Hoosier Mountain Bike Association

Club News & Information (H.M.B.A.) => Trail Design, Construction, and Maintenance => Topic started by: Paul_Arlinghaus on April 13, 2014, 08:52:23 AM

Title: Rock Armoring
Post by: Paul_Arlinghaus on April 13, 2014, 08:52:23 AM
Rock Armoring:  When trails cross drainages, the drainages may stay wet longer than the rest of the trail.  Rock armoring is the best solution to these locations (bridges and culverts are other solutions). When rock armoring it is important that the armoring creates a low spot at the center of the rock armoring section. 


It is also best to use the largest rocks in the center and use flat edges to create a seem between the rocks that allow water to flow between the rocks.

A common mistake when rock armoring is to pile in rocks and with out creating a low channel.  This pushes the water around the rock armoring and just moves the mud hole around the armoring.

When armoring Stream Crossings, the armoring must be able to handle the force of the water in flood conditions.

The images below show the rock armoring of a large ravine at O'Bannon Woods.  This ravine can flow with a lot of force.


The Biggestrocks that we could move were used.


The stream bed was dug down to half sink the rocks into the ground.  The rocks were lined up edge to edge.


Here is a final picture. This armoring project took 14 volunteers a about 6 hours to build.  Fortunately we have plenty of rocks to work at O'Bannon.

When working at locations that don't have flat rocks, consider raising funds to buy limestone rock.  Its best to order 10 to 12 tons at a time and have it delivered on pallets.  Cost per ton ranges from $85 to $100.
Title: Re: Rock Armoring
Post by: Doe on April 13, 2014, 09:00:37 AM
Good info, Paul. Thanks for posting.
Title: Re: Rock Armoring
Post by: Paul_Arlinghaus on May 08, 2014, 08:19:08 AM
I will start posting some pictures of rock armoring that I see on the trails with comments.  Please don't take offence if I provide comments on a project you did.  I have spent a lot time rock armoring and have done plenty of rock armoring projects that didn't work out the first time.

The good part of rock armoring is that if your armoring project doesn't work, the hard part is done (getting the rocks to the location).  It is much easier to rework the armoring the second time.


This shows a rock armoring project where there is still running water a week after the last rain. Notice that water is flowing down the center of the armoring and that the dirt on either side of the armoring is dry.  The low spot of the trail is the center rocks and the seem between the rocks is letting much of the water flow below the tire tread.


This armoring project was almost perfect.  The rocks are aligned with a nice seem down the middle.  But the rock armoring is too high.  The rocks aren't the low spot on the trail and the water is flowing around them.  The rocks just need to be lowered into the ground to create a low spot on the rock tread.


Here is a mini culvert.  It is working great now.  The long term concern is that if the small opening below the rocks fills with dirt, then the culvert will fail.  As long as trail maintenance crews make sure the opening under the rocks stays open this will work great.

Another option would have been to lay the rocks as drawn to get the water to flow over the rocks. 

This is the fun part of rock armoring.  There are many ways to do each project and it is fun to try different techniques and see if they work. 
Title: Re: Rock Armoring
Post by: DeepVI on May 08, 2014, 09:39:34 AM
Everything's better with pictures.  Great visuals for quality armoring.  Great thing about dirt and rock, if it doesn't workout, move it around until it does.
Title: Re: Rock Armoring
Post by: Fett on May 08, 2014, 10:29:10 AM
I know of a couple of my rock armouring efforts that fall under the category of "what not to do"
Title: Re: Rock Armoring
Post by: Jeff Blum on May 08, 2014, 11:06:19 AM
I know of a couple of my rock armouring efforts that fall under the category of "what not to do"

That's how we learn!