The Problems Facing Contractors Undertaking Excavation Works

By Author: Peter Ashcroft
Total Articles: 17
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The Problems Facing Contractors Undertaking Excavation Works

Every year in the UK there are some 60,000 cases of contractors striking underground cables, water pipes, gas pipes, telecoms, fibre-optic cables, and more. That works out to around 230 every working day of the year, and many such strikes cause significant injuries to workers, and sometimes they are fatal.

Part of the problem is that there are untold hundreds of thousands of miles of such services, so they are all over the place. They can even be in places where you might not expect to find them at all. If you were going to excavate in the middle of a field of sheep, for instance, you probably wouldn't stop to think that there might be underground services running across it. However, it might just be the shortest route between two villages and that is why the utility concerned decided upon that solution.

The short answer is to assume that utilities are buried where you are about to dig, unless you know otherwise. However, even though you may have obtained STATS from the utilities in the area showing where their cables or other services lie, these ...
... are not always accurate so you cannot rely on them. You should only ever use them as a guide.

This is why you must always undertake a thorough survey of any area where you need to excavate. Furthermore, even though your survey shows that there are no services in the spot that you are going to dig, you must process with caution. You can dig down about a foot, and then use your instruments to survey again. Why? This is because there may well be services buried deeper down that the CAT and Genny were not able to locate from the surface for the simple reason that they were too deep to obtain a signal from them. So you need to check every so often as the work proceeds, because otherwise you could go straight through something that your survey told you wasn't there!

Electric cable strikes can cause serious injuries or fatalities as a result of explosive arcing current and any fire or flame that might also erupt when a cable is struck by the sharp point of a tool. This can also happen if a cable is severely crushed by a heavy machine which causes internal contact between conductors or metal sheathing and a conductor. Injuries caused by such a cable strike are typically severe burns to hands arms, face, and body. Electric shock is also a possibility but not so likely.

If other services such as gas pipes are nearby, they could also be at risk of damage from an electricity cable strike, and if this is the case there could be further explosion and fire. Incidents can also arise from cables which have been damaged earlier and which have not been reported or repaired and have deteriorated further with age.

A direct hit on a gas pipe can also cause fire and explosion if damage causes an immediate leak, but there are also instances of damage which causes a leak some time later. Poor reinstatement can also cause damage if the pipe is not properly supported, and this may result in a leak later on.

Striking water pipes or sewers is less likely to cause injury, but nonetheless a fierce jet of water may do so and may also carry with it stones or other debris from the soil around it. Water leaks can also affect other services nearby and may result in soil erosion. Water could enter a damaged gas pipe or electricity cable, and damage could also result in flooding and/or rapid collapse of the sides of an excavation, trapping workers.

All of the foregoing are reasons why all contractors should undertake a full survey of any area of excavation using the CAT and Genny. Used in combination, these are the two main tools for cable avoidance, but even then, they have their limitations. This is why all persons who are going to undertake surveys for the detection of underground services should attend a proper training course in the use of the CAT and the Genny, and also understand that they DO have certain limitations. If they were fool-proof, there would not be 60,000 cable strikes every year.
Sygma Solutions is the leading provider of training in the use of the CAT and Genny for cable avoidance in the UK. The company provides a series of courses which are recognised by the EUSR, CSCS, and The Survey Association.