Punch-through Mechanisms Of Spudcan Foundations In Multilayered Clay

Spudcan punch-through failure could be regarded as a major cause of foundationfailure of offshore jack-up rigs, punch-through often can do great harm to the platformeven complete failure of the platform. At present, SNAME suggest approximateformula to evaluate the foundation ultimate bearing capacity. However, the formula isnot applicable for the varied geological conditions, so, the experimental method andfinite element analysis method are adopt to solve punch-through.Centrifugal model test is an effective method for copying in-situ stress field. itsadvantage is that by raising the centrifugal acceleration in a contractible modelsimulate the process the spudcan penetrating into clay, and get the same stress level asin-situ test. According to this topic, the whole model centrifugal model test and halfcentrifugal model test were performed. Half model centrifugal model test combinedwith PIV analysis can accurately get the velocity vector diagram of soil, and obtainthe flow mechanism and failure mode of soil. Full model test get the load-depth curvefor different penetration to estimate whether punch-through occur.Centrifugal model tests cost a lot and are not easy to repeat, therefore, numericalsimulation is adopt using ABAQUS finite element analysis platform, basing the resultof the centrifugal model test. To Stimulate the problem of spudcan penetrating intoclay, the traditional finite element simulation method will not convergence because ofthe large deformation, and often get bad results. Coupled Eulerian-Lagrangian method(CEL) uses Euler unit to simulate the foundation and Lagrange unit to simulate thespudcan. This approach can complete simulation of the dynamic process ofpenetration, and also can solve the problem of large deformation in the process ofcalculation. CEL method was adopted to simulate the process of spudcan penetratinginto stratified soil, and the results of centrifugal model test verified the reliability ofCEL analysis.Through centrifugal model test and CEL finite element analysis, the followingconclusion were given:(1) The theoretical calculations as SNAME recommended are hard to makeaccurate predictions of the bearing capacity of the process of spudcan penetrating intolayered clay. (2) Half model centrifugal model test combined with PIV analysis got thevelocity vector diagram of soil, illustrated the characteristic of punch-throughphenomenon. When the strength of the stiff clay was twice more than the soft clay,punch-through may occur, spudcan penetrating into2-3m higher than the surface ofthe stiff clay and through the stiff clay.(3) Plastic zone is obtained by CEL finite element analysis of the process ofspudcan penetrating into layered clays. By the curve of penetration and plastic zone,punch-through mechanism which was called “double punch-though” was interpreted.