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101.
大气环境质量综合评价是一个城市环境质量考核的重要指标,改进的密切值法是其中一种切实可行的评价方法。通过对1991-2000年10年间广东省三大城市——广州、深圳和珠海的大气环境质量进行综合评价,发现20世纪末,大气环境质量最好的是珠海市,最差的是广州市。与广东省平均水平相比、三大城市中。广州市污染程度高于全省平均水平。从空气环境质量的变化趋势来看,自1997年开始,三大城市大气环境质量趋于好转,为新世纪城市空气环境质量改善提供了良好的基础。 相似文献
102.
Rajasekhar Balasubramanian Chanbasha Basheer Kang Lisa Siao Wei See 《中国地球化学学报》2006,25(B08):183-183
Microorganic pollutants such as polycylic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPHs) are known to be present in urban ambient air. These organic compounds are prone to atmospheric transport and deposition over long distances, thus enabling them to accumulate even in regions remote from their sources. Deposition from the atmosphere can be via direct deposition and exchange with crops that may be directly or indirectly ingested by humans. It can also take place via wet and dry deposition and air-water exchange. Following their deposition, these microorganic pollutants tend to accumulate in soils, sediments and in human and ecological food chains. There are many reports in the literature on the atmospheric concentrations of microorganic pollutants, but there are few reports and data in Asia. This study was performed in Singapore to determine the relative amounts of persistent organic pollutants and TPHs in ambient aerosols. One of the important sources of these organic compounds in Southeast Asia is thought to be biomass burning (vegetation fires). Hence, air sampling was conducted during both smoke haze and non-haze periods. The data obtained from this study will be presented and discussed. 相似文献
103.
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106.
Rock fracturing by explosive energy: review of state-of-the-art 总被引:1,自引:0,他引:1
M. R. Saharan H. S. Mitri J. L. Jethwa 《Fragblast: International Journal for Blasting and Fragmentation》2006,10(1):61-81
A study of the dynamic rock fracture initiation and propagation due to explosive energy is presented through a detailed state-of-the-art review. Explosive energy dissipation in crushing and fracturing is examined and the various means to enhance the explosive energy utilization for dynamic rock fracturing are reviewed. The study highlights the need for a better understanding of the dynamic fracturing process particularly in the presence of in situ stresses in the rock mass. 相似文献
107.
The stochastic nature of the cyclic swelling behavior of mudrock and its dependence on a large number of interdependent parameters was modeled using Time Delay Neural Networks (TDNNs). This method has facilitated predicting cyclic swelling pressure with an acceptable level of accuracy where developing a general mathematical model is almost impossible. A number of total pressure cells between shotcrete and concrete walls of the powerhouse cavern at Masjed–Soleiman Hydroelectric Powerhouse Project, South of Iran, where mudrock outcrops, confirmed a cyclic swelling pressure on the lining since 1999. In several locations, small cracks are generated which has raised doubts about long term stability of the powerhouse structure. This necessitated a study for predicting future swelling pressure. Considering the complexity of the interdependent parameters in this problem, TDNNs proved to be a powerful tool. The results of this modeling are presented in this paper. 相似文献
108.
Compressibility and swelling characteristics of Al-Khobar Palygorskite, eastern Saudi Arabia 总被引:1,自引:0,他引:1
Expansive soils are found in different locations in eastern Saudi Arabia. The area is arid with high temperatures, highly variable humidity and an excessive rate of evaporation compared to the low precipitation. This resulted in the formation of water sensitive soils. In the present investigation, line valve buildings for a sweet water feeder (1118 mm in diameter) were constructed on a highly expansive material consisting mainly of brown palygorskite and gray palygorskite with thin sheets of gypsum and limestone. Block samples from both palygorskites were brought to the laboratory and cores as well as remolded samples were obtained from the blocks. The two palygorskites were found to be highly plastic and have a very high swelling potential. The liquid limit (LL) and plastic limit (PL) values for the brown palygorskite are 261% and 140%, respectively. The gray palygorskite has a LL of a 285% and a PL of 123%. The oedometer free swell tests for the two palygorskites produced an expansion ranging between 31.8% and 42.5% for the remolded samples. However, the expansion for cores ranges between 8.3% and 19.3%. The constant volume pressure tests produced a stress in excess of 4240 kPa. The swell potential reached a steady state after four days while the swelling pressure reached a steady state in about 3 h. The paper addresses the geology of the area, the characterization of the geomaterial including mineralogical composition using X-ray diffraction and SEM techniques and the swelling characteristics of the material. 相似文献
109.
To estimate static and seismic active earth pressure (Pad) on a rigid retaining wall, numerical analyses using different step sizes have been carried out in this paper, based on the
modified Culmann line method by considering Coulomb’s planar rupture surface. Equivalent pseudo-static seismic forces are
considered in the analysis. A new concept of modified unit weight by considering ground surcharge is introduced under static
and seismic conditions. By numerical analysis, area of soil (A) has been estimated to obtain the ratio of A/A0 where A0 is θh2, θ is the angle between retaining structure and ground surface and h is the vertical height of the wall. This ratio remains constant for a particular type of soil and has been used to estimate
the maximum active earth pressure using force diagram. Results are provided in tabular form for easy calculation of the coefficient
of static and seismic active earth pressure. Present results by considering the new technique, compares well with the results
obtained by earlier researchers. 相似文献
110.
S. Tadisetty K. Matsui H. Shimada R. N. Gupta 《Rock Mechanics and Rock Engineering》2006,39(4):383-393
Summary. Discontinuous manual observations and irregular caving characteristics of roof rocks often lead to improper decisions resulting
in accidents and production loss. Hence, systematic monitoring of the hanging roof behind the chock shields is necessary for
safe and productive mining operations. A real-time application was successfully implemented in an Indian mine for forecasting
of hanging roof behaviour to enhance safety and productivity. This paper reports the functioning of real-time TWAP (time weighted
average pressure) analysis in the forecasting of hanging roof behaviour in real time. 相似文献