Soil-Pile-Structure Interaction at Lyttelton Oil Berth

The Oil Berth at the Lyttelton Port is a critical infrastructure link for the South Island which suffered extensive damage due to the Canterbury Earthquake Sequence of 2010/2011. A replacement Oil Berth is proposed. Design of a new wharf presents three key challenges: (i) keeping the existing wharf operational during construction to maintain a steady supply of oil and petroleum products to the upper South Island; (ii) meeting the seismic design criteria for critical post-disaster infrastructure, and (iii) significant dredging of the berthing pocket to future proof the Oil Berth for larger ships.

A finite element slope stability model was created to assess the stability of the slope and to estimate the bending moments, shear forces and displacements of the wharf piles. A back analysis of the slope was undertaken using surveyed slope movements recorded during the Canterbury Earthquake Sequence to establish baseline seismic soil parameters and validate the model. These parameters were used to complete a seismic slope stability analysis for the proposed breakwater. Soil-pile- structure interaction analysis was undertaken to determine the pinning effects of the wharf piles on the slope. The wharf piles were then analysed to determine the demands imposed on the piles by the expected slope movements. Incorporating the pinning effects of the wharf piles in our analysis increased the calculated seismic factor of safety for the existing breakwater to a level acceptable to the client. This work has resulted in the new berthing line being closer to shore without the need for expensive ground improvement works.