The discovery of deep trenches adjacent to suction caissons acting as anchors for semi-taut mooring systems has led to a reassessment of geotechnical design assumptions, such as: trench formation across the full front face of the caisson down to the level of the mooring chain padeye; gap formation behind the caisson; and reduction in reverse end-bearing. Such assumptions require potentially time-consuming numerical analysis in order to assess the optimal depth of the padeye and anchor design holding capacities. The paper describes the extension of an existing upper bound analysis, AGSPANC - based on the Murff-Hamilton upper bound solutions for laterally loaded piles - to include a trench in front of the caisson. The software was validated against independent finite element modelling with two different ‘industry-standard’ packages, PLAXIS3D and ABAQUS. Anchor responses with and without a trench were considered, for both shallow (e.g. at 25% of caisson embedment) and deep (65% of caisson embedment) padeye positions. The overall level of agreement between the three analysis approaches was good, although significant differences were found for certain cases.
Mark F. Randolph, James Doherty, Michael P. O'Neill, Xiaowei Feng, Jean-Christophe Ballard and Camilo Melo
Keywords: analysis, design, mooring, suction anchor, trench
Publisher: DFI