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421.
422.
China is arguably one of the countries where the most tunneling and underground projects are being performed. Recently in China, it has often been necessary to construct tunnels under many types of conditions and to develop new techniques. Currently, some advanced construction techniques cannot be appropriately applied to different types of underground conditions, and many traditional methods are still often used. However, because of the progress in tunnel boring machines (TBM), innovations are required for the construction method. This article introduces the current situation of TBM both in western countries and in China, and examines the future of TBM in China. 相似文献
423.
李凤鲁 《中国海洋大学学报(自然科学版)》1987,(2)
本文连续报道南海西沙群岛星虫类的第三部分即石管星虫属(Lithacrosiphon)。本属系1902年由Shipley氏订立。据文献记载属中的种均分布于热带海,通常钻孔于珊瑚石中。作者仅鉴定了马岛石管星虫(Lithac-rosiphon maldivensis Shipley)一种。本属在中国海是首次记载。 相似文献
424.
Lêda Maria Fraga Moacir Jose Buenano Macambira Roberto DallAgnol Joo Batista Sena Costa 《Journal of South American Earth Sciences》2009,27(4):247-257
Age and origin of the charnockitic rocks of the central part of the Guyana Shield have been a matter of discussion. These rocks have been interpreted either as Transamazonian granulites metamorphosed around 2.02 Ga or as 1.56 Ga old igneous charnockites. Recently, most of the Roraima charnockitic rocks have been recognized as igneous rocks and included into the Serra da Prata Suite (SPS). Five Pb–Pb single-zircon evaporation ages were obtained for samples representative of different facies of the SPS and these constrained the age of the charnockitic magmatism between 1943 ± 5 Ma and 1933 ± 2 Ma. This charnockitic magmatism may be related to a post-collisional setting after the evolution of the Cauarane-Coeroeni Belt (~2.00 Ga), or may represent a post-collisional (or intracontinental?) magmatism related to orogenic activities along the plate margins around 1.95–1.94 Ga. 相似文献
425.
The reinterpretation of the time and deep sections along CDP Profile 1632 revealed different previously unknown structural features: (1) a buried bar and a Late Pliocene regional unconformity, the Bol’sheretsk and Lebed subaerial shield volcanoes, and the Koni-P’yagina and Magadan megadikes at its level; (2) morphological evidence for the nappe structure of the Okhotsk Arch (homoclinal thrust slices of the acoustic basement with ramp half-grabens in the frontal part and a pull-apart zone with a solitary diapir in the Kol’skii Trough, which divides the arch into two allochthonous megablocks with opposite vergence of their thrusts), which is related to a divergent sheet decollement, probably, at the M discontinuity. 相似文献
426.
盾构施工仿真及其相邻影响的数值分析 总被引:32,自引:5,他引:27
针对地下结构传统的简化计算方法的不足,采用适应性较强的有限元法,对盾构隧道施工过程中的施工步骤、管片与土层接触面以及开挖过程中地应力释放等多方面进行了有限元模拟,并且利用同济曙光软件计算和分析了盾构施工对临近构筑物的影响以及地层的变化情况,从计算结果来看是较为满意的。能够为盾构隧道衬砌的设计和施工提供有益的参考。 相似文献
427.
The volcano-sedimentary succession around Wadi Zaghra in Sinai, at the northernmost segment of the Arabian Nubian Shield, comprises volcanic rocks interbedded with rather immature sediments. The succession is dominated by intermediate to silicic volcanics of medium-to high-K calc-alkaline affinity. It is divided into two units, the lower unit includes intermediate rocks and dacites interbedded with graywackes, semi-pelites and pelites and topped by polymict conglomerates. This unit is subjected to folding and regional metamorphism(up to garnet zone) and is intruded by quartz diorite-granodiorite inducing, locally, low-pressure contact thermal metamorphism. The unmetamorphosed upper unit encompasses acid volcanics intercalated with litharenite, sublitharenite and minor arenite. The rhyolites of this unit pertain to the highly fractionated granites and are characterized by an agpaitic index(NK/A) ranging from 0.87 to 0.96. They may reflect either extensive interaction of subduction-related magmas with the continental crust or a change in the tectonic regime. The present lithological and geochemical characteristics of the studied sediments together with available zircon ages indicate rather distal provenance of their detritus. This detritus comprises fluvial-alluvial sediments accumulated in the intermontane basins, which are half-grabens or tilted fault blocks. The tectonic setting of the depositional basins is active continental margin and continental island arcs. Geochemical patterns of the Zaghra volcano-sedimentary succession indicate their correlation with the Dokhan Volcanics-Hammamat Clastics sequence of the Eastern Desert of Egypt. Also, the Zaghra volcanics display geochemical similarities with those exposed in Sinai, at the Rutig, Ferani and Iqna Shar'a areas. The Zaghra succession is dated as Ediacaran but is not related either to the ensimatic island arc assemblage or to the rift-related assemblage formed during the early stages of the break-up of Rodinia as previously thought. 相似文献
428.
《地学前缘(英文版)》2019,10(6):1981-1992
Late Neoproterozoic adakitic magmatism within the Eastern Arabian Nubian Shield has been dated at633.2±9.0 Ma(2σ).These magnas intrude the forearc Ad Dawadimi Basin,which is composed of metapelitic schists and greywacke along with ophiolitic melanges of boninitic affinity which underwent inversion and deformation by~620 Ma.This adakitic magmatism,while intruding parts of the Ad Dawadimi Basin,predates this deformation,but is possibly coincident with basin closure.As adakitic magmatism requires melting of an amphibolite or eclogitic source,empirical and experimental constraints require anomalously hot supra-subduction zone mantle.Considering that this magmatism immediately predates basin inversion,these magmas possibly pinpoint the timing of the slab breaking,marking the terminal stages of arc magmatism,terrane accretion and the influx of hot oceanic asthenospheric mantle.This influx of hot asthenospheric mantle may also be responsible for postcolltsional A-type magmatism. 相似文献
429.
皖南旅游资源空间结构分析 总被引:75,自引:1,他引:74
旅游资源是旅游区域空间竞争的物质依托,其空间结构影响旅游区域的空间竞争。该文运用最近邻指数R、β指数、γ指数、通达度指数、平均径路长、紧密度指数6种分析技术,对皖南旅游资源的空间分布形态以J支空间网络结构的连接性、通达性等进行了全面的分析,认为目前皖南旅游区内各景区点之间的空间联系较弱,加强和加快构建皖南旅游区旅游交通网络,提高旅游交通网络结构的连接性、通达性水平,是皖南旅游区面临的一个重要问题,紧密度指数C=0.74表明,较为紧凑的区域形态为改善旅游交通网络结构的性能提供了较好的基础。 相似文献
430.
两种坐标系转换计算方法的比较 总被引:1,自引:0,他引:1
出于对目前常用的两种坐标系转换模型的学习和理解,对原本适合于小角度坐标转换的布尔莎模型进行了拓展,使其适合于任意角度坐标转换。将改进后的7参数布尔莎模型与13参数的大角度模型,结合盾构三棱镜法解算盾首盾尾坐标的工程实例,通过大旋转角和小旋转角两组数据以及编程实现两者的对比,并得出了结论。 相似文献