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561.
Suction caissons are widely used to support offshore fixed platforms in coastal areas. The loadings transferred to suction caissons include the eccentric lateral force induced by waves and self weight of the platform structure. However, under this kind of combined loading conditions, the failure mechanism of caissons with shallow embedment depths is quite different from conventional deep foundations or onshore shallow footings. The behaviour of caissons subjected to combined loadings may be described with the "failure locus" in force resultant spaces. Here the failure loci of smooth caissons are studied by use of finite element approach, with the embedment ratio of caissons varying in the range of 0.25~1.0 and eccentricity ratio of horizontal loadings in 0~10. The platform settlement and tilt limits are involved into determination of failure loci, thus the platforms can avoid significant displacements for the combined loadings located inside the failure locus. Three families of loading paths are used to map out the locus. It is found that the shape of failure loci depends on 3 non-dimensional parameters, and the failure locus of a given caisson changes gradually from the elliptical curve to hooked curve with increasing shear strength of soil. The lateral capacity of short caissons may be enhanced by vertical forces, compared with the maximum lateral capacity of long caissons occurring at the vertical force being zero. The critical embedment ratios partitioning elliptical and hooked loci are proposed. 相似文献
562.
Thermal and hydrothermal effects of Triassic–Liassic basalt flow deposition on sedimentary series of the Argana Basin are responsible for major modifications in detrital clays, until 20 m in depth. It expressed by transformation of detrital smectite to corrensite and moreover to chlorite, and by increasing illite crystallinity. On the 2 m of sediments located immediately under the flow, magnesium-rich hydrothermal fluids have caused precipitation of new mineral phases. To cite this article: L. Daoudi, J.-L. Pot de Vin, C. R. Geoscience 334 (2002) 463–468. 相似文献
563.
Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays 总被引:7,自引:0,他引:7
1 .IntroductionCoastalstructuresoftenencountersettlementandstabilityproblemsofsoftmarinefoundation (Liuetal.,1 999;Zhouetal.,2 0 0 0 ;Liuetal.,2 0 0 3) .Manyresearchershaveillustratedthatnaturalmarineclaysaregenerallysubjectedtotheeffectsofsoilstructureduringtheirdepositionalandpost depositionalprocesses (Zhangetal.,1 995;Hongetal.,2 0 0 3a ;2 0 0 3b) .Thesoilstructureofnat uralmarineclaysiseasilydamagedduringsamplingandhandlingbecausenaturalmarineclaysgeneral lyhavehighwatercontentandlowsti… 相似文献
564.
为了阐明黏土方法治理有害赤潮的生态环境效应,研究了有机改性黏土对海水中营养盐和溶解氧、化学耗氧量、pH等主要水质因子的影响。结果表明,有机改性黏土对营养盐,尤其是磷酸盐有一定的吸附作用,吸附量随水体中磷酸盐浓度的增加而增大,不同有机改性黏土对海水中磷酸盐的吸附能力为:有机改性黏土Ⅰ〉有机改性黏土Ⅱ〉有机改性黏土Ⅲ。通过有机改性黏土对磷酸盐的吸附再释放作用研究,进一步探讨了磷酸盐释放作用对赤潮异弯藻(Heterosigma akashiwo)、东海原甲藻(Prorocentrum donghaiense)等赤潮生物生长的影响。实验结果表明,经过有机改性的黏土有利于提高其对磷酸盐的吸附能力,降低对磷酸盐的解吸率,缓解海水富营养化程度,虽然少量被吸附的磷酸盐能缓慢释放,但仍不足以维持赤潮生物的正常生长。同时利用有机改性黏土治理赤潮能显著改善溶解氧、pH、化学耗氧量等水质指标,有利于治理赤潮后的环境修复。 相似文献
565.
566.
The idea of modified water masses is introduced and a cluster analysis is used for determining the boundary of modified water masses and its variety in the shallow water area of the Huanghai Sea (Yellow Sea) and the East China Sea. According to the specified standards to make the cluster, we have determined the number and boundary of the water masses and the mixed zones.The results obtained by the cluster method show that there are eight modified water masses in this area. According to the relative index of temperature and salinity,the modified water masses are divided into nine different characteristic parts. The water, masses may also be divided into three salinity types. On the TS-Diagram, the points concerning temperature and safinity of different modified mater masses are distributed around a curve, from which the characteristics of gradual modification may be embodied. The variation ranges of different modified water masses are all large, explaining the intensive modification of water masses in th 相似文献
567.
On the basis of the current measurements at 200,500 and 800 m from moored current meters with the time series data from March 17 to April 15 at the mooring station (20°49′57″N, 120°48′ 12″E) and the hydrographic data obtained in the Luzon Strait during the spring of 2002 cruise, the circulation in the investigated 相似文献
568.
569.
中国北方沙尘暴与气象要素关系的初步研究 总被引:4,自引:1,他引:4
为研究沙尘暴形成机理以及各气象要素对沙尘暴的作用,利用1954~2000年我国北方地区7个台站的月降水量、大风日数、月平均气温和沙尘暴日数资料,以相关性分析为基础,采用了建立大风修正指数,线性拟合,滑动相关的方法,深入探讨其相关关系。结果表明沙尘暴与同期降水呈负相关,而与前一年降水的相关不明显,但有极值对应;与大风和大风修正指数呈明显正相关,并从结果比较可知大风修正指数可以很好地反映沙尘暴的发生规律;沙尘暴日数与前冬气温呈负相关,但是减去趋势后负相关消失,这反映了两者的相关关系主要是趋势相关;计算20年滑动相关,由6个台站一致的变化趋势得出结论:相关值的大小与下垫面的荒漠化程度有很大关系。 相似文献
570.
A Modified approach for calculating dynamic shear modulus of stiff specimens by resonant column tests 总被引:1,自引:0,他引:1
1 Introduction Study of the shear modulus to represent the static and dynamic properties of geotechnical materials is a basic topic in the geotechnical engineering and many researchers (Hardin and Black, 1966; Zhang and Li, 2003; Richard and Richard, 1988; Yuan et al, 2000; Soo et al, 1995) have investigated this phenomenon. The resonant column device provides a powerful tool for testing the shear modulus and damping ratio of the soil-like materials. In 1984, the ?rst resonant column device… 相似文献