Water level is decreased during foundation pit excavation to avoid water inrush under confined water pressure. Cut-off wall is often used as waterproof curtain to partially cut off the dewatered aquifer. When a foundation pit is located in a built-up area and the underlying confined aquifer is not cut off, the drawdown must be minimized outside the pit to avoid land subsidence in buildings and pipelines. The coupling effect of the cut-off wall and pumping well is used to control the drawdown outside the foundation pit. However, the coupling mechanism is not intuitively well understood because of the limitations of existing experimental methods. In this study, transparent soil was introduced to model the coupling mechanism in the physical model test. High-purity fused silica and mixed paraffin oil were used as skeleton and fluid to simulate the confined aquifer and groundwater. Industrial solid dye and paraffin oil were used as tracers. A camera was used to collect flow information. Tests were performed for the combinations of cut-off wall and partially penetrating pumping wells. The insertion depth ratio of the cut-off wall most effectively influenced the drawdown. The layout of the pumping wells in horizontal direction influenced water level distribution and flow rate. The optimal depth of the pumping wells was 1–5 m above the bottom of the cut-off wall, and the optimal horizontal distance between the cut-off wall and the pumping wells was 25% of the pit width. Non-Darcy flow was observed within the range of 0–10 m around the bottom of the cut-off wall. These results were significant in understanding the cut-off wall and pumping well coupling effect on foundation pit dewatering.
By analysing comprehensively the factors such as theoretical sea level, abnormal fluctuation of sea level, rising amplitude
of floodtide water level and land deformation, a rising amplitude of 22-33 cm of relative sea level by the year of 2030 is
forecasted in the Zhujiang Delta. From the forecasted amplitude of 30 cm, using hydraulic and hydrometric models the scope
influenced by sea level rise is delimited and the reappearing periods of floodtide water level, protecting ability of embankments,
design parameters of water conservancy project, drain waterlogging, saline intrusion, resource of mud beach and comprehensive
prevention measures are discussed. 相似文献
According to archaeological data from about sixty samples the relative stability of physical and human geographical environment
in the tropical zone of China is discussed in this paper. Because of the superior natural environment, sufficient food resources
and a sparse population resulting in the absence of social requirement to transform the productive forces, the advancement
of economy and society was stagnated during prehistorical period in China’s tropics. Compared with northern China, the appearance
of ground stone tool stagnated about 3,000 years, the beginning of Bronze Age, about 1,000 years, and the agriculture, 2,500–3,000
years. The no ceramics age continued till the early Neolithic Age and the appearance of colour or white ceramics was 2,000
years later than that in northern China. The life form of migration to gather and to hunt continued till the middle Neolithic
Age, and the fixed settlement based on agriculture 1,000–2,000 years stagnated. The clan commune just appeared at the end
of the Neolithic Age which was 2, 000–3,000 years later than that in northern China. 相似文献
This paper examines the increased potential risk of tidalinundations in the Pearl River delta, China, due to futurerises in sea level. The research is based on tidal recordsof 54 tide gauges distributed across the delta plain, andemploys mathematical calculations to predict potentialrises of water level in different parts of the delta undera number of flood scenarios. After assessing a 72-yeartidal record of Hong Kong and factors such as estuarinebackwater effects and long-term geological subsidence,it suggests that a 30 cm rise in relative sea level at themouth of the estuary is possible by 2030. Based on theprediction and five freshwater discharge scenarios, thepotential impacts on water levels across the delta plain arecalculated. Three zones are identified as least affected,heavily affected and severely affected. The impacts arealso translated into return periods of water level. It issuggested that in a large part of the delta plain, returnperiods will be shortened and hence will be increasinglyvulnerable to tidal inundation. Finally, managementimplications are discussed along with assessment ofthe adequacy of the existing tidal flood defences, as well asevaluation of the cost implications if they are to be improved. 相似文献
1 Introduction Voluminous literature has resulted from study of the geology and tectonic evironments of post-orogenic granitoids in eastern Tianshan (He et al., 1995; Han et al., 1997; Gu et al., 1999, 2001; Li et al., 2003; Chen et al., 2004). Previous contributions (Hu et al., 1997; Li et al., 2003) indicate that major events of continental collision in northern Xinjiang occurred around 300 Ma. Then, the tectonics converted from compression to extension, resulting in the uplifting of th… 相似文献
The global warming has obviously been causingthe Arctic sea ice shrinking and thinning during thelast 30 years, which would increase free ice waters andenhance biological productivity. These changes willimpact the source and sink of carbon in the ArcticOcean and subarctic waters as well as a feedback tothe global change[1—3]. The Chukchi Sea is located in the southwest ofthe western Arctic Ocean and the Bering Sea in thenorthwest of the North Pacific Ocean. Both seas are 1997—2001) and… 相似文献
