纺锤形桩靴基础在双层地基中的穿透破坏特性试验研究
发布时间：2018-07-20 20:46
【摘要】：随着海洋石油、天然气资源的开采,自升式海洋平台的应用日趋普遍。自升式海洋平台结构的支撑体系为位于平台底部三个相互独立的桩腿,每根桩腿靠独立的纺锤形桩靴基础支撑在海床上。海洋平台的安全性能与纺锤基础的承载力有着直接的联系,因此对纺锤基础承载特性的研究受到越来越多学者的关注。海洋地基通常由砂土覆盖黏土双层地基组成。纺锤基础在此类地基中,当上部荷载超过临界值时,基础快速刺入下部黏土层,发生穿透破坏。穿透破坏发生时间很短,可引起海洋平台的倾覆,造成巨大的经济损失。因此研究纺锤形桩靴基础在此种地基形式下的贯入特性至关重要。本文在总结以往学者研究成果的基础上,进行了多组物理模型试验,研究了砂土地基、砂土覆盖黏土层地基形式中纺锤基础的贯入特性。本文开展的主要研究工作如下：(1)砂土地基模型的制备：模型试验中,砂雨法为最常用的成样方法。常规砂雨法能制备出中密、密实状态的砂样,松散砂样的制备较为困难。为获得相对密实度范围更大的砂样,利用自主研发的撒砂装置,在讨论常规影响因素如流量、落距等的基础上进一步研究了出砂头移动速度、筛网层数、出砂头移动路径等因素对砂样相对密实度的影响。通过改变这些控制因素制出了松散状态的砂样。分别通过不同大小的圆盒与CPT方法对砂样的均匀性进行检测,检测结果表明,制备出的砂样均匀性较好。分析对比不同的均匀性检测方法,圆盒检测方法简单易操作,但检测结果误差较大；CPT方法较为可靠。(2)砂土地基中的物理模型试验：在进行上砂下黏双层地基中的离心贯入试验之前,首先进行了多组1g室内与离心状态下的贯入试验。研究了砂土地基中砂土相对密实度、基础直径、基础形式对贯入特性的影响。结果表明,随着砂土相对密实度及基础直径的增大,贯入阻力增大。1g试验中观测了基础贯入过程中的土表位移变化,给出了贯入时的影响范围大小。(3)纺锤形桩靴基础在上砂下黏双层地基中易发生穿透破坏。在砂土地基贯入试验的基础上进行了多组上砂下黏双层地基中的离心模型试验。研究了基础直径、砂层的相对密实度、黏土层不排水抗剪强度、砂层相对厚度、加载方式等因素对贯入特性的影响。在此基础上探讨了应力控制加载模式下基础的刺穿破坏速率。结果表明：砂层相对厚度、基础直径、黏土层强度是影响峰值贯入应力的关键因素。应力控制加载条件下,基础发生穿透破坏的速率较大,历时较短,且黏土层强度越低,破坏时的刺穿速率越大。不同的加载方式下,基础的贯入特性曲线并无显著差异。
[Abstract]:With the exploitation of offshore oil and natural gas resources, the application of jack-up offshore platform is becoming more and more common. The supporting system of the jack-up offshore platform is three independent pile legs at the bottom of the platform, each of which is supported on the seabed by independent spindle pile boot foundation. The safety performance of offshore platforms is directly related to the bearing capacity of spindles, so more and more scholars pay attention to the research of the bearing characteristics of spindles. The ocean foundation is usually composed of sand-covered clay double-layer foundation. In this kind of foundation, when the upper load exceeds the critical value, the foundation rapidly penetrates into the lower clay layer and breaks through. The time of penetrating damage is very short, which can cause the overturn of offshore platform and cause huge economic losses. Therefore, it is very important to study the penetration characteristics of spindle-shaped pile boot foundation under this kind of foundation form. On the basis of summing up the previous research results, this paper has carried out many sets of physical model tests, and studied the penetration characteristics of the spindle foundation in the form of sandy soil foundation and sandy soil covered clay layer foundation. The main work of this paper is as follows: (1) preparation of sand soil foundation model: sand rain method is the most commonly used sampling method in model test. It is difficult to prepare loose sand samples with medium density and dense state by conventional sand rain method. In order to obtain sand samples with larger relative compactness, the sand head moving speed and the number of screen layers are further studied on the basis of discussing the conventional influencing factors, such as flow rate and drop distance, using the self-developed sand sprinkler. The influence of the moving path of sand production head on the relative compactness of sand sample. Loose sand samples are produced by changing these control factors. The uniformity of sand samples was tested by circular box and CPT method with different sizes. The results showed that the uniformity of sand samples prepared was good. By analyzing and comparing different homogeneity detection methods, the circular box detection method is simple and easy to operate, but the error of the test result is large. CPT method is more reliable. (2) physical model test in sand soil foundation: before the centrifugal penetration test of upper sand and bottom viscous double layer foundation, several groups of penetration tests were carried out in laboratory and centrifuge state. The influences of relative compactness, foundation diameter and foundation form on the penetration characteristics of sand foundation are studied. The results show that with the increase of the relative compactness of sand and the diameter of foundation, the displacement of soil surface is observed in the process of foundation penetration with the increase of penetration resistance. The influence range of penetration time is given. (3) Spindle pile shoe foundation is easy to break through in upper sand and bottom clay double layer foundation. On the basis of the penetration test of sand soil foundation, centrifuge model tests were carried out in multiple groups of upper sand and bottom clay bilayer foundation. The influence of the diameter of foundation, the relative compactness of sand layer, the undrained shear strength of clay layer, the relative thickness of sand layer and the loading mode on the penetration characteristics are studied. On this basis, the puncture failure rate of the foundation under stress-controlled loading mode is discussed. The results show that the relative thickness of sand layer, the diameter of foundation and the strength of clay layer are the key factors affecting the peak penetration stress. Under stress-controlled loading condition, the penetration rate of foundation is larger, the time is shorter, and the lower the strength of clay layer is, the higher the puncture rate is. Under different loading modes, there is no significant difference in the penetration characteristic curve of the foundation.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U674.381
本文编号：2134728
[Abstract]:With the exploitation of offshore oil and natural gas resources, the application of jack-up offshore platform is becoming more and more common. The supporting system of the jack-up offshore platform is three independent pile legs at the bottom of the platform, each of which is supported on the seabed by independent spindle pile boot foundation. The safety performance of offshore platforms is directly related to the bearing capacity of spindles, so more and more scholars pay attention to the research of the bearing characteristics of spindles. The ocean foundation is usually composed of sand-covered clay double-layer foundation. In this kind of foundation, when the upper load exceeds the critical value, the foundation rapidly penetrates into the lower clay layer and breaks through. The time of penetrating damage is very short, which can cause the overturn of offshore platform and cause huge economic losses. Therefore, it is very important to study the penetration characteristics of spindle-shaped pile boot foundation under this kind of foundation form. On the basis of summing up the previous research results, this paper has carried out many sets of physical model tests, and studied the penetration characteristics of the spindle foundation in the form of sandy soil foundation and sandy soil covered clay layer foundation. The main work of this paper is as follows: (1) preparation of sand soil foundation model: sand rain method is the most commonly used sampling method in model test. It is difficult to prepare loose sand samples with medium density and dense state by conventional sand rain method. In order to obtain sand samples with larger relative compactness, the sand head moving speed and the number of screen layers are further studied on the basis of discussing the conventional influencing factors, such as flow rate and drop distance, using the self-developed sand sprinkler. The influence of the moving path of sand production head on the relative compactness of sand sample. Loose sand samples are produced by changing these control factors. The uniformity of sand samples was tested by circular box and CPT method with different sizes. The results showed that the uniformity of sand samples prepared was good. By analyzing and comparing different homogeneity detection methods, the circular box detection method is simple and easy to operate, but the error of the test result is large. CPT method is more reliable. (2) physical model test in sand soil foundation: before the centrifugal penetration test of upper sand and bottom viscous double layer foundation, several groups of penetration tests were carried out in laboratory and centrifuge state. The influences of relative compactness, foundation diameter and foundation form on the penetration characteristics of sand foundation are studied. The results show that with the increase of the relative compactness of sand and the diameter of foundation, the displacement of soil surface is observed in the process of foundation penetration with the increase of penetration resistance. The influence range of penetration time is given. (3) Spindle pile shoe foundation is easy to break through in upper sand and bottom clay double layer foundation. On the basis of the penetration test of sand soil foundation, centrifuge model tests were carried out in multiple groups of upper sand and bottom clay bilayer foundation. The influence of the diameter of foundation, the relative compactness of sand layer, the undrained shear strength of clay layer, the relative thickness of sand layer and the loading mode on the penetration characteristics are studied. On this basis, the puncture failure rate of the foundation under stress-controlled loading mode is discussed. The results show that the relative thickness of sand layer, the diameter of foundation and the strength of clay layer are the key factors affecting the peak penetration stress. Under stress-controlled loading condition, the penetration rate of foundation is larger, the time is shorter, and the lower the strength of clay layer is, the higher the puncture rate is. Under different loading modes, there is no significant difference in the penetration characteristic curve of the foundation.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U674.381
【参考文献】
相关期刊论文 前2条
1 张波;;浅析全球海洋石油工程市场现状及发展趋势[J];石油化工管理干部学院学报;2009年02期
2 曾虹静;王忠涛;罗强;栾茂田;郭莹;;自制砂土装样设备及其控制要素分析[J];人民长江;2012年11期
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