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81.
82.
A Physical and Numerical Investigation on the Stability of Shallow Tunnels in Strain Softening Media 总被引:11,自引:0,他引:11
Summary The behaviour up to failure of shallow underground openings is discussed on the basis of some laboratory, small-scale model tests and of finite element simulation. The experimental results are first illustrated. They were obtained from two-dimensional (plane strain) and three-dimensional tunnel models tested under standard gravity conditions. Then, the phenomenon of strain localisation that characterizes the medium surrounding the model tunnels is discussed, recalling two alternative approaches for its numerical interpretation. On this basis, a finite element procedure for strain softening analyses is outlined and applied to the simulation of the tests in both two- and three-dimensional conditions. The comparison between experimental and numerical results leads to some conclusions on the influence of strain localisation on the overall behaviour of shallow tunnels and on the stability of their headings. 相似文献
83.
Water and water related matters are important issues in water scarce countries like the Republic of South Africa. This is
especially true for the agricultural sector that relies heavily on the availability of water for irrigation to ensure a secure
food supply. In South Africa, present day irrigation projects rely on government subsidies and are usually large undertakings
beyond the reach of individuals or small communities. The sustainability of such large irrigation projects is still a matter
of debate. A 100 years ago a different set of rules applied. Irrigation could only be achieved by hand-dug furrows that supplied
water in relatively small quantities to small farming communities. This paper investigated such a small community, the Leeukloof
farming community in the Western Cape Province of the Republic of South Africa. For the past 93 years this community has maintained
a furrow that supplies water not only to farms bordering the Perdeberg River, which supplies the furrow with water, but also
to farms not bordering the river. The authors try to reconstruct the changes in agricultural practices brought about by the
furrow, methods of water extraction during each phase, as well as the development and role of the furrow system. The perception
by the community of the necessity of this method of water extraction from the river system is also investigated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
84.
Helen Ruth Aspaas 《GeoJournal》2004,61(3):281-289
Women in many rural areas of the US often engage in small-scale businesses as one of several avenues for contributing to household
incomes. In those geographical areas that contain a significant minority population, many of the women's businesses display
the cultural diversity of the regions in which they live. Likewise, women's roles as economic providers as well as wives and
mothers are reflected in the manner in which they operate their businesses. Candida Brush suggests that women's strategies
for operating their businesses are highly integrative because women's business decisions are intertwined with familial responsibilities,
household economic demands and desires to contribute to their communities. Hispanic and Native American women in the Four
Corners region of southwestern US and African American women in central Virginia participated in interviews in which they
responded to numerous short answer and open-ended questions about their businesses and decision-making strategies. From these
interviews an image emerges of rural minority business women who are operating their businesses at the nexus of family obligations,
economic necessities, cultural ties and with a commitment for serving their communities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
85.
John M. Logan 《Environmental Geology》2004,46(3-4):456-467
Studies of marble panels from the exterior of two buildings document the processes leading to bowing of the material. Bowing of panels is most extensive in those areas that are exposed to direct or reflected thermal energy. The thermal anisotropic behavior of calcite results in grain-boundary separation, grain sliding and microfracturing. The resulting loss of strength is one factor leading to bowing. The development of bows further reduces the panel strength as the outer portions elongate by inelastic deformation mechanisms. Laboratory experiments cycling marble samples for over 200 cycles at three temperatures up to 107°C above room conditions show similar strength losses as the natural situation. The second factor contributing to the bowing process is the release of residual elastic strain. The strain is in part stored in the marble from its geologic history, but may also be accumulated during thermal cycling due to the properties of calcite. Marble panels have been found to bow when stored outside, but not attached to any framework, indicating that the release of residual strain is a critical factor in producing the bows. 相似文献
86.
Abstract Spatial and temporal variations in radiative fluxes influence glacier mass‐balance in mountain areas. The primary goal of this study was to assess differences in solar radiation on three glacial cirques located in the Maladeta Mountain massif (Central Spanish Pyrenees), and analyse their implications on glacier development and morphology. A quantitative approach is adopted to obtain the values of solar radiation (direct, diffuse and global radiation), combining several field data parameters (measured at 55 control‐points) with the solar radiation modelling package Ecosim. The data obtained confirm that the morphologies of the glacial bodies developed in the three cirques have a good correlation with the spatial variation on solar radiation inputs, favouring also the conservation (Aneto and Coronas cirques) or total vanishing (Llosás cirque) of the glacial remnants analysed here. The study shows how strongly in this Alpine‐Mediterranean context solar radiation — firstly as a function of latitude and time of year, and locally as a function of topographic slope, aspect and shadowing — controls the mass‐balance and the spatial distribution of melting in small glaciers, having an effect on the development of their morphologies. 相似文献
87.
长江三峡GPS处理结果和应变背景场 总被引:1,自引:0,他引:1
采用BerneseGPSSoftware 4 .2对长江三峡工程诱发地震监测系统GPS监测网络 1998~ 2 0 0 3年的 6期观测数据进行了处理 ,结果表明 ,三峡库区与华南块体的水平相对运动在 0~ 3mm/a(± 0 .1~± 2 .0mm/a) ;蓄水导致的垂直形变区域主要集中在茅坪 香溪 巴东库段 ,近岸点垂直沉降的量级在 10~ 35mm左右 ,最大峰值区域香溪约 35mm(± 8.6mm) ,垂直形变沿远离库中心方向迅速衰减。采用贝塞尔双三次样条函数模型拟合该地区的应变率 ,推算各类水平应变场 ,结果表明 ,蓄水前各种应变背景在 10 -9/a~ 10 -10 /a量级。作为构造稳定地区 ,三峡库区近期因蓄水导致大规模形变 ,从而诱发中强地震的可能性不大 相似文献
88.
Abstract The rates of the accumulated and continuous displacement of solifluction lobes in the Kangchenjunga area, eastern Nepal Himalaya, were determined using glass fiber tubes and a strain probe. Ground temperature, precipitation and soil moisture were monitored at two sites, whose altitude differed by approximately 100 m, to understand the solifluction process. The average movement rate of the glass fiber tubes on a 31° slope at altitudes of 5412–5414 m a.s.l. was approximately 11 mm/year, being almost threefold greater than that observed on a 22° slope at 5322–5325 ma.s.l. There was no significant difference in the depth of displacement at these sites. The continuous displacement measurement near the ground surface at 5414 m showed permanent downslope movement from early July. Such movement may be attributed to additional moisture supply during the monsoon season. The amplitude of the displacement cycle was highest at the ground surface, and decreased to virtually zero at and below 20 cm in depth. Probable factors leading to the relatively slow rates of downslope displacement at the surface and depth at the studied altitudes are the lack of concurrence of the freeze–thaw cycles and the high moisture condition in the soil, and the low moisture retention capacity of the soil because of steep slopes and superficial desiccation. The rate of displacement may be more pronounced at altitudes above 5600 m because of the freeze–thaw cycles during the summer season. 相似文献
89.
论述了张北MS6.2、沈阳ML4.1、内蒙古ML5.9、日本北海道MS8.0、俄蒙中交界MS7.9、青海昆仑山MS8.1地震前后,锦州地震台体积式钻孔应变仪观测震前异常的变化规律。通过计算潮汐因子、振幅因子、3点线性平滑滤波残差值等方法,识别异常。结果表明,体应变异常资料与地震有一定的相关性。 相似文献
90.
关于数字化记录中前兆信号的分析 总被引:1,自引:0,他引:1
王亮 《地震地磁观测与研究》2005,(Z1)
介绍了如何用MATLAB工具软件—小波分析的基本理论对数字信号进行数字滤波,着重分析和研究了呼和浩特地震台形变观测资料出现各种信号,提出了小波分析理论对台站实际工作的重要性。 相似文献