When Deck Pours go Bad
So I’ve had a request from one of you excited civils out there to expand upon my throw away comment this morning about a deck collapse on site. I should have known that simply mentioning a concrete pour would have caused a ‘Civil Twitch’
Three days before a site closure for the Easter long weekend a concrete deck pour had been scheduled. In the region of 300m^3 were scheduled to be poured on a deck half suspended over a previously poured concrete slab and half over formwork suspended off a sloped batter. Halfway through the pour the formwork gave way and a partial deck collapsed occurred causing the site to be evacuated and effectively closed for five days.
No one was injured during the incident – Through the use of exclusion zones and Partially due to the fact that the collapse occurred half an hour before a scheduled evacuation rehearsal – The site staff had been prepped and ready for an emergency drill.
Concrete deck pour complete with undersigned additional ventilation/ natural lighting
Investigation into the incident uncovered a number of key failings which led to the deck collapse:
1. The Pre pour formwork inspection by an engineer had occurred a number of days before the pour.
2. A significant amount of rainfall had occurred the night before the pour – enough to cause standing water in the basement of the project– changing the condition of the batter upon which the formwork supports had been placed. (effectively the surface of the batter had water running down it, an
3. The ‘shelves’ cut into the batter to place the formwork supports on were insufficient to distribute the load
4. No post rain, or pre pour inspection occurred the morning of the pour (no Question 2.4 moment, Has the situation changed?)
The result? an industrial investigation, union action, a new site manager and add 4 weeks and thousands of dollars to your program please!
Holdfast Training Services Trial Blog 
I always knew ytou were in the wrong stream
Love it to death….. I don’t suppose there’s any piccies of the falsework and formwork…as was…as it were?
Thanks Tim, I repreat Johns plea for more photos of the failed bits pre and post if possible. I’m amazed that digging this out and reworking it all has only added four weeks to programme with the associated itch hunts and added layers of concern.
Looks good Tim. For you all in Oz – interesting to know how many concrete pour collapses JHG has experienced over the last year and what/how cross-company lessons identified are distributed. The fact that you are aware of each others collapses is an easy one to drop into CPR as an example of quality CPD and highlights the value of the blog.
I heard about the deck collapse last week but there was no specifics given (just that it was a JHG project). I’ve not heard of any other concrete pours that have gone wrong David. There does seem to be a fairly good passage of information across all the companies that Leighton holdings own (Thiess, JHG, Macmahons and Leighton contractors). Recently there is a big focus from safety and management on temporary works – most likely because of this incident. The other one mentioned was a material hoist on the side of a building that was not installed properly and the car tilted over while still attached 5 floors up with 3 people inside (all escaped unharmed).
Unfortunately there are no picture of the failed falsework due to the fact that there was a significant exclusion zone underneath the the deck from effectively the collapse up until the completion of remediation works – access for permit holders only. Understandably they didn’t want photos splayed all over the internet – I only managed to get this one by opportunistically getting myself on a community engagement visit to the adjacent college and snapping out the window.
In terms of the speed of remediation the area that required cutting out and repairing was only about 10 M x 7 m so there has been a fairly speedy recovery.
In terms of passage of information, we too were briefed on the Alimac incident at Newcastle with the 3 people trapped inside.
I must say that I am struck at the effect of the ‘Strategic Corporal’ when it comes to H&S and the effect that they can have, rather than the legislation and JHG procedures which are often seen as a paperwork only exercise. From what I have seen Safety Culture appears to very much be in it’s infancy over here.
Funny you should ask David, I was thinking exactly the same thing. As some of you will remember I had a similar experience about this time in my attachment.
Whilst pouring a relatively small suspended slab (320m3) the formwork setttled 30mm, which cause a whole hullabaloo. Unions, Worksafe, investigations, quality assurance – all great CPR stuff.
1. The formwork was inspected prior (2days) by a third party engineer, and again on the morning of the pour by the formworkers and JHG (me). There was only slight remediation necessary after the 3rd Part engineer, and the morning inspection was OK.
2. Water was also the cause. The Concreters (Grano’s to Aussies, which I like to think comes from the term ‘Granolithic,’ used to describe tha nature of the material being placed, but as this is Australia, probably derives from a old concreter called ‘Gran’) were continually washing off their tools in the same spot and left the hose on. The fall of water washed the sand substrate (which had a slight slope on it) away down a void along the side of a pilecap that had not been compacted properly (I assume that the vibro roller did not want to damage the concrete). The ground density and comapction check was only required at a rate of 1/500m2 so was in my view entirely inadequate.
3. The incident was agreed with ‘Worksafe’ (equivalent H&S Exec) to be a ‘settlement’ so I expect that it was never published outside of the project. For that reason I expect that the investigative report recommendations didn’t get spread around the business.
The subsequent investigative report that I was involved with made several recommendations:
1. Perth Sand Penetrometer tests should be conducted to verify the compaction of the ground in the vicinity of the falsework soleplates.
2. Full third party inspection should take place immediuately before concrete is poured, and after ant significant rainfall.
3. Concreters should be better controlled in reference to their use of water (both for quality issues and safety.
4. The JHG safety procedures were adequate for the task
These measures were implemented site wide with immediate effect and were actually pretty effective at controlling formwork issues. Until another incident in my last month. A restricted view of a supporting beam with a couple of boards of Ply at a step down, did not allow the 3rd party engineer to see that it was overspanning. Error x 2 by the subbie, bad judgement by the 3rd party engineer not to get a ladder to check. The result was that the aluminium beam was overloaded and tore in the lower flange allowing the deck to locally collapse. Pour aborted, big investigation, drilling and cutting concrete heard continually for my last month on site (I refer to this as the sound of mistakes; not an uncommon sound on the project).
Timo, that slab looks like it was a nasty one especially as there appears to be shedloads of PT ducks running both directions across the deck and nowhere immediately obvious to cut back to form a construction joint. I guess it was a case of concrete cut it square, drill and epoxy new starters, and redo the PT. I agree with Richard that 4weeks seems only a small slip in schedule – was the build ahead of schedule before the incident?
Enjoy the sound of mistakes!
Tell you what Timo, we can chat it through at Sappers In The City (Perth) – I know you will love that!
The PT was an issue, however the deck was cut back to the edge of the slab poured to the left of the shot, and to almost the edge of the slab to the right of the shot. The deck to the north of the slab was poured with tie ins giving basically three sides of the square to tie into. Then they poured it.
But it’s all concrete and mud to me! no one as excited about all that shiny ductwork!
See you tomorrow at the lucky shag nicky boy!
Nice post! I’ll look out for excess water on my site…erm about 10m from the sea!