Air Spading near underground services

[David Humphries]

Slightly unusual job this week.

 

We have a number of reservoirs at work which are having their Dam structures reinforced.

 

One of these dams has a number of underground services running along it including gas (yellow), mains electricity and street light cables (both red).

 

The blue line is where the gas pipe is being re-routed due to the reinforcing works.

 

The new route of the gas pipe runs through the root protection area of two large London Planes (Dbh > 104 cms)

 

 

 

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[David Humphries]

.......The new route of the gas pipe runs through the root protection area of two large London Planes (Dbh > 104 cms)

 

The contractors were planning to use a digger to trench out the new route which would undoubtedly have severed substantial roots from both trees.

 

We decided to utilise an airspade to excavate the trench instead.

 

Firstly we had the area scanned with a Cat & Genny to confirm where the existing services were. (can't always trust service maps )

 

 

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[David Humphries]

a few hours of soil excavation (down to about 400-500mm) revealed the roots that will need protection when the pipe trench is excavated fully.

 

 

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[David Humphries]

Some sizable roots uncovered running down toward the reservoir edge.....

 

These will be further uncovered by the airspade/hand digging whilst the digger excavates out the trench.

 

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[David Humphries]

Although we've used the airspade to uncover roots before we hadn't worked near to known underground services.

 

On top of our own generic & site specific R/A's and SSoW the only guidance we could find on carrying out work on or near underground services was the HSE document HSG47 (2014) 'Avoiding danger from underground services'

 

Avoiding danger from underground services - HSG47

 

 

 

Does any one else know of any further docs available on the subject?

 

 

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[JaySmith]

Interesting project David. Have you looked in the AA book - Tree roots in the built environment or the NJUG doc?

[biggarlogs]

Just out of interest ,wouldn't the compressed air jet damage roots by injecting air into them and by physical damage to the root surfaces? I know it will be less than a digging bucket crashing through them .

[treeseer]

Hmm not aware of such on this side of the pond, but I will dig a bit for that.

 

biggar, the air tool can peel the skin off of roots, but I think they are designed well enough that air is not injected into them!?!

[AA Teccie (Paul)]

Although we've used the airspade to uncover roots before we hadn't worked near to known underground services.

 

On top of our own generic & site specific R/A's and SSoW the only guidance we could find on carrying out work on or near underground services was the HSE document HSG47 (2014) 'Avoiding danger from underground services'

 

Avoiding danger from underground services - HSG47

 

 

 

Does any one else know of any further docs available on the subject?

 

 

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Hi David, someone's already mentioned NJUG v.4 (attached) but this is more focused on protection of tree roots.

 

Have you tried that very well known search engine and perhaps some keys words, e.g. "method statement for excavations for underground services"

...hint, hint.

 

Cheers..

Paul

 

PS Think BS5837 has a section as awell but again focused on tree protection measures.

V4-Trees-Issue-2-16-11-2007.pdf

[David Humphries]

Just out of interest ,wouldn't the compressed air jet damage roots by injecting air into them and by physical damage to the root surfaces? I know it will be less than a digging bucket crashing through them .

 

from our experience we've found that fine roots (and associated mycorrhiza) can be torn away from the parent root by the force of the compressed air and it can also dislodge stones (& other debris) which can cause impact damage to other roots. But generally, the air doesn't rupture through the root bark on mature roots.

 

With care, this level of damage can be limited, and the fine root hairs can regenerate over a short period of time. Particularly in loosely compacted soils.

 

This below vid shows the airspade/root interface at relatively close range (from about 2.40 secs)

 

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