AWS measurements provide a unique and effective means to validate rain estimates derived from instantaneous
space measurements, which is a main scientific focus of this study.
Validation results indicate that all techniques exhibit better performance for more evenly spread rain events while exhibiting
lesser performance for weak and sporadic rains for which validation sampling becomes more of a problem. Validation statistics
show that climatologically-local techniques such as the PMM and LUT algorithms perform better than techniques developed in
climatologically different regimes, indicating the well-known dependence of rain physics on the immediate environment. Nevertheless,
the validation results suggest how the rain determination parameters including attributed rain and threshold brightness temperature
could be optimized locally before application. As others have found, the most difficult problem with satellite infrared techniques
is in the detection and quantification of heavy rainfall events arising from uncertainties in discriminating non-precipitating
anvil clouds from convective clouds. However, for the set of algorithms under examination here, given the sharp resolution
of the validation measurements, it is evident that the CST algorithm exhibits superior performance in differentiating between
non-precipitating anvil and heavy rain.
Received January 4, 2002; revised March 11, 2002 相似文献
263.
Major and trace element, and Sr-Nd isotope constraints on the origin of Paleogene volcanism in South China prior to the South China Sea opening 总被引:15,自引:0,他引:15
Sun-Lin Chung Hai Cheng Bor-ming Jahn Suzanne Y. O''Reilly Bingquan Zhu 《Lithos》1997,40(2-4):203-220
Paleogene volcanic rocks crop out in three sedimentary basins, namely, Sanshui, Heyuan and Lienping, in the attenuated continental margin of south China. Lavas from the Sanshui basin which erupted during 64-43 Ma are bimodal, consisting of intraplate tholeiitic basalt and trachyte/rhyolite associations. Similar to Cretaceous A-type granites from the nearby region, the felsic member shows peralkaline nature [Na2O + K2O ≈ 10–12%; (Na + K)/Al≈ 0.98−1.08], general enrichment in the incompatible trace elements and significant depletion in Ba, Sr, Eu, P and Ti. Although both types of the Sanshui lavas have rather uniform Nd isotope compositions [Nd(T) ≈ +6 to +4]that are comparable to Late Cenozoic basalts around the South China Sea, the felsic rocks possess apparently higher initial Sr isotope ratios (ISr up to 0.713) and form a horizontal array to the right in the Nd vs. Sr isotope plot. Closed system differentiation of mantle-derived magmas in a ‘double diffusive’ magma chamber is considered for the bimodal volcanism, in which the trachytes and rhyolites represent A-type melts after extensive crystal fractionation in the upper portion of the chamber. Such A-type melts were later contaminated by small amounts (1–3%) of upper crustal materials during ascent. On the other hand, composition of lavas in the other two basins varies from tholeiitic basalt to andesite. Their Sr and Nd isotope ratios [ISr ≈ 0.705 to 0.711; Nd(T) ≈ +1 to − 5] and generally correlative Nb-Ta depletions suggest a distinct magma chamber process involving fractional crystallization concomitant with assimilation of the country rock. We conclude that these Paleogene volcanic activities resulted from the lithospheric extension in south China that migrated southwards and eventually led to opening of the South China Sea during 30-16 Ma. 相似文献
264.
Hong GH Kim YI Lee SH Cooper LW Choe SM Tkalin AV Lee A Kim SH Chung CS Hirose K 《Marine pollution bulletin》2002,44(7):660-665
The concentrations of 239+240Pu and 137Cs in zooplankton and nekton in the Northwest Pacific and Southern Oceans were measured during the period 1993-1996. The object of the sampling was to assess the potential impacts of existing submerged anthropogenic-radioactive materials in the western North Pacific as well as the East China Sea. Samples from the Bransfield Strait of the Antarctic Ocean provided a control source impacted by only atmospheric bomb fallout. No particularly elevated levels of 239+240Pu were found in zooplankton samples from the Northwest Pacific, although significantly lower levels of 239+240Pu were found in three mixed zooplankton samples from the Bransfield Strait. The body burden of 239+240Pu in zooplankton appears to reflect concentrations in ambient seawater with some variation. Some additional measurements of 137Cs in fish are also reported here to complement existing databases and for future reference in the regional marine environmental radioactivity monitoring effort. 相似文献
265.
In a typical ground water flow model, lakes are represented by specified head nodes requiring that lake levels be known a priori. To remove this limitation, previous researchers assigned high hydraulic conductivity (K) values to nodes that represent a lake, under the assumption that the simulated head at the nodes in the high-K zone accurately reflects lake level. The solution should also produce a constant water level across the lake. We developed a model of a simple hypothetical ground water/lake system to test whether solutions using high-K lake nodes are sensitive to the value of K selected to represent the lake. Results show that the larger the contrast between the K of the aquifer and the K of the lake nodes, the smaller the error tolerance required for the solution to converge. For our test problem, a contrast of three orders of magnitude produced a head difference across the lake of 0.005 m under a regional gradient of the order of 10(-3) m/m, while a contrast of four orders of magnitude produced a head difference of 0.001 m. The high-K method was then used to simulate lake levels in Pretty Lake, Wisconsin. Results for both the hypothetical system and the application to Pretty Lake compared favorably with results using a lake package developed for MODFLOW (Merritt and Konikow 2000). While our results demonstrate that the high-K method accurately simulates lake levels, this method has more cumbersome postprocessing and longer run times than the same problem simulated using the lake package. 相似文献
266.
Summary Interannual variations of the summer monsoon onset over the South China Sea (SCS) have been studied using data from over
seventeen years (1979–1995) of NMC global analysis and of Outgoing Longwave Radiation (OLR) observed with NOAA polar-orbitting
satellites. It was found that the summer monsoon onset in the SCS occurs abruptly with a sudden change of zonal wind direction
from easterly to westerly and an exploding development of deep convection in the whole SCS region in the middle of May.
Based on the criteria defined in this paper for the SCS summer monsoon onset, the average onset date over the SCS from 1979
to 1995 is around the fourth pentad of May. The airflow and general circulation over the SCS changes dramatically after the
onset. The ridge of the subtropical high in the western Pacific in the lower troposphere weakens and retreats eastward from
the SCS region with an establishment of westerly winds over the whole region. During the SCS monsoon onset, the most direct
impact in the vicinity of the SCS are the equatorial westerlies in the Bay of Bengal through their eastward extension and
northward movement. An indirect influence on the SCS onset is also caused by the enhancement of the Somali cross-equatorial
flow and the vanishing Arabian High over the sea; the latter may be a signal for the SCS onset.
There are quite significant interannual variations in the SCS onset. In the years of a delayed onset, the most profound feature
is that the easterly winds stay longer in the SCS than on average. Deep convection activities are suppressed. The direct cause
is the abnormal existence of the western Pacific subtropical high over the SCS region. Moreover, compared to the average,
the equatorial westerlies in the Bay of Bengal are also weaker in the years of a delayed onset. No significant changes for
the cross-equatorial flow at 105 °E are observed for these years. It has also been found that the interannual variations of
the SCS onset are closely related with the ENSO events. In the years of a delay, the Walker circulation is weaker, and the
sea surface temperature (SST) anomalies in the western Pacific are negative.
Received April 14, 1997 Revised July 11, 1997 相似文献
267.
An unusually thick and soft clay, which is called Busan clay, has been deposited throughout the Nakdong River estuary, South Korea. Although many reclamation works have been carried out in the area since early 1990s, large- and small-scale slope failures have taken place mostly during the soil placement on the clay. A case history briefly describes failure of a breakwater resulting from overestimation of the undrained strength, obtained from laboratory testing. An attempt has been made to examine the methods for determining the undrained strength from field vane testing. For this, the undrained strengths from field vane testing were obtained using different correction factors and compared with each other at five sites in the area. An alternative correction method applicable especially for Busan clay was found, using a range of corrected strength ratios. Further, relationships between the depositional environment and the undrained strength of the clay have also been investigated. 相似文献
268.
The thruster is the crucial factor of an underwater vehicle system, because it is the lowest layer in the control loop of the system. In this paper, we propose an accurate and practical thrust modeling for underwater vehicles which considers the effects of ambient flow velocity and angle. In this model, the axial flow velocity of the thruster, which is non-measurable, is represented by ambient flow velocity and propeller shaft velocity. Hence, contrary to previous models, the proposed model is practical since it uses only measurable states. Next, the whole thrust map is divided into three states according to the state of ambient flow and propeller shaft velocity, and one of the borders of the states is defined as critical advance ratio (CAR). This classification explains the physical phenomenon of conventional experimental thrust maps. In addition, the effect of the incoming angle of ambient flow is analyzed, and Critical Incoming Angle (CIA) is also defined to describe the thrust force states. The proposed model is evaluated by comparing experimental data with numerical model simulation data, and it accurately covers overall flow conditions within ±2 N force error. The comparison results show that the new model's matching performance is significantly better than conventional models'. 相似文献
269.
S. G. Chung K. Nagendra Prasad T. S. Nagaraj J. G. Chung K. Y. Jo 《Marine Georesources & Geotechnology》2004,22(1):1-20
It Naturally cemented soft clays have components of strength and stiffness, which cannot be accounted for by classical soil mechanics (Leroueil and Vaughan 1990). This stems from the influence of structure caused by cementation due to environmental factors. It is necessary to evaluate the cementation bond strength at preyield and postyield stress levels of loading, to understand comprehensively the observed response from micromechanic considerations. This helps to better understand and evolve approaches to model the constitutive behavior in a consistent manner, according to the physical phenomenon of formation of cementation as an additional component to what is otherwise normally regarded as frictional behavior arising only from particulate nature of clays. Comparing the behavior of deep deposits of Pusan soft clays under stress with corresponding response of the same clay in its remolded state, it has been possible to take into account particulate and nonparticulate responses. The evolution of cementation bonding is modeled for different Pusan clays with the yield stress in oedometer compression as a normalizing parameter for obtaining the generalized relationship of cementation bonding with increase in stress. The already established model for determining the remolded behavior is appropriately modified to assess the behavior influenced by cementation. The model proposed consists of parameters, which are determined in routine investigations. 相似文献
270.