What seemed like a small issue at the time, a 114mm gap would cost 35 men their lives. At the time, the decision was made to close the gap using concrete ballast, also known as kentledge. A quick fix, it was believed, with no one anticipating the fatal consequences of this choice.
The trouble began when the two half-girders on the west side of the West Gate Bridge, between spans 10 and 11, were brought together. A camber difference of 114mm was discovered, and to avoid delays, engineers suggested using kentledge—concrete blocks weighing 8 tons each—to realign the girders. The idea was that a concentrated load placed near mid-span would solve the issue.
However, the amount of kentledge used far exceeded what had been approved, leading to overstress on the structure. This misuse caused a buckle to appear on the upper panel, signaling a partial failure of the bridge.
The same method had been employed previously on the Milford Haven Bridge collapse, a tragedy that shared similar construction features. In response, additional steps were taken to reinforce the West Gate Bridge. However, by the time these changes were made, parts of the structure were already vulnerable.
The work to fix the buckle in span 10-11 set off a chain reaction. On October 14, 1970, a formal instruction was given to straighten the buckle “without further delay.” On the morning of October 15, the process began with the removal of bolts. While some progress was made, distress signals began to appear. The buckle spread, and the structure shifted, causing signs of further distress.
Around 11:00AM, a decision was made to call for workers to leave the bridge. However, it was too late.