No.14 Rigging Site Report 1
We were asked to remove a group of trees that were posing a danger to a stretch of railway line in Shiojiri. The wires ran 20,000 volts.
Two of the trees had collapsed and were laying propped up.
The climbing anchor tree had a split crotch.
Luckily there was a large drop-zone and plenty of experienced ground staff.
It was an opportunity to give the rigging sling a real test and apart from 1 pulley (which could have been a ring but we ran out) every rigging point was set up with the 13 or 16 rigging sling.
The Job
1. Secure split climbing anchor.
Using a 14mm double braid with spliced rigging ring.
Pulled hand tight with a 2:1 until the leads (branches) closed a little and tied off with a cow hitch.
2. Set climbing anchor.
SRT on a choked running bowline.
3. Secure no.1 fallen Acacia.
Using a polyester covered vectran rope which was tied low down on the climbing anchor acacia with a running bowline and girth hitched to the fallen acacia with a small buckingham portawrap/1/2” whoopie.
Pulled hand-tight and locked off.
Coiled and stowed the excess rope.
4. Set Rigging Anchors.
Used a Pinto rig spliced onto a loopie and girth hitched it low down on the climbing anchor tree.
A 1-ring rigging sling was positioned as a craning point (to lower the cut branches directly into the drop zone).
This was the only ideal anchor branch that we came across in the whole job!, everything else was either split or had collapsed at the root system.
A large portawrap was placed behind the working tree to i) compress the timber and ii) give the ground rigger a stable footing.
The first task was to remove the fallen acacia.
The fallen tree had broken branches off the climbing anchor acacia and compressed tops on the smaller lower trees.
It was a puzzle to see where we could cut and when.
This was all critical as the fallen acacia extended over the 20,000 volt railway wires.
The tips were lifted up in small pieces , 100kg maximum, and lowered into the drop zone.
Once clear of the wires the trunk section was cut and dropped into the drop zone where it was cut and stacked.
After all the natural props had been removed the tree was lowered by the climber with the portawrap.
The craning point was used to lower a couple more small branches and then cut and removed by Iwasa san while I set the rigging for the second problem.
The second acacia had fallen and propped itself on to the top of the climbing anchor tree,
which was a shame because the position of it was perfect for the second set of rigging.
The two top leads had split in the same way as the climbing anchor tree. I couldn’t guess at the stability of it but didn’t want to use Iwasa san’s climbing lead so proceeded to brace the fallen acacia in order to use it as a rigging anchor point.
5. Secure split rigging anchor.
Using a 16mm double braid with spliced rigging ring. Pulled hand tight with a 2:1 until the leads (branches) closed a little and tied off with a cow hitch. (Red)
6. Secure whole tree with a triangular brace.
Using a 2-ring rigging sling anchor in a karamatsu, passing through a 1-ring rigging sling on the acacia (Blue) and tying off to a
second karamatsu.
Ground riggers made a mechanical advantage and tightened the 16mm double braid support rope.
The no.2 acacia had two natural props, one low down on the sakura and right at the top where it sat on the other acacia.
We used the tree as a craning point and installed a 2-ring
rigging sling (Green) while keeping the pinto rig pulley installed to compress the timber.
The tips of the sakura may have struck the wires so we post-stretched and swung the branches sideways onto a balanced sling-pick.
I’ll go through the stages of such rigging.
i) The craning point should be off to one side of the branch needing to be cut.
ii) the rigging rope will be attached at the balance point of the rigged section.
iii) The ground riggers will pull the rigging rope hand tight and load the portawrap with an appropriate number of wraps in order to hold the piece securely but let it move when necessary.
iv) The climber will position his face cut down and slightly away from the craning point.
v) The back cut is made slowly and the ground rigger holds tight to the lowering line.
There is clear communication between climber and ground rigger at this point.
vi) as the rigged section moves slowly down it post-stretches the rigging rope.
At the appropriate time the hinge wood is cut in order to move branch tips sideways toward the craning point.
After the rotation has stopped and the ground rigger and climber are happy with the position of the rigged section the hinge wood is severed and the section lowered to the ground for cutting and stacking.
This maneuver ensures of no shock-loading.
Four leads remained after the removal of the sakura.
All were attached to split crotches and none could be cut and dropped because of the wires.
At some point the top natural prop had to be removed and this gave an un-known quality to the next task.
I decided to use a vertical speed line that would drag the leads backwards away from the wires.
7. The triangular brace was re-tightened.
The climber then made his way to a comfortable position on the left lead and with the help of the ground rigger set-up a VSL.
I must apologise for the lack of descrptive photographs and it is thanks to Osaka san that any photos were taken at all.
The following day when the situation was more accomodating I photographed the set-up of a VSL on a karamatsu.
i) install a 1-ring rigging sling above your cut position.
ii) make a face cut.
iii) pass the rope through the ring and tie it below your cut.
iv) ground rigger will attach the rope to a portawrap ensuring that some slack is left in the line.
v) back cut is made.
The first lead was the largest (left hand side) and comfortably missed the wires.
The second lead supported the fallen acacia.
In this video you can see the no2 tree drop a little as my tree sits up.
The remaining two leads were rigged in the same way and the rest of the trees were free cut and then felled.
Iwasa san, Suzuki san, Osaka san, Paul, Ootaki san, Sekini san, Matsuoka san, Railway staff.
Rigging Tools Used:
60M 12mm double braid rigging line (samson 'nystron') + tenex sling & steel karabiner.
45M 16mm double braid rigging line (yale 'polydyne').
30M 10mm vectran/polyester rigging line (english braid).
2x large portawrap + deadeye sling.
1x small portawrap + whoopie sling.
2x '16' rigging slings.
1x '13' rigging sling.
2x ring spliced deadeye.
1x pinto rig + loopie sling.