Holdfast Training Services Trial Blog

All – some pictures from Bahrain on my page  – interior works, exterior works, blockwork and roof installation for anyone interested!

http://www.roselliott.wordpress.com

Keep going everyone and best wishes,

Ros

Has nine months really passed, time on attachment has gone very quickly. As I leave Liverpool Street here is a quick update on my areas of responsibility.

Site in General. At the time of my departure we had just completed the concrete pour for the penultimate slab at 78SSL and works had commenced on the excavation to the final level 73 SSL. All in all some 2,400m3 of concrete poured and nearly 2000 tons of steel fixed in the preceding slabs. The final excavation would prove the most complex as a the break out of the pile wall to create the access tunnels to the platform would need completed. During the breakout of the pile wall a temporary section of slab would be required carry loads across the sections of pile wall. I have intentions to return to the site to witness the pile wall breakout as the plan is to use a steel and diamond rope in a winch to cut the piles like a cheese wire……I would like to see that as the piles are 1200diameter with heavy steel reinforcement, but I have been told it is possible.

Installing steel at the penuletimate slab level & view of the running tunnels adjacent to site

Depressurisations wells. My part completed wells installed, working and a steady decline of the pore pressure had allowed the cessation of works to be lifted and the excavation to continue. Having now entered the Lambeth Groups of soils and with the wells firmly in the course grain gravelly layers the amount of water being pumped had dramatically increased from 200-300litres per day to20,000 per day. All was going well up until my last day when we arrived at work to discover the site flooded from an over flowing settlement tank, the cause turned out to be that the contract excavating the tunnels adjacent to our site had turned their dewatering system off on the Monday and it had taken a week for the recharge of the ground water to reach our site. Although the wells we had installed were capable of pumping the increased amount of water we did not have sufficient storage capacity. It also turned out that the young apprentice responsible for monitoring the flow rate had neglected to do this and so the increase in water flow had not been picked up.

Installing the depressurisation wells & the well head of the vacuum edjector depresssurissation system

Precast Concrete. Leading the charge for Laing O’Rourke I had at the time of leaving managed to secure my greatest legacy to the Liverpool Street site, the use of precast concrete sections to complete the Northern Wall of Blomfield box. Through the use of negotiation skills, professional engineering judgment, coercion and by being a deviousness and sneaky bustard I coordinated efforts and produced the Value Engineering proposal that convinced Crossrail Engineers that the use of Precast Concrete was in fact the best option in terms of engineering risk, H&S and commercial risk.

The complicating factor in the design of the precast concrete sections was Crossrails insistence that as they would be required to take structural design responsibility then they would design the wall sections and inter wall connections. As the wall is to be next to live LU track and undercover the wall must have little to no maintenance burden and cannot use any materials that release toxic fumes when burnt. As a result Crossrail had designed the walls connections as an insitu concrete stitch creating two problems for us as the contractor to overcome; Firstly this insitu stich requires the reinforcement within the wall to be tied to the structural frame of the building and then concrete poured between the steel to join the wall and structural frame together to form what engineers have described as a monolithic structure. Secondly how do we turn and ten support the wall sections during construction. The walls have a long slender overhanging nose section that cannot be used to support the wall during fixing and pouring. With the temporary works team we had developed a rough scheme of manoeuvre using Perri Strong backs to create legs to support the wall. These legs then had to be offset from the wall sections to allow the site operatives access to fix steel and pour concrete. As a result at my time of departure I was working with the temporary works team to model the loads on the connections. At the time of departure we were on the 6^th iteration of concept designs from the design consultants Motts….

I have now moved to Arup, London office without a speck of mud insight. I am now surrounded by a mix intellectual geeks and glamorous Europeans. I have discovered the free lunches that accompany the lunch time CPD sessions and have attended two this week already. The festive season has already started with a wear your s***test shirt to work day and festive if not geeky pub quizzes…John I am sorry to disappoint but my team came last at the geotechnical Christmas quiz…….

My final walk in the tunnels and on site

The documents I refer to below are mainly (not exclusively) for those following the IMechE route. However, I believe that it is worth all PET students considering the end state. Personally, I failed to spend enough time in Phase 1 considering it, i.e. chartership.

I would commend to you all that it is worth investing some time in digging out the UK Standard for Professional Engineering Competence. Having put your hands on that document then read it and spend time understanding what the statements really mean, as they are in my opinion rather vague. Whilst you are at PEW you are in a good place to speak with you mentor and ensure that as you head out to industry you get immediately after those tasks that provide evidence for competence and where appropriate reject opportunities that don’t provide evidence or decent personal development.

There are a few documents out there that are easy to find if you know to look for them (www.imeche.org):
– UK Standard for Professional Engineering Competence. (http://www.engc.org.uk/ukspec.aspx)
– Competence profiles – Guidance for applicants and assessors. Part 2 industry classification (K) – The Army.
– IEng and CEng guidance notes.
– Guidance on the Preparation of an MPDS Final Personal Report and Development Action Plan.

As a closing remark, I recognise that Phase 1 has its own pressures and putting this off appears an acceptable COA. However, if you do decide to follow this advice it will save you hours of time working out what the EC is looking for and may prevent you being burdended with a task during Phase 2 /3 that adds no value, except to the company that is sponsoring your attachement.

In an early blog I described how the load path of the new steelwork on the tower extension is pulled up and into the core through Macalloy bars.

This is required since the existing pre cast columns crank inwards towards the bottom of the building, inducing a large moment that cannot be dealt with.

The existing column crank can be mid picture

In the temporary construction condition, whilst the diagonal Macalloys are not employed (because we were building them) the weight of the steelwork is propped off level 30.

This load passes down the existing pre-cast perimeter columns and into the foundation.

The red steel is the temporary steelwork sat on the top of the existing columns

I undertook analysis of the existing structure to determine how much steel we could erect before we reached the limit of the crank. I can report that my calculations to determine the allowable load were alright since the building is still here. Knowing the actual factor of safety during this operation was exceptionally difficult so we will never know how close we were.

Installation of the hangers has been slow because of a number of issues.

1.  PC Harringtons did not cast the correct size holes/voids in the core to allow the mega steel embedment to fit into. This required us to break out additional concrete.

Void for the embed

2.  The slipform at the top of the structure meant we could not lift the embedments into the holes until the slipform was completely removed/dismantled. This meant there was no concurrent activity

Back plate in place

3.  Access to the embedments is difficult. We used a combination of traditional scaffolding, proprietary platforms and scissor lifts to access the embedments.

Access to the embed

4.  Since the embedment elements are critical to the structural integrity of the permanent works each segment of work has to be inspected and signed off by the structural engineer, Mace and sub-contractors prior to moving on. This took a lot of my time as well as wasting progress.

5.  Our resident engineer on site is useless. Although he is supposed to be a qualified engineer, he is not willing to take any responsibility or give a direct answer to anything. At every instance he has to refer back to his office for advice.

6.  We are dealing with two sub-contractors to deliver the one element. This has required almost daily meetings to ensure progress is maintained.

So what.

1. I think we could have planned better for this operation (who never says this?)
2. Design information was scant. Its lack of detail seems to have then impacted upon the whole operation. Since there were so many unknowns I think higher risk was accepted prior to construction than really should have.
3. We should have used 3D software to map out how the reinforcement and steel interfaced. The slipform precluded particular vertical reinforcement being fixed during slipforming. This should have been picked up. We were then in a position fighting to get hold of every piece of reinforcement that was available.
4. The Structural Engineer’s designer of the embedment elements should have given us a presentation of how he designed them, and why particular elements were important. This would have allowed us to make more informed decisions on site and understand risk better.

Macalloys in place

So inclusion.

Communicating how a structure or element of it is designed is key. If the contractor doesn’t ‘get it’ then there is real risk failure could occur. Sub-contractor engagement, liaison and partnership is key to ensuring that shared progress is optimised. There was little motivation for the concrete contractor to get the job done, but lots of motivation for the steelwork contractor. Modelling of complex nodes, connections and elements is worth the time, effort and expense as it ultimately reducing time, cost and improves quality on site during the installation.

Here are some other photos of the embed.

Jacking in progress

Lift off once the macalloys were tweeked

Some images of BP Miller in the North Sea with circle and ‘H’ lights installed.

Whilst Pete and co. bask in Aussie sunshine, thought I’d post this picture taken in Buffalo (5hrs north of me) showing the impending snow storm advancing across Lake Erie!!!!  It was 24degC last weekend, and dropped to -8degC last night…concreting cold weather plans coming to the fore!

There were 3 main noteworthy occurrences when I was back in the UK for my 3 weeks of summer leave.

Pier 2
The columns on pier 2 were poured and the bracing was not installed correctly (as per the designers drawings). My site engineer had the drawings with the clear notes on them as to where the bracing should have been. However the leading hand convinced that it would be fine not to follow them and that it wouldn’t budge. This was not the case. One of the props holding the form in position failed and buckled during the pour. This was only noticed after the pour and no effort was made to try and fix this. The 2 columns needed to be poured on separate days (unlike the planned one day) as the 9m long vibrator got jammed in the reo at the start of the first column. There was no mechanical 9m hose to replace it, only an air vibrator (which has a larger diameter hose and head, meaning it is more likely to get jammed). The pour continued with this replacement and the damaged vibrator was cut off and left in place in the column. I say it was cut off, but what really happened was they hooked a crane up to the hose and tried to pull it out. That only succeeded in snapping the hose off. When I returned and saw the columns there was a noticeable slant in it. This was confirmed by the survey of the columns. The contract is very clear that the allowable tolerance for this type of element is +/- 25mm and at 57mm is well out.

I checked the formwork system and came up with a way to make it work, even though there was 65mm difference between the 2 columns. However it is up to the clients rep whether they will accept this. They are well within their rights to have the column demolished and redone correctly, however the rough estimate is that will cost around $100000 (all paid for by JHG). To make matters worse the first 3 spans of the bridge depend on span 2 being lifted in by 2 cranes sitting on either bank (one 350t and another 250t). So spans 1 and 3 can’t go in till span 2 is up. By not being able to pour pier 2 headstock the whole sequence is delayed. There is also the added pressure that the 350t crane is only available for a small window. Outside of this we will need to find another crane, which will cost much more to get on site. I made sure that the bracing on pier 1 columns was much more robust, it meant the pour was delayed by a day but both columns were well within tolerance so it was worth it in my opinion.

Broken pile
The piling rigs have now moved onto bridge 2 to start work, having crossed the Bruce highway during a night time road closure without incident. With the end of piling on bridge one this was a suitable time for a handover to another engineer who was initially only responsible for the bored piles and retaining wall. With everything handed over I was rather amused when on second pier of piles in bridge 2 they managed to snap a pile.

The clients rep blamed us, and we blamed unforeseen ground conditions. There was no-one from the clients team on site at the time, yet they are still claiming that the piling subcontractors “pulled the pile”. For those that don’t know the term, when driving a pile they can have a tendency to deviate from the vertical. In the early stages of driving some minor corrections can be made, but once a decent length of pile is in the ground any attempt to “pull the pile” into position can damage and even break the pile. To back up our case we have over 800 piles that have been installed as per our sequence without incident. I’d like to think that it was my steady hand on the tiller which stopped any piles breaking, however that is merely a happy coincidence. The next step is waiting for direction from the client. Any action prior to this could be a waste of time. Looking at things the way they are I see 3 possible options open:

1) Ignore it. Cut the pile off below the blinding level and don’t tie it into the cap. This requires the designers to go back and look at what support/resistance the pilecap as a whole needs to provide. All the other piles in the pier are well over capacity. The steelwork in the cap would likely need to be redesigned to ensure the forces are transferred away from the gap of the broken pile.

2) Use it as is. Use what capacity there is in the broken pile and tie the pile into the cap as though there was nothing wrong with it. This would also need the same checks as option 1, as the capacity of the broken pile would be unreliable over the lifespan of the bridge. In effect its just option 1 but not wanting to waste what has already been driven.

3) Drive another pile adjacent to the broken pile (towards the centre of the pier). This would be within the 3xD that the piles are currently spaced at, the steelwork would need to be redesigned in the pilecap and access to the position for the piling rig would be difficult (but not impossible). If the pile did break because of a large discontinuity then this pile may too also get damaged.

The Spaniard
Soon after my return there was a visit from “the Spaniard”. This is one of the executives from Groupo ACS who own Hochtief, Hochtief in turn own Leighton holdings, they then own John Holland. So lots of the executives from John Holland were on site to wander around. It was all to do with cashflow and why we were going over budget. His opinion/answer was that we needed to secure our revenue streams before acting on something. The example used was the large pile offcuts that we have on site. The additional cost for these offcuts should come from the client (in his opinion) as the piles are barely making it into the underdrive allowance. My simplistic understanding agrees with him. You would expect that most piles would be at the design toe depth, or that the average for the site as a whole would be close to the design toe (with some in the underdrive and some in the overdrive). However the vast majority of piles are sitting 3m above that design toe. My guess is that the designers were overly cautious in their design, and to reduce the risk of not reaching capacity, went for longer lengths of piles. By reducing the design risk they have created more work for the contractor, but at least there is plenty of capacity in the piles! The recent development that has come as a direct result of the claim for the pile offcuts is the direction from the clients rep that all piles must be driven to design toe. This is adding extra time to each pier, and could potentially damage the piles. The size of the hammer is such that were it used at full drop height the piles would likely split. The PDA gauges were connected after the split occurred to confirm it, and to give an indication of where the pile was damaged (roughly 3m below surface).

I’ve also got my hands on some aerial shots of site that were taken just before I went on leave. They’re worth waiting for the page to load to have a look at as the detail is pretty good.

Having treated my self to a weeks ‘summer’ leave last week, I returned to what can only be described as widespread mayhem on the secodnary lining team. Three members of the team had left, including my line manager. Rats and sinking ships. I am still employed as a section engineer on the ‘binocular section’ of the crossover between the two running tunnels. The tunnel design and construction varies over its length dependent on function. For example, the running tunnels which maintain a uniform shape over a long distance, are driven by tunnel boring machine and lined with pre cast concrete panels for speed of drive. Enlargement works foR platform tunnels and concourses, including irregular shapes are ordinarily excavated and lined with steel fibre reinforced sprayed concrete. Uniquely, the binocular section uses a sprayed concrete primary lining, in composite with a cast in situ bar reinforced secondary lining. I will focus on this here. Binocular Section Function. In operation, the running tunnel will divide into two; the left hand side will form a crossover to the opposing running tunnel. The binocular sections are located in the areas noted EBX and WBX, at the point where the tunnel divides in two.The design is also shown in section, and is mirrored westbound and eastbound. The internal profile, defined here by the bold line, designates the secondary lining, which is all cast in situ. Design. The front face of this section details a relatively large span at approximately 12.6m. This would be considered challenging to complete entirely in sprayed concrete. But the ‘figure of 8’ design creates high stress zones at the confluence of the two tunnels. This requires support which is designed in the form of the ‘binocular wall’ shown as the upright in blue. You will note that in comparision to the remainder of the secondary lining, the wall itself has large proportions. This design copes with the temporary state during the excavation of the second tunnel and prior to ring closure. Sidewall Issues. Aside from the day to day frictions that I will not cover here the casting of the invert, headwall and binocular wall sections passed largely without incident. However, the right hand sidewall was poured in my absence, with some issues. The profile of the sidewall is formed by the use of bespoke poystyrene void formers, which are designed and laser cut by a specialist contractor. They are supported by RMD Kwikiform temporary works, again designed by sub contractor. Despite being contracted out, temporary works repsonsibility falls to us, so I got involved here to check design calcs, and made some adjustments for buildability purposes. Designs are shown below You will note that the profile presents a tricky detail for the pouring and vibration of concrete at the lowest point, particularly given the congested steeelwork incorporated here. Way ahead of this pour, I sought to preempt this issue by designing, in conjunction with the supplier, a self compacting mix, which I trialled and had approved. This was supposed to replace the existing mix, which was also susceptible to entrapping air due to the type of polyfibre it contained. (See previous blog about mix designing – a delight).   Thus I went on holiday happy that I had forecast a design risk, conducted some analysis, came up with a solution and communicated it effectively. (See John, I was listening…) I returned to this…. The poor resolution on this phot doesnt give you the full joy of this. You may note pock marking across the bottom 2/3 of the wall. This is caused by a proliferation of air bubbles trapped in the lower section, exacerbated by poor vibrations. As it turns out, the old mix was used despite my amended activity plan explicitly stating the new mix to be used. The entrapping of air is quite obvious here. I suspect, if the wall was cored, that the mix would have a relatively low density, and may fail on compressive strength as a consequence. You will also note the cold joint which runs the length of the wall. Apparently, pre planned road closures causing traffic in London, delayed the follow on wagons by approximately 4 hours between pours. With no engineer on site when it finally arrived, the site foreman continued the pour based on ‘whether we can still get a poker in the mix’. Conclusions The loading path in this section of wall puts the wall predominantly in compression. That said, there are performance requirements pertaining to flexural strength. Assuming there are no major voids at the cold joint, this should not present an immediate structural problem. My concern is the threat of water intrusion and consequent acid attack in the high sulphate environment of our local ground, over a 120year design life. However, it is likely that these concerns remain on the aesthetic rather than the structural in this instance. The air entrainment is a bigger concern. Although the contractor kindly offered to patch repair the surface to bring it in line with the clients specified surface finishes, I feel like they are missing the engineering risk. I demonstrated the effect on compressive strength that a lover volume can have in my failed mix design trials, and I suspect in we were to core this, we may find voids and poor encapsulation of the rebar, along with a low compressive strength. The client has yet to request this but Im certain it will. I find it hard not to be deeply frustrated and cynical about all this. All of these issues were foreseen and planned for, but coherent planning of a task from start to finish is simply not in the culture here. A single responsible person for these task s is not easily identifiable and noone is held to account.  A common theme throughout my attachment here is that progress always trumps quality, and even cost. These problems were caused by not following the instructions, and a lack of engineering oversight, combined with a rigid application of quality, through the inspection and test plan that I wrote to govern this. The rush to complete, and consequent mistakes made have achieved a delayed program, and extensive rework. We are under an NEC (C) Target Cost contract, so as long as we raise this issue through a Non Compliance Report, the ‘pain’ is shared with the client. So incompetance on our behalf of the contractor has led directly to waste of public money…not only frustrating, but actually quite immoral. In other news, I’ve found something as uncomfortable, as a John Moran Q&A. Tough Mudders Electric Shock therapy

The article below was taken from the Mace news page, and again I thought it was quite interesting!!  I’m hoping I don’t miss the mark again Joe!  Nothing like a bit of crane ‘appreciation’ top trumps!!!

How to build the world’s largest crane

Faced with building the biggest observation wheel in the world, the Dubai-I team is no stranger to challenges or to beating records. And this month was no exception with the delivery and erection of the Mammoet Platform, Twin ring Containerised (PTC) 200DS, the world’s biggest crane.

The PTC 200DS was designed and built by Mammoet in Holland and has spent the last two years in Texas working at an offshore oil assembly depot lifting a 120m spar as part of a deep sea drilling platform. It was disassembled in April 2014 returned to Holland, cleaned, maintained and thoroughly inspected prior to travelling the 6000 plus nautical miles to the UAE Port of Jebel Ali.

To transport the huge crane the 221 containers had to be offloaded and then placed onto articulated vehicles where they were then transported by road to the Bluewaters Island site in Dubai. They were then offloaded by one of the three crawler cranes and laid out in order of erection sequence by the site based team of trained Mammoet erection specialists. The crane is so large that the operation required one LR1600 crawler crane @ 600Te capacity, two No 250 tonne and one 180 tonne crawler crane sited in the unloading and distribution area.

During the erection there have been several critical lifts, in some instances three of the four crawler cranes were used to carry out a single lift. The critical lifts have been impressive and professionally executed by the Mammoet erection team. The most demanding of these was the lifting of the back mast from horizontal to 70 metres with all cranes travelling 60 metres in unison whilst lifting a load of 340Te.

Senior Project Manager Piers Sidey said: “The fact that this will be the largest observation wheel in the world by some margin presents huge challenges on several fronts. The designers are pushing the boundaries to find effective and economic solutions. When you double in height the forces, stresses and deflections are magnified many more times. Secondly since we need to maximise off-site assembly as far as possible the wheel will be delivered in very large pre-assembled sections up to 118 metres long and 1800 tonnes in weight. Hence the need for one of the biggest cranes in the world.”

The Mammoet PTC in numbers:
221 containers required to transport PTC200DS
3,400 tonne lifting capacity
830 tonne – weight of Dubai-I leg
1,800 tonne – weight of Dubai-I spindle and hub which will be single lift at over 100m high
123 metres – length of boom
55 metres – length of jib
182 metres – total height at tip of jib
87 Te – weight of hook block
123 metres and 415 tonne – heaviest lift during construction by three cranes

Here is a pdf with some more info of the process of DubaiI crane process.

I noticed an interesting article in the NCE mag this week (kind of rare I know!) about the relevance of EuroCodes to Temporary Works design and the use of the term ‘Safe Working Load’ (SWLs).

The key issue the author brings up is how do you use a prop with a ‘Safe Working Load’ in a EuroCode compliant design?  Was the prop originally designed to EuroCode? Is it ok to assume the ULS capacity is 1.5 times the manufacturers stated SWL?

Having done a few temporary works designs now using just SWL (with no factors at all), as well as with ‘old BS’ verification and new EuroCode verification it certainly is a bit of a muddle.  Proprietary equipment specifications can have a myriad of terms which can be confusing, so sticking with Safe Working Loads in my view is essential.

Has anyone come across this problem???

Temporary Works Article