Reliability Analysis On Bearing Capacity Of Vertical Loaded Piles Of Ocean Platforms

In offshore engineering, the design methods of foundations are incompatible with those of upper structures. The design of upper structure of platforms is based on reliability theory but the same procedure may not be easy to be adopted in foundations design. Consequently it becomes an apparent obstacle to boom of offshore petroleum industry. Therefore it is necessary to carry out rational reliability analysis on pile foundations of platforms and develop the Load and Resistance Factor Design (LRFD) that is suitable for Bohai oil fields.In this thesis, the following work has been involved:A database management system is established in order to operate and analyze the data of the geotechnical properties of subsoil. It includes almost all the borehole logs and properties of the subgrade in Bohai oil fields.Via the database, a random field model has been developed and the correlation function and deviation reduction function have been simulated.A calculating mode for single axially loaded piles of platform foundations is built on the basis of the database and design experience. The reliability analysis is implemented using the advanced first-order second-moment method based on statistical calculation. Furthermore, the influence of variation in loads and soil properties on reliability index and partial factors is assessed.Finally, the calculated partial factors are compared with those advised by American Petroleum Institute (API)Through above analysis, some conclusions may be achieved and mainly three of them are listed as follow. Firstly sensitivity analysis shows that the most important uncertainties are due to uncertainties in the extreme environmental load parameters and soil strength parameters of the thicker and deeper soil layers and soil layer that surrounds the pile pit. Secondly, as the increase of vertical load or its variability, the reliability index and safety factor both decrease and the resistance of surrounding subsoil is mobilized gradually. When the variability of soil resistance goes up, the global reliability of pile foundation goes down although the resistance partial factor becomes small. Finally the partial factors recommended by API are proved to be suitable for the pile foundation design in Bohai oil fields.