Wave Equation Analysis And Design Method Of Driven Pile For BOHAI Drilling Platform Engineering

Driven pile with long shaft, large diameter and high bearing capacity have been used increasingly in offshore pile foundation application. Offshore pile construction is a highly complicated systems engineering since extreme task environment and great difficulty in driving. So the design proposal with science rationality become very important, which determine the success or failure for offshore pile engineering. However up to now the interaction among pile, soil and hammer during the driving period has not been taken into account in the design for offshore pile in China. Pile driving problems were often occurred, sometimes engineering accident was serious that cause very rough work for remedial treatment. Therefore, finding a rational design method is a urgent task. One dimensional wave equation analysis was introduced into the design for offshore driven pile in this paper, and put forward information piling method and optimized design method. For details, see as below:1.The optimized design method for driven pile in this paper has very important and practical significance for offshore pile foundation engineering. This method includes two phases. The first phase is based on the wave equation analysis, the interaction among pile, soil and hammer during the driving period and driveability analysis for selected pile and hammer are simulated practically to determine initial design plan. The second phase is to drive tested pile and carry through the piling monitoring test, to validate and adjust the parameters of pile, soil and hammer in the initial design plan, and achieve optimized design plan. This kind of design idea is closely link to piling process, that makes the design much accord with practical mechanical behaviour in the pile and soil and breaks through the current design principle with major statics analysis.2.The driveability analysis is a key in the optimized design method for driven pile. Based on wave equation analysis program WEAP, several improved model was put forward in this paper, such as intermission piling soil resistance recovery model can calculate the soil resistance change at any depth during the period of pause piling; soil plug action can be considered for open end steel pipe pile; residual stress effect withinthe shaft also can be taken into account during continuous piling process for long pile. All these improved calculation makes the driveability analysis much accord with practical piling process.3. Piling monitoring test was introduced into piling process and information piling method was put forward in this paper. So, piling on site can be guided and controlled by real-time measured datas.4. The calculation of pile bearing capacity is very difficult and important parameter in the piling monitoring test. Based on wave equation signal match program CAPWAP and lucubrated for pile-soil parameters, key step in the matching was concluded and a optimized manual matching method was put forward in this paper, such as a new method to select correctly measured records; a new method to calculate the pile average velocity by wave-up and wave-down curve; a new convergence standard for matching calculation; and a new method to estimate the unit skin resistance by the slope of wave-up curve. All these improvement make the calculation of pile bearing capacity much reliable.5. By the successful application in the design of super diameter driven pile for BDPPF offshore oil gas field drilling platform, this optimized design method presented in this paper is science rational.