Holdfast Training Services Trial Blog

The last few weeks have been hectic to say the least trying juggle sevral different sites. Dickson Rd Overbridge progresses but not in synch with the programme. I have re-written the programme which has been scrutinised by the Construction Manager and he concedes that a completion date of 20 Dec is realistic. The issue here is the backfill, we requested the backfill to be done quite specifically (recall my sketch in an earlier post) which battered back to the level of the top RW. We intended to step up to the next RW level by forming up shutters and vertically blinding with snape sand to the required RL then we would repeat for the next one. This was the method used at Eastwood Rd Overbridge but with hindsight we should have just backfilled to the level of the wingwalls and then backfilled to the formation level of the next RW as we progressed. Because Eastwood Rd has displayed signs of settlement due to poor backfill/compaction the Construction Manager has stressed to me that we must get it right this time and so I have decided to prioritise the deck so that we can backfill against the blade wall before starting the RW’s. We have currently completed the wingwalls at both abutments and will pour the deck/diaphragms in one pour this week. Once the deck is complete this props the structure so that we can start to backfill either side simultaneously up to the RL of the first RW’s. Meanwhile I hope to prefab the steel for the first RW bases so that we can lift them into place once we have backfilled, excavated part of the batter and blinded the area. We can then keep alternating from abutment A to B backfilling and pouring the RW’s in pairs. This issue with the battered back backfill means we have significantly reduced our working areas at either abutment which coupled with the fact that we have rail track through the span means the requirement for craneage (if that is a word) has significantly increased and will continue to do so. I had no choice but to hire a 130T crane the other day to strip the shutters from abut A wingwalls and move them over to the abut B purely because of reach where normally I would use a mobile 25T Franna crane – the cost was $7000/day compared to $3000/day and this will be typical from now on as we complete the RW’s. The batter also means the backfill at the edges will not be adequate enough and we will have to excavate and then re-compact.

Eastwood Rd Overbridge is showing signs of settlement on both sides which has been attributed to poor compaction by the civil team doing the backfill – not the first time this has happened. As this bridge is open to the public I am currently monitoring to see if it still moving which early indication says no it isn’t. However there are some worrying looking cracks on the traffic barriers as you can see from the photos.

        Down Under!

I have also had 6 x LV pits and conduit runs to build at Cowpasture Rd Substation. These look simple but have been an absolute nightmare, they seem to be massively over designed and the 200m walls are practically full of steel. We have poured 4 of the 6 with the 2 pits that lead up an access track to a utility metering panel not yet started. The lids are placed on top at the moment but we will need to concrete them in and over them but I plan to do all 6 at the same time as I will have to order a small quatity of our usual 40MPa mix but with agg of 10mm or less so that the concrete will form into the metal lids. I have had to get another FRP subcontractor in for these pits as the one I was using also works on Dickson Rd and I need all their available manpower for the bridge. Their steel fixer practically refused to do another one after the trouble he had fixing the first two and the constant moaning that came with it I was happy to hire in another subby! All this work is on dayworks which I estimated to take 650 hrs, I last calculated I had about 100 hrs left in the budget to complete the last 2 but with a bit of JH labour in reserve.

I also have a number of Non Conformance Reports (NCR) and associated RFI’s to deal with on practically all the remaining bridges and a few retaining walls but nothing exciting. These are mainly crack repairs, patching work and out of tolerance ‘as-built’ surveys. Settlement at the approach slabs on just about all the bridges has occurred up to about 30mm which is noticeable on the pre-cast parapet sections and on Cowpasture Rd viaduct the approach slab has settled showing a gap between the walkwy and slab which you could get your hand down. This has bee recorded by the client but has subsequently been covered over by ballast and tracj by the rail team so if any remedial work will be required it will be a complicated job. The RW’s in this section have also settled and a gap has appeared between two adjacent panels. The movement has been 70mm back and 20mm down which the designer has said is acceptable has they were expecting movement of up to 100mm. The rectification method will be to fill the gap with a grout but this is on the back burner for now as I have no manpower or time to invest in it at the moment. There is also the issue of improving the access track that is below the wall so we can carry out the work. This small RW (RW14Ua) sits on top of a larger RW (RW14U) which has also settled but the corner of the wall rests upon the corner of the pile cap to Byron Rd bridge. This has resulted in the corner of the wall being crushed and the concrete has broken away. This is also another job on the list but will require the corner to be broken out the ‘stiffjoint’ material and appropriate gap reinstated between the wall/abutment/pile cap and then the corner re-formed. There are also another two corners which have not crushed but will have to have the same treatment so that if the wall does settle on that side then it will not crush. The fourth corner does not rest on the pile cap.

 RW 14U

 RW 14Ua

The Scalabrini Creek Underbridge conduit issue continues. I have had acceptance from the client and the services designer to cut the conduits that do not have a joint for expansion providing that we have operational controls in place for installing the cables. This basically consists of liaising with the rail team so that they are aware of what we are doing and making sure that they have procedures in place for installing the HV cables with a gap of about 50mm at the EJ’s. As all the pulling ropes have been installed using a compressor that blows a sock down the conduit with the cable attached to its tale, the only real concern is any sharp edges on the conduits that have been cut. As the forces involved when they pull theses cables through can be quite high any burring on the edges could damage the cables along its entire length. The metal cover plates will remain off so that a visual can be maintained while the cables are installed but will be bolted back down once they are in place. The main issue at the moment is how to actually cut the conduits. Myself and the supervisor had a go ourselves last week as we had no other labour available at the Rail Team are hounding us to get this done so that they can install power to Leppington station ASAP. We managed to cut the top ones easily enough with a Panel saw from Bunnings (B&Q) but the lower 150mm dia conduits are about 700mm down within the joint and there is only a 70mm gap, not really enough to even get your hand down. I have had two different concrete cutting subbies out to have a look and one said they had a wire cutting diamond saw which sounds hopeful. The construction manager was concerned it might not give a smooth enough cut and asked me to look into Hydro dem (UHP water cutting). He hasn’t yet seen the handy work of the two oxygen thiefs I had to employ on dayworks the other day to cut the upper conduits on the other abutment – if he had he wouldn’t be worried about a rough finish! Having looked into hydro dem companies in the area and having seen this sort of stuff in action when cutting into bomb casings I really don’t want to mess around with that stuff for the sake of cutting  a few UPVc conduits so I intend to give the diamond wire saw a go as soon as they can do it – which I was hoping would be this afternoon but they have now said next week.