Assessment of Earthquake Induced Lateral Displacements at Transpower Hayward HVDC Link Pole 3Upgrade

Abstract

Transpower New Zealand Ltd owns and operates the High Voltage Direct Current (HVDC) link which transfers power between the North and South Islands of New Zealand. The link is a critical lifeline in the electrical distribution system. Transpower proposed upgrading the Haywards facility at the north end of the HVDC link from 700 MW to 1200 MW. The development included construction of a new convertor station (the Pole 3 building) which was located within 150 m of the active Wellington Fault. This fault could generate a Magnitude 7.3 earthquake with a 1 in 2,500 year return period peak ground acceleration of 1.01 g. The terrain in the area of the substation is relatively steep and the site was developed by cutting into higher ground and placing the material as un-engineered fill into the gullies. The new Pole 3 building straddles the cut fill interface with rock at shallow depth at one end and up to 25 m of uncontrolled fill at the other end. A key geotechnical design issue was to assess how far the underlying fill could move in the design earthquakes so that the base isolators in the new building could be designed. This paper outlines the analytical methods to assess likely lateral fill movements.