Study On Boot-driven Pile Of Jack-up Platform Based On Sand And Subsoil

With the increasing demand for resources,offshore oil and gas exploitation is a new direction of marine resources development.Offshore platform is widely used in the world.Spudcan foundations of various geometrical shapes are commonly used to support offshore oil and gas drilling(jack-up)RIGS.A series of hazards may occur when jack-up drilling platform spudcans are operating on complex foundation,among which "puncture" incidents account for the vast majority of platform accidents.Improving the shape of spudcan is a good way to reduce platform accidents and save costs.At present,there are few studies on spudcan in complex terrain.Spudcans are the key devices for pile driving and pulling on drilling platform.The soil foundation with the upper sandy soil and the lower clay is "hard on the top and soft on the bottom",which is more prone to "puncture phenomenon".This thesis also introduces and analyzes the research on the insertion and extraction of spudcan under different foundation conditions.In this thesis,the finite element method is selected to study the pile driving operation of spudcans,and the advantages of CEL method in simulating pile driving operation are compared and analyzed.Compared with the traditional finite element method,CEL calculation results are easier to converge and more accurate.The advantage of numerical calculation is that it takes into account many problems that are not considered in the standard of conventional calculation formulas,such as the uncertainty of geological soil layer in the ocean,soil backflow,the structural shape of spudcan,puncture problems and so on.Then the reliability of CEL numerical method is verified by proportional test.The concrete parameters of soil were measured and recorded through triaxial test and ring tool method,and then the simulation of pile driving test was carried out.Four equal-scaling model spudcans were established to simulate pile driving under the condition of upper sand and lower clay.The resistance curves of the spudcans at different insertion depths were established respectively,and the test data were compared with the simulation data.It is verified by comparison that CEL numerical simulation can replace the scale model test.Finally,the differences between the hemline type spudcan and the perforated type spudcans compared with the common spudcan in the process of pile driving were investigated.It was found that the hemline type spudcan had a great improvement in the problem of puncture.Then delve into the skirt length,skirt wall thickness for the resistance of the spudcan insert change,in the skirt length is less than the soles of the bottom pile found skirt length of pile is of little influence on the overall resistance,skirt spent long cause problems of jack-up platform of traction,so choose the appropriate skirt length spudcan has far-reaching significance to the design.The wall thickness of the skirt has a certain influence on the soil accumulation at the bottom of the spudcan during pile driving.It is found that the increase of skirt wall thickness reduces the total amount of soil stored at the bottom of spudcan,thus leading to faster compaction effect.The greater the wall thickness,the lower the puncture distance,which has a positive significance for the safety performance of the jack-up platform.In order to increase the passage of soil through the spudcans,the mechanism of pile driving by open-hole spudcan was studied.It was found that the open-hole spudcan also had a positive effect on the occurrence of puncture,but the upper soil in the pile driving did not flow out through the holes,but stayed in the holes,and the soil was constantly compacted.Comparing the four,six and eight hole spudcan with different radius of holes,it is found that the holes are all blocked when the piles are driven.The resistance curves of piles with different openings are eventually imitated into the same model along with the depth resistance curves,so the curves are roughly the same.