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981.
发展中的板块边界:天山-贝加尔活动构造带 总被引:5,自引:1,他引:5
亚洲内陆的强地震密集地发生在天山-贝加尔一线,但该处并不存在一条连续的大断裂,学术界对这个问题的认识长期相左。文中分析了这条地震带的时空分布、分区特点、应力状态和活动周期,计算了欧亚大陆的布格重力异常场、均衡重力异常场,反演了上地幔的密度分布和剪切波速分布。发现在这个部位的70~250km的深部有一条北东向的密度、速度陡变带,它是新生代的冷地幔和热地幔的交界带,与浅部构造存在立交关系,对亚洲大陆的现今构造运动和应力场具有重要的控制作用。这个带的地震不同于传统意义上的板缘地震和板内地震,是一种因为深浅构造不同而造成的结构性地震,性质上为大陆内缘地震。文中还就深浅构造的空间立交关系、时间镜像关系进行了讨论,指出在南北地震带和伊朗东侧地震带的立交结构也与上地幔构造有关。天山-贝加尔活动构造带是正在发展中的板块边界,是大陆内部的一个典型构造,北侧为稳定的俄罗斯-西伯利亚次板块,南侧为活动的中国-东南亚次板块。 相似文献
982.
983.
通过对一个滨海多层含水层系统的考察,该含水层系统由上、下弱透水层和介于中间的承压含水层组成,海底露头处被淤泥层覆盖.建立了描述该系统中地下水水头随潮汐波动的数学模型,并得到其解析解.该解析解与六个基本参数有关,分别是承压含水层的海潮传播参数,淤泥层的无量纲透水系数,上下弱透层与承压含水层贮水率的比率 (无量纲)和上下弱透层的无量纲越流.当这些参数取某些特殊值时,我们的解便化简为前人考虑的几种简单情形对应的解.分析表明,承压含水层中地下水水头波幅是上、下弱透水层贮水率和越流系数的减函数,是淤泥层相对透水系数的增函数;波动相位(时滞)是上、下弱透水层贮水率和越流系数的增函数,是淤泥层相对透水系数的减函数. 相似文献
984.
Anil Misra Lance A. Roberts Steven M. Levorson 《Geotechnical and Geological Engineering》2007,25(1):65-77
Load displacement analysis of drilled shafts can be accomplished by utilizing the “t-z” method, which models soil resistance
along the length and tip of the drilled shaft as a series of springs. For non-linear soil springs, the governing differential
equation that describes the soil-structure interaction may be discretized into a set of algebraic equations based upon finite
difference methods. This system of algebraic equations may be solved to determine the load–displacement behavior of the drilled
shaft when subjected to compression or pullout. By combining the finite difference method with Monte Carlo simulation techniques, a probabilistic load–displacement analysis can be conducted. The probabilistic analysis is advantageous
compared to standard factor of safety design because uncertainties with the shaft–soil interface and tip properties can be
independently quantified. This paper presents a reliability analysis of drilled shaft behavior by combining the finite difference
technique for analyzing non-linear load–displacement behavior with Monte Carlo simulation method. As a result we develop probabilistic relationships for drilled shaft design for both total stress (undrained)
and effective stress (drained) parameters. The results are presented in the form of factor of safety or resistance factors
suitable for serviceability design of drilled shafts. 相似文献
985.
Sitharam G. Thallak Sireesh Saride Sujit Kumar Dash 《Geotechnical and Geological Engineering》2007,25(5):509-524
This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced
soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using
biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity
improvement factor (If) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes
the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay
bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it
is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case
indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft
clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed
close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar
geogrid layer at the base of the geocell mattress. 相似文献
986.
987.
988.
989.
990.
Peter Malik 《Environmental Geology》2007,51(5):707-711
Hydrograph analyses of groundwater depletion process in the spring were used for estimation of karstification degree and groundwater
sensitivity to pollution in the whole catchment area. Differences of individual depletion hydrographs enable assessment of
the anticipated extent of absorption, attenuation and self-purification processes during the groundwater penetration through
the rock environment between its infiltration and its outflow in the spring. The method was applied in the SW part of the
Velka Fatra Mountains (Slovakia) “Tlsta” hydrogeological structure. In total, 209 individual recession curves from 20 gauged
springs were analyzed. Depending on characteristic groundwater depletion hydrographs with independent sub-regimes, categories
of groundwater sensitivity to pollution were defined. Finally, resulting sensitivities to pollution were linked to lithostratigraphical
units in the area. 相似文献