Recent recovery of the sunken fishing vessel Ehime Maru, was performed near Honolulu using a shallow staging area in a protected reef environment. Project restrictions prevented a geotechnical subsurface exploration and allowed only two mooring piles, prompting contingency pile design using empirical calculations for a range of possible conditions. Design assumptions and acceptance criteria were modified during pile installation using hammer resistance observations as the primary indicator of geotechnical conditions.
Following tragic sinking of the Ehime Maru fishing vessel near Honolulu in 2001, emergency salvage recovery operations were organized in a planned staging area (Fig. 1). Strict budget and schedule requirements for staging area construction severely limited time, permitting and the feasible scope of work. A design-build format was informally adopted to complete mooring pile installation in six weeks. The pile design approach will be discussed including structural load assumptions, soil assumptions, pile material assumptions, and pile equipment assumptions. A parametric study of pile driving criteria and lateral capacity for a range of anticipated potential geotechnical and equipment conditions was performed. Pile driving observations were then used to immediately calibrate assumptions for pile acceptance.
The absence of subsurface data for geotechnical design and severe schedule restrictions created an atypical design framework. Rapid assessment of potential ranges of design variables and rational selection of design assumptions was required with unusual degree of uncertainty for professional practice (McClelland, 1980). Budget constraints also precluded non-intrusive subsurface methods or Pile Driving Analysis (PDA) dynamic instrumentation (Rausche, Goble and Likins, 1985). Assumptions for structural loads and pile materials had to be resolved prior to installation, while soil conditions, equipment conditions, and pile length had to be resolved during installation. The project sponsor knowingly presented an unusual cost-schedulequality equilibrium where schedule and budget had clear priority over performance.