Holdfast Training Services Trial Blog

If you want to see a pained expression worse than Ryan’s when he realises the last chocolate digestive has been taken, walk into your offices and utter the words ‘we’ve had a HV cable strike!’

My last blog commented on the progress I was making towards my DO’s with work on the Dwarf Wall, HV ducting and student mentoring. I have completed 192.652m of the 619.310m Dwarf Wall, which is as far as I will now take it. This is no bad thing as I got as much experience out of it as was likely. The student has fledged and flown the nest to start work on the second rail load out silo for IRFT 2.

The HV ducting and deluge main proved more challenging than it first appeared and there were a whole host of learning points from the experience.

As part of the preparation for the work I organised a GPR survey to identify all the existing ABP services crossing the area we would be excavating through. This all formed part of the various permits and RAMS I completed, as mentioned in my previous blog and in detail for AER2. We successfully undermined 5 sets of existing HV lines at various points, a number of live water mains and several fibre optic telecommunication cables without incident. On the last HV cable crossing this happened:

Unfortunately it was the primary HV line to the main unloading jetty (location shown in photo below), powering all the infrastructure including the cranes, where 2 container ships were being unloaded at the time. It was also during the crossing of the main access road to that jetty that we were only allowed access to for one 12 hour period. Balls.

The first photo shows the primary 11kV line that we hit and the fibre optic cables that ran in parallel. There happened to be a secondary HV line directly underneath the primary that subsequently proved useful. By the skin of our teeth only the armour surround to the cable had been pierced not the inner cable and it never went bang despite being wrenched a few inches up by the excavator bucket.

So what happened??

This was my section of works but in the greatest tradition of every troop commanders favourite sapper, I wasn’t there at the time boss! The previous night I had issued the permit to dig, briefed the team (including the engineer who would cover for me in the morning) and prepared the road closure procedures for the following day. The route of all the cabling was identified through the GPR drawings, checked with a CAT scan and sprayed in red onto the road. The following morning the team set to work and the road tarmac was cut using the road cutting saw.

This is where a small series of errors came together resulting in the strike.

The road cutting saw creates a lot of dust that when suppressed by the accompanying water unit covers everything around it in a thick slurry, including red spray paint marking routes of HV lines.

The team that I had briefed the night before got pulled onto another task early on in the works (operator availability as ever) and the replacement crew, despite having also attended the evening brief, were not given a thorough HOTO or up-to-date brief by the engineer or foreman. The tarmac line that had been cut was assumed to be the line of excavation to the full depth of the ducting, as the red spray was no longer visible they just cracked on and dug away.

The engineer left in charge hadn’t noticed the red spray was no longer visible, assumed everyone had understood the brief as well as himself and was taking photos of a manhole to one side when the incident occurred.

The foreman working on the task had only arrived on site the day before, had been briefed but wasn’t really ‘acclimatised’.

I’m sure you’ll all say ‘yeah yeah’ but my timing couldn’t have been worse as I walked into the works area to hear the foreman shout ‘whoa, whoa, whoa, that doesn’t look too good …….ah Joe you’re here……take a look at this…..’!

So what did I do??

After calming down and realising nothing had gone bang, nobody had been BBQ’d, (thanks Harry for those inspiring HV strike H&S videos), and everything on the jetty was still working, I basically conducted a 4C’s operation! Train hard fight easy and all that.

I phoned my section manager (who thought I was joking) and informed the on-site health and safety advisor.

I soon had a battlefield tour on my hands as every man and his dog came down for a nosey and a photo.

Everyone was fairly pragmatic about the situation, some more so than others and I had to laugh when the foreman suggested poking it back into the ground and covering it in concrete before the client found out!

The main HV line serviced the whole jetty, the secondary line powered just the cranes and ancillary equipment ie the vital unloading equipment. After much discussion it was decided that the power would be switch to the secondary line for 2 hours so the primary could be inspected but allowing the unloading of the ships that were docked to continue. Once complete the main line was switched back on and a cordon was put into place until the ships had been completely unloaded. This then gave us a 12hr window, between the high tides, a couple of days later to get it fixed prior to the next ships arriving. The damages for a ship in port not being unloaded are huge, so realistically that was the only choice.

So what I have learnt?

Technically.

GPR Survey. The investment in a GPR survey is worth every penny and I cant recommend it highly enough in similar circumstances. The amount it reduces the risk alone is worth the investment. The cable we hit, we knew the location of, which makes it even the more frustrating. The CAT & Genny is very good for identifying services but proves difficult on our site due to the industrial nature of the fill that makes up the top 5-7m of ground as it is full of metal and old cabling. In addition the clients existing service drawings, that formed part of the initial tender, are woefully out of date and hugely inaccurate and some of the electrical cables service night time facilities so the CAT SCAN may miss them in the day, the GPR survey will not. The GPR survey allowed us to identify the services and then we could use the CAT SCAN to confirm the locations as it much easier to use on this site once you know the path of the service. I was also surprised with the accuracy of the GPR depth estimations as 90% of the time they were spot on. This has led to my insistence on getting the same done over my new site for the substation build I will be conducting, as there are a number of services including HV around the existing substation that mine will replace. I suppose the ground is a risk whatever way you look at it!

How to fix HV lines! The armour was cut away and replaced followed by a mould that was pumped full of resin to reinstate the outer casing. This was then re-sleeved with the ducting. We also used the 12 hour period to complete the undermining of the lines and fit our 12 ducts into the manhole as can all be seen in the photographs below.

Managerially.

Health and Safety. Don’t skimp on the paperwork. The H&S advisor rightly conducted an investigation and after his initial enthusiasm to hang someone was dampened, he used the opportunity as a lessons learnt scenario. He concluded that the paperwork was actually to a standard that he had rarely seen on the site! The RAMS, drawings and permits to dig I completed were comprehensive, up-to-date and everyone had been fully signed up so my arse was covered. I even suggested an additional measure that has now been adopted on site similar to the sign off sheets seen in the military when a memorandum is circulated to ensure everyone has read and understood the permit to dig. Up to that point everyone had to read and sign the RAMS but only the operator and banksman had to sign the permit to dig that contained the up-to-date drawings and service details.

Communication. Absolutely key. It was clear that much of the error had come from the change-over of the plant operator and banksman and the lack of communication between the team largely assembled in the morning. There were various levels of information amongst the team and everyone assumed everyone else knew what was going on. The lack of communication invariably led to the strike and was the main learning point from the H&S investigation.

Control. I wasn’t on the site at the time of the incident (have I mentioned that?!). I had handed over to another engineer the night before who knew of the HV line (I had sprayed it out with him) but he had been taking photos of the manholes we had constructed the day before when the incident happened. If I had been there I would like to think that I would have been more resistant to the change of plant operator and at least stopped the incident as I had lived and breathed those services for the preceding weeks. I was a little disappointed with the whole episode from a personal perspective as we had conducted a number of crossings to this previously without incident, and we stumbled at the last fence.

I have now completed my summer leave and have started setting up my own mini-site for the sub-station construction I have been given the independent command of. The design is yet to be completely finalised but this week I have cracked on conducted the GPR survey (as mentioned above) the CAT SCAN and dug a number of trail holes to confirm the services. I am taking the design co-ordinator down to the site this afternoon as a number of my discoveries (railway lines, CFA piles, pile caps, sheet piles etc) are likely to force additional redesign – watch this space.