Meyer, V. (ed.), Frontiers in Offshore Geotechnics III: proceedings of the Third International Symposium on Frontiers in Offshore Geotechnics (ISFOG 2015), Oslo, Norway, 10-12 June 2015, CRC Press, Boca Raton, pp. 1253-1260.
10 Jun 2015
Standard industry practice for ensuring adequate spudcan capacity during a design storm event is based on assuming that the maximum preload applied during installation defines a ‘proven’ measure of the spudcan capacity under pure vertical load. However, in reality the preload only defines the vertical capacity for conditions applicable during installation, when the spudcans may exhibit an undrained, drained or partially drained response, depending on the rate of spudcan penetration, spudcan dimensions and soil properties.However, during a stormevent, a number of rapid load cycles are applied and hence soil that exhibited a drained or partially drained response during preloading, might respond with a weaker undrained response and in addition suffer degradation due to cyclic loading. Under these conditions the ‘proven’ monotonic installation resistance may be an unconservative measure of the storm capacity. This paper presents a detailed case study, which explores these issues, where a jack-up rig was successfully installed in very challenging site conditions, comprising alternating layers of uncemented carbonate silty sand/sandy silt and mud. The soils at this site were found to be highly prone to cyclic degradation, offer varying drainage conditions between installation and storm loading and also exhibited multiple punch-through risks.