Numerical analysis and verification of pile penetration into stiff-over-soft clay

Abstract

A numerical model for jack-up penetration process was built based on the geotechnical centrifugal model test by Hossain M S. The soil flow mechanism and the relationship between penetration depth and penetration resistance were analyzed based on numerical results. The distribution pattern of the spudcan bottom pressure was investigated for the first time. The numerical results are in good agreement with Hossain M S experimental results, which indicates that the proposed model is reliable. The numerical results show that, soil flow failures, such as surface and interface swelling, cavity formation, and soil backflow, happen in the penetration process; the lower the strength ratio between stiff and soft clay is, the smaller the volume of stiff block under the spudcan is, the more continuous and uniform the stiff clay distribution above the spudcan is, and the deeper the cavity is. The higher the soil unit weight, the more the backflow stiff soil above the spudcan and the shallower the cavity. The soil unit weight has almost no effect on the stiff soil shape and volume under spudcan. The higher the strength ratio between stiff and soft clay or the lower the soil unit weight is, the more likely the punch-through occurs. The bottom pressure first increase, then decrease, and increase sharply, from inside to outside, which proves that the linear assumption of the spudcan bottom pressure in ‘Rules for Mobile Offshore Drilling Units’ does not conform to the fact. Key words: jack-up, penetration process, numerical model, spudcan bearing capacity, spudcan bottom pressure