随机场理论在港口工程和海洋工程地基可靠度中的应用

发布时间：2018-03-18 08:24

  本文选题：可靠度理论　切入点：随机场理论　出处：《天津大学》2014年博士论文　论文类型：学位论文

【摘要】：可靠度理论是一种先进的设计理论，目前已经在结构工程安全评估中得到广泛应用，而将可靠度理论引入岩土工程稳定性分析目前还在探索中，其主要障碍在于由工程勘察获得的土性指标的点方差过大，使计算的土工结构物（边坡、结构物地基基础和挡土结构等）的失效概率过大，与结构物的实际安全程度不相符。失效概率计算结果与设计经验的差距使人们一度对可靠度理论能否应用于岩土工程设计产生怀疑。 采用随机场理论，通过考虑土体的空间相关性来探求土体物理力学指标的真方差，用其代替传统的点方差，使计算的土工结构物的失效概率在合理的范围内，这是建立岩土工程可靠度分析的关键性问题。由于建立随机场模型需要大量的相对比较均匀的土性资料，而积累这种数据的难度较大，费用较高，因此目前国内外关于这个问题的研究进展缓慢。 随着我国沿海地区经济的快速发展，许多海港码头和经济开发区都建在新近围海造陆形成的陆域。由于这些区域的开发时间比较集中，工程勘察比较密集，容易汇集大量的土层物理力学指标，因而具备了建立地基土性随机场模型的有利条件，为在土工结构物设计中采用可靠度理论打下了基础。本文针对天津滨海新区新近围海造陆区域的粘性土坡和地基，采用理论研究、现场试验和计算统计分析等手段相结合的方式，对土性指标的随机场特性进行了比较系统的研究，并讨论了其在港工地基和海洋工程结构物地基可靠度分析中的应用。对其可靠度问题进行了研究，得到了规律性较好的研究成果，使之能够方便的应用于工程实践。本文的主要研究成果和创新点如下： （1）为建立天津滨海新区新近围海造陆区域土体物理力学性质的空间随机场特性，采用了现场钻孔取样、静力触探等方法获取了大量的描述土体物理力学性质的参数。 （2）将随机场理论应用于土性指标统计中，发展了既能考虑土体互相关性又能考虑自相关性的土性指标统计方法，，使得计算结果更合理。 （3）对应用完全不相关距离求解折减函数的计算方法做出了改进，不但理论上有所突破，而且计算方法更为简洁。 （4）根据提出的土性指标统计方法，对依托工程的土性指标按随机场理论进行了分析，得到了依托工程的土性指标相关距离、完全不相关距离和方差折减函数值。 （5）对不同土性的折减函数计算结果进行分析，得到了方差折减函数的变化规律，实际工程中ω/b值对应的折减函数值可通过本文得到的折减函数变化规律插值计算，使随机场理论更方便的应用于实际工程的可靠度分析。 （6）针对港口工程中最常见的岸坡稳定问题、地基承载力问题，建立了极限状态方程，应用本文提出的方差折减方法编程计算了大量工程的失效概率，与直接应用可靠度理论计算的结果及定值设计法的安全系数进行对比，发现折减后的结果更符合实际。这些工程算例对应的可靠指标值将为以后相应规范的制定提供依据。 （7）港工地基规范中采用地基土的固结不排水强度（CU）评价地基可靠性，只能评价正常运营状态的地基可靠性，对于施工期地基稳定性应采用不固结不排水强度（UU）来评价，本文在这方面进行了有益的探讨。 （8）目前海洋工程中地基可靠度研究较少。本文以温度应力作用下海底管线稳定性分析为例，建立了理想海底管线低阶屈曲模式的极限状态方程，应用本文提出的土力学指标的方差折减方法，结合工程实例编程计算了设计管线的屈服失效概率。与直接应用可靠度理论计算的结果及定值设计法的安全系数进行对比，发现折减后的结果更符合实际。相同的方法可用于其他类似的海工结构物地基可靠度计算。
[Abstract]:Reliability theory is a kind of advanced design theory, has been widely used in structural engineering safety assessment, the reliability theory to the stability analysis of geotechnical engineering is still in the exploration, the main obstacle is that the little square survey of soil index obtained by engineering the difference is too large, the soil structure calculation (the slope structure, foundation and soil retaining structure) the failure probability is too large, the actual safety degree and structure do not match. The calculation results and design experience of failure probability of the gap so that the people were on the reliability theory can be applied to the doubt of geotechnical engineering design.
The random field theory, by considering the spatial correlation of soil to explore soil physical and mechanical indexes of true variance, variance to replace the traditional, the failure probability of soil structure is calculated in a reasonable range, which is the key to establish the reliability analysis of geotechnical engineering. Since the establishment of random field model take a relatively uniform soil data, and the accumulation of such data is difficult, high cost, so the current research progress on this issue at home and abroad slowly.
With the rapid economic development of China's coastal areas, many ports and economic development zones are built in the newly formed land reclamation area. Because of the development time is relatively concentrated, engineering intensive, easy collection soil physical and mechanical indexes of large, and has favorable conditions for the establishment of the foundation soil random field model, laid the foundation for using the reliability theory in soil structure design. According to the Binhai New Area of Tianjin reclamation area newly soil slope and foundation, the theoretical research, field test and statistical analysis of computing means a combination of random field characteristics of soil parameters are studied in the system, and discusses its application in the analysis of port engineering foundation and ocean engineering structures in the foundation. The reliability of the study, obtained a good regularity The research results can be applied to engineering practice conveniently. The main research results and innovation points of this paper are as follows:
(1) for the space establishment of Tianjin Binhai New Area recently reclaimed soil physical and mechanical properties of the regional characteristic of the random field, the field drilling sampling, CPT method to obtain the parameters describing the physical and mechanical properties of soil mass.
(2) the random field theory is applied to the statistics of soil index, and a statistical method of soil index is developed, which can consider the cross-correlation between soil and self correlation, making the calculation result more reasonable.
(3) an improvement is made for the calculation method of reducing the reduction function with complete unrelated distance, which not only has a breakthrough in theory, but also a more concise calculation method.
(4) according to the statistical method of soil index, the geotechnical index based on the engineering theory is analyzed according to the random field theory, and the correlation distance and the complete irrelevant distance and variance reduction function value are obtained based on the engineering.
(5) the results of analysis of different soil reduction function, obtained the reduction function of variance reduction function, the corresponding value can be obtained through the reduction regularity of interpolation function to calculate the Omega /b value in practical engineering, the reliability analysis of the application of random field theory is more convenient in practice engineering.
(6) according to the slope stability of the most common problems in port engineering, the bearing capacity of the foundation, established the limit state equation, this paper presents the application of variance reduction method for programming to calculate the failure probability of a large number of engineering, computing and direct application of the reliability theory and the definite value design method of safety coefficient were compared, found fold after the reduction results more realistic. The reliability index of these examples will be the future value corresponding to the corresponding specification provides the basis for the development.
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