What lies beneath may be trouble!

Lynda Greenin Public Places

"Much to the bemusement of the operator, this did not happen and, yet, when the probe was removed from the soil, water gushed down the probe hole. It couldn't be stopped, so where was it all going?"

With any sportsturf or landscape contract that involves work underground, the options for knowing what lies beneath are limited. It is often left to the contractor to scan an area electronically to ensure nothing is left to chance.

For contractors, greenkeeping staff and sportsturf managers, this still may not provide enough information. Even armed with plans showing the layout of underground services, some utility material (piping etc) are not always in the same position as indicated. For example, on a recent parks contract in London, a map was obtained from the local utility company which showed a former air raid shelter where the water pipes had been placed across its roof and would be safe from machinery spiking. In reality, the pipes were laid off to one side of the shelter, thereby halting the contract before it began!

Undetectable dangers

Gas pipes can lurk undetected. Can you forgive men laying a sewer pipe and not marking it on their own plans? How simple are the rules to say "mark on this plan where you put this pipe"; "we want you to put a pipe here" and "x marks the spot"? Should these utility services be placed at a certain depth and, in reality, do contractors care sufficiently if a lack of quality control encourages sub-standard performances?

Some water pipes are plastic and undetectable but, when you puncture them, they create problems. It's nice to draw a straight line on a plan to show where the pipes have been placed. It's a shame that the person with the pen or mouse is never on site to see where the obstructions actually are and if the piping has been moved!

BT fibre optic cables are another example of what lies beneath. If you hit these, the fines metered out will erase your profit margins or even your company! Avoid these and keep an eagle eye open for them, even if you are told they are not present. BT dark green boxes act as a warning and ensure that contractors are fully aware of where the cables are.

Compaction Panning

Another area which had an underground services issue recently was a local amenity park where fairs, car boot sales and other assorted fun days are held.

Articulated lorries delivered goods to these events until a period of heavy rain created havoc. Flooding caused a major headache, and compaction panning was thought to be the case as to why the water was not draining away. The survey and scanner provided a clear indication of where the BT fibre optic cables, water, gas and electric lay, so the all clear was given to apply remedial work on the compacted areas.

A specialist machine was brought in which placed a probe 500mm into the soil and the water drained away.

The following day a different machine was brought in to reach one metre and this was used to treat some rather large puddles.

When the probe reaches one metre depth and compressed air is discharged, the top surface of the ground moves slightly, showing that the air has fractured the soil to the top surface.

In this instance, much to the bemusement of the operator, this did not happen and, yet, when the probe was removed from the soil, water gushed down the probe hole. It couldn't be stopped, so where was it all going?

This park is close to London, so was there an underground tunnel underneath or perhaps an air raid shelter of some type?

It turns out that it was an air raid shelter - one large enough to accommodate seventy people and, because we had effectively 'peppered' the roof, no more fairs or large circus tent events may now be held here until the local authority have investigated further. It's a miracle that the artics didn't crash down below the surface!

The biggest problem now is the reason the water was sitting on the surface in the first place; it probably lay on the roof of the air raid shelter. Now that the probe has penetrated the roof, water can filter its merry way along the roof and freeze and damage the framework of the shelter. If its' concrete, then this will start to shatter when rainwater turns to ice. With lots of probe holes penetrating the roof, it probably won't take much to drop the roof. The probe actually encountered a hard object, at only 200mm, before breaking through.

Contractors beware!

The moral of this article is that, just because someone can give you a pretty drawing, it doesn't mean that your site is clear, or that even the service providers have remembered to put their services on their own drawings!