Author Topic: HKD expansion anchor tests  (Read 793 times)

Offline MarkS

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HKD expansion anchor tests
« on: January 11, 2017, 12:54:14 pm »
Before heading out to China in 2015 we decided to test some Hilti HKD anchors in a quarry. We'd used some similar anchors the previous year, and were impressed at advantages they appeared to offer over other spit-type anchors and throughbolts. On the flip side, we weren't really sure about their strength other than from anecdotal evidence, so it seemed like a good idea to test them out.



They're similar to the Raumer Rainox anchors with the cone held at the back of the anchor, but rather than hammering the anchor over the cone, the cone is held just at the base of the threaded section and the cone is hammered into the back of the anchor. Crucially, that avoids the problems highlighted in the 2013 Ario Caves Project report in terms of hole depth: provided the hole is shorter than than the length of the anchor plus the length of the cone, the anchor appears to set fine, and the lip prevents the anchor from being able to be recessed into the hole. An additional bonus is that they require a 10 mm diameter hole rather than a 12 mm hole. There's plenty of detailed information at on the Hilti website.

Our testing wasn't rigorous or especially systematic, but hopefully it might give a useful idea about the strength of these anchors.

We did almost all the tests axially (i.e. pulling perpendicular to the rock face) for simplicity, and over 5-10 bolts, the average force required to extract the was around 5-7 kN. The weakest anchor we tested took around 4 kN to extract, and this had been placed intentionally poorly, only tapping the cone in very lightly. For one anchor where we really belted in the cone, it held a steady 15kN, which was as much as we could test it to.

We did attempt a radial test (i.e. parallel to the rock face) which, unsurprisingly, comprised a fairly poor set-up. The anchor placement was appalling, and without even hammering in the cone at all, it held 7 kN before the rock started fracturing badly.

On the expedition itself we bolted a fair few pitches with no problems from these anchors at all. For future trips where expansion anchors are likely to be the only feasible option, I would certainly have a strong preference for these over spits, Rainox anchors or throughbolts for standard rigging.

Attached photos by Chris H - proof of the 15 kN!


Offline marysboy

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Re: HKD expansion anchor tests
« Reply #1 on: January 11, 2017, 01:52:29 pm »
Also Cambridge (CUCC) have used these for years on their Austrian expo

http://expo.survex.com/handbook/rig/boltin.htm

Offline Rob

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Re: HKD expansion anchor tests
« Reply #2 on: January 11, 2017, 01:53:42 pm »
What would you say are the main advantages over 8mm throughbolts?
The end is where we start....

Offline MarkS

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Re: HKD expansion anchor tests
« Reply #3 on: January 11, 2017, 03:49:20 pm »
What would you say are the main advantages over 8mm throughbolts?

Partly just the relative ease of rigging/derigging without having to mess around with nuts and washers and partly because when using 8 mm throughbolts I've experienced some problems with rock fracturing at the surface when they're being hammered in. As I think we discussed on another thread, we also had some problems with nuts left in-situ corroding and adhering to the threads (although that's avoidable by removing them).

If your throughbolt hole has to be more than 47 mm or so, the HKD anchors require less rock to be removed so it's likely that a battery will go further.

Online SamT

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Re: HKD expansion anchor tests
« Reply #4 on: January 11, 2017, 04:58:14 pm »
what happens if you over drill the hole depth. I assume you cant set the drop in properly.  I've always found the advantage of through bolts is that you can just slightly over drill them i.e. not be too worried about exact depths.

Your hanger is already made up with bolt, washer, nut, maillon, so you just insert it, hammer home, nip it up and off you go. Not much chance of dropping anything. And you dont need an additional 'setting' tool d/tangling off you.

Surely dropping 'drop ins' while bolting is just as (if not more) fiddly as removing nuts etc on the de-rig.

If you re-rig a pitch, then you just need a big bag of nuts with you (with a few spares obviously)

Take your point re nuts/corrosion. but unless you're using stainless drop ins, this will always be an issue.

Studs are also easier to spot when re-rigging.

Just thinking off the top of my head really.

Offline MarkS

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Re: HKD expansion anchor tests
« Reply #5 on: January 11, 2017, 05:11:19 pm »
I think some of the advantages/disadvantages are certainly subjective. And there are definitely pros and cons to each. I just wanted to highlight them for people who may not have come across them, and to give some info on extraction forces.

The advantage in my eyes over using other spit-type anchors is that the hole depth does not need to be exact, and over-drilling isn't an issue.

Offline Pitlamp

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Re: HKD expansion anchor tests
« Reply #6 on: January 11, 2017, 06:27:27 pm »
We've been using these type of anchors for about 30 years; never had problems for pitch rigging (but see below). Many of the big avens in Peak Cavern's Far Sump Extension were climbed then rigged on HKDs, long before there was non diving access.

Here are just a couple of thoughts thrown in which may help; the drain on the battery of a drill is not purely related to the volume of rock removed. A longer but narrower hole may involve greater friction. The only way to verify which hole diameter / depth combination requires less battery energy consumption is a controlled test.

The only time I had cause for slight concern was when using them to aid climb up very steep overhanging walls. I've occasionally noticed when swinging about (creating reciprocating rotational forces on the anchor) they sometimes start to creep outwards slightly from the hole. This creeping has absolutely nothing to do with the tensile strength of the anchor - but would in itself influence the strength of the anchor considerably. I've never had one pop or fail as a result - maybe because it suddenly focusses one's attention on not swinging about. But it's just something to bear in mind if choosing anchor locations when pitch rigging. I suspect in pure shear (the radial test referred to by the O.P.) they are extremely strong in decent rock.

A feature of Thrubolts is that they grip deeper below the rock surface of course, so may have an advantage if the top few centimetres of the rock is chossy. If in doubt though, put loads of extra back ups in.

Yours was a useful post MarkS (as of course were others which followed.)


Online SamT

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Re: HKD expansion anchor tests
« Reply #7 on: January 11, 2017, 11:12:49 pm »


The advantage in my eyes over using other spit-type anchors is that the hole depth does not need to be exact, and over-drilling isn't an issue.

Ahh. ok.. so the little lip on them stops it pushing into the hole when you set it... that makes more sense. 

I've got a gert bag of them in the garage but have never used them in anger.

Offline MarkS

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Re: HKD expansion anchor tests
« Reply #8 on: January 12, 2017, 08:27:28 am »
We've been using these type of anchors for about 30 years; never had problems for pitch rigging (but see below). Many of the big avens in Peak Cavern's Far Sump Extension were climbed then rigged on HKDs, long before there was non diving access.

Interesting to hear; I hope I didn't imply they are a recent thing. Just that I'd spoken to several people who had not used them

Here are just a couple of thoughts thrown in which may help; the drain on the battery of a drill is not purely related to the volume of rock removed. A longer but narrower hole may involve greater friction. The only way to verify which hole diameter / depth combination requires less battery energy consumption is a controlled test.

Certainly. In our experience we got significantly more HKDs per battery than we did 75 mm throughbolts. As well as friction we speculated that the hammer energy of our drill may have been better suited to 10 mm holes than 8 mm holes.

Ahh. ok.. so the little lip on them stops it pushing into the hole when you set it... that makes more sense. 

Although you can buy equivalent anchors without the lip, which don't seem to really offer any advantages over other similar expansion anchors.

Offline Leclused

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Re: HKD expansion anchor tests
« Reply #9 on: January 12, 2017, 08:53:42 am »
What would you say are the main advantages over 8mm throughbolts?


If your throughbolt hole has to be more than 47 mm or so, the HKD anchors require less rock to be removed so it's likely that a battery will go further.


Are you sure? For the HKD you are using 10mm drill vs a 8mm drill for the througbolts.

From experience : We use 8mm througbolts when exploring in the Anailarra system and we drill 50-60 holes with one battery with a small bosch drill.  (also see the topic about the drill http://ukcaving.com/board/index.php?topic=18585.msg244356#msg244356 )
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Offline MarkS

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Re: HKD expansion anchor tests
« Reply #10 on: January 12, 2017, 09:23:48 am »
What would you say are the main advantages over 8mm throughbolts?

If your throughbolt hole has to be more than 47 mm or so, the HKD anchors require less rock to be removed so it's likely that a battery will go further.

Are you sure? For the HKD you are using 10mm drill vs a 8mm drill for the througbolts.

Assuming the 10 mm diameter (r1 = 5 mm) HKD anchors with a hole depth of 30 mm (l1 = 30 mm), for the equivalent volume of rock to be removed from an 8 mm hole for a throughbolt (r2 = 4 mm) the depth of the throughbolt hole (l2) is:

π r12 l1 = π r22 l2

That gives a value of l2 = 46.9 mm for the throughbolt hole depth, so anything deeper than that will remove more rock than the hole for the HKD anchor.

Offline Leclused

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Re: HKD expansion anchor tests
« Reply #11 on: January 12, 2017, 09:46:43 am »
What would you say are the main advantages over 8mm throughbolts?

If your throughbolt hole has to be more than 47 mm or so, the HKD anchors require less rock to be removed so it's likely that a battery will go further.


Are you sure? For the HKD you are using 10mm drill vs a 8mm drill for the througbolts.

Assuming the 10 mm diameter (r1 = 5 mm) HKD anchors with a hole depth of 30 mm (l1 = 30 mm), for the equivalent volume of rock to be removed from an 8 mm hole for a throughbolt (r2 = 4 mm) the depth of the throughbolt hole (l2) is:

π r12 l1 = π r22 l2

That gives a value of l2 = 46.9 mm for the throughbolt hole depth, so anything deeper than that will remove more rock than the hole for the HKD anchor.

Thanx,

I should measure how deep we drill our bolts but I think it wil be close to 4-5 cm. So no or little difference in rock removal.

In some case we also use longer bolts by I assume you also use the HKD M8x40.

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Offline Pitlamp

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Re: HKD expansion anchor tests
« Reply #12 on: January 12, 2017, 01:46:43 pm »
Another factor of course is the battery energy used to lift the drilling dust all the way back up the flutes; the dust will be in contact with a greater surface area of metal in a longer narrower drill.

But - blimey - modern drilling and bolting methods are luxury. The first time I ever inserted a bolt for a pitch belay as a youth was a 1 inch rawlbolt. It took three hours with a star drill and heavy lump hammer. Even today, every time I place a modern lightweight bolt effortlessly with battery power I think about those days - and grin (mainly in gratitude for modern gear).   :)