【作者】 刘润；

【导师】 闫澍旺；

【作者基本信息】 天津大学 ， 岩土工程， 2001， 博士

【摘要】 近年来,随着海洋石油事业的迅速发展,作为海上油气开采的重要设施——海洋平台不断兴建,海洋平台工程是近海油气开发中至关重要的环节。 目前海上平台的结构设计采用了以可靠度理论为基础的设计方法,但在地基基础设计方面的研究工作进展较小,使得海工结构物的结构设计方法和地基设计方法很不协调,因此运用合理的、系统的、可靠度分析方法开发出适用于我国海域的荷载与抗力系数,是我国海洋平台设计面临的重要课题。 对土性参数进行归档整理以确定其统计特性及概型分布是可靠度分析和建立设计表达式的前提。本论文在收集和整理渤海SZ36—1油田现有的勘察钻孔资料的基础上,建立起包括环境荷载、钻孔信息、土性指标及力学指标的数据库管理系统,这一系统不仅可快速而准确的完成对钻孔资料的查询与数据维护,而且可对土性参数进行统计运算和概型分布检验,从而为地基可靠度分析打下了坚实的基础。 岩土结构物通常占有相当的范围,所以研究空间的平均特性是最重要。但土性指标的试验数据往往是对钻孔取样而言的,试样的尺寸远远小于土层的某一范围土体的体积,由此得到的土性参数属于“点特性”。本文首先根据数据库提供的统计分析结果建立了随机场模型,实现了由“点特性”到“空间平均特性”的过渡,而后根据随机场理论对SZ36—1油田的土层进行分析,得出了相应的相关函数、相关距离和方差折减函数。 可靠度分析的关键是确定稳定性的计算模式。论文在分析数据资料并结合以往设计经验的基础上,建立起海工结构物浅基础的稳定计算模式、桩基础的竖向承载力计算模式,对SZ36—1油田已建和拟建的固定式、自升式平台的地基进行可靠度分析,从可靠度角度对其稳定性进行评价;对渤海中已建和拟建的桩基工程进行可靠度分析,从可靠度角度对其稳定性进行评价,检验API规范规定的桩基承载力分项系数对渤海油田桩基设计的适用性,并给出推荐值。 在工程实际中,往往存在着很多不定因素,致使结构的响应是随机的。这样,在可靠度分析中面临的不再是确定性的而是不确定性的问题,可靠度分析就是综合各个变量的不确定性来评价结构的承载力。对于大型或较复杂的结构,往往必须依赖于数值解法,随机有限元法将成为有力的工具。论文编制了随机有限元计算程序,分析在工作应力状态下地基土中的应力分布、变形情况及其各自变异性的分布规律,进而计算出地基中各点的可靠度指标和安全系数。为了进一步得到地基的整体可靠度指标,论文提出了寻找地基失效模式的方法,根据地基中可能产生的滑动线及计算的点可靠度指标计算地基的整体可靠度。 在以上分析的基础上,对其它海域工程的地基可靠度分析方法提出了指导性的建议,为推动我国海洋工程的地基基础实现用可靠度方法进行设计的进程做出了贡献。更多还原

【Abstract】 With the rapid development of petroleum industry, platforms that take as the importance facilities, have been building continuously. The platform plays an important role in investigating, exploiting, producing, transporting and storing oil in offshore engineering.The designing method for upper structure of platform is based on the reliability theory. It has been found that the same procedure may not be easy to be adopted in foundation designing. This leads to an incoordination between the methodologies of designing upper structure and foundation of a platform. As a result, more attentions should be paid on studying the foundation design method of offshore structures. Modifications of these factors or development of new factors suitable for a different type of structural framing should be based on a rational system reliability analysis. In this thesis, the following work has been involved:1. When the reliability method is applied in foundation design, the statistic characteristics of subsoil have to be known. In this thesis, a database management system has been established, in order to manage and analyze the data of the geotechnical properties of foundation soils. This database includes almost all the borehole logs and properties of the soils of SZ36-1 Oil Field.2. Based on the database, the stationarity and ergodicity of a soil profile in SZ36-1 Oil Field have been examined and a random field modeling has been established. The correlation function, correlation distance and variation reduction function of SZ36-1 Oil Field have been simulated.3. A calculating model for shallow foundations has been established, on the basis of the established database and design experiences. As an example, reliability analysis for a foundation of self-raising platform has been performed. The calculated partial factors have been compared with those recommended by the API Criterion.4. In order to analyze the reliability of the shallow foundation of ocean structures, two-dimensional perturbation stochastic FEM(PSFEM) has been developed. As an example, a practical project, Bohai-6, has been calculated with this program. The reliability indexes calculated by PSFEM changing with safety factors have been compared with those calculated with the limit equilibrium method recommended by the Criterion for foundation design.The developed method may give a guidance for how to introduce the reliability theory in designing soil foundations of ocean structures.更多还原