Problem complying with APN 12

[roythegrass]

We are laying a patio partially within the RPA of a TPO tree (upon application the LA didn’t want to know!)

In compliance with Arboricultural Practice Note 12 (APN12) and BS5837 the layers are as follows,

starting from the ground up:

Ground

Geo textile membrane

Geocell (or similar) cellular root protection system in filled with aggregate.

Geo textile membrane

Sharpe sand.

Pavers.

The infill for the Geocell is specified as angular sub base aggregate. However angular aggregate has sharp edges which could puncture the overlaying Geo textile membrane with the weight of the sand, pavers and foot traffic thereby allowing the sand to wash through. How can this be resolved? Two layers of Geo textile?

Any advice would be much appreciated.

[Gary Prentice]

The sub base material shouldn't really be so sharp as to puncture the top, separating textile. And the textiles should be of good enough quality not tear.

 

Something sounds amiss, 3D confinement systems are designed for loads up to 20 tonnes, if I remember correctly, so you should be having construction probs with a patio.

[Chris at eden]

I agree with Gary about the sharp edges, you should be using clean angular stone, shouldn't be that sharp.

 

The 20t thing is dependent on the depth of the Cellweb:

 

75mm - footways and cycle tracks.

100mm - up to 6t. e.g. cars and light vans.

150mm - up to 30t. e.g. Fire engine and delivery vehicles.

200mm - 30t - 60t. e.g. HGV and construction traffic.

 

These weights are direct from Geosynthetics and I stress they are approximate but they will help you with the spec if you need it. They have a questionnaire they send out that then goes to their engineers.

 

Cheers

[Gary Prentice]

Do you come in search of my posts to correct me, Chris?

 

I thought, at 3.30 this morning, that 20 t may have been a bit inaccurate but used it, anyway, to try to get across the point that something was wrong and the OP shouldn't be having issues. I photo of the stone might be informative.

 

Another question. Is the geotextile cellwebs own (other makes are available) or a B&Q/Ebay type weed fabric?

 

I've recently written a site specific method statement for it's use for a drive in an RPA, so should have known better:blushing:

[Chris at eden]

Do you come in search of my posts to correct me, Chris?

 

:

 

On the contrary mate, I was agreeing with you. The thickness issue is a slightly dodgy one as if you ask Geosynthetics they will always say run it by their tech specifiers first. They made a point of saying those numbers I provided which I got from them is just a guide and shouldn't be relied upon fully.

 

You may have a point about the B and Q membrane, I put some down in my garden last week and you can tear it with your fingers.

[Gary Prentice]

On the contrary mate, I was agreeing with you. The thickness issue is a slightly dodgy one as if you ask Geosynthetics they will always say run it by their tech specifiers first. They made a point of saying those numbers I provided which I got from them is just a guide and shouldn't be relied upon fully.

 

You may have a point about the B and Q membrane, I put some down in my garden last week and you can tear it with your fingers.

 

It's alright Chris, I was alluding to you always having the correct facts and figures to hand to correct my ball park figures. Twenty ton was a daft remark considering the variations that the modules come in - I should have thought more.

 

At a recent mini seminar the speaker passed around the 3D stuff, much more robust than you'd imagine so I'd think the separating membranes are of similar quality.