Trouble At Mill
Trouble at Mill
So it has been a while since I have contributed anything. I have been placed I charge of the bulk excavation and installation of rock anchors. Brisbane Casino Towers is now down to Bulk Excavation Level across half of the site and I am supervising the detailed excavation before handing over to the Structural Site ‘engineer’ (the lack of capitals is deliberate). The last 2 months have been somewhat of a rollercoaster and I have learned a great deal from the experience. With the approach of AER 2 it is a good point to review some of the issues that I have had overcome.
Loading Platform
In order to assist with the extraction of soil from the site a loading platform was designed to carry a 47 Tonne excavator. The loading platform was situated on the Hope Street side of the excavation. On 14 April 2016, the braces on the loading platform buckled, halting all loading out of soil and stopping all construction materials from being loaded in. There was a two day delay while engineers could assess the problem and carry out repair work.
The braces buckled due to movement in the secant pile wall that induced a load that exceeded the capacity of the I wrote a TMR on the buckled braces and the stability of the platform down to foundation level. It turns out that at full excavation the wall movement could cause failure and I recommended some alternate tension only restraints back to the secant pile wall as well as a brace back to the loading platform deck to limit the effective length. We held a conference with the designers who were reluctant to admit any wrong doing and just wanted to replace the braces like for like. My PM’s decsion was that we had the sign off from a qualified engineer so it wasnt a problem!
Thankfully the 47 T excavator has now gone and a long reach (33T) has replaced it. The sub-contractor has decide not to risk it (I may have had a word in his ear) so is leaving the excavation high underneath the platform until the platform is removed which has therefore limited the deflection of the retaining wall and the effective length of the plunge columns.
Wallap Analysis. Caution should be used in future projects in the extent to which Wallap analysis can be relied upon for predicting deformations. A safe approach to take is to assume that a wall will deform and design accordingly. Future deformations should be quoted within a range (for example 25-50 mm) to give the appropriate level of understanding to those unfamiliar with geotechnical analysis.
Safety. The Australian approach to safety is similar to the UK’s but different. The Union are seen as the gatekeepers of safety and not the government. Occupational Health and Safety are Australia’s version of version of HSE but they don’t have anything like the powers. Instead Union delegates hold builders to ransom over safety and the approach can seem sporadic at best. BM have a minimal approach to PPE and it is not unusual to see guys laying concrete in board shorts.
If provoked will strike!
Industrial Relations. Seemingly minor issues are over inflated to put pressure on the state and national governments or employers. The Union effects almost everything in the construction industry and sub-contractors can be blackballed and banned from site even if they have gone through a comprehensive tender process. Walk-outs are common and safety/welfare incidents can be orchestrated to give the pretence for a walk out. To make matters worse if workers down tool for safety reasons they are entitled to a full day’s pay and can even be paid to leave site for a 2hr meeting/march. My site is only around the corner from the Union Headquarters so workers are typically called in for rent a mob demonstrations. It is so bad that you cannot even use the word ‘union’ in correspondence. I had a walk out on site relating to cracks in the secant pile wall when I was drilling the first row of ground anchors. Despite displaying the monitoring results and analysis of the wall the Union delegate held the company over a barrel making various demands before allowing the boys back to work. As a consequence our survey budget has been blown out of the water monitoring wall deflections daily. The only consolation I have is that as bad as they are here they are even worse in Melbourne – you have my sympathy Jo.
![IMG_2697[1]](https://pewpetblog.com/wp-content/uploads/2016/05/img_26971.jpg?w=351&h=468)
First footing in and boom the steel budget gone
Budget. Money is really to tight to mention on this job. BM bought the work from the client in the hope of becoming the preferred contractor. As such we are trying to cut costs all over the place. The decision has been made not to pour blinder and we are laying the footing straight onto the phyllite rock. Incredibly BM have run out of money for steel after our first footing. At tender the consulting engineer estimated 50 Kg/m3 as opposed to the 80-100 Kg/m3. We have blown that in the first mammoth pad footing. Another Brisbane Casino Towers budgeting classic. We are debating the merits of back charging the consultant as we speak.
Pile Tolerance. The secant pile wall is the permanent solution for the retaining wall. At a depth 18 m the worst offending piles are off by approximately 200 mm and need to be ‘scabbled’ back in order to fit the ground anchor walers on. This causes an issue as the cover is supposed to be only 150 mm, so far we have not hit steel and I am beginning to wonder if they are reinforced! The piling contractor (Franki) actually haven’t done a bad job as out of the 264 piles on the job only 8 are problem children. I have been told by the Franki that you would be unlikely to see this type of wall beyond 6 m in depth in Europe.
Programme. We are currently 10 days behind programme and Delta are due to pay $15,000 a day for every day they delay the basement handover. So this could be quite expensive for them. BM are less interested in pursuing the Liquidated Damages (LD) are more interested in getting the time back as BM’s LDs to the client for delayed completion are nearly 3 times that. So why did these companies agree to the LDs, well they are part of how business gets done down under and are routinely incorporated into every contract. Normally the LDs are not pursued because there is a small construction community but given the tight budget that BM are operating under they have very little choice.
I have probably written enough for one post but I will follow up with another article on rock anchors and engineering in rock.
Rich/Dam0
PSB![IMG_2714[1]](https://pewpetblog.com/wp-content/uploads/2016/05/img_27141.jpg?w=595)
Calcs are indicative only!! (The brace is 6 m long)
Holdfast Training Services Trial Blog 
Doug, I know it is a hairy old PEW cliche, but the best attachments for learning are the ones where you get to observe the screw ups of others. Roz Elliot’s experience on the Adelaide Super Highway is the best example to date that I have seen, but you are coming up fast on the rails to overtake her.
I haven’t even mentioned the RTA by the hauliers yet.
Doug,
Fascinating. John had mentioned the buckling issue, I would have thought your work on this could feature strongly at CPR. I’d been keen to know how far out WALLAP was with deflections observed. I had an issue recently with a WALLAP output and needed to compare it with another bit of modelling software to check outputs were sensible. If you wanted more, and had not seen it, there is an Annex (A10?) At the back of CIRIA C580 which looks a bit more on the background to WALLAP. I am surprised deflections of an excavation depth like yours were so different to the analysis, or was the problem that the temporary works platform designer assumed the braces were attached to something stationary? Was the wall being monitored for deflections?
The position the platform braces join the wall at seems close to the propping location. Did you look to see how much extra strain was induced in the props, how close were they to capacity?
Was there any surprise at a design figure of 50kg/m3 for reinforcement in the commercial team? Did anyone think it was low? If the steel amount has increased (doubled) do you now have a steel fixer shortage as twice as much steel to fix?
Pile cover. 150mm seems high. How was that figure got to. Means a low ‘d’ value so likely to limit pile capacity. What are your pile diameters? Finally who is Franki?
Wallop analysis has produced some worrying results 0 deflections in some and over estimates in others. It’s the misplaced belief that the deflections will happen like predicted that is dangerous. There was a common belief that the wall would stay still ‘it’s concrete right’?
The braces are close the walers but this is linked to the capacity of wall/economic design of plunge column. Routine monitoring was and is taking place. Targets are placed at capping beam, prop level and the second anchor level. So +5, 0 and -7 m.
Franki is franki pile the designer of the plunge columns and secant piles. The 150mm cover is probably due to the tolerance needed in a 24 m pile not to mention it needs to go through 9 m of highly acidic soil.
QS. The mistake seems to have happened at tender. None of us were on the job then. I have 80-100kg/m3
Doug,
With such a militant workforce do BM and other main contractors factor in union action to their programme in the same way that you might factor in crane down time?
It’s a factor of life down here so it comes as part of the risk. If you want to be a tier one contractor you have to accept the union. BM employ their union delegates who also double as med cover. It’s a kind of hug them close mentality and it can work. The problem comes when the delegate has to dance to the Hqs tune.
Doug
How did the movement cause a load that exceeded the capacity of the members?
Without repeating your TMR – can you assist my understanding? I’m struggling to visualise.
Rich, in my head, which means I may be off the mark, but I would consider Young’s modulus as stress divided by strain. A movement will have caused a change in length, I.e. a strain. Therefore knowing Young’s modulus for steel you can find what stress this creates and compare to a buckling stress. If the movement induced strain gives a larger stress than a design value, I.e. factor of safety of less than 1 then that would indicate a problem.
The steel eurocode probably has loads of extra Greek letters involved but it probably can be distilled to something more manageable.
I’d wait for Doug’s answer though!
Doug – a quick sketch would be good.
Damo you are spot on. The wall tries to strain the brace which in turn produces a stress which then exceeds the buckling capacity of the brace. You can see from the pictures there are some massive props and walers that were deformed by 10 mm and the braces were treated like spaghetti. The consultant fundamentally misunderstood the problem.
Doug
A good all round blog. How are the utilities coming along?
Are there any ‘c’ works related to the utilities?
Kind regards
Neil
Neil, I have been pulled of services in favour of PT concrete and the removal of the supports. Which may include a temporary prop system. Damo I may need some advice as we are looking to retrofit hydraulic props off the capping beam.
I do have to sort out the drainage layer underneath the slab and a permanent dewatering solution for the site. Drainage layer currently 200mm of 20 mm aggregate.
This is good stuff.
Damian – I may have to reread your thesis! You know the background to soil springs and the unreliability of the use of stiffnesses let alone modulus of subgrade reaction- so Doug’s proposal regarding reporting low confidence in deformation estimates is all good.
On the piling execution issues; cover and position. I draw your attention to the execution codes ( in the UK BS EN 1536 and 1538) This is the performance expected of a reasonably competent contractor. The idea is, if the consultant required greater accuracy then this would have to be specified; by the same token , if the contractor underperformed- well then there would have to be a bloody good excuse.
John, noted. I have a pre (mis?)-conception that FReW tends to overestimate deformations based on stiffness (which I know is unreliable), therefore to actually see this in reality I thought was surprising. However, as you say, WALLAP being based on the modulus of subgrade reaction, who knows what that might tell you. I found the likelihood of entering the ‘correct’ modulus is about zero so very much agree with the low confidence/giving a range of movement is the best way of assessing risk. I’ll try to dodge the bullet by saying a recommendation was for future work to look at deformations through observation of data from inclinometers and targets and compare this with computer analysis.