Model Tests On Effects Of Spudcan Penetration And Extraction On Adjacent Piles In Sand

Mobile jack-up is a novel form of offshore drilling platform,usually consists of a buoyant platform and self-elevated supporting structures.Due to its flexibility,large bearing capacity for self stability and heavy storage,and adaptability in deep waters,mobile jack-up is now extensively adopted in the offshore engineering.The mobile jack-up often operates near an existing offshore jacket platform to conduct oil drilling works,during which large soil deformation can be induced by penetration of its large-diameter foundation(also known as spudcan),affecting stability of the adjacent piled foundation of the platform.In view of scarce related research,1g small scale model tests were conducted to investigate the effects of spudcan penetration on an adjacent laterally-loaded pile in sand.Specifically,the study includes:First,effects of spudcan penetration and extraction on the adjacent piles were evaluated.The adjacent piles that are under Under the condition of pile head load and pile head constraint are flexural deformations due to the horizontal movement of the soil which is induced by spudcan penetration.This paper investigated the effects of spudcan penetration and extraction on the adjacent pile with different pile head constraints and pile head loads.Extreme working conditions were determined based on the location of maximum bending moment along the shaft among different penetration depths.It is found that the bending moment is changing obviously when spudcan penetration,and the bending moment is large enough after spudecan extraction.Second,soil pressure was measured by pressure cells to investigate soil pressure change patterns during spudcan penetration.Limiting resultant soil pressures were also compared with those determined based on the API codes and the relationships between resultant soil pressure and the relative soil displacement at 2.5D below the soil surface were derived and analyzed.Finally,the P-? effect of vertical loads was also investigated in different spudcan operation stages: spudcan penetration,working stage,extraction and after-extraction.The coefficients of P-? effect at different stages were obtained.The changing pattern of the coefficients was analyzed to evaluated the effects of spudcan penetration on the P-? effect.By comparison of the coefficients during and after spudcan extraction,the effects of spudcan extraction and residual influence were also analyzed.The effects of pile head constraints were investigated by conducting parallel tests on a free-head pile and a elastically-constrained-head pile.