Exploratory root trenches

[Rick2517]

This situation is purely hyperthetical as I am trying to expand my tree knowledge and move 'underground' as the tree root system is an area I have neglected somewhat.

 

 

A TPO'd oak tree with an RPA of 452m2. There is a proposed development which will encroach into the RPA by 2 to 3 mtrs. Assuming the presence of roots which is very likely, exploratory trenches are to be dug to explore the practicality of extension within the RPA whilst ensuring the continued health of the tree. The canopy spread is approx 4 mtrs from the stem.

 

What dimensions generally should the trench be dug? or should an airspade be used if possible to avoid too much unnecessary damage to roots which I presume would only be at a depth of approx 30 cm at this distance from the stem.

 

Anyway any help/info would be appreciated.

 

Regards

 

Sean

[Rick2517]

Hi....the above post is from me arb talk member Sean. I didn't realise the computer I am using was still logged in under a different member. If a moderator could please change this thread to Sean's thread if possible it would be appreciated.

 

Cheers

 

Sean

[Nimby]

Hmm don't understand the RPA figure! What is the diameter of the tree and does it stand alone?

[Rick2517]

Hmm don't understand the RPA figure! What is the diameter of the tree and does it stand alone?

 

 

Diameter is 1000 mm and yes it is a stand alone.........

 

 

To be honest I'm just trying to find out a little about exploratory trenches. This situation is from a tree survey and plans I looked at on the net and wanted to learn about exploratory trenches etc.

 

Cheers

 

Sean

[Paul Barton]

This situation is purely hyperthetical as I am trying to expand my tree knowledge and move 'underground' as the tree root system is an area I have neglected somewhat.

 

 

A TPO'd oak tree with an RPA of 452m2. There is a proposed development which will encroach into the RPA by 2 to 3 mtrs. Assuming the presence of roots which is very likely, exploratory trenches are to be dug to explore the practicality of extension within the RPA whilst ensuring the continued health of the tree. The canopy spread is approx 4 mtrs from the stem.

 

What dimensions generally should the trench be dug? or should an airspade be used if possible to avoid too much unnecessary damage to roots which I presume would only be at a depth of approx 30 cm at this distance from the stem.

 

Anyway any help/info would be appreciated.

 

Regards

 

Sean

 

Assuming your RPA is plotted as a circle centred around the tree, your RPA has a radius of 12m from the stem, right?

 

Therefore, if the proposed extension encroaches 3m inside the RPA, there is still a 9m distance between the tree and the extension.

 

Whether or not breaking ground to investigate the presence of roots is needed will depend on the site conditions - if the ground conditions are broadly similar all around the tree then it would be sensible to assume, using the BS RPA calculations that roots will be present. That far from the tree they are most likely to be small diameter/fibrous roots rather than anything of a size that would affect the anchorage of the tree (although fibrous roots do assist with anchorage).

 

An air-spade excavation along the line of the proposed footprint would quickly tell you what quantity and size of roots are present - with the least possible damage to roots assuming the tool is used correctly. However, given the expense of such equipment with operators, a careful hand-dig should suffice. I would have thought a depth of 30cm will tell you enough, but bear in mind that soil conditions play a major factor in rooting depth. In a compacted soil roots tend to head towards the surface where water and air are most readily available but in a loose texture free draining soil they will often be deeper.

 

Other options to think about - could a mini pile and voided raft system be used for the foundations so that root damage is minimised? Is it justifiable to alter the shape of the RPA of the tree? Is the soil a shrinkable clay - how may this affect foundation depth? If it is a shrinkable clay this is another reason to use a pile and raft system....