【作者】 贾斌；

【导师】 李锦辉；

【作者基本信息】 哈尔滨工业大学 ， 土木工程， 2019， 硕士

【摘要】 如今随着石油等不可再生资源的紧缺,世界各国开始向海洋寻求资源,海上自升式钻井平台在石油开采的过程中扮演着重要的角色,为了自升式平台的重复利用,在作业结束后,其平台会将桩靴和桩腿同时上拔,然后移至下一地点继续作业。目前关于桩靴的研究主要集中于桩靴贯入下压,关于桩靴上拔的研究还相对较少。本文基于有限元方法、随机场理论和蒙特卡洛模拟建立了随机有限元模型,研究桩靴上拔的影响因素、上拔阻力的构成、上拔阻力公式的修正、空间变异性黏土对桩靴上拔的影响。本文基于大型有限元软件ABAQUS建立了桩靴上拔的有限元模型,采用修正剑桥模型,考虑了桩靴上拔的孔隙水压力与有效应力的变化,并且与离心机实验结果进行对比验证。通过编程的方法将桩靴所受的上部阻力、下部阻力、孔隙水压力、有效应力求出,对可能影响桩靴上拔的各向等压固结试验参数λ、回弹参数κ、破坏常数M、泊松比v、初始孔隙比e、上拔速率进行了参数分析,研究它们变化时对上拔阻力的影响的大小以及变化趋势。研究土体的回流情况、荷载位移曲线、应力分布云图,对水平锚的上拔公式进行修正使其可应用于桩靴上拔阻力的计算,并通过计算本文所建模型验证其具有一定可靠性。发现桩靴上拔过程中,超孔隙水压力是上拔阻力增加的主要因素,且超孔压的分布并不均匀。通过塑性指数跟剑桥模型参数的关系,建立关于塑性指数的随机场,对随机场和均质土的桩靴上拔的结果进行对比分析,研究随机土中桩靴上拔的失效机理,观察其超孔压和有效应力的变化,取代表性节点进行分析,对比随机土和均质土应力分布的异同。基于蒙特卡洛模拟对桩靴上拔进行了空间变异性研究,统计性分析空间变异性的作用,对上拔阻力的最大值和最小值进行分析,研究上拔阻力、上部阻力、下部阻力的分布和拟合函数,并用95%置信水平的卡方检验值进行卡方检验。黏土的空间变异性对桩靴上拔阻力有较大影响,较强的空间变异性将降低上拔阻力。更多还原

【Abstract】 Now with the shortage of non-renewable resources,like oil,the world began to ask the ocean for resources.The offshore jack-up drilling platform in the process of oil exploration plays an important role.For the sake of the repeated use of the jack-up platform after the operation,the jack-up drilling platform will pull the spudcan and the leg,and it will then continue its work in the next site.At present,the research of the spudcan mainly focuses on the penetration of spudcan,while there are relatively few studies on the extraction of spudcan.Based on the finite element method,random field theory and Monte Carlo simulation,the random finite element model is established in this paper to study the factors affecting the uplift of spudcan,the composition of uplift resistance,the modification of uplift resistance formula,and the influence of spatial variability on the uplift of spudcan.In this paper,based on ABAQUS,a large finite element software,a finite element model for the uplift of spudcan was established.The change of pore water pressure and effective stress in the uplift of spudcan was considered by using the Cambridge model,and the results were compared and verified with centrifuge experiment results.By the method of programming,we calculate upper resistance,lower resistance,pore water pressure.We carried some parameter studies and analyze the influence of them,such as the compression index λ,swelling index κ,stress ration M,Poisson’s ratio v,the initial void ratio e and pulling rate.The backflow of soil,load displacement curve and stress distribution cloud diagram were also studied,and the uplift formula of horizontal anchor was modified to make it applicable to the calculation of spudcan.The model established in this paper was used to verify its reliability.It was found that the excess pore water pressure was the main factor for the increase of the uplift resistance during the uplift of spudcan,and the distribution of the excess pore pressure was not uniform.We used the relationship between the Cambridge model parameters and the plastic index to build the random field of plasticity index,and compared the results of homogeneous soil with random soil.The failure mechanism of extraction were also studied.Some representative nodes were chose to observe the change of excess pore pressure and effective stress and compared the similarities and differences between random phenomenon of soil and the homogeneous soil.Based on Monte Carlo simulation,we carried out on the spatial variability of the spudcan and studied of the influence of the spatial variability by statistical analysis.The reason of maximum and the minimum of pulling resistance were analyzed.We studied the distribution of resistance,upper resistance,lower resistance and tried to find their fitting functions.We did chi-square tests on them with a 95% confidence level.The spatial variability of clay has a great influence on the uplift resistance of spudcan.更多还原