Research On Bearing Capacity Of Spud Foundation For Jack-up Self-elevating Drilling Platform

Jack-up self-elevating drilling platform is a kind of mobile ocean engineering vessel which can lift itself.Because jack-up self-elevating drilling platforms have good performances,strong functions,and good versatility,so in the recent decades,they have got widely used in offshore oil engineering,such as platform construction and maintenance,the pipeline laying and repairing,the oil drilling and so on.Having independent big spuds is one of the most important technique characteristics of jack-up self-elevating drilling platform.The basic precondition of spud foundation application is that it can be penetrated into the soil during setup and can be pulled out before towing.How to determine the spud penetration depth to make it satisfy the bearing capacity and can be pulled out safely is a critical issue.Two methods,finite element numerical simulation and traditional formulas of soil mechanics are adopted in this research.The dissertation analyzes the vertical bearing capacity of the spud foundations under static load and discusses the influencing factors.The main contents of the research are as follows:1.The research status of jack-up self-elevating drilling platform home and abroad has been reviewed and summarized.2.The traditional theories of soil mechanics are used to study the bearing capacity formulas of the spud foundations on uniform and layered soils,and the potential for punch-though.Considering the interaction between spud foundation and the soil,the methods of predicting the penetration depth on different kinds of soils have been summarized.3.The vertical bearing capacity of the spud foundations under static load has been analyzed by ABAQUS,which is a numerical simulation software of finite element and takes the contact interaction between spud foundation and the soil into account.By using ABAQUS the vertical resistance-penetration responses are studied and different influencing factors on the penetration resistance are discussed,which include the size dimension of the spud and the soil natural parameters,such as the cohesive strength ,elastic modulus and internal friction angle of the soil,as well as the friction coefficient between soil and spud foundation.On this basis the fluid-solid coupling method in ABAQUS is applied to study the vertical resistance-penetration responses furthermore,and analyze the change discipline of pore water pressure after penetration.4.Taking jack-up drilling platform Bohai No5 for example ,the dissertation compares the numerical simulation results with the theoretic analysis results under preload of 21MN.In general,good agreement is found between them,thus verifying the validity of ABAQUS FEM software in engineering design.