PAS 128 Accuracy Zone Modelling

The accurate detection, identification, verification and location of underground utility assets has always been a difficult task, subject to interpretation and inaccuracies. According to the ‘PAS 128:2014 Specification for underground utility detection, verification and location’ having insufficient or unreliable information leads to:

• risk to the safety of workers and to the public;
• abortive and unnecessary work;
• damage to third party assets;
• inefficient design solutions.

Working in collaboration with a number of our clients Catsurveys has identified a missing element in the underground infrastructure modelling environment – the point at which infrastructure data meets design data. It is at this crucial point that all data needs to provide the most confidence and certainty to make sure that project design is optimised and de risked.

Even if we use the best technology coupled with the best survey teams on site there will always be a margin of error in the data collected. This margin of error is based on a range of different influencing factors and is defined in the PAS 128:2014 document, which explains each survey method confidence level (quality level QL) which can be applied for each detected or undetected underground asset.

With our unique PAS 128:2014 accuracy zone modelling methodology we are able to provide the best possible data to support design solutions.

Figure 1 - Chart of horizontal and vertical accuracy for QL-B (informative); PAS 128:2014

How does it work?

We use our bespoke algorithm which applies the rules of the relevant PAS 128:2014 accuracy zone to each survey point.

As per the standard our algorithm makes calculations for each surveyed, detected point using following inputs:

• Utility size, diameter;
• Detected depth;
• PAS128:2014 Survey Type B Accuracy Level (QL).

On the completed underground utility network data we apply our bespoke modelling program which automatically draws the accuracy zone around each cable and pipe. The appearance of the accuracy zones can be set to user preferences.

How can it support the design solutions?

At early stages the PAS 128:2014 accuracy zone information can be compared with planned design information. This gives a much clearer indication of available space, installation risks and potential utility clashes. After a clash detection assessment any potential areas of concern can be investigated further to find alternative design solutions.