RESPONSE STUDY OF JACKET PILES INDUCED BY SPUDCAN PENETRATION

摘要

Mobile jack-up rigs are frequently cantilevered over production jacket platforms to drill new wells or rework existing well for the offshore oil and gas at shallow and middle water depths. The proximity of the rig to the existing fixed platform will affect the performance of pile foundations of the platform and may cause some distress to the adjacent pile foundation by spudcan penetration. With the increasing accidents with respect to the spudcan penetration and spudcan-pile interaction caused severe economic losses in offshore engineering of China, solving these problems is an urgent and significance assignment at present. Since the spudcan-pile interaction is a typical offshore geotechnical large strain large deformation problem, a numerical approach based on the large strain technique is a valid solution tool for evaluating spudcan-pile interaction. The paper addresses additional responses of the adjacent pile induced by spudcan penetration in single clay profile and clay overlying sand profile using two different large strain large deformation numerical approaches. One is called two-stage approach. Firstly, ALE (Arbitrary Lagrangian Eulerian) approach is used to the displacement field of soil is calculated at the free field without adjacent piles, and then bending moments of piles investigate through conventional beam-column model. Another is CEL (Coupled Eulerian Lagrangian) approach to analyze the adjacent pile responses induced by spudcan penetration through three dimensional numerical model including spudcan, soil profile and adjacent pile. The feasibility of two approaches was verified through comparison between numerically predicted and experimentally measured results. Variations of pile bending moment induced by spudcan penetration are demonstrated with different pile length, spudcan-pile clearance and soil profiles. Comparisons of the numerically predicted pile bending moment and the experimentally measured values show that the both are close agreement for the different spudcan-pile clearance at the spudcan penetration depth of less than 15m in NC soil profiles. However, an apparent discrepancy lays on that the second positive peak bending moment from the numerical calculation by the beam-column model moves up to a higher depth than the measurement for the 40m pile length.