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南沙群岛珊瑚礁工程地质特性及大型工程建设可行性研究

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I 摘要 南沙群岛位于我国南海最南的海域,蕴藏着极其丰富的石油、天然气及生物 资源。在保卫南沙、开发南沙海洋资源的过程中,将不可避免的遇到珊瑚礁工程 地质问题。珊瑚礁是一种工程性质较为特殊的岩土类型。为了开发海洋资源,指 导珊瑚礁工程建设,本文综合分析了南沙群岛区域工程地质特征、珊瑚礁地形地 貌、海洋水动力环境、沉积物特征等资料,从工程地质角度对珊瑚礁各地貌单元 的工程适宜性进行了评价,对礁灰岩和钙质砂进行了室内试验分析,主要研究内 容和结论如下: 1、分析了珊瑚礁的区域工程地质环境、海洋水动力条件、地形地貌特征、 岩土体条件等因素对岛礁工程建设的影响,对珊瑚礁的礁体类型进行了划分,结 论认为可干出的环礁和台礁比较适合各类工程建设,其中环礁的礁坪是理想的工 程建设场所。 2、根据珊瑚礁地貌环境特征将珊瑚礁划分为 6 个地貌相带,深入分析了各 个地貌相带的环境特征以及工程地质性质,并将礁体浅层碎屑堆积土体划分为四 个结构类型,对各个地貌单元进行了工程适宜性评价。 3、对南沙群岛渚碧礁的礁灰岩进行了室内的声波测试、巴西劈裂试验、单 轴和三轴压缩试验,分析了礁灰岩的声学特性和密度、岩石孔隙率的关系,研究 了礁灰岩的强度特性及变形破坏特征。 4、通过8个钙质砂的室内载荷试验,研究了不同相对密实度、不同板型、不 同含水状态下钙质砂地基的承载力和变形特性,对钙质砂地基的荷载传播规律进 行了测试和研究,对比分析了钙质砂和石英砂的承载力和变形特性的差异,并分 析了这种差异产生的原因。 5、综合分析珊瑚礁礁坪的工程地质环境、岩土体结构、礁灰岩和钙质砂的 力学性质及强度后认为,环礁的礁坪完全适合修筑人工岛和机场跑道以及各类其 他工程设施,礁灰岩和钙质砂同时也是良好的建筑材料,可就地取材用于岛礁的 工程建设。 6、研究了利用钙质砂填筑飞机跑道的可行性,并通过计算分析表明,钙质 砂地基经过碾压后,如果变形模量达到 25MPa 以上,则沉降量有望达到小于 150mm 的要求,否则需要采取加固措施。中国科学院博士学位报告 II 最后,对本文的研究成果进行了总结,并对课题今后的研究进行了展望。 关键词:南沙群岛,珊瑚礁,钙质砂,礁灰岩,工程地质,声波测试ABSTRACT III Study on Engineering Geological Properties of Coral reefs and Feasibility of Large Project Construction on Nansha Islands Wang Xinzhi (Geotechnical Engineering) Directed by Prof. Wang Ren ABSTRACT Nansha Islands which locate on the southernmost South China Sea hold in store abundant oil, natural gas and biology resources. It’s inevitable to deal with engineering geology of coral reefs when safeguarding and developing Nansha Islands. Coral reef is a kind of peculiar geological body which has special engineering characteristics. In order to empolder ocean resources and instruct engineering construction, this thesis synthetically analyzed regional geology, terrain, deposit sediments, hydrology, and sediments of coral reefs, have systemically studied the mechanical characteristics of calcareous sand and coral reef through indoor tests. 1. Many factors including regional engineering geology environment, hydrodynamic environment, terrain, physiognomy have been studied to evaluate their influence to coral reef engineering. It’s considered that atoll reefs and table reefs are suitable for engineering construction and the reef flat on atolls is most perfect. 2、Geomorphology of coral reefs was divided into 6 phase belts and the environment characteristics and engineering geology were thoroughly studied. The chipping deposit of superficial layer of coral reefs was divided into four kind of structure type and the feasibility for engineering construction of each zone was estimated. 3、The relationship between wave properties and density , porosity about reef limestone which is sampling from Zhubi Jiao in Nansha Islands are studied. And strength characteristics and failure pattern of reef limestone are analyzed through Brazil splitting test, uniaxial compressive strength, triaxial compressive strength. 4、8 indoor plate load test of calcareous sand have been done to study bearing capacity and deformation characteristics of calcareous sand ground about different relative compaction, different load plates, dry and saturated sand as well as quartz sand. The difference about bearing capacity and deformation characteristics between calcareous sand and quartz sand is analyzed. 5、It’s considered that the reef flat of atoll reefs is suitable to build man-made island, aerodrome runway and other structures after studying the engineering environment of reef flat , mechanical property of reef limestone and calcareous sand which are also good architectural materials. 6、The feasibility of constructing runway of using calcareous sand was studied. The settlement of calcareous sand will be reduced to less than 150mm if deformation modulus exceeds 25MPa after rolling. Otherwise, the calcareous sand ground should be reinforced. At last, the achievements of the research in this paper were concluded, and the direction of this thesis was also presented based on the shortcoming of the author’s research. Key words: Nansha Islands, coral reef, calcareous sand, reef limestone, engineering geology, wave tes中国科学院博士学位报告 IV 目 录 第一章 绪 论 ························································································1 1.1 研究目的及意义...........................................................................1 1.2 珊瑚礁工程地质的研究现状.......................................................3 1.3 珊瑚礁大型工程建设的现状.....................................................12 1.4 本文主要研究内容.....................................................................14 第二章 南沙群岛珊瑚礁地质概况······················································16 2.1 南沙群岛珊瑚礁概况.................................................................16 2.2 南沙群岛区域地质构造.............................................................25 2.3 南沙群岛区域地形地貌特征.....................................................31 2.4 南沙群岛区域地层特征.............................................................37 2.5 南沙群岛区域海洋动力环境特征.............................................39 2.6 南沙群岛区域气候特征.............................................................41 2.7 本章小节.....................................................................................44 第三章 珊瑚礁工程地质特性······························································45 3.1 珊瑚礁体工程地质分带.............................................................45 3.2 珊瑚礁地层岩性特征.................................................................50 3.3 珊瑚礁岩体结构特征.................................................................57 3.4 本章小节.....................................................................................59 第四章 礁灰岩的力学性质··································································60 4.1 礁灰岩的结构类型.....................................................................61 4.2 礁灰岩的声波特性.....................................................................64 4.3 礁灰岩单轴抗压强度.................................................................71 4.4 礁灰岩抗拉强度.........................................................................74 4.5 礁灰岩三轴压缩强度.................................................................76 4.6 本章小节.....................................................................................77 第五章 钙质砂的力学特性··································································79 5.1 钙质砂的物性参数.....................................................................80 5.2 钙质砂基本力学性质.................................................................83目 录 V 5.3 钙质砂室内载荷试验.................................................................85 5.4 本章小节.....................................................................................95 第六章 珊瑚礁大型工程建设可行性分析··········································96 6.1 珊瑚礁机场建设选址.................................................................96 6.2 礁体稳定性分析.........................................................................99 6.3 跑道土基稳定性及沉降分析...................................................100 6.4 本章小节...................................................................................107 第七章 主要结论与展望····································································109 7.1 主要结论...................................................................................109 7.2 展 望........................................................................................111