# Berm help - Firming it up



## CptSydor (Sep 20, 2007)

Looking for a little help here. I've recently started doing a lot more trail design and work in our local area which is comprised of old coal strip mining mud dumps. The terrain is very abrupt, short steep hills, primarily gravel/silty soil. I've been building a trail and there was a natural curved ridge that I shaped into a large berm. Unfortunately the ridge is void of trees, gets lots of sun exposure and is very sandy. The berm is after a steep, straight descent where you are carrying good speed.

I need to firm up this surface of the berm. I heard a suggestion of mixing some concrete into it. If so, what is the process for doing this. 

Any other suggestions? Bring in some other material, maybe some clay if I can find it?


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## leeboh (Aug 5, 2011)

Sand is not what you want, try some loam and clay mixed in. For the top few inches at least, plus watering it in and packing it with tampers and flat shovels.


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## CptSydor (Sep 20, 2007)

leeboh said:


> Sand is not what you want, try some loam and clay mixed in. For the top few inches at least, plus watering it in and packing it with tampers and flat shovels.


We have minimal loam and clay. It would really require seeking it out and likely moving it extended distances. If it comes to that, I'll do it, but I was maybe hoping for bit easier of a solution.


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## Miker J (Nov 4, 2003)

No easy solutions.

Least hard would be to bury rocks under the soil of the berm.

Almost any berm I build is fisrt layed out with stones. Then covered with dirt.


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## leeboh (Aug 5, 2011)

CptSydor said:


> We have minimal loam and clay. It would really require seeking it out and likely moving it extended distances. If it comes to that, I'll do it, but I was maybe hoping for bit easier of a solution.


 Got a river nearby? Maybe some spring overflows with some mud? Sand is not what you want, get anything beside that. Wheelbarrow and shovel. Start there.


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## Chris Clutton (Nov 8, 2006)

Not cheap but I've seen pavers work well on sandy berms in the Sierra Nevada Mts.


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## aero901 (Apr 11, 2012)

We use Turfstone permeable pavers on berms with non-optimal soils that regularly erode. Not an easy or cheap solution, but it works.


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## KeithNorCal (Jun 7, 2016)

Miker J said:


> No easy solutions.
> 
> Least hard would be to bury rocks under the soil of the berm.
> 
> Almost any berm I build is fisrt layed out with stones. Then covered with dirt.


I'm not a fan of pavers so I'm with Miker J on this. Rocks under the soil. He's also right that there are no easy solutions.


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## twd953 (Aug 21, 2008)

Miker J said:


> No easy solutions.
> 
> Least hard would be to bury rocks under the soil of the berm.
> 
> Almost any berm I build is fisrt layed out with stones. Then covered with dirt.


From the OP's post, it doesn't sound like the foundation of the berm is the problem, but rather the tread itself. Using a rock foundation can be a good technique, but it won't do anything to keep the face of the berm from eroding away down to those rocks. In this case I think he needs to either use different soil or mix something in to change the composition of the soil.


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## twd953 (Aug 21, 2008)

CptSydor said:


> I need to firm up this surface of the berm. I heard a suggestion of mixing some concrete into it. If so, what is the process for doing this.
> 
> Any other suggestions? Bring in some other material, maybe some clay if I can find it?


TLR: You could use cement, but it may not be the best idea.

For the novel length reply, read on:

Regarding "concrete", I've seen some poor attempts at this turn out badly on a natural surface trail, but the concept isn't entirely without merit.

Portland cement (the key ingredient in concrete) is used us used in engineering/construction to create controlled density fill which is often used when backfilling around pipes where you can't get good soil compaction. It's also used for stabilizing road bases prior to paving on roadway projects.

I've been involved in a number of projects where we have mixed Portland cement in to stabilize contaminated soils/sediments. We've turned some pretty soupy sludge (think pudding) into material firm enough to drive a loaded dump truck on.

The key is to use it sparingly. You're not trying to create a concrete skate park here, just mix enough into your soil to give it some strength. The design specs I've seen for road stabilization work use about 3% Portland cement by weight, and a bit higher than that if you're stabilizing something really soft/soupy.

You don't want to end up with a solid mass that is cemented together which will just crack and fall apart, but rather something that still feels and acts rather "soil like".

It's impossible to say if it will work with your soil types. We always do lab testing with soil samples to refine our mix designs to get the soil strength properties we need.

You can experiment with a bag of cement and a wheelbarrow full of soil. Mix the ingredients relatively dry, then add a bit of water to hydrate the cement. Don't add too much water, you're not making soup, you just want it to be moist. Then spread it out, compact it, and let is sit for a few days/weeks to see how it turns out.

If the foundation of the berm is pretty solid, you could do this mix on the top 6" of soil tread, but it's going to be labor intensive and you may need a water source.

Honestly, this isn't something that I would recommend doing unless you don't have another option. I'd rather not use cement in on a natural surface trail out in the woods, but you're description of this trail being on a "coal strip mine mud dump" leads me to believe that aesthetics may not be the biggest concern in this instance.

I'd first look at what other soil types you have in close proximity and do some experimenting those, or blend them together to get something that works.

With any soil work, and especially with berms, there is an optimum range of moisture content (varies by soil type) that work well for compacting the soil. To dry or too wet and you won't get good compaction and your work won't hold up. Check out what you've got for soil nearby, play around with it at varying moisture contents and see how well it packs down.

Also, when building berms, it is really important to compact the soil as you go. I often see guys building berms by throwing all the dirt into a pile, shaping it, then slapping the face with a shovel or using a plate compactor. That does a great job compacting the top 6" of soil, but you're 3ft tall berm is going to shrink to 2 ft or less in a year when all that poorly compacted soil deeper down consolidates.

Do yourself a favor and pack it in as you go. You don't want much more than 6 or 8" of uncompacted soil depth before you pack it down.

If you're building by hand, have one guy on the berm spreading the dirt around and walking back/forth compacting the soil with your boots. If I've got a couple guys shoveling or dumping wheelbarrow loads on the berm, I can usually direct them where I want the dirt, spread it around with a rake and walk back/forth on it to tamp it down.

Summary if you're still reading: No easy solution.


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## Harold (Dec 23, 2003)

twd953 said:


> Portland cement (the key ingredient in concrete) is used us used in engineering/construction to create controlled density fill which is often used when backfilling around pipes where you can't get good soil compaction. It's also used for stabilizing road bases prior to paving on roadway projects


I used this method when I was in Texas to firm up the base for a flagstone patio I built in my yard.

I was WAY less scientific about the process than you are, but I raked some Portland cement into the sand in my yard (DEEP prehistoric beach sand), wet it with the garden hose, and placed the pavers. Later that year, a hurricane dropped a tree onto that patio, and it didn't budge, so I did something right.


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## jochribs (Nov 12, 2009)

During my time of building dirt jumps, the way that we made a good base/shape for the jumps and berms was to dig down to the sub surface dirt. At this point, and with our flatties, we would scoop out bricks/blocks of dirt. With a twist of the shovel, we would place these blocks with a smack. We would build the foundations and general shape of everything this way. It was extremely solid. Some looser dirt would be thrown in during this process to fill any voids as we went. The overall shape was covered with a good few inches of the same deeper dirt that was not in chunks. The whole thing was smacked silly with the flatties in a pulling smack sort of a motion. Once it was packed enough, it would be shaped/shaved to perfection with the flatties. 

I'm not sure that this jives for what you need or what you can do with your setting, but we never put anything but dirt in our dirt. We learned the hard way early on, that anything inside your jumps/berms makes working on them, changing them subtly etc. a real PITA. Not to mention that logs will rot.

Edit...By not putting anything but dirt in our dirt, I don't mean to condemn using the cement like TWD recommended. Sounds like it could help if you can't find anything good, deeper.


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## jochribs (Nov 12, 2009)

Harold said:


> Later that year, a hurricane dropped a tree onto that patio, and it didn't budge, so I did something right.


Yeah, I'd say so!


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## cmc4130 (Jan 30, 2008)

twd953 said:


> . . .
> 
> With any soil work, and especially with berms, there is an optimum range of moisture content (varies by soil type) that work well for compacting the soil. To dry or too wet and you won't get good compaction and your work won't hold up. Check out what you've got for soil nearby, play around with it at varying moisture contents and see how well it packs down.
> 
> ...


Exactly. Must dampen (if it's dry dirt) and pack each layer as you go.


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## cmc4130 (Jan 30, 2008)

Cement mixed into a berm:







from this thread:
What is Trails? | Page 29 | Ridemonkey Forums

Ride Report from Benefit Jump Jam for Mike Aitken | Ridemonkey Forums










Steamboat:









Winter Park "Rainmaker":









Keystone:


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## twd953 (Aug 21, 2008)

johchribs I think your approach is pretty sound depending on soil type. Obviously, if you're working with very sandy soils, it doesn't have enough cohesion (i.e. it just crumbles) so you can't cut out the blocks with a shovel. 

But for soils with a higher clay and/or silt content, you're approach is good. 

I'm with you 100% on the nothing but dirt in your dirt. We have a local builder that goes so far as putting all of the soil for his berms through a sieve to screen all of the gravel and rock out.

Rocks will tend to work their way to the surface as the berm ages and then tires catch and rim them out leaving holes that grow. 

Fortunately, where I build we have perfect soil for building berms. No gravel or rocks in it, unless we run into an old abandoned fire road.


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## twd953 (Aug 21, 2008)

Those first couple of photos are about what I was thinking it would look like. That grayish color doesn't really blend in to the natural environment. No biggie on a pump track or in a bike park, but not as aesthetically pleasing in a natural surface trail. 

Hard to tell from the photos how much cement was used and how hard that set up. Too much cement and I hope you like the berm, because it's going to be a pain to move it should the need arise. That, and you make it too hard and brittle, and eventually it's going to crack and start chunking out.

Still, I think in the right place, with the right mix of cement it can work really well.


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## jochribs (Nov 12, 2009)

Twd, yes that was definitely building with good earth, and our pits tended to get pretty deep, unless we spread them out. Doesn't work for all situations for sure. But in a dirt jump setting where you had drains designed around everything, and gaps between, there was plenty of areas to get the dirt from. 

The other thing that the OP didn't bring up is whether it is dry where he is or not. Rainy/really damp days made for some messy clothing, but the building went well and glued up nicely.


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## CptSydor (Sep 20, 2007)

Thanks for the further information everyone. Lots to read and process.

Using alternative materials here is not a problem. As was mentioned, the area is all old strip mining and environmentally insensitive so to speak. Not that it's my preference, but it's not a concern. We are the only user group and no worries about logging, development, or anything else. Area is New Brunswick Canada, so New England type weather.

The berm was already built so to speak, I just had to shape it. Most of our terrain is 'ridges', the old left over piles from when they dug up the coal. They vary in size, but lots of terrain is series of trenches and ridges, looking like a set of waves. Sometimes they can be wide, other times pretty narrow and pointy. One of the ridges comes out of a large hill and was curved. So I sent the trail down the hill and just sculpted the ridge into a berm.

Here is a picture, not of the actual berm, but the one in question leads into this. But maybe you get an idea. I'm not building the berm from scratch, just etching out. Turns the surface of the berm in question is sandy. The rest of the soil around does okay, but this berm is pretty high speed and impact, so I want to make sure it's firm. Regardless, I've got some good ideas and going to just have to give it a shot. I think I'm going to do my best to find some better soil around first. The section rides okay right now, so I've been focusing on getting the rest built for now.


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## twd953 (Aug 21, 2008)

CptSydor said:


> Area is New Brunswick Canada


Canada? Why didn't you say so in the first place? Just mix some maple syrup into your berm and you're good to go. :thumbsup:


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## CptSydor (Sep 20, 2007)

twd953 said:


> Canada? Why didn't you say so in the first place? Just mix some maple syrup into your berm and you're good to go. :thumbsup:


That stuff's expensive. Liquid gold in these parts.


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## leeboh (Aug 5, 2011)

Not syrup, poutine. That stuff will hold together anything.


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## Loren_ (Dec 3, 2006)

We've used a 12:1 dirtortland cement mix here to armor some trouble areas. The resulting trail looks pretty much like compacted earth - hardly any gray at all.

A small tiller makes mixing pretty easy.


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## J.B. Weld (Aug 13, 2012)

So people are paving trails now?


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## cmc4130 (Jan 30, 2008)

Rock berm


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## Loki (Oct 15, 2004)

I came across this when doing research on pump tracks. Might be the ticket.

G3® Commercial Surface - Brought to you by TechniSoil Global, Inc. | Innovation for Modern Landscapes


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## KeithNorCal (Jun 7, 2016)

Loki said:


> I came across this when doing research on pump tracks. Might be the ticket.
> 
> G3® Commercial Surface - Brought to you by TechniSoil Global, Inc. | Innovation for Modern Landscapes


Interesting. That looks pretty cool, at least for landscaping if not trail building.


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## endo_alley (May 28, 2013)

We have been doing a lot of trail work with the local mountain bike advocacy organization and the local (Colorado) forest service for the last few years. We always use fairly large rocks as a foundation for our bermed climbing turns. We usually dig in base rocks that are 200-300 pounds each. And slope the base in to the hill (battering) so that gravity wants the base rocks to roll up into the hill. Also it seems like good advice in setting the design of the trail to do so in such a way that, as you are descending the trail and approaching the (climbing) turn the trail grade reverses up hill into the turn. This grade reversal before the turn, and another exiting the turn is a good way for the trail to shed water. Greatly reducing any erosion in the turn. Of course the trails need to be built with an outslope profile wherever possible to eliminate water channeling down the trail. We usually line the berm with the best mineral soil we can find. Don't forget to pack enough soil on the outside of the turn so that plants will grow there and help hold the whole thing together.


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