Cutting trees with detcord

[JV44]

Does anyone here know the formula that correlates the number of wraps of detcord to a given diameter of a tree?
I will be using detcord with 100g PETN/m, but of course I can use information on any other weight as well. I plan to do the blasting on November 13th, will post some pictures afterwards.

[Doug]

I have a friend who was a British Paratrooper. He has told me in the past that he has used this method for rapid clearing of landing sites. I will ask him if he has any information of value. Is there a particular diameter of tree you are intending to fell, or will there be a few of differing sizes?

I have a feeling (knowing what Para's are like) they probably just wrapped round as much as they could, but I will ask him anyway.

[JV44]

That would be very helpful, if you could get some information from your friend. Maybe he even knows the correct formula, although you are absolutely right to assume they never used it correctly........
The trees I will be working on should be about 10"-15" in diameter.

[Ropik]

My demolition handbook says that you can cut trees up to 15 cm in diameter with one wrap of normal detcord per one cm of diameter. Sad to say, no notice about "what's the grams per meter count for this damn detcord" is present, but the 100 g/meter cord has much more power than standart one I am sure.

[JV44]

"Normal" detcord would probably be 12g/m, one wrap of that per cm sounds about right. That would translate to one wrap of the heavy cord per 8cm of diameter. Do they give a percentage by which this has to be increased for larger trees?

I guess 40g-detcord would be better suited to the application than the 100g-cord I will be using. However, my non-commercial license is limited to 500m of detcord, no weight specified-of course I would not use anything other than the heaviest cord I can get my hands on.

[SweNMFan]

My army's detcord contains 10g/m PETN and we where tought to use 1 wrap around per 10cm diameter (rounding up)

[JV44]

One wrap per 10cm sounds like very little to me-only about 3 grams or 45 grains of PETN for a 10cm tree?

[Boomer]

One wrap per 10cm diameter? 3g for a 10cm tree? NO!
60g for a 2 meter monster tree? NEVER!!! :rolleyes:

They either told you bullshit, or they meant millimeters! And even then the charge weight must increase with the square of the diameter.

The blasters manual says “charge weight = dia x dia / 200” for internal charges, and “charge weight = dia x dia / 40” for external charges (in inches and pounds). IT advises to either put it all on one side, or on two opposing sides if both charges can be detonated in the same instant.

Assuming a complete wrap, initiated at two points, is at least as efficient as two opposed charges, this translates to 10 wraps of the 100g-cord or 100 wraps of the 10g-cord for a 10” tree. This rules out the thin cord (100-150 meters per tree!). It also explains why Ropiks book says “up to 15cm” : for usual cords it is waste if more than a few wraps are needed.

I would try a different approach: Bring a battery drill and drill two holes at 90 degree, nearly at the same height, 90% diameter deep, then insert the 100g-cord to full length. I bet this works for at least the 10” trees, especially if they bear load. I have split 15” OAKS with ONE cartridge of 30% ammonia dynamite in well stemmed holes! In contrast to cartridges you need a much smaller (but longer) drill, making it easier for the battery.

[Ropik]

Trees more than about 15 cm in diameter look like mummies when you try to wrap around them enough meters of detcord, yes.
Boomer, charge wrapped around the entire circumference of a tree is much more effective than one placed on the side. Another book of mine says: "When you can wrap the charge completely around the tree, reduce it's weight by one-third".
Charges placed in the demolitioned thing are always more effective than ones placed on the surface - no energy is wasted and "blown away" from the target - , but I think that somebody interested in cutting trees with a detcord will be after the shortest time of preparation of the whole shot and the most simple way to prepare trees for it, not after the most economical way to put them down.
JV44, 10" trees are pretty much too grown up to cut easily with the external primacord charge(though I never saw a 100g/meter detcord, sounds to me like very pretty handful(or cordful?) of power). In your place, I would extract the PETN and make simple plastique with a vaseline. After this, I would proceed to cut the trees with normal charge, maybe mudcapping them - depends on number of trees. If you can prepare the blasting site, definitely go for the Boomer's advice.
Good luck.

[JV44]

I am not licensed to extract explosives from detcord. As I have to notify the local authorities prior to every blasting operation, I always have to expect someone at the blasting site to oversee the work. The cord by itself will have to do. 100g/m is fairly powerful and should work well, I hope. There used to be a brand named "Resa-Schnur" with 300g/m, which would be perfekt. It does not seem to be available in Germany anymore though.

This is a system someone recommended for fast application of the charges.
http://www.thw-halberstadt.de/fotos/Tauchen%20HBS%2005.2004/image004.jpg

[JV44]

Today I verified experimentally that one wrap of 100g/m Detcord per 10cm diameter works well indeed. I cut some trees and logs from 15cm to 35cm in diameter. Most cuts were very clean, only one oak had some splinters left standing, although it was severed completely.
The noise was quite impressive without any confinement of the charges. Pictures and video footage will be available in a couple of days, if anyone is intererested.

[JV44]

Here are some pictures of yesterdays experiments.
Before:http://sn.allround-pc.com/spreng/images/2-1.jpg
After: http://sn.allround-pc.com/spreng/images/2-4.jpg

Before:http://sn.allround-pc.com/spreng/images/3-1.jpg
After:http://sn.allround-pc.com/spreng/images/3-3.jpg

We also took some Videos:
Video1 (http://sn.allround-pc.com/spreng/spreng2-low.mpg), Video 2 (http://sn.allround-pc.com/spreng/spreng3-low.mpg)

[hereno]

Wow.. great stuff.

Thats some chunky cord, what is its main purpose? demolition? Im assuming its a little too expensive to just blow up trees with, of course its worth it for amusement value (whats it worth?).

Thats an awful lot of smoke for PETN isnt it? Maybe I havnt used enough of it by itself to notice but usually I get an orange flash but not much smoke.

BTW.. "only" limited to 500m lol..

[JV44]

Heavy cord has many applications, like demolition of thin concrete structures, contoured blasting in tunneling operations, cutting trees, blasting blocks out of rock and so forth.
500m of detcord isn't exactly a lot of explosives, just 50kg with the stuff I use. I can renew the license if I need more, but it is an annoying procedure. To put things in perspective, for commercial blasting I commonly use 5000-8000kg of explosives and several hundred detonators in one shot.
The PETN itself does not produce a lot of smoke. The wrapping of the cord does, however. The smoke also smells a bit different than when you are using pure PETN.

[hereno]

Oh, I was assuming you can "hold" up to 500m at a time, as in you can keep buying up to that limit. Here theres a 100m limit that you can store without a magazine (non-commercial) but you can keep buying it as much as you want.

The wrapping of the cord does, however

That explains it! I expect there would be quite a lot of filler in that cord to keep the explosive in place. More of a problem with the heavy stuff as she'd all run out the end!.

[JV44]

The PETN is used pure, except a small amount of dye to make it pink. There is no filler to keep keep the explosive in place, however it is pressed fairly well, so it does not usually spill more than a couple of grains after you cut it. If you knead the cord you can easily empty any length of it though.

[JV44]

http://sn.allround-pc.com/spreng/images/frame2.jpg
A nice shot from one of the videos, quite an impressive fireball for a charge of less than 1000g.

[hereno]

Looking again at the pictures, it seems you went a lot further then 1 wrap per 10cm like you said, or are you refereing to other shots you done.

It would be interesting to find a decent sized tree, wrap it once with cord down the bottom, run it up a couple foot or so then wrap twice, up a bit more and wrap 3 times etc... maybe using the 12g/m cord to join the rings together. That way you get a gauge of its "cutting ability". More interesting then just blowin'em up! It would sure make an interesting photo .. *hint hint*

I wasn't clear, by "filler" I meant the ropey stuff below the plastic covering, meaning there is a lot more "wrapper" then meets the eye to create the smoke. (at least there is "ropey" stuff in the stuff here :D )

[vurr]

when using TNT contact charge:
weight(grams)=diameter^2(centimeters) x coeff of tree
(=0.8 for dry aspen /1 for wet/;
=1 for pine ,fir /1.25 wet/;
=1,6 for dry birch,oak,maple/wet =2)

if diameter over 30 cm: multiple by (actual d)/30

inner charge is 1/4 of external (hole depht 2/3 diam )

and non-contact charge: W(kg-s) = 30 x treecoeff. x D(diameter of most distant wooden object to cut,metres) x R^2 (distance from charge/located at centre of tree group/ to most distant object's centre,metres)

[SweNMFan]

I finaly found my field notes.. 1 wrap of our 10g/m detcord per cm diameter..