I'm intrigued by this. I understand DCA pull-test every resin anchor after installation. Do you know if they pull-test ground anchors too? (Genuine question.) I am interested in how they judge the ground anchor is safe for a given usage, given it is being placed into a softer and variable medium. Is it purely down to the feel of the installer? I am also interested in the corrosion susceptibility of the steel ground anchors, and how that is managed (ie the installer knows it is likely to corrode, without it being inspectable below ground at the critical spot). Are they a given thickness/ grade of steel, are they replaced after a given time period?
The Derbyshire Caving Association is part of the British Caving Association national anchor scheme. There are a set of nationally recognised installation protocols using specific types of anchors.
thedca.org.uk
DCA do not pull-test ground stakes. I have done some limited personal testing on 16mm rebar and Lyon anchor pins, and have experience using some ground anchor safety systems for work and rescue. Testing stake placements to any serious load would no doubt render the anchor unsafe for further use and then another would need placing and testing anyway. Start off with a bit of metal strong enough not to bend under the desired design load and made in a shape that resists cutting through the ground in the direction of pull like a knife. It should of course also be placed in a location where there is no risk of it being extracted out of the ground with an upwards force.
Since starting my time as DCA Projects Officer (9 years) we have only installed a handful of ground anchors when it was the only option, and all were in 304 or 316 stainless steel.
Several years ago Eldon Hole got approx 30mm dia stainless rebar set into the bedrock with resin. This was done by skilled volunteers that did that kind of installation on cliffs and embankments for a living. These are really more like a massive P bolt than a ground stake though.
More recently, we have made up metre long T-section 70mmx70mmx8mm 304 stainless stakes to ready replace backup anchors on shaft tops if the original was reported to us as unsafe. These are typically only used to protect a rigger as they open a shaft lid and rig to the bar/bolts inside. Only one of these has been placed so far and that is at Snelslow Swallet's '1984' shaft to protect the DCA resin anchor installer who did the rest of the BP bolting in the shaft (we're also waiting on a new lid with integral belay bar to be fabricated).
Don't ask how much these cost! Flat side is in the direction of pull to give resistance to cutting through the ground, and the notch on the back helps keep slings or rope located on the stake.
The quality of the anchor placement is assessed at the time of installation and is based on the ground type and ease of driving the stake in. Essentially if there was any doubt about the security of the backup anchor, we'd not install it. We'd place as many as we felt were needed. We cannot quantify the strength of any individual ground anchor placement, but pulling a 70mm x 750mm flat face of steel through compacted ground horizontally is something that would be basically impossible for a single person to achieve when pulling their body weight against it whilst rigging a shaft top. If we needed to install these for someone to actually hang on, then we'd install more than one for sure.
I'm sure DCA would happily work with CNCC and the BCA to come up with a national approach to ground anchors where they are necessary. If a shaft needs one then someone will put one in anyway, so it might as well be us with the budget and skill to do it in a way that lasts forever.
