Study On Load-Bearing Mechanism Of Spudcan For Jack-up Unit In The Process Of Penetration And Extraction

In order to better study the load-bearing mechanism of the spudcan for jake-up drilling platform in the process of penetration and extraction, the particle flow (PFC) theory is introduced but not restricted by the traditional macrocosmic continuity hypothesis. By relating the microstructure of the soil with macro mechanics, a homogeneous soil model without acceleration of gravity and a consolidated soil model with 200g acceleration of gravity are established. The author firstly modeled the Ballbar penetration to measure the soil strength, and then modeled the penetration of the spudcan and the immediately extraction after penetration.Thesis detailed the load-bearing mechanism of the spudcan in the process of penetration and extraction from the aspects of soil reaction stress, stress of the soil, displacement field and velocity field. Conclusions abtained are as follows.1) Soil reaction stress qu acted on spudcan. The changing tendency of the soil reaction stress qu that acted on spudcan with depth is similar to that happened to soil strength Su when penetrating and extracting with Ballbar at the same depth. For homogenous soil without acceleration of gravity, the reaction stress qu acted on spudcan during the penetration and eatraction is 200kPa, which is 13.3 times of soil strength 15.0kPa. For consolidated soil with 200g acceleration of gravity, the reaction stress qu acted on spudcan during the penetration increases linearly with depth. Its maximum value 415kPa is 13.8 times of the maximum value 30kPa of soil strength during the penetration. Also the maximum value 100kPa of the reaction stress qu is 13.8 times of the maximum value 7.2kPa of soil strength during the extraction. The soil reaction stress qu acted on spudcan during extraction is mainly depended on soil weight above spudcan.The soil reaction stress qu acted on spudcan does not reverse immediately once the spudcan is extracted, which is due to the soil extrusion during penetration. Spudcan still be acted on reaction force by the soil. The bearing capacity factor Nc of spudcan in this studyis about 13.5.2) Soil stress around spudcan. The smaller the distance to the spudcan, the larger the variation ranges of the soil. The stress area in x direction stress affected by penetration and extraction is larger than that in y direction stress. The stress changing tendency with depth in both x and y direction for the soil below the spudcan is similar to that happened to Soil reaction stress qu acted on spudcan during the penetration.3) Soil failure mechanism with plastic flow. For both the homogeneous soil without acceleration of gravity and consolidated soil with 200g acceleration of gravity, in some penetration depth, the soil below spudcan flow towords the top of spudcan; in some penetration depth, the soil at the top of spudcan flow towords the below of spudcan. In the process of spudcan penetrating in consolidated soil at surface, there is a phenomenon of soil upheaval at the surface, and a pile hole be formed. Soil fillback with plastic flow occurs in some depth, and it can't affect soil shape at surface. The radial deformation area of the pile hole is about 1.5 times of the spudcan diameter. The soil deformation in other soil area is very small. The stability number Ns ? is 6.88.