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View Full Version : #02 Astroboy Topic: Rock Armouring


scratchy
20-11-2006, 07:37 PM
Well we are lucky enough to have one of the more active fairies in one of the most active clubs in OZ lend us his time. Try to keep discussion relevant to this topic (yes we will do NS at some time).

Without further ado I bring you.... Astroboy!!

Style of tracks: I have been mainly focussed on the core trails advocacy stuff up until late last year when I dived head long into Majura and then Stromlo. Stromlo has been a great opportunity to develop a lot of trail building skills, and I am certainly looking forward to using the new-found skills to finish off the work we started at Majura Pines late last year. My plans there? To deliver singletrack trails that are just fun to ride, whether your out on a social ride with mates or belting through at top speed in pursuit of a podium finish. My vision would be to add more of the type of trail features that give trails that, dare I say it, ‘free-ride’ character – rock armouring, bridges, log rides. Things that add variety and give the rider a range of experiences all on the one piece of track, but are still ridable by the average Joe (i.e. not super technical). Also looking to put in a MTB skills park as part of a Stromlo Stage 1 extension.
Name: Reece Guihot
Age: 32
Location: Canberra

Background: Got into trail building through my involvement in the CORC Trails Advocacy Team. There are a couple of older trails down here that need some serious work or replacement, and I thought that if I was going to get people along to help fix them then I sorta needed to know what I was doing and talking about. Hence my decision to dive headfirst into Stromlo trail volunteer co-ordination. It’s not like the opportunity to work with one of Australia’s best trail builders comes along all that often.

Mistakes made?: Earlier this year I decided to repair a trail that runs along a slope, which had bermed out and was collecting water. Rather than doing it properly and digging out a full bench cut I decided to just rid the trail of the berm and off-camber the trail, with gravel thrown into the sunken spots on the bottom edge of the trail. It hasn’t held up that well – the gravel is shifting and has mixed with the dirt to reform the berm (as it doesn’t pack down like the dirt). So the plan now is to head back early next year and do it the right way – bench cut the sucker and give it the full-monty treatment. The moral to the story here – build it right, build it once (famous IMBA proverb).

I also skimped on rock size when armouring some gullies back in December, which might require some work in the future to replace it with bigger ones (see my rant below).

Favourite Tool: Two actually - a standard plastic garden rake, and my mattock with the (lighter than wood) fibreglass handle. It’s a lot lighter than the standard one, which means you can swing it for longer. With these two tools and a bit of rain to compact it down afterwards there is not much you can’t do.

Free Fairy or Pro Fairy Free

Online Resources: IMBA website would have to be number one (www.imba.com). There is just so much stuff on there. The ‘Save The Trails’ forum on www.mtbr.com is also good to keep an eye on. (Ever wondered where the McLeod got its name. You’ll find the answer there). And I’m finding this ‘new’ Farkin Trail Building thread becoming a great resource which appears to be helping people solve real trail issues (access AND building) in their local area.

Your Topic Rock Armouring: We have used this technique to address some of the drainage issues at Majura Pines. It appeared that some of the gullies never dried out, and the bottom of them where the trail went was a permanent mud bog. So we are in the process of rock-armouring, realigning or bridging each of the problem ones. Rock armouring is certainly my preference – if done properly it requires virtually no ongoing maintenance, and is fun to ride over.

General Rant There is really not much I can say about rock armouring of trails that IMBA doesn’t say ten times better. They have some great guidance on the different techniques/styles and great examples. If anything, a couple of pointers from me would be:

- Never skimp on rock size. When rock armouring a trail anything smaller than a basketball is next to useless. You want the rocks to be solid and steady even without the dirt locking in the joints between, because constant use will shift them around if they are too light.
- Have on hand a good variety of different size and shaped rocks. Doing rock armouring on a trail is like playing a supersized game of Tetris – you will end up swapping and rearranging the same rock 3 times before you get a good fit.
- Always ensure that you align the gaps between the rocks so they are parallel to the flow of any water. You want the water to me able to run between the rocks where possible.

And while I’ve got the opportunity here’s another revelation. Don’t build illegal $hit, period. It really doesn’t help, and just means your local trails advocacy group needs to spend more time responding to angry council letters rather than on proposals for legal trails.

Always happy to help out where I can if people have trail access issues – just drop me a line at trailsNOSPAM@corc.asn.au (remove NOSPAM before sending). Having the opportunity to work with a great team of other CORC trails people gives me a good sounding board for new ideas and possible directions (they soon tell me whether an idea has legs, or if it’s ‘going straight to the pool room’).

Dozer
21-11-2006, 07:37 AM
Nice read lads, rock armouring is a must on any trail that has run off effects and it usually makes the track better for the rider because of the rocks. It is all part of the sustainability myth..........rocks erode slower than dirt!
I will remember your "mistake" when I undergo such tasks.
Nice one.;)

demo man
21-11-2006, 09:39 AM
Thanks Scratchy, like Reece said, this area on Farkin is becoming a real gem!

And Reece, for those who don't know, is about the busiest trail officer in Aus right now. He's a blerrie legend!

Good reasd, props to both of you!

FR Drew
21-11-2006, 11:30 AM
Reece: The Blerrie Legend.

Now there's a title!:)

Oh yeah, I forgot to mention when Scratchy asked that I'd done some stuff at Stromlo. Hmm, someone did warn me that I'd pay for it on Tuesday. Guess they were right huh?

Dumbellina
22-11-2006, 05:22 PM
Great read lads.

There can never be enough rock armouring in high erosion points. Although some I have seen pics of trails where the packing has been so poor you get a rough uneven surface that is difficult for newbies (or the plain lazy), and chicken lines appear around the rocks in the dirt (and causing even more erosion).

Dumbellina
02-12-2006, 09:56 PM
I rode on a CORC social ride lead by one Mr Astroboy on the new trails around Stromlo.

All I could do when I go back to my mate's place was txt anyone who cared in Sydney: "Stromlo Rocks".

The climb is never more than 10%, there are more switchbacks, rock armouring, grade reversals, bench cuts, cutting on switchbacks than an IMBA textbook. Does that make for a boring ride? Hell no. There was oodles of singletrack that weaved its way up and down Mt Stromlo, with tonnes of alternative lines, chicken lines and challenges to spice things up. It just amazed you that you had climbed from the event centre up to the summit when it barely felt as thought you were climbing much at all.

The only issue was that all pervasive grey dust - anyone who did the Scott 24 knows who I mean - that concealed rocks and ruts for the unprepared. Like the Scott course, the grey blanket is a product of the drought - rain would normally pack it down and bind it together. Apparrently the fires and the years of being a pine plantation also caused the natural soil to degrade to this grey menace. But it was a small issue on an otherwise excellent ride and trail.

The trail is aimed at the intermediate rider, not overly technical but something that could go beyond most beginners. It was a fun ride for the average rider, very well designed and built, and also using the natural features (like granite boulders) and the steep terrain very well.

It reminded me what riding a well designed and built trail should be like. I felt it when I rode Tumut State forest and Sparrow Hill. I feel it now on the rejuvenated Mt Majura. But for most of us Sydney riders we ride on old walking or maintenance trails. Today showed me what MTB should feel like - fun, fast and sustainable. I am not saying that Sydney trails are not fun or are slow and unsustainable. Rather, that if you start afresh and do it properly first time, the results are much different - and issues like rerouting, closures and frequent maintenance become nullities.

Macr
02-12-2006, 10:25 PM
years of being a pine plantation also caused the natural soil to degrade to this grey menace.
I was taught that at school, but reading this study (http://www.forest.nsw.gov.au/publication/forest_facts/pine/myths/default.asp), by the Department of Primary industry | Forests says otherwise (If you believe that they haven't change the facts to cover up).

Dumbellina
04-12-2006, 03:06 PM
And tobacco companies believe nicotine is not addictive;
Coal and oil companies dispute global warming, and
State forests dispute soil degradation by exotic pine plantations.

We have the trinity of corporate heads in the sand...

astroboy
05-12-2006, 12:53 AM
I'd be hard to convince that pines do not screw the soil. Talking with one of the Stromlo trail builders whose friend is a soil expert (Mmm, fun) pines do actually remove a 'coating' from soil particles. This coating is what allows the soil particle to bind with ones next to it, hence why it is very hard to re-pack dirt in pine plantations. Not sure of the validity of this claim but I have seen enough of symptoms like this at Stromlo and Majura to be convinced. The only way we are able to get soil to bind is to actually get the soil from 4ft down. The areas where the trail has been built out from the wall (like around Magpie rock) is the decomposed granite that we excavated and barrowed in, and has been pressing down well with the water. On the other hand, whacking the grey dust near the surface with the whacker packer to get it to try and cling together was useless. Just turned to powder.

BTW Thanks for the feedback on the trails Dumbellina. Hope to see you again next time you are in Canberra. Drop us a line next time you are down and if you are keen we'll hook up for a ride, and talk about alternate realities where MTB trails get funding over new roads and every city has ace MTB facilities.

Cheers.

Astro

Macr
05-12-2006, 07:14 AM
As I said I was taught differently to what that page stated. I was taught that pines leached the life out of soil and part of this effect was to turn the soil grey. I was just shocked, because I wanted to back my teachings up with fact and that is what came up

FR Drew
05-12-2006, 08:41 AM
Actually, if you read the link the onl;y things it really says specifically are what effect pines do/don't have on soil acid levels and what effect they do/don't have on nutrient levels. There's not much there at all about soild compaction, friability, texture, inter granular adhesion qualities etc.

And hidden in amongst it all is this litle gem:

However, changes in the nature of surface soil organic matter is still likely with pines because of the high carbon-to-nitrogen ratio found in the needle litter under pine plantations.


Basically they can still leave the soil completely rooted and not contradict the article you've linked at all...

Dumbellina
05-12-2006, 05:50 PM
Its hard for Forests NSW to dispute what everyone sees with their own eyes. The only place I have seen that dreadful grey soil is under pine plantations.

BUSHPIG
21-05-2008, 05:16 PM
great red fellas. I find rock armoring a must also for all the berms i make. For instance, there is one that comes of a off camber horseshoe that pretty much stops you from sliding down the hill. without the rocks i think that the berm would be useless!
once again
great read, looking forward to future's

by the way, i have herd that the engineers that build the airport runways on pore country's (that are unable to afford asphalt or whatever Aust uses?) spread urea (a chemical fertilizer) on the soils, because it really compacts it.
just an idea if your caught in a trail situation.?
cheers:)