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431.
Guo-Wei Li Thang Ngoc Nguyen Andrew Cudzo Amenuvor 《Marine Georesources & Geotechnology》2016,34(2):154-161
This article studies the effect of dynamic cyclic loading and surcharge preloading method on the post-construction settlement of low embankments. Soil samples obtained from the soft ground under an embankment were consolidated by surcharge preloading followed by static and dynamic cyclic loading in the odometer. The results show that the consolidation deformation of the soil samples is independent of the frequency of the dynamic cyclic loading, which was simulated to follow the half-sine wave, and this is consistent with the energy concept. The post-construction settlement increases with increasing amplitude of cyclic load and the effectiveness of surcharge preloading depends on the difference between magnitude of surcharge and amplitude of the cyclic load. Based on the consolidation theory combined with the test results, a formula has been proposed to compute the post-construction settlement of a low embankment under cyclic loading. 相似文献
432.
Strategies for High Precision Processing of GPS Measurements with Application to the Amery Ice Shelf,East Antarctica 总被引:3,自引:0,他引:3
A number of statistic Global Positioning System (GPS) measurement campaigns have been made on a floating Antarctic ice shelf,
the Amery Ice Shelf, as part of ongoing glaciological studies designed to investigate the ice shelf dynamics, grounding zone
definition, and ice shelf strain. Such studies ar fundamental to improving out knowledge of the Antarctic ice-sheet mass balance
and dynamical models of ice sheet/ocean interaction. This article describes two techniques used to process the statistic GPS
data. One approach uses a segmented version of the classical static methodology, and the other approach adopts a new sequential
processing technique. Both approaches yield similar results for the station coordinates and demonstrate the potential of GPS
for extracting the tidal signal on the ice shelves and giving information on the dynamical motion of the ice sheet. To verify
our results for the vertical component, we compare the ice shelf GPS tidal signal with a tidal model derived from tide gauge
measurements at nearby Beaver Lake. Comparison of the GPS results with the tide model give good agreement in amplitude at
the few cm level (GPS results always larger) but clearly shows evidence of phase propagation of the ocean tidal wave under
the ice shelf. Improving the resolution of the tides over the ice shelves will be of tremendous benefit for future satellite
missions, such as Ice, Cloud and Land Elevation Satellite (ICESAT), and the integrated use of GPS and satellite data will
be fundamental for any on-going Antarctic ice sheet mass balance studies. ? 2000 John Wiley & Sons, Inc. 相似文献
433.
Monsoon-induced upwelling off the Vietnamese coast 总被引:1,自引:0,他引:1
Joachim W. Dippner Kim Vinh Nguyen Hartmut Hein Thomas Ohde Natalie Loick 《Ocean Dynamics》2007,57(1):46-62
During the southwest monsoon from July 8 to 28, 2003, an interdisciplinary cruise took place in the central area of Vietnamese upwelling with “MV Nghien Cuu Bien” in the South China Sea. Physical observations in the upwelling area are analyzed with respect to local/regional wind forcing and far field forcing. Nutrients and phytoplankton measurements are discussed with respect to exchange processes between different water masses. The wind-induced coastal upwelling by local wind forcing is much weaker than in the previous years due to weaker-than-normal winds. This can be attributed to the far field forcing of the 2002/2003 El Niño event which modulates the upwelling intensity. The atmospheric conditions reflect the typical situation after an El Niño event which weakens the wind-induced coastal upwelling, reduces the latent heat flux, and results in higher-than-normal sea-surface temperatures. The general circulation pattern during SW monsoon is driven by the spatial asymmetry in the monsoon forcing. The flow pattern is characterized by an upwelling-induced northward undercurrent and a recently detected southward countercurrent. The resulting stretching deformation of this flow pattern forms an offshore jet between ~12°N and 12.5°N and causes a local enhancement of the upwelling intensity. The upwelling due to stretching deformation is a peculiarity, which makes the Vietnamese upwelling area different to other upwelling areas. A budget of the upwelling components is presented: the strongest contribution in 2003 to the Vietnamese upwelling is the dynamical upwelling due to the clockwise rotation of the northward undercurrent. The internal radius of deformation separates the upwelling area from the offshore area as well as different water masses. Mekong River and the Gulf of Thailand waters which are offshore show nutrient depletion. Therefore, high chlorophyll maxima cannot be explained by nutrient supply from river runoff. The dynamical upwelling brings in nutrient-rich Maximum Salinity Water into the euphotic zone. This causes a subsurface chlorophyll maximum between 20 and 40 m water depth along the northward undercurrent. Deflection from the Redfield ratio in the C:N ratio and negative excess nitrogen identifies the region as nitrogen-limited which may favor cyanobacteria blooms. The consequence is a unique feature in new production: in the upwelling area, new production is based on upwelled nitrate, whereas offshore in the nutrient-depleted Mekong and Gulf of Thailand water, new production is based in addition on nitrogen fixation. 相似文献
434.
Shang Yonghui Nguyen Hoang Bui Xuan-Nam Tran Quang-Hieu Moayedi Hossein 《Natural Resources Research》2020,29(2):723-737
Natural Resources Research - The primary purpose of this study was to develop a novel hybrid artificial intelligence model, with a robust performance, to predict ground vibration induced by bench... 相似文献
435.
436.
Determination of groundwater solute transport parameters in finite element modelling using tracer injection and withdrawal testing data 总被引:1,自引:0,他引:1 下载免费PDF全文
Nguyen Van Hoang 《地下水科学与工程》2021,9(4):292-303
The groundwater tracer injection and withdrawal tests are often carried out for the determination of aquifer solute transport parameters. However, the parameter analyses encounter a great difficulty due to the radial flow nature and the variability of the temporal boundary conditions. An adaptive methodology for the determination of groundwater solute transport parameters using tracer injection and withdrawal test data had been developed and illustrated through an actual case. The methodology includes the treatment of the tracer boundary condition at the tracer injection well, the normalization of tracer concentration, the groundwater solute transport finite element modelling and the method of least squares to optimize the parameters. An application of this methodology was carried out in a field test in the South of Hanoi city. The tested aquifer is Pleistocene aquifer, which is a main aquifer and has been providing domestic water supply to the city since the French time. Effective porosity of 0.31, longitudinal dispersivity of 2.2 m, and hydrodynamic dispersion coefficients from D = 220 m2/d right outside the pumping well screen to D =15.8 m2/d right outside the tracer injection well screen have been obtained for the aquifer at the test site. The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119, which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.035 5 (while 1 is the worst and 0 is the best fit). 相似文献
437.
Groundwater resources have considerable influences on the human population and socioeconomic development of Vietnam and the Mekong River Delta (MRD). This paper presents an overview of the relationship between climate change and groundwater in the MRD, including the challenges, strategies and technical measures. Our results showed that groundwater levels are related to other climate and hydrological variables (i.e., rainfall, river levels, etc.); therefore, the impacts of climate change on the groundwater resources of the Mekong delta are significant, especially on groundwater recharge. Based on the results of this study, it is recommended that groundwater development in the future should focus on reducing groundwater harvesting, enhancing groundwater quantity by establishing artificial works and exploiting surface water. This study suggests that the Artificial Neural Network (ANN) model is an effective tool for forecasting groundwater levels in periods of 1 month and 3 months for aquifers in the natural and tidal regime areas of the delta. 相似文献
438.
The Bouwer and Rice method is a line-fitting method used to estimate the hydraulic conductivity of an aquifer by means of a slug test. When considering a relatively impermeable layer, called a filter cake, which may form at the interface between a cutoff wall and the natural soil formation, the assumptions of the Bouwer and Rice method are violated. A modification of the Bouwer and Rice method is proposed that incorporates the concept of a flow net, whereby the geometry of the cutoff wall and filter cake is effectively considered in estimating the hydraulic conductivity of a vertical cutoff wall. 相似文献
439.
Soil salinity and sodicity are environmental problems in the shrimp farming areas of the Cai Nuoc district, Ca Mau province,
Vietnam. In 2000, farmers in the district switched en masse from rice cropping to shrimp culture. Due to recent failure in
shrimp farming, many farmers wish to revert to a rotational system with rice in the wet season and shrimps in the dry season.
So far, all their attempts to grow rice have failed. To assess soil salinity and sodicity, 25 boreholes in shrimp ponds were
analysed in four consecutive seasons from 2002 to 2004. The results showed that soil salinity was quite serious (mean ECe 29.25 dS m−1), particularly in the dry season (mean ECe 33.44 dS m−1). In the wet season, significant amounts of salts still remained in the soil (mean ECe 24.65 dS m−1) and the highest soil salinity levels were found near the sea. Soil sodicity is also a problem in the district (exchangeable
sodium percentage range 9.63–72.07%). Sodicity is mainly a phenomenon of topsoils and of soils near the sea. Both soil salinity
and sodicity are regulated by seasonal rainfall patterns. They could together result in disastrous soil degradation in the
Cai Nuoc district. 相似文献