At 11:50 a.m. on 15 October 1970, a 112m span of the West Gate Bridge, known as span 10–11, collapsed during construction. Approximately 2000 tonnes of steel and concrete came crashing down into the muddy banks of the Yarra below, taking workers and their machinery, tools, and sheds with them.
When the two half girders on the west side, span 10–11, were brought into close proximity up in the air it was established that a camber difference of about 11cm existed between them. The engineers proposed that the vertical difference of level could be taken out by using kentledge (ballast) to push down the north half span relative to its south counterpart. Ten cube-shaped concrete blocks, each weighing about 8 tonnes, were on site from a previous operation, and it was thought that these would give about the right order of load to remove the camber difference.
The act of adding the kentledge was the precipitating cause of a buckle that appeared on the inner upper panel around joint 4–5 north. The buckle was a clear indication that partial failure of the structure had occurred.
Workers were given instructions to remove some bolts from the northern half at mid-span to remove the buckle. After about sixteen bolts had been loosened there was significant slipping of the two plates relative to one another such that the loosened bolts were jammed tightly in their holes and could not be easily removed. Eventually about 30 bolts were removed from the box 5 side of the splice, and about seven bolts from the box 4 side, all close to the longitudinal centre line. The buckle spread right across one half of the bridge. An hour later both halves of the span collapsed.
The whole 2,000-tonne mass plummeted into the Yarra mud with an explosion of gas, dust, and mangled metal that shook buildings hundreds of metres away. Homes were spattered with flying mud. The roar of the impact, the explosion, and the fire that followed could be heard more than three kilometres away.
Thirty-five workers lost their lives that day; many others were injured. Most victims were those working on top of the bridge at the time of the collapse. Some men were lucky enough to be on their morning break away from the site; others simply ran out of the way before the bridge fell on top of them.
An expert technical committee was immediately established to investigate the scene. The following morning, amid nationwide grief and horror, then Premier Sir Henry Bolte announced the establishment of a Royal Commission, chaired by Mr Justice Barber, to investigate the cause of the collapse. Its report, tabled in parliament in 1971, left no party associated with the collapse blameless and stated that:
"Error begat error . . . and the events which led to the disaster moved with the inevitability of a Greek Tragedy."
If the above description was whetted your appetite, take a look at the following two web sites for more details of the disaster:
West Gate Bridge Memorial
Disaster at West Gate
The first-listed site is the better one, and has a full description of the lead-up to the collapse, the collapse, and the aftermath.
The sections of the bridge at the cache location were tested by Monash laboratories as part of the investigation into the cause of the collapse. Do yourself a favour and read the information boards on site. There isn't much to read, and it will enhance your enjoyment of the cache. The next time you drive over the West Gate Bridge, spare a thought for the men who went to work on 15 October 1970, but didn't return home that night.
The difficulty rating of 2½ stars above just represents the median of the possible difficulty ratings. The challenge of this cache is retrieving it unobserved. Just how difficult this will be, will depend on the day you choose, and the time of that day. It will be exceedingly difficult, if not impossible, to retrieve and replace this cache at around lunchtime on a university day. The cache was placed on a weekend during the term break. The following table gives you a guide to the difficulty level for this cache:
||Weekend during term break.
||Week day during term break.
||After hours during term.
||Class hours during term.
||Lunch time during term. (Forget it!)
Finding the cache is relatively easy; retrieving it might be a different matter. Please be careful! Stealth will be required at most times! If there are people about, give it a miss, and come back later. Also, be aware that there are many windows overlooking the cache site. You may be observed!
The cache container is a 2L Sistema clip-top box.
The initial contents are:
Quartz car clock
Stress ball/juggling ball
Builder's tape measure
Bag of marbles
Koala lapel clip
Magnetic key holder (might make a useful micro cache)
Tiger Balm Plus
Mini back pack/camera case
Log book, stash note, and pen
As always, please replace the cache exactly where you found it to discourage accidental discovery.