The interaction between the spudcan foundation of mobile jack-up rig and the piled foundation supporting the adjacent jacket platform is commonly referred as "spudcan-pile interaction". In the present study, this issue was investigated using small-scale model tests under normal gravity condition in soft clay and sand-over-clay profiles. The parameters examined included the clearance between the pile and the spudcan edge, seabed layering and pile head fixity. When subject to lateral soil displacement during spudcan penetration, a fixed headed pile experienced negative bending moment on its pile head and positive moment along the lower pile shaft. The magnitude of pile moments reduced with increasing distance between the spudcan and the pile. For soil profile of sand overlying clay with spudcan punch-through failure, the piles experienced greater bending stress during spudcan penetration as compared to those in single clay soil profile. Compared to fixed headed piles, free head piles experienced smaller bending moment at shallow spudcan penetration depths owing to permissible displacement of the pile head. Conversely, the bending stress shifted from negative bending moment to positive bending moment at the mid-pile shaft as the spudcan advanced deeper into the soil reaching. The positive pile moment reached its maximum magnitude at the spudcan penetration of 1.5 spudcan diameters and subsequently reduced after this spudcan penetration depth.
The relatively large mobile jack-up rigs are founded on three trussed frame legs and each supported on a foundation with conical underside termed spudcan. For offshore drilling sites involving mobile jack-up rigs, only the jacket platforms are fixed and permanent at the sites. The jacket platform is typically supported by steel pipe piles. Mirza et al., (1988), Le Tirant & Perol (1993), and SNAME, (2008) reported that during the installation of jack-up spudcan into the ocean floor, the adjacent platform piles experienced additional bending stress that may affect the service life of the existing jacket platform. As such, the interaction between spudcan and piled foundation could be an issue (SNAME, 2008; Randolph et al., 2011).
