While there may be records of where underground services – such as water, power, gas and so on – are located, but these may not always be entirely accurate. This means that when mistakes occur, or when extension work needs to be carried out, time and money can be wasted trying to find a specific cable, pipe or joint. However, developments in new underground location technology are bringing extremely accurate underground location information within the reach and budgets of today’s utilities, contractors and construction companies

Why is accurate underground location such a problem? Most utility companies and other organisations that manage or own underground services, do keep underground records, but it is hard to ensure their accuracy, partly because many of these services were installed decades ago, when accurate records were not always kept. Today’s utilities may have an approximate idea of a service’s location, but not the precise spot.
Also, it is not hard for records to become out of date. Changes in the above ground layout – such as a housing estate or business park being built – can mean that the relation between the underground service and above-ground landmarks changes. Although above-ground markers may exist for these services, they may be moved or even removed during construction work. Digging holes in the wrong place is an expensive business. In addition, utilities and their contractors are under pressure to minimise the amount of time carrying out ‘street works’ and face penalties if they exceed the granted time limits. The problem is exacerbated by the fact that the ground beneath our feet is becoming increasingly congested, with many services crammed into the same space. This can make it extremely difficult for any contractor, engineer or surveyor working in that area, because there is the potential to inadvertently damage the pipes or cables of another organisation, costing money and delaying project completion. During the past few years, there have been calls within the industry for a more coordinated approach to utility management in the UK, with the formation of the HAUC (Have All Utilities Co-ordinated). While this is to be applauded, unfortunately initiatives such as HAUC have to fight against the fact that many utilities must focus on immediate priorities.

Why hasn’t this been addressed before?
Since underground location is such a big issue, why has it not been higher on the agenda? The answer is that until recently, the location-finding technology available had limitations and relied on considerable effort and manual input on the part of site workers. As a result, many utilities and their contractors have made minimal investments in location-finding equipment.
If accurate underground location was easier to achieve, then it is likely it would move higher up the agenda. Techniques for recording and finding underground services have been around for years, but have all had their limitations. Starting at the least ‘high tech’ end of the range, there are the good old-fashioned above ground markers that we are all used to seeing: cheap and visible, but basic and easy to move.

Underground location techniques
Moving up a step, there are various radio frequency-based techniques that have been around for a while. They fall into two categories: passive and active radio detection. Passive mode is based on the knowledge that any metallic pipe or cable naturally picks up and re-radiates a signal, so it is easy to track an existing pipe along its course. The drawbacks are that it depends on metal content and a sufficiently strong signal, which is not always the case. Fibre optic and CATV services are notoriously difficult to find. In addition, this approach depends on knowing roughly where the cable or pipe is located and does not provide any means to record more detailed information once found.
Active radio detection involves applying a transmitter unit on to a pipe or cable, or holding it above the ground on the point where it is expected to be. Someone then walks along holding a receiver, which detects the signal and emits a beeping sound that increases in relation to the signal’s strength, or proximity to the cable or pipe. This system is relatively straightforward, but is limited by the fact that it will detect any other pipes or cables in the immediate area, potentially creating confusion. Again, active radio detection depends on knowing the approximate whereabouts of the pipe or cable and does not provide a simple mechanism for recording location data.
Rather more sophisticated is the passive electronic location method. Instead of depending on the pipe or cable to emit a signal, small markers are attached to the pipe or cable during the installation process, whether at regular intervals or simply at key junctions. The markers are usually ball-shaped, but can take other forms and contain a fluid that ensures the marker is always horizontal and optimally positioned to respond to an electronic signal. This information is then stored on a handheld device, which is then used on future occasions to find the pipe or cable. Markers can be allocated different colours and radio frequencies, to distinguish between kinds of services.

The latest developments
All the techniques described so far focus on finding cables and pipes, rather than helping utilities to build up accurate, detailed records in the first place. However, there is a new kind of underground location technique emerging. Developed by 3M, this enables utilities to not only accurately locate installed services, but to create highly detailed records in the first place.
ID marker systems are an extension to the existing concept of passive electronic location, but have added ‘intelligence’. Each marker ball contains an ASIC (application specific integrated circuit) and are used in conjunction with more advanced handheld locators. When the ball is placed into the trench, the locator’s LCD interface is used to record the ball’s unique 10 digit serial number, plus up to 256 bits of data. This might include: when the marker was installed, by whom, name of utility, depth and the nature of the junction or joint it is marking.
Also, the handheld locator can be connected to GPS (satellite) systems, so that the exact co-ordinates of each marker ball are correctly recorded. The GPS systems may, in turn, be connected to databases and CAD drawings held by the utility, so over time, a set of detailed records can be created. When future work needs to be carried out, the information is downloaded back to the handheld locator and, if information about a particular marker ball has changed, can be modified.
ID marker balls can be read to a depth of 1.5 metres, which is sufficient for most utilities, but not all, such as waste. In these instances, the hole needs to be backfilled until the ball is at the right level. There also needs to be 10cm between the ball and a metal pipe, but again, ways are being found around this.

What kind of investment are we talking about?
Investing in the equipment starts at less than 1500 Euros. Compared to the overall costs of most excavation projects, this represents a small investment and one that could provide a rapid pay-back. There is a small amount of additional effort required by the contractor or utility’s on-site staff, but it will save time in the long-run. It can even be seen as a way for contractors to differentiate themselves in a highly competitive market.
Accurate underground location is achievable. Every time a hole is dug, the opportunity is there. Valid reasons for not having accurate underground locations are disappearing, while the benefits are clear.

(By 3M Trading Ltd.)