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991.
Shi-Jin Feng Wei-Hou Shui Li-Ya Gao Li-Jun He 《Marine Georesources & Geotechnology》2013,31(2):130-142
High energy dynamic compaction (HEDC) is adopted in a coastal reclamation area because the grain size of backfilled soil mostly ranges between 20 cm and 100 cm. The in situ tests for evaluating the effectiveness of HEDC were performed on the backfilled soil ground. The crater depth per drop and the whole test zone elevations before and after HEDC were measured and analyzed. Dynamic penetration tests and spectral analysis of surface wave (SASW) tests were used for investigating the improvement depth. Furthermore, the allowable bearing capacity of HEDC treated ground was determined based on the results of plate-load tests. It was found that HEDC did not cause the ground surface heave during construction, and was more effective than low energy dynamic compaction (LEDC) in terms of applied energy utilization. Based on the test results, the improvement depth of HEDC at this site was not less than 14 m, and there was no obvious weak layer within the range of improvement depth. The allowable bearing capacities were larger than 160 kPa. The investigation results indicate that the HEDC technique is an effective way for improving backfilled coarse-grained soil in coastal reclamation areas. This technique helps to achieve both greater improvement depths and higher ground bearing capacities as compared with LEDC. 相似文献
992.
993.
现已绝灭的古老松柏类植物似纵属Elatides在中生代北半球中高纬度植被组成研究上具有重要意义。甘肃酒西盆地早白垩世地层中发现了Elatides的营养枝和雌球果,并保存有较好的碳膜,对它们进行了详细的宏观形态和微细特征研究。根据营养枝、叶角质层、花粉、球果、苞鳞和种子的特征,鉴定这些化石为2个种:Elatides harrisii Chow和Elatides curvifolia (Dunker) Nathorst。其中:Elatides harrisii的突出特征是,花粉球形且具乳状小突起、表面光滑无纹饰,侧面观具褶皱;Elatides Curvifolia的显著特点为,着生于苞鳞腹面基部的种鳞先端三裂,具三枚胚珠。这些特征与现生杉木Cunninghamia非常相似,推论Elatides与现生Cunninghamia可能具有亲缘关系。通过对Elatides地质历史和地理分布的研究,发现该属的演化方向与中生代大陆漂移的方向具可比性,因而为板块构造学说提供了又一古生物学佐证。 相似文献
994.
TJ-1模拟月壤承载特性的现场试验研究 总被引:1,自引:0,他引:1
采用TJ-1模拟月壤作为试验材料,通过静力触探、静载荷试验的对比分析,探讨适合月壤承载力计算的经验公式,以期为未来载人登月时宇航员和着陆器登陆可能涉及到有关月面承载能力的问题提供必要的参考。首先,使用近255 t TJ-1模拟月壤人工制备出13 m×12 m×1.2 m试验用地基,后在试验地基均匀布置6个静力触探测点和2个静载荷试验测点进行测试。针对太沙基承载力计算半经验公式以及规范和国内外学者提出的12个适合中密实砂土静力触探承载力计算的经验公式,对试验结果进行探讨。发现直接运用太沙基提出的半经验公式计算月壤承载力结果明显偏小,而由联合试验小组提出的经验公式 能够用来近似计算月壤地基承载力。计算结果表明,该经验公式在计算承载力时能够与静载荷试验值较好的吻合。 相似文献
995.
A generalized limit equilibrium method for the solution of active earth pressure on a retaining wall
In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed. Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem. 相似文献
996.
通过分析中国大陆76个地磁台站2008年1月1日至2010年12月31日地磁场Z分量日变幅的时空特征,得到结论如下:①在时间上,回归分析和傅里叶分析结果表明,所有台站地磁Z分量的日变幅均有明显的周期性变化,周期主要有365天、183天、122天、73天等,其中365天的周期振幅最大(即年周期)。②空间上,地磁场Z分量日变幅随纬度整体呈非线性变化,在25°N附近存在拐点(极大值点),在15°~25°N,日变幅随纬度的增加而增加,在25°~50°N,Z的日变幅随纬度的增加而减小。③通过地磁场Z分量日变幅时空分布与等效电流对比,结果显示地磁场Z分量日变幅的时空变化特征主要是由等效电流的时空演化决定的。④若粗略地把地磁场Z分量日变幅最大值所处的纬度视为等效电流的焦点所在的纬度,则焦点所在纬度夏季最高,春秋季次之,冬季最低,逐日焦点变化最大可达10°。 相似文献
997.
998.
以福建及粤赣地区内陆为分析区域,基于该区域的地质构造环境,主要使用测震学分析方法,结合GPS、形变等手段的研究成果,研究分析该区域与周边地区地震活动的互动关系。结果发现,青藏亚板块和中国台湾地区的强震活动对福建及粤赣地区内陆地震活动有影响,地震活动具有较明显的相关关系。 相似文献
999.
Hong-Di He Wei-Zhen Lu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(8):1053-1061
This paper reports an investigation on the periodic variation of pollutant levels at a typical traffic intersection of Hong Kong. Carbon monoxide, carbon dioxide and particulate matters (PM x ) were measured respectively and the measured data show periodic variations with the traffic signal intervals. The power spectral density (PSD) approach was used to inspect the trends and periodic oscillations of measured pollutants. Singular spectrum analysis was applied to decompose the measured data into statistically significant non-linear trends and oscillations in the process. From the results, most of the trends tend to increase due to the upcoming rush hour during the experiment. In addition, all the oscillations changed regularly with a period of 136?s, which is coincident with the traffic signal period and the frequency calculated by using PSD. The trends, together with the oscillations, collectively explain the most percentage of the variability of the data in the time series and provide the principal components of the data in understanding the periodic variation of the pollutant concentration. It can be deduced that vehicle emission is the major contributor to the air pollution in downtown area and pedestrians should be more alerted when crossing the busy traffic intersections. 相似文献
1000.
Erping Bi Yulong Liu Jiangtao He Zhao Wang Fei Liu 《Ground Water Monitoring & Remediation》2012,32(1):53-58
In order to collect baseline information on the environmental occurrence of volatile organic compounds (VOCs) in groundwater in East China, shallow groundwater samples were collected from five alluvial plains in East China in 2008 to 2009. All samples were analyzed for 54 VOCs representing a wide variety of uses and origins. Sampling sites were mainly selected in the areas to be susceptible to contamination from human activities in terms of previous hydrogeological survey. The data of all samples showed a variety of different hydrogeological systems with potential sources of VOCs, with 36 of the 54 VOCs being found. The most frequently detected compounds include naphthalene (56.9%), chloroform (16.9%), 1,2‐dichloroethane (16.2%), 1,2‐dichloropropane (13.1%), and 1,2,3‐trichlorobenzene (12.3%). The concentrations of methylene chloride, 1,2‐dichloroethane, carbon tetrachloride, trichloroethene, 1,2‐dichloropropane, and tetrachloroethene exceeded the relating drinking water standards. Future work will be needed to identify those factors that are most important in determining the occurrence and concentrations of VOCs in groundwater in China. 相似文献