Overlaid and Compiled Plans: Why They Invite Assumptions

0:04Hello everyone. I'm Pete Ashcroft, director at Sigma Solutions. We're a specialist training company providing training and utility detection. Personally, I've been delivering training for about 23 years now, working all over the UK and I spent time with tens of thousands of teams locating, excavating every day in our foot for paths. Today's little presentation is to talk about overlay stats plans or what some might call a QLD drawing. For anyone that doesn't know, when I

0:34talk about stats plans, I'm talking about the utility plans provided by the utility owner. They come as individual plans from the provider, showing one type of service per plan. They are famous for being inaccurate, and I often describe them as plans of where utilities should have been put, not always where they have been. We're making advances in digital technology. Information is demanded quicker and it's being provided quicker. There are facilities out there making it easier than ever to obtain these plans. However, what I'm now seeing more and

1:06more of is compiled drawings or overlay drawings. This is where the individual stats plans have been compiled and overlaid into one drawing. And I'm seeing these being used more and more on site by teams that are doing excavations. I do not agree with this and I strongly believe that individual plans should always be be used by teams performing the excavations. When we compile these drawings onto one plan, although it might seem simpler, we lose important information and we start to

1:37make assumptions. And this is one I want to try and highlight in this mini session. I also want to be clear this session and my observations are in relation to teams on the ground using these plans while excavating. Overlaid stats may serve a purpose for other activities like planning and design. So let us begin. We're going to look at a little example just for this small section of footpath which is near our office and training center in in Wigan.

2:07And the first drawing that I want to show you for this area is the again the individual stat. This is an extract from electricity northwest showing us the electric cables that are in that area. For anyone that doesn't know, orange is LV. If we give this individual drawing to somebody working in that footpath, the information that we're giving to them is that there is an LV cable in that footpath and there are three house connections. Anybody that knows starts knows that that could be inaccurate. The

2:40position of that cable in that footpath could be at the curb. It could be in the middle. It could even be in the road. But the information that we're giving to someone by giving them this plan is that there is an LV cable there. Let's now look at the gas plan for the same street. So this is an extract from the gas drawing. And what this plan is showing us that in that same footpath, there's also a gas pipe. Again, position may be inaccurate, but the information that we're giving to

3:10somebody is there is a gas pipe present in that footpath. Also note on this individual plan, we have offset measurements here. We also have the pipe diameter, but the important one here is we have the material. This is important because this is telling me it's plastic. We can't detect that with a cat and Jenny. And remember, most of the teams that are excavating on site do not have the benefit of GPR. They're relying solely on cat and jennies, which only locate metallic. So, we've got this information and this

3:40information, but the information we're mainly providing here is that there is a gas pipe in that footpath. Now, we look at the water again plastic and again the information we're giving someone is there's a water pipe in that footpath. Moving on, this is Virgin Media. And once again, the main information we're giving to people is that there is a virgin cable in that footpath. So when we issue these individual stats out to people to summarize, the main information we're giving them is in that footpath where you're working, there is

4:11an electric cable, there is a plastic gas pipe, there is a plastic water pipe, and there is a virgin media cable. Now let's say instead of giving those individual plans, we now give to the team that are excavating an overlay drawing where they've all been compiled. And let's look at the problem. It does look a bit confusing, but that's not the main concern here. The main concern here is this plan is telling that same person that working from the curb towards the

4:41boundary, we have a water pipe. We then have the virgin media. We then have the gas and then we have the electric. But the truth is it could just as easily be electric, gas, water and virgin. They could lie in any combination. The position of these here is how they have fell on that drawing. And we're wrongly providing information of how they sit in relation to each other. So why is that important?

5:11Well, if we look at this example again here and notice that we have the electric cable which we can detect with a cat and Jenny. The team on site locates electric cable. Now remember the gas that we have here is undetectable. It's plastic with a cat and Jenny. So once he's found the electric cable and marked it here, the assumption he's going to make is that the gas pipe is on the left hand side and on the right hand side there is nothing. It's completely clear. But the point is that that gas pipe could just as likely be here as

5:41here. And this is what I mean by the assumptions that we're now causing by giving this information, especially if we don't explain it properly. They could fall in any combination in that area. One more quick example for you. This is in Scotland. So for anyone that hasn't seen this before, this is the Scottish power drawing. They show LV cables in brown. So it's very similar um story here. We've got a footpath and we have a proposed excavation going on. We give

6:11this individual plan to the team doing the excavation and that plan is telling them there is an electric cable in that We then give them the gas drawing. Gas drawing once again is telling them there is a gas pipe in that footpath. Again no material, no offsets. All these missing from the overlay drawings that you've just been looking at. Okay. So the information we've given again is in that footpath you have an electric cable, you have a gas pipe. Let's look at a different type of overlay drawing the same footpath. And again what we're now

6:42telling them is the gas is on the left and the electric's on the right. So when he's detected the electric, where is he going to think the gas is? And again they could easily be the other way around. Remember these are stats drawings. They're not survey drawings. These are the existing information. you haven't been surveyed. It's taken from records and we're assuming a position in relation to each other. Once again, notice the detail that's missing as well. And the final one that I want to show

7:12you is this one. Same section. So, it's a bit of a mess here, but this is telling us we've got water, water, electric, electric, BT, electric, gas. But again, they could be in any order. They could be in any order. Look at this gas pipe coming down here. What information is missing? Let's look at the original stat for this and look at the information that's been missed being brought across and see how relevant this is. That is the same gas pipe. On the original stat, we know straight away that that's actually a medium pressure

7:43gas pipe. This is really important information that's missing. It's also telling me that this is steel and this is plastic. So that's the information we're missing again from overlay drawings. So I hope you find that useful and I hope it explains the reasons why I have concerns about this approach. The outcome of so many strike investigations uses reasons relating to assumptions being made. Going down this road is

8:13actually encouraging assumption. If we do still insist on using compiled or overlay plans, at least make sure the teams using them understand these limitations and the points I've highlighted in this video and please feel free to share it with them. The main one being the position of utilities in relation to each other is assumed and could be completely wrong. So, as I said, I hope you found it useful. If you need any further info, please contact me at pete sigma symmetolutions.com.