钙质土中锚固基础设计研究

发布时间：2018-05-01 22:55

本文选题：重力锚 + 钙质砂　；参考：《天津大学》2014年硕士论文

【摘要】：对钙质土的研究始于上世纪60年代,由埃索(ESSO)石油公司在Bass Strait建设的一组石油平台,在1970年施工过程中发现桩极易贯入,在约0.67m的桩段进行了拉拔实验,结果表明其实际值只有设计值的20%,造成了重大损失,因而引起了人们的关注。国内对钙质土的研究始于上个世纪80年代,国家科委把南海钙质土的研究列为“八五”科技攻关项目,对钙质土以及建于其上的结构物的研究引起人们的重视。由于钙质土的物理力学性质特殊,一般的锚固形式不适用于这种土质条件,作为一种古老的锚固形式--重力锚却能很好的适用于此类土质条件,而在国内,重力锚研究的相对较少,目前也没有太多的资料针对钙质砂中的重力锚,有关重力锚的规范仅给出了重力锚的大体设计要求,对于重力锚承载力特性没有明确的研究。本文对钙质土(包括钙质砂以及礁灰岩)的物理力学性质进行相关的研究以及对锚固场址的土质进行了总结,讨论了不同锚固形式的使用条件,最后确定重力锚为最佳选择。通过规范给出的重力锚设计原则以及相关计算公式,可以初步确定重力锚尺寸,并计算得到重力锚的水平承载力,与有限元计算的结果进行比较,可以发现两个结果一致,进一步验证了有限元模型的可靠性,通过有限元对重力锚在水平荷载作用下破坏机理的研究,可以发现重力锚水平承载力影响因素,最终确定重力锚的最佳尺寸,然后进行局部结构的计算以及整体抗倾覆计算,最后采用有限元对串锚进行模拟与计算,得到其水平承载力特性。通过锚固场址土质条件的分析和有限元分析重力锚在水平荷载作用下破坏机理得到以下结论:(1)对钙质砂尤其是带礁灰岩层的土质条件,作为锚固形式,重力锚优于其他形式的锚,如拖曳锚、桩锚、平板锚。(2)通过有限元模拟,当土体参数不变,重力锚体积以及其他参数不变时,仅改变锚底面面积,锚的水平承载力先是随底面积面积增加而增加,随后随面积的增加而减小,并且正方形底面优于矩形底面。其原因是破坏机理不一样,底面积较小时主要是土体局部破坏,面积较大则是土体浅层破坏。除底面积外,最敏感的影响因素是锚底与土的摩擦系数,水平承载力随摩擦系数增加呈线性增加。(3)有剪力键或裙板的重力锚水平承载力明显高于平底重力锚,这是因为安装剪力键或裙板后,锚底土体破坏模式发生改变,由浅层破坏向下发展,滑动破坏面变大,承载力也就提高了。研究表明剪力键最优道数为12道。(4)通过对串锚的模拟,可以发现,串锚中的锚单元受力不同于单个锚的受力,破坏形式不同于单个重力,水平承载力不是简单的单个锚水平承载力的叠加。
[Abstract]:The research on calcareous soil began in the 1960s. A group of oil platforms constructed by Essos ESSO oil company in Bass Strait. During the construction in 1970, it was found that the piles were easy to penetrate, and the drawing experiments were carried out at about 0.67 m. The results show that the actual value is only 20% of the design value, which has caused great losses, and has attracted people's attention. The research on calcareous soil in China began in the 1980s. The research of calcareous soil in the South China Sea has been listed as the scientific and technological research project of the eighth Five-Year Plan by the State Science and Technology Commission, and the study of calcareous soil and the structure on which it is built has attracted people's attention. Because of the special physical and mechanical properties of calcareous soil, the general form of anchoring is not suitable for this kind of soil condition. As an ancient form of anchorage-gravity anchor can be well applied to this kind of soil condition, but in our country, There are few researches on gravity anchors, and there is not much data for gravity anchors in calcareous sand. The general design requirements of gravity anchors are only given in the criterion of gravity anchors, and the bearing capacity characteristics of gravity anchors are not clearly studied. In this paper, the physical and mechanical properties of calcareous soil (including calcareous sand and reef limestone) are studied and the soil quality of anchoring site is summarized. The application conditions of different anchoring forms are discussed, and the optimum choice of gravity anchor is determined. Through the design principle of gravity anchor and relevant calculation formula, the size of gravity anchor can be preliminarily determined, and the horizontal bearing capacity of gravity anchor can be calculated. Comparing with the result of finite element calculation, it can be found that the two results are consistent. The reliability of the finite element model is further verified. Through the study of the failure mechanism of the gravity anchor under horizontal load, the factors affecting the horizontal bearing capacity of the gravity anchor can be found and the optimum size of the gravity anchor can be determined. Then the local structure and the whole anti-overturning calculation are carried out. Finally, the finite element method is used to simulate and calculate the anchor, and the horizontal bearing capacity is obtained. The failure mechanism of gravity anchor under horizontal load is analyzed by means of the analysis of soil quality and finite element analysis of the anchoring site. The following conclusion is drawn: 1) the soil condition of calcareous sand, especially the limestone bed with reef, is regarded as the form of anchoring. Gravity anchors are superior to other anchors, such as towed anchors, pile anchors, flat anchors. Through finite element simulation, when soil parameters are constant, gravity anchor volume and other parameters are invariant, only the floor area of anchor is changed. The horizontal bearing capacity of the anchor increases firstly with the increase of the bottom area, then decreases with the increase of the area, and the square bottom is better than the rectangular bottom. The reason is that the failure mechanism is different, the small bottom area is mainly the local failure of soil, and the larger area is the shallow failure of soil. In addition to the bottom area, the most sensitive factor is the friction coefficient between the anchor bottom and the soil. The horizontal bearing capacity increases linearly with the increase of the friction coefficient. The horizontal bearing capacity of the gravity anchor with shear bond or skirt plate is obviously higher than that of the gravity anchor with flat bottom. This is because after installing the shear bond or skirt plate the failure mode of the soil under the anchor is changed from shallow failure to downward and the sliding failure surface becomes larger and the bearing capacity is increased. The results show that the optimum number of shear keys is 12 channels. 4) through the simulation of anchor, it is found that the force of anchor element in anchor is different from that of single anchor, and the failure form is different from that of single gravity. The horizontal bearing capacity is not a simple superposition of the horizontal bearing capacity of a single anchor.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU476

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