海洋平台大直径超长桩动态沉桩阻力及溜桩机制研究

发布时间：2018-06-25 20:06

本文选题：大直径超长桩 + 溜桩　；参考：《天津大学》2015年博士论文

【摘要】：随着海洋开发向较深水域拓展,海上采油平台需要采用大直径(直径2m以上)、超长(入土深度100m以上)的桩基。由于桩和锤重量很大,在沉桩过程中经常会发生桩体无需锤击而自由下沉的现象,称为溜桩。溜桩的发生轻则会冲断定位的钢丝绳,使得桩和锤损坏;重则造成桩锤滑落大海,或断桩等重大事故。目前国内外对这方面的研究还比较少。本文在研究溜桩机理的基础上,以极限平衡理论、能量守恒理论、扩孔理论等理论为依据,提出了判断沉桩过程中产生溜桩的条件和判断溜桩区间的计算方法。理论计算的准确性取决于地基土在沉桩过程中的性态参数取值的合理性,为此本文通过室内试验和现场实测数据分析,对沉桩过程中地基土体中孔隙水压力的发展及其对沉桩阻力的影响、桩-土界面土体的疲劳特性等问题进行了较为深入的研究,为溜桩分析的参数选取提供了依据。同时,对于沉桩过程中发生过溜桩现象的桩基的承载力的评估是工程界最关心的问题,本文通过对打桩过程中和打桩后地基土体中的超孔隙水压力的产生和消散的规律的研究,从而分析了桩基承载力的时效性。本文的主要研究内容及特色可概括如下:1、本文综合动态极限平衡原理和利用CAPWAP打桩分析方法对动测实验数据进行反分析,揭示了溜桩现象发生的机理。在研究溜桩机理的基础上,以极限平衡理论、能量守恒理论、扩孔理论等理论为依据,提出了判断沉桩过程中产生溜桩的条件和判断溜桩区间的计算方法。2、桩基贯入过程中沉桩阻力的计算对溜桩区间判断有着极为重要的作用。目前普遍采用的API规范提出的土阻力计算方法,用于设计阶段的桩基承载力计算则偏于安全,但是用于评估溜桩区间计算时,则误差很大且偏于危险。本文提出的方法考虑了边载效应和动力效应;分别针对无黏性土与黏土提出了合理的的静桩端阻力与静桩侧摩阻力计算方法;引入了灵敏度概念提出无黏性土与黏性土的动侧摩阻力折减因子,因此计算的溜桩区间更为合理。3、静力触探原位测试方法是获得土性参数较为准确的方法。根据大直径超长桩的沉桩特性,提出了根据静力触探实测数据分析动桩端阻力与动桩侧摩阻力的方法;提出计算桩端阻力的影响范围与桩侧摩阻力折减因子沿桩身的的分布;结合有限元分析比较黏性土中不同锥头阻力系数的计算结果;据此提出了适合黏性土端阻力计算的锥头阻力系数,建立了应用原位测试数据计算沉桩阻力的方法。4、超长桩桩侧摩阻力对桩基承载力的贡献是主要的。通过研制大型直剪仪来研究桩与土体的摩擦特性,总结不同颗粒粒径砂土与软黏土在不同密度下的糙度变化,提出工程中适合的使用值;由于桩身下沉过程类似一个持续剪切的过程,应用环剪仪对典型砂土、粉质黏土与黏土进行大变形残余强度的试验,并分析了不同剪切速度、循环荷载与黏粒含量等因素对残余强度的影响。对桩土的摩擦特性做了较为充分的总结。5、国内外针对打桩过程中产生超孔压对桩侧摩阻力的影响的研究较少,而大直径超长桩沉桩过程中桩侧摩阻力的大幅度折减与超孔隙数压力的产生有着密切的关系。本文将现场孔压监测试验数据与应用剑桥模型的扩孔理论相结合,建立了打桩过程中产生和消散的规律,据此研究了桩基承载力的时效性。6、以荔湾3-1导管架平台工程与丽水项目为例,应用提出的理论与方法对平台桩基的沉桩过程进行了分析研究,计算得到的自由入泥深度与溜桩区间与实测值吻合。
[Abstract]:With the development of marine development to the deeper waters, the offshore oil production platform needs to adopt the pile foundation with large diameter (more than 2m diameter) and super length (above the depth of 100m). Due to the large weight of the pile and the hammer, the pile body is often free from sinking without hammering during the pile sinking process. It is called the slide pile. In this paper, based on the theory of the limit equilibrium, the conservation of energy and the theory of reaming, the condition of judging the pile driving in the process of pile sinking is put forward. The accuracy of theoretical calculation depends on the reasonableness of the values of the parameters of the ground soil in the pile sinking process. Therefore, the development of the pore water pressure in the foundation soil and the influence on the resistance of the pile in the foundation soil and the fatigue of the soil of the pile soil interface in the process of pile sinking are analyzed by the indoor test and the field measured data. In addition, the evaluation of the bearing capacity of pile foundation in the process of pile sinking is the most important problem in the engineering field. The study of the regularity of the dispersion has been carried out to analyze the timeliness of the bearing capacity of the pile foundation. The main contents and characteristics of this paper can be summarized as follows: 1, in this paper, the principle of dynamic limit equilibrium and the reverse analysis of the dynamic test data by using the CAPWAP pile analysis method have been carried out to reveal the mechanism of the occurrence of the slide pile. Based on the theory of limit equilibrium, conservation of energy and the theory of enlargement, the condition of judging the pile driving in the process of pile sinking and the calculation method of calculating the interval of the slide pile.2 are put forward. The calculation of the resistance of the sinking pile in the process of the penetration of the pile foundation is very important for the judgement of the interval of the slide pile. The soil resistance proposed by the commonly used API standard is currently used. Calculation method, the calculation of the bearing capacity of the pile foundation used in the design stage is partial to safety, but the error is very large and dangerous when it is used to evaluate the interval calculation of the slide pile. The method proposed in this paper takes the side effect and the dynamic effect into consideration, and the calculation side of the static pile end resistance and the side friction resistance of the static pile is put forward respectively for the unviscous soil and clay. With the introduction of the concept of sensitivity, the dynamic side friction reduction factor of cohesionless soil and cohesive soil is introduced, so the calculation of the sliding pile section is more reasonable.3. The method of static cone penetration in situ test is a more accurate method to obtain soil parameters. According to the pile characteristics of the large diameter and super long pile, the analysis of the pile end according to the measured data of static cone penetration is proposed. The method of resistance and frictional resistance of pile side is put forward, the influence range of pile end resistance and the distribution of pile side friction reduction factor along the pile body are calculated, and the calculation results of the resistance coefficient of different cone heads in clay soil are compared with the finite element analysis. Accordingly, the resistance coefficient of the cone head suitable for the viscous soil end resistance meter is put forward, and the application in situ measurement is established. The test data to calculate the resistance of pile sinking.4, the contribution of the lateral friction resistance to the bearing capacity of the pile foundation is main. Through the development of a large direct shear apparatus, the friction characteristics of pile and soil are studied, and the roughness changes of different particle size sand soil and soft clay under different density are summarized, and the suitable use value in the project is put forward, because the pile body is sinking over. The process is similar to a continuous shear process. The residual strength of typical sand, silty clay and clay is tested by the ring shear apparatus, and the effects of different shear velocity, cyclic loading and clay content on the residual strength are analyzed. The friction characteristics of the pile and soil are fully summarized.5, the pile driving process at home and abroad is made. There is little research on the effect of the excess pore pressure on the side friction resistance of the pile, and the large reduction of the friction resistance in the large diameter and super long pile is closely related to the generation of the excess pore number pressure. In this paper, the field pressure monitoring test data is combined with the theory of the expansion of the Cambridge model to establish the pile driving process. According to the law and the law of dissipation, the aging.6 of the bearing capacity of the pile foundation is studied. Taking the Liwan 3-1 jacket platform project and the Lishui project as an example, the pile sinking process of the platform pile foundation is analyzed and studied by the proposed theory and method. The calculated free mud depth is consistent with the measured value.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P751;TE951;TU473.1

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