Holdfast Training Services Trial Blog

Background
The piling subcontractor has been achieving a very impressive level of productivity now that the hammers are finally fixed. In the initial planning stages of the project it was estimated that they would complete 4 normal piles per day, per rig or 3 spliced piles. Recently we have been seeing the rigs regularly reach 7 or 8 piles in one day. The piles that are being used on site are produced in a local factory. This factory has limited capacity, however started weeks in advance of the piling rigs arriving on site. The precast piles that can be produced per day in the factory is limited to 5 of the longer single length piles or 10 of the sliced piles. The plan had been that with the factory starting ahead of the piling rigs they would have enough stock to keep the site supplied and there would be no shortage of supply. The graph below shows the state of pile supply currently. The piles must cure for 7 days before a hold point can be released and they can be used on site. We are now at the stage that there are 7 day old piles arriving on site.

The contract states that John Holland are required to supply 4 standard pile a day per rig, however this would mean that the crews are stood around waiting for most of the day incurring extra costs to the piling sub contractor. To reduce the costs, an informal agreement was made to stand down one of the rigs and go with just one on site. This would allow 3 cranes to be off hired by the piling subbie and dramatically reduce his costs. The crew from the second rig could then move to another job. The one crew that remains would then work much more efficiently.

Issue.
Last week I was called and asked for an instruction to demobilise the second rig. I was going to do no such thing. It ended up being a bit of a stand-off between the Senior project engineer and the piling subbie, with costs of around $16000 per day starting to mount at the end of the week. In the office we were rechecking everything we had signed and all the documents that we had to prove we had met our side of the contract, while collecting the evidence of where Caporn had failed to meet their end.

The outcome
Thankfully there was a dispute resolution process in the contract, with named senior executives from both companies (the regional manager from John Holland and the company director from Caporn) to undertake negotiations. If this hadn’t resolved the issue then it would have progressed to expert determination and finally arbitration or litigation. But it seems that all is well for now. Rig 1 never stopped working and a resolution has been reached that seems to be keeping everyone happy. We have agreed to supply 36 piles per week to the pilers and they have demobilised one rig and the associated cranes. The whole issue is making me look even more closely on the daily reports that I sign and check on the site diary kept by myself and the undergrad that is looking after the piling.

With a variation from the client this has also provided the opportunity to get some piles from another source. As such the piles for the extra spans that have been added will arrive earlier than if the winner of the original pile supply contract had won the variation. They still submitted a price, but it was much higher than previously, which made it a no brainer to go to a different factory.

Other stuff

The speed that we are cycling through our forms has picked up now, which is good as this is on the critical path and we are now meeting our own targets. The downside has been a drop in quality with some of the elements being produced. In particular the columns seem to be problematic when it comes to consistency of the finish. The worst one so far was on pier 12 (shown above) where you can see the reinforcement exposed and the yellow thermocouple cables (luckily the columns have the least number of monitoring points). I’ve still to write the procedure for how we are going to fix this, and the sections at the top of columns where (after pouring too much) the excess had to be jackhammered out and some of the workers got a bit too enthusiastic. With the root cause being the over pour on the columns there is a lot of effort being put into monitoring that area.

There were a few temp works issues that have come up too. The method for cutting and breaking down the piles has had to be checked and some extra controls put in place. This was brought on due to the piles only just reaching into the underdrive, meaning up to 7.5m needing to be cut off. I’ll maybe include that in a follow on post early next week. I’ve signed of reinforcement schedules to the end of bridge 1 and I’m starting to plan ahead to the abutments and pier 1 and 2 (though it turns out there is no money in the budget for sheet piling…might be speaking to John about possible alternatives very soon)

I also dragged myself round the Brisbane marathon last week and managed a half decent time considering I had done no training. Tim also stopped by mid week while travelling down the coast and we went to grab a steak. By chance we caught some amateur bull riding in the ring at the back of the pub – just your average Wednesday night in Rockhampton.

DB suggested that I might like to record my thoughts post CPR, so this blog is an amalgamation of Steve Dollimore’s email to me immediately after his CPR and my thoughts and views post my CPR (both written before results).

I understand that it is quite early for the current course but it is really worthwhile thinking about this now, as the groundrush at the end of Phase 3 and Phase 4 can be pretty full on!

 

Reports

I spent quite a while on the reports (2k (Experience Report) & 4k (Project Report)) to try and get them just right, working on the assumption that if it was covered in the required detail the interview would be easier. In reality, I probably agonized over these a little too much and left far too many ‘hooks’ as it is not possible to cover everything in enough detail.

I found the reports to be good revision of my time on attachment, but highlighted just how little useful information I had gathered to support my attribute claims. I know this will probably go unheeded, but it is well worth thinking about your CPR docs now and gathering the required info as you go so that you have relevant photos, calcs, or standards to refer to when compiling your reports. As a rough guide, if you are using something as an example for your DO’s it is probably worth building a decent pack of evidence in prep for your report.

If you can get the reports final drafted prior to leaving your Phase 3 attachment, you should get a civilian perspective on what you have written.

 

Preparation

The CPR rehearsals with the lecturers/mentors are really worthwhile. Be prepared by re-reading past AER/TMR’s and most importantly ER and PR. Prepare your presentation well in advance and have a good couple of run throughs prior to the event. (I left this late and only managed a couple of practices before the mock – I think I could have gained more from the experience if I was more prepared.

It is worth doing a second/third mock with somebody willing, to gain a second perspective (I borrowed Steve Dollimore’s recent knowledge and a civilian mate who had just been through CPR). As a result there were very few tough questions that had not considered). I think using a non-military mate worthwhile as they will have a more similar perspective to the reviewers (i.e. not tainted by green).

 

Presentation

The CPR presentation should tell an interesting story, not just be a list of attributes. I found that writing a script then leaving bullet points on the back of the presentation slides was most useful (avoided the temptation to read it).

Scripting is good to ensure you contain the correct information but be careful not to come across too wooden. It should be an informal style presentation that is interesting.

Don’t get sidetracked when you notice them writing during the presentation, at the range you are it is obvious you are looking!

Buy a presentation flipchart early – not many places sell them. A3/A4 is a personal choice, but I would argue that at the range of about 1m across the table from your reviewers, an A4 flipper is perfect (and cheaper).

Keep slides clear. A few photos, or one big one without wording I would say is best.

 

Interview

The interview runs for about 60mins, and I would say is broken down into 15mins fro presentation Q’s, 30mins PR Q’s, and 15mins ER Q’s, with a few randoms thrown in for good measure. By randoms I mean unrelated questions about the ICE, and your views on Civ Eng in general. For example “What can you offer the ICE?”

You can largely guess what the presentation questions will be based on your preparation. This is a good chance to demonstrate sketching ability, either built into the presentation, or to elaborate on something in it after. Don’t sketch in the middle of the presentation – it kills time and looks too planned and therefore suspicious.

In honesty, I don’t really remember much of the interview; it really was over in a blur. I remember being highly attuned to the reviewers reactions to my answers though (At one point one said “Oh dear, that’s not good!” but I was unsure whether it was my answer of the situation I was describing that merited the reaction).

I think all of the reviewers had conducted CPR’s at the RSME before. I was hoping for a couple of newy’s who would be interested in Afghanistan, but that wasn’t to be. That said there were several questions on the military, “How does the Army approach E&D?” “Describe how you did something in AFG?”

I found it interesting that there appeared to be no outright technical questions. Whether there were but I didn’t think they were that technical, or there just were not any I cannot fully remember. The interview was more like an informal chat about my experience that was genuinely quite relaxed. I am not sure if I actually relaxed, but at one point I even strayed onto who the greatest Briton was! (My view that IKB should have come top over Winston C in the UK documentary (Backed up by Jeremy Clarkson) a while back was enthusiastically agreed with).

 

Written Test

Everyone seemed to be pretty happy with their written questions, ranging from views on military future to management strategy.

You are looking at an intro, 6 paragraphs of narrative, and a conclusion – about 1000-1200 words. 

I handwrote, as I think that you can easily waste time by re-writing on a computer, and it also shows you can work without IT. I think only 1 of 4 used a laptop.

The time goes very quickly, but do not skimp on the essay plan, it will keep you focused.

 

Aftershocks

Good to be done, but a 2 month wait for the results is a little too much. Obviously we all spoke to each other afterwards to dissect the interviews and share with each other how we probably f@*ked it up, but retrospectively looking at it I think we all tend to focus on the bad bits and take for granted the level of knowledge that we portray without thinking about it.

Ultimately, there is nothing that we can do now, but I am not burning my notes just yet!

 

Overall

The reviewers will most probably stay in the mess overnight. Therefore time breakfast right to chat in the morning. It is important to show you are normal, even if you are not. 

I think we all spent a lot of time the week before review chatting with JM and RF. In my case, probably worrying too much about the trivia. Without blowing too much smoke up their proverbials, they know their stuff having worked in industry, and offer sage advice that makes you think a little more. Just chatting about engineering puts you in the mindset and helps hone your vocabulary prior to interview.

It is not worth researching your reviewers. I don’t think anybody did from our course, but purely from the work addresses we could work out the rough bent of each of them. It made no impact on the questions asked.

Its not as bad as you think it will be – the reviewers are old pros and they went beyond the call of duty to calm you down.

 

 

Hope that helps. I don’t know the result yet, but will happy to chat through the process and prep with anybody either way nearer the time.

Enjoy the rest of your attachments. Take lots of photos!

 

Westie

Hi all

Some shots from my site in Bahrain for your interest on http://www.roselliott.wordpress.com. Quite tame in comparison to your sites and not so many dramas – but thought you may be interested all the same.

Slipforming of the core at the South Bank Tower began back in May. The 12^th of May to be precise. 12 floors to slipform, from +106m AOD to +154m AOD. That is 48m total.

Slipforming a reinforced concrete core is supposed to be fast, efficient and financially economical. PC Harringtons (our concrete contractor) sold slipforming the core at a pace of 1.5m a day, 5 days a week. So by more complicated maths this makes:

        Duration = 48m / 1.5m per day = 32 working days, or roughly 6 weeks

Therefore,

       Date for completion = 12^th May 14 + 6 weeks = 20^th Jun 14

Sadly, this date for the completion of the core was not met. We topped out today! 5th Aug 14!

Thus,

       Actual duration of slipping = 5 Aug 14 – 12 May 14 = 67 working days

So,

     Actual Speed of slipform rise = 48m / 67 days = 0.71m per working day

At 10 hours work per day, this makes:

     Actual Speed of slipform = 0.71m / 10 hours = 0.072m per hour  

                                                or 72mm per hour

                                                or 1.2mm per min

                                                or 0.020 mm per second

                                                or 20 micro m per second, on average.

A common snail has a speed of 0.001m/s, or 1mm/s, or 1000micro m/s. Therefore 50 times faster than our slipform has climbed!

As I said, the planned speed (or rate) of slipping was 1.5m per day.  That makes the achieved speed of the slip 48% of the planned rate! Is this adequate? It has to be asked whether this was the most economical method of building the tower.

At the South Bank Tower we have a rare set of site conditions. The build ability of tower is generally poor, the complexity of reinforcement is high, the burden of temporary works is also high, access is limited, competition for hook time on the tower crane is high and weather conditions 150m above ground mean that it can be less than conducive to work.

I’ve decided to explore this issue in my latest TMR. What alternative systems could have been used to build the core? Should the tower have been purely steel? Additionally, should Mace have known that achieving a rate of rise of 1.5m a day was over-ambitious? And how was this reflected in the contract to deliver the slipform?

I also want to explore whether the project was influenced by the fact it wasn’t fixed price at the start, and had it been fixed would we still have taken the same decision to slip it.

Having spent the last 6 weeks inside the slip on a daily basis I can confirm it can be fraught, manic and a desperate place. There was never quiet second. PCH performed as best they could in my view. The slow pace was not due to laziness, insufficient resources or commercial will. We as Mace have driven PCH to get this core finished but the sheer complexity has denied us the rate that is normal for a slipform. Other slips on the project (10 floors high) have flown up without issue.

There is very little literature available on the rate of slipforming. Is anyone aware of any? I plan to work out the financial cost the slow slip has caused, and quantify the impact this has had to the project.

 

The Danville flood wall remediation is now in full swing, and is taking up all my time (not helped by the 5hr return journey to site), so my attention has switched from the HQ DLA.  To be honest, it’s no bad thing as struct/civ involvement is now minimal, and I’m not getting much more from it.  Instead of being a small fish in a big pond, I now have the con which is really satisfying.

I have managed to get hold of some photos of the damage caused by the Hurricane in 2011 to the wall – the raise d’etre for my remediation project…

 

 

 

 

 

 

 

 

 

The list of issues we’ve had is endless; the primary headlines are as follows:

– Unforeseen ground conditions.  The biggest issue to date – who would have guessed??

• The temp shoring plan was designed by Larson’s group and hinged on tie-ing into an existing sheet pile on the north end and into the existing concrete wall on the south.  Of course, as luck would have it, despite us supplying drawings that showed a sheet pile, there hasn’t been one found to date.  As such, the excavation on the north end has had to cease at 5ft until a solution is devised – initial discussions with the designers suggest trying to minimise cost and time by using some of their H-piles they have in their yard and slotting in timber lagging between them.  Of course there will be an REA submitted by the prime for lost hours and unforeseen ground conditions (USACE has to approve any new design iot prevent Heath Robinson work…and the approval is allowed to take 30 days!).  This will be heated negotiation – from our standpoint, though the drawings were wrong, we did not dictate the shoring design of tieing into the sheet pile so the risk of it being there was borne by the designer.  The other issue resulting from the lack of sheetpile is how the actual wall will now end, as we had designed it to tie into the sheet pile.  After much debate, we agreed that if a sheet pile was there it wouldn’t do much anyway to cope with an extreme flood event as seen in 2011.  In addition, we are fully conscious that this design is extreme overkill and forced onto us by the Dept of Transport – we would have been content to leave the remedial solution of rock armour fill and be done with it.  Thus the wall will end abruptly but be surrounded by rock armour.

• The geo-analysis and boreholes indicated the necessity for drilling through ‘rock’ (betw 8-10ft) in order to gain their sample to 22 ft.  That therefore pushed the shoring design immediately away from sheet piles to the present circular tubes with welded bolts and plates and timber lagging.  To date, I can count on one hand the amount of ‘rocks’ (>30cm) that have been excavated – normally parts of broken up concrete wall used as emergency fill; the remainder is 95% gravels – everyone is therefore asking the question as to what happened with the borehole samples (3 taken; 1 every 10m), especially as the shoring redesign was one fo teh main causes of several months of delay.
• The damaged concrete wall is now starting to be unearthed – we are unsure how much is there but I estimate at least an 18ft length (x 2ft width) at present.  This will incur removal costs that have not been agreed upon as yet as it was guess work as to how much we would find…additional homework with answering RFPs.
• The 18inch reinf concrete pipe that runs perpendicular through the site taking runoff from the road to the river was initially decided to be dealt with by propping it up.  Upon excavating down to it, it is actually damaged so has been removed and temporarily replaced with a plastic pipe.  This has actually expedited site work, but we will have to pay for a new one.

–  QC and safety ability of the prime.  The prime has used their own guy as the QC rep and the safety offr. That is fine…if he was actually capable. Every time I have been on site there have been issues.  To be fair at the moment there is not a great deal to check QC wise, so errors are pretty obvious.  Annoying that I have to pick them up which results in disappointed Dad type chats…to a 50+ yr old! Somewhat aggravating as well that every question I ask, his comeback is: ”Let me ask the sub”! (the sub is essentially running the show!).  Another classic was my question on D+2 – ‘where’s the E&S control’ (a pre-req for any constr); reply: ‘there isn’t any’!  Needless to say that was the wrong answer; upon me going through E&S plan which he submitted to USACE I then asked where the Inlet protection was (i.e. filter bags attached to drain grillages) to which his response was: ‘What’s inlet protection?’…queue more disappointed Dad expressions, turn the page and show him the drawings!! As for safety, his inability and inaction has now become almost humorous – taking photos of welding (with welder and assistant not wearing eye pro!), workers not wearing high vis (in a heavily trafficked zone), standing right next to an area that has caved in behind the shoring and not thinking to do anything about it.  Sadly, today I’ve been writing up an assasination on him upon request of the USACE area engineer who will use it as additional arsenal when chatting with the prime’s CEO and scoring their performance on the gov database. These nuggets are but just a few of his errors; he takes great photos though!

– Specs, drawings and standards…who wins?  Well, of course standards do, then specs and drawings.  The ‘as-built’ drawings (built in the ’70s) show joint spacings at 30ft intervals.  As a result, the contractor has planned their formwork, rebar etc for such spacings under the pretense that the wall is to be built ‘as-built’ (total wall distance is 90ft).  However, they have now seen that our specs say that joint spacings should be a maximum of 24ft, and the designers drawings show 20ft.  Our answer to their obvious clarification RFI was that backed up by ACI and ASTM – a max of 24ft for a gravity walls.  Queue – delays, rework, REAs, but again our standpoint is that construction must be done by specs unless superseded by standards – both of which coincide; we cannot be blamed or pay-out for errors resulting from using as-built drawings that were not built to today’s specs.

– Means and methods.  As the government’s (client’s) representative we cannot dictate means and methods; this is quite useful at times for keeping one’s hands clean of risk, however I find it exceptionally frustrating when seeing things on site that can be expedited with a bit more planning and forethought, enabling concurrency of work.  The QC manager however, though not particularly capable, is quite receptive to my ‘suggestions’ or ‘if I was to do it, then …’.  A potentially major problem has however cropped up as a result of not knowing the means and methods when approving plans in piece meal.  I have grave concerns that there is no sediment control on the most obvious largest issue – the excavation; thankfully the plant op is pretty handy so debris has been minimal if not nil, but all it will take is one storm and tornado and the pristine protected trout stream will become but a cloud..and the Dept of Environment will be throwing down a rather hefty fine…on the contractor mind, not us.  Just because we approved the drawings does not absolve the contractor of responsibility or risk; our rational for approval was that the dewatering diversion dyke would also act as a sedimentation barrier hence we approved it…the diversion dyke is part of the dewatering plan which still hasn’t been approved yet for a variety of fairly minor issues, and has been held up by the QC manager for a week having mislaid its location in the approval chain on the bespoke USACE IT system that we use for communicating drawings, specs, RFI, REAs, submittals, payments etc.

In other news, the family headed out on a long weekend roadtrip through Pennsylvania into New York state, stopping off for one night at Finger Lakes renown for its countless wineries, then up to Niagara Falls – amazing experience, and well worth the miles!    

   Blomfield Box Depressurisation Design.
Situation General. A review of the ground water monitoring was carried out earlier this month by the design authority (Mott McDonald) following concerns raised over the effectiveness of the current and the future depressurisation designs proposed by the primary contractor (Laing O’Rourke). The design authority highlighted its concerns over the proposed equipment and methods to be used to depressurise the sand and silt layers within the Lambeth Group of soils, on which London and much of the South East of the UK based.
Ground Investigation. There wasn’t one. Prior to ground works commencing on site the site was occupied by a building. The handover of the site was delayed. On the handover of site piling works commenced and no site specific ground investigation was completed, considered to be a luxury rather than necessity given the delays already against the programme and the potential financial implications of further programme delays. Despite the lack of a ground investigation the ground was assessed and has subsequently been proven during the excavation to follow the form typical for London Clay overlying the Lambeth Group of soils.
Engineering Risk .In the case of C502, the engineering risk is not asses to be the ingress of water to the excavation but the risk is due to the high pore pressure within the soil increasing the risk of base heave at the base of the excavation and shear failure of the exposed soil between the contiguous pile wall. In order to design against this risk the requirement is reduce the pore water pressure in order to increase the effective stress and thus the strength of the soil at the base of the excavation. Whereas water ingress is a property of a high permeability soil, high pore water pressure is a result of low permeability soil and as such the two conditions require different well designs to address the riskAdditional risks are identified as programme delays whilst works are halted pending the approval and implementation of an appropriate depressurisation system.

Contiguous pile wall with gaps exposing soil.
Current Depressurisation. The C502 contract and site (Liverpool Street) is in close proximity to the running tunnels being constructed adjacent and beneath the C502 site by the C510 contract. The nature of tunnelling has required C510 to have carried out depressurisation of the ground and since Aug 2013 C510 have been pumping at a rate of 300 to 600 l/hour from a system of ejector well points. The well points have been located in the sand / silt horizons identified during the C510 ground investigation. The ground investigation had shown that the pore water pressure was above the accepted levels specified by Crossrail. Following pumping by C510 the pore water pressure was demonstrated to have been reduced through the monitoring of a network of piezometors. In contrast C502 had adopted a deep large diameter well system with submersible pumps that are situated beneath the sand and silt layers within the Lambeth group of soils and have only achieved 100 to 200 per day. The two concerns that have been raised are:
1. C502 does not appear to have taken into account the effect of the depressurisation effect of the C510 ejector pump system in artificially lowering the pore water pressure. On completion of the running tunnels parallel to the C502 site, C502 will no longer be able to rely on the effects of C510 pumping.
2. The use of submersible pumps within the Lambeth group of soils will not be efficient enough in lowering the pore water pressure to within the acceptable levels due to the low permeability of the sands and silts.

In the case of C502, I have assessed that the current depressurisation system that has been employed is not appropriate for addressing the actual risk posed to the project. The above graph clearly shows the impact of the c510 ejector pumps on the porewater pressure with a steady decline in the pressure, althoug it still remains above the Amber levels set by Crossrail. Over the period of Dec 13 C510 stopped pumping during a pause in works. Over this period C502 continued to pump however the porewater pressure rapidly rose within the laminated beds. Then steadily reduced once C510 recommenced pumping, but still remaining aboe the amber levels. This is clear evidence that the current well design is insufficient to address the risk of high porewater pressure.

Well Design. Although further research is required to understand the details of the plethora of different well systems available currently, it is important to ensure that the correct system is employed to address the identified risk. The systems can loosely be categorised as Deep Well system or Vacuum assisted systems

Vacuum Assisted Wells. The basic principle of a vacuum system is that by generating a vacuum within the well an area of low pressure is formed which in turn lowers the porewater pressure. These systems are best employed in soils of low permeability in which pore water does not freely flow and must be drawn out of the soil to lower the overall porewater pressure.

 Diagram showing layout of vacuum well system & Onsite Vacuum well

Submersible Pump Wells. A submersible large diameter well relies on a high permeability soil to create an area of low pressure and to establish a hydraulic gradient. These well systems are suited to high water flow and are used to address the risk of ground water ingress to a site.

 

Diagram showing submersible well system

Conclusion The publication of a report from Crossrail that has required C502 to revise their depressurisation system has caused a level of disagreement on site with many of the engineers seemingly missing what the actual risk. There appears to be a common misconception amongst the site engineers that high volumes of ground water ar symptomatic of high pore water pressure and the risk of base heave. As a result many do not share the Crossrail concerns of high pore pressure posing the risk of base heave and are appose to utilising a vacuum system that will delay the programme and cost ultimately more to install and run.
I can hear Johns words once again” never assume anyone really knows what they are talking about”

Following the PFA ambush of last week, BFK have found themselves backpedalling to find a solution. A contract wide issue that is still being discussed by senior management up in the ‘Deathstar’; however, down at Fisher St, we critically need a self compacting mix trialled and approved before the middle of next month, should the PFA risk manifest itself. So with an empty chair where the materials manager used to sit, and our Materials Tech jumping ship, we were down to a cast of one….

Requirements  

The client’s materials and workmanship specification for cast in situ dictates mix design and trial requirements as follows:

Temperature:  2 key points:

• At the time of deposition of the concrete, shall be in the range 5 degrees and 30 degrees. (A planning figure for expected heat gain is approx 10 degrees per 100kg of cement per m^3. Our mix contains 270kg per m^3, and therefore a 27degree heat gain on a 30 degree ambient temp would remain in spec because….
• The upper temperature limit of the placed concrete should not exceed 60 degrees C. Designed to minimise the risk of thermal cracking.

 

Testing. During trial mixtures need to demostrate results for:

• Compressive Strength
• Consistence
• OvenDry density
• Fresh Density
• Bleed
• Segregation

Testing is conducted on at least three specimens from at least three batches, andis in accordance with Annex A of BS EN 206-1:2000 and is a thrilling good read!

Temperature Testing

In order to demostrate the temperature gain and the max temp value, a 1m^3 sample is poured into a ‘coffin’. This coffin is installed with thermocouples which will measure the core temp, surface temp and the ambient temp during curing. This setup is shown below.

Temperatures will be recorded by the data logger at a rate of every 30mins for two weeks.

Concrete Strength

Requirement:

In Situ Concrete strength requirements, C8/10(12hrs), C32/40(28 days)

Test cubes will be crushed at the following frequency, in accordance with the specification. 1 x 12hr, 1 x 24 hr, 3 x 7 day, 3 x 28 day, 3 x 56 day. This frequency will give indicative early age strength gain for reassurance, followed by the criteria test at 28days. This allows concurrent activity…I have written the Materials Compliance report for approval by the client on the basis of the early age stregth gain;it has been approved, on the caveat that it does gain the 28day strength. If this criteria is not met at 28days, the 56 day cubes will be crushed, and the results will be demostrated to the client for approval.

Consistence

A slump/flow test is conducted in accordance with BS EN 12350-2. A critical feature of the self compacting mix in this instance is the workability. The location in the works dictates that the concrete pour would be difficult/unsafe to effectively vibrate into position, and thus a flow to allow movement into these areas is an imperative.

The specification requires samples to acheive a flow result of 490mm – 650mm. This sample achieve and average measurement of 550mm. Additonally, bleed was visually inspected on this sample and considered to be the within limits

Segregation

Three cylinders of 150mm diameter and 300mm height were cast for the batch. The cylinders are then sliced into 6 sections of equal thickness. The mass of each slice is then measured and the density calculated to determine density variation throughout top to bottom of the sample. The average variation from the top to bottom of the cylinder shall not be greater than 10% of the mean density of the concrete

So with help from the concrete supplier, we’ve designed and tested a self compacting concrete mix, that thus far is performing as required by the specification. If it continues this way, my mix design may well be used throughout cast secondary lining throughout the western tunnels. Terrifying….

BUT…before there is a mass protest/retirement at PEW!

Just as I was about to publish this, I’ve just received a slightly panicked email. Due to concrete suppliers switching to GGBS after the PFA shortage, and a problem with the discharging of ships at the Port of Entry at Tilbury, UK GGBS stocks are currently at 30%! Brilliant…

 

The project has evolved in recent weeks with several variation orders taking the total value of the work from £63m to £121.5m. These additions include £6.5m worth of variations to the initial contract covering a number of smaller embellishments and alterations, £2.5 for a RC slab in the coal yard adjacent to the site, £2m for a radial arm stacking conveyor also for the coal yard and £47m for IRFT 2. IRFT 2 is a sizeable extension to the facilities currently under construction including 4 more RC Biomass storage silos, an extension to the existing conveyor system and another rail load out facility and accompanying silo. The work on the coal yard slab and the piling for IRFT 2 has started and extends the duration of the whole contract from October 14 until July 15. Part of the site (phase 1) was commissioned on 22 May 14 and now fully operates from the lorry load in area to the rail load out facility. This allows large Biomass container ships to dock at the port, where HGVs can be loaded directly and then the pellets can be transferred to the rail load out point for onward movement to Drax power station. Part of this commissioning included testing and individually commissioning all of the electrical, safety, dust and fire suppression systems and the establishment of an operations team to run the facility. To date over 13000t of wood pellet have been loaded and transported to Drax power station. The completion date for IRFT 1 phase 2 (the rest of the site) is currently delayed by 22 working days / 30 calendar days and as such performance testing of the plant is scheduled to begin on 13 October 2014, the site is running a 12 hour day / 7 day week to maintain progress. The progress for IRFT 2 is currently on schedule with work having started on 09 June 14.

The current site.

Roof truss lifted onto silo 1.

My part in this, the dwarf wall, continues although at a slower pace due to increased pours for the roof slabs to cap the IRFT 1 silos, but I now have other projects to keep me busy in my section of works.

The Dwarf Wall continues.

These additional duties are allowing me to knock off quite a few of the harder to achieve DO’s.

I am now also responsible for the excavating and placing of several 100m’s of HV ducting and a water deluge main for the fire suppression system of the previously constructed Conveyor 620 system. Whilst technically simple the mountain of paperwork I have had to complete for each section has allowed me to gain some purchase working towards the difficult DO’s. The ducting effectively runs between the various substations, old and new that border my section of works, hence the responsibility, and cross a significant number of existing live and non-live services.

Ducting runs into a future manhole.

I have completed an overarching method statement and risk assessment for the task, breaking it down into individual sections or ducting runs between the existing and to be constructed manholes. This includes the procedures for working parallel to and crossing over existing services including live HV cables; a detailed traffic management plan due to several road closures (not popular with the client, ABP, running a very busy port) and the safety precautions for working in deep excavations.

Prior to this I had to conduct an in-depth analysis utilising all the available drawings provided by the client, utility companies and a Graham commissioned GPR survey to pinpoint all the services. I then verified these findings with a CAT Scan survey having just completed the CAT and Genny course (one for the CPD record).

I have then been briefing the subcontractors outlining the programme of works, the methodology, the risk mitigation procedures and any residual risk before getting them to sign up prior to sending all the data through to the client for their final approval.

All of this activity has allowed me to progress towards a number of DO’s (B2, C1, D1, E2).

I have also volunteered to mentor a year-long placement student who started in earnest last week. This additional responsibility has allowed me to consolidate my experiences to date and share MY extensive knowledge. I felt it necessary to step off on the right foot so I immediately grilled him for definition of undrained shear strength to gauge the depth of HIS knowledge…..there was a long pause…..an awkward shuffling of the feet…..a look to the left and the right for moral support…..and then came the McGuirk 1000yard stare…..he didn’t know, can you believe it?? I couldn’t. What are they being taught at uni these days? I gesticulated wildly, banged the desk and was about to unleash my pavlovian response when I got distracted by a chocolate digestive. I’m surprised I’m still talking to this simpleton but I’ll tough it out for now as it is proving another excellent opportunity to knock off some DO’s (C3, D1 and 2 and E4)!

I should have the ducts finished by the end of this week, the wall by the following week prior to my summer leave. On my return I am likely to be given an independent command……my own bespoke site about a mile down the road to build a sub-station all by myself! I have also requested to be part of IRFT 2 rail load out silo slip forming team to ensure that I get the maximum exposure to as many different construction processes as possible. No real reflections this time but plenty of DO progress.

Well the Network Rail Road was meant to open on the 26th Apr but due to various issues that I will go into a bit later that did not happen and only a small portion was opened. Grand opening number two was the 30th Jun and I hoped to write a great blog with pictures of us all celebrating a milestone, but 2 weeks later we are still not finished. So why has such a simple task of building an access road been so difficult I hear you all ask. Let me explain…

Here is what was explained to me back in Feb:

Mission: To construct the Network Rail Access Road once all services have been installed.

Concept of Operations
Intent: To open the Network Rail Road for construction traffic.

Scheme of Manoeuvre: Install deep foul drainage, then surface water drainage, followed by shallow services such as HV, potable water, rising main and comms, install the final road build up and surface.  The diagram below highlights the main locations with the road running along the left side of the picture.

Main Effort:  To open the road for construction traffic use by 26 Apr.

Constraints:  The road is bounded by the Network Rail arches (the main line into Victoria) in the West, the sheet pile cofferdam of the basement in the East and the River Wall to the North.

Again it all sounded pretty straightforward, the sub-contractor had a realistic looking programme and they had already made good headway on part of the deep drainage when I turned up in Feb.  So what has gone wrong?

Issue 1.  The major problem has been a temporary works issue that arose from a contractual decision.  The capping beam of the sheet pile cofferdam for the basement was originally in the groundworks sub-contractors (O’Keefe) package but as a cost saving effort it was taken out and put into the concrete frame sub-contractors scope (Byrne Brothers).  With the contractual team happy in the thought that they had saved a few pennies the construction team carried on building.  It then became apparent at the start of March that we kind of needed the capping beam to hold up the road that we were building and now the contractor had changed it wasn’t going to be built for a few more months. 

Solution: To cut a long story short we ended up getting O’Keefe to design a temporary retaining wall for the road to allow the construction of the road and the formation of the capping beam.  This was in the form of a king post wall made from UCs and trench sheeting and pre-cast L-sections (my idea stolen from John’s retaining wall lectures!).  The pre-cast sections were suitable for south of the pumping station where they would fit in with the services but not for the north.  These were installed quite quickly and the south section of road was opened on the 26th Apr as planned.  The king post wall installation added another 6 weeks and probably 10’s of thousands of pounds to the cost of the groundworks package. 

Issue 2:  The road level was designed to give enough cover for the shallowest main service which was the rising main.  The Project Director wanted as many of the smaller branch connections to supply the bridge arches (mostly clay drainage pipes) in as possible prior to the surfacing of the road.  Once constructed it was apparent that these were not going to have enough cover under the road.

Solution:  Ramp over them, chuck some trench plates over the top and hope they don’t get trashed! 

Issue 3:  Nobody had actually designed the northern section of the road.  The design engineers Buro Happold had helped with the suggested temporary levels of the main part of the road and this was signed off by the Carillion Temp Works Designer (TWD) (who doesn’t work on site or solely on this project).

Solution: The Carillion Project Manager suggested an idea to the TWD, he said no, we amended the design to his comments, the Environment Agency Flood Defence Consent people said yes so we cracked on and built it. 

Issue 4:  On the grand opening take 2 on the 30th Jun the Project Director walked the road with Byrne Brothers (who will be the main user) and they deemed it was not fit for purpose.  Despite being built to the designs it was both not wide enough (for 2 way traffic) and too wide (not enough room to construct the capping beam).  They had intended to have unloading areas for the tower cranes and vehicles passing at numerous points along the road. 

Solution:  Remove the pedestrian walkway, push the vehicle barriers closer to the edge, make it wider in the north (ignoring the design of one TWD and using another ones design that allowed for more surcharge on the sheet piles) and hold your breath and close your eyes as your truck squeezes past the artic lorry:

 

So what have I learnt from this rather frustrating and costly ordeal? 

Communication is key.  The section engineer in charge of Byrne Brothers is too busy to attend construction team meetings and therefore has never communicated the actual intended use of the road.  If the sub-contractor and I were told that they intended to unload vehicles then we could have flagged up the width issue months ago.  We could have also planned the barrier system to ensure the widths were adequate rather than build everything then strip it out again.

Plans should be war gamed.  The decision to remove the capping beam installation from the groundworks package has significantly affected the road construction.  Changes to the plan should be communicated and discussed with everyone that it may affect so problems can be identified early. 

Have a clear reporting chain.  Too many people have been involved in making rushed and ill-informed decisions with regards to the road and nobody has been the single point of contact in charge of it’s construction.  I was given the responsibility of monitoring the installation but it became apparent that I had not be told the end user’s actual requirements.  Decisions were made by the Construction Manager that then didn’t work on site and he should have delegated the responsibility of designing a solution to me or one of the other section engineers who work frequently on the site.  We could then brief potential solutions to allow the senior management to make an informed decision.

Well tomorrow I get to draw up the second sketch of remedial works and hopefully some white line loading bays will get painted on the road on Sat and I can have the grand opening take 3 on Mon.  In the mean time I will be trying to help design an elevated footpath to help widen the road some more!  I think a more detailed (and slightly less sarcastic) analysis of these technical and managerial issues associated with the Network Rail Road could be the next TMR topic for me.

 

Situation.
The northern wall of the Blomfield Box Superstructure runs parallel to the London Underground District line. A heavy duty fence had been erected to provide the required barrier between the two sites and to protect both personnel working on site and trains from construction activity. Concerns over safety and constructability of the current design of an insitu RC wall and aluminium rain screen cladding.
Build-ability: With the heavy duty hording in place there is no means to access the other side of any formwork to strike the formwork once the concrete has been poured. Left in place form work was looked at to overcome this issue but the issue of affixing the rain screen cladding would still be a problem.
H&S: In order to construct the rc wall and cladding access from the track side would be required to erect formwork and to fix the rain screen. Due to the live track this would only be achievable during engineering hours (0100-0500 daily) during which time the track is in places still live other than those sections that work is taking place.
Commercial: The closure of the line and works completed during engineering hours is very expensive with cost payable to both London Underground for line closure and in overtime for the Laing O’Rourke operatives. It would also have a knock on effect of additional labour cost as those working over night would not be available to work the next day shift, therefore additional operatives required to ensure the day work is not affected.
The proposed solution was to use a precast concrete cladding section that could be lowered into place and fixed from the inside to remove the problem of live track side working and to reduce the need to work in engineering hours. The requirement for the precast is as per the Project Managers Instruction below:
1 Change the cladding arrangement at Blomfield Box North Elevation from the current “aluminium rain
screen on RC/ Blockwork substrate”, to single skin Pre Cast concrete plank spanning vertically as per

a. Liaise with C138 – Peter Churton, and agree: 1) Loading; 2) Fixing restraint requirements; 3) Any
changes required to the concrete profiles; all to be subsequently recorded and agreed in an ICD.

b. Design, detail, manufacture and install cladding in such a manner that the works can be achieved
without the need for temporary access/disruptions to the railway face of the building.

c. The joints in the PC planks to be detailed with solid mortar/ grout infill with adjacent planks locked
together by interlocking rebar detail, generally as provisionally agreed with C138/ CRL during visit to
Explore this winter.
The issue that has now arisen is that the PMI was issued having not consulted all departments and has been to constraining in its direction and has resulted in a period of abortive works that have subsequently lead to compensation proceedings.
The new issues:
Non Structural: the precast wall is now to be a cladding/fascade and not a structural wall. This means all connections must not become load pathways and load the wall. As the superstructure will now be acting as canterlever and we have been told to assume a 20mm deflection the connections must be flexible enough to account for this.
Fixed grout connections: The connections have been stipulated as grouted. This has given us a number of issues: Firstly the grouting of joints means that there will be no flexibility in the joints, therefore the panels will need to be stacked on top of each other and that the 20mm deflection will need to be accounted for in the connection between the superstructure and the precast panel and not between the panels themselves. Secondly the purpose of using precast panels was to remove the requirement to access from the LU live track side. The use of grout to seal the connections still requires some form work to prevent the grout flowing out of the connection during pouring and then the form work would have to be struck from the track side.
Architecture and planning: the accepted precast drawings by the architects and the planners show the precast panels fixed externally to the superstructure. This however requires that the precast panels are fixed to the original rc wall location as there is no structural plinth directly at the base of the precast panels new location.
Heavy duty fence line: Having set off down a proposed method of affixing the precast panels to the superstructure and having though we had resolved the structural and architectural issues I thought I would just check the fence alignment. One survey and painful lesson in using AutoCad I discovered that the space between the heavy duty fence and the precast panels would only leave 40mm of space in which to manoeuvre the panels into place. Time spent in reconnaissance and all that….In during my investigation of the heavy duty fence line I raised concerns that should we proceed with installing any wall be it RC or Precast once fixed in place there would not be room between the electrical cable rails and the new wall to access the fence to allow for its removal. As a result the fence would become a permanent feature. This I knew to be unacceptable to LU.
M&E: The show stopper however has come in the form of permanent services. The original design of the services was hard against the RC wall. The new precast panels once fixed external to the superstructure would only leave 200mm gap. This presents a maintenance issue as the connections would have to be exposed in order to account for any deflection and would therefore require inspection and maintenance. Having raised this with Crossrail and that we would need alterations to the M&E it soon transpired that this was not possible without incurring huge redesign costs. IN addition the possibility to use access hatches through the M&E ducts to conduct future inspections and maintenance would also cause large commercial issue in the future. The ducting is to be used to provide ventilation to the shaft, station platform and running tunnels. Any interruption to the ventilation would result in the closure of the station. As a commercial business this requirement for periodic station closure to maintain the precast panel connections is not acceptable by Crossrail.
Conclusion:This fire and forget approach is becoming a bit of a theme on site with departments and individuals reacting to issues and concerns raised without fully working through the consequences. While in this case it was for us to resolve the issue the constraints placed on the changes allowed little room for manoeuvre. After all the design changes and arguments over the structural design of the panels and waterproof connections the elephant it the room turned out to be the heavy duty fencing. Originally proposed as a means to avoid live track side works the precast panels still require the fence to be removed and this can only be done live track side.
We are back to square one, the PMI has been retracted and we have been instructed to now propose a new solution or accept the original designs and the risk that are associated with this. The abortive works that have been completed have now been passed to the commercial team to proceed with compensation proceedings against Crossrail and all for a getting out of the office and fully understanding the situation on the ground. This episode harks back to John and his lessons on retaining walls in that the designs only show the wall in place but if temporary situation won’t allow you the path to the permanent state then you may need to rethink the permanent state. And a lesson from myself in that sometimes the temporary and permanent conditions must consider not only the engineering risk but also the commercial and other department risks.