Mountain Bike Reviews Forum banner
1 - 20 of 27 Posts

·
Zach Attack
Joined
·
174 Posts
Discussion Starter · #1 ·
We just finished cranking out this new stone arched bridge. This one is much smaller than the other one we built and only has a four foot span and is three foot wide. The good news is that it only took two days for mostly one person to build!
This is up near Downieville on the Sandusky Trail. There are some more photos on our new site, foresttrailsalliance.org that we just started.


I am better with the hoe than the computer and will work on up loading some new photos(dial up)
z
 

·
Zach Attack
Joined
·
174 Posts
Discussion Starter · #9 ·
Thanks for your interest. If you google Ferrocement, you can see some incredible projects, it is a concentration of reinforcement embedded with acrylic mortar. We are using this because of it requires only 10% mass of a normal concrete structure which is sweet when hauling the stuff on a trail.

I will see if I can upload some more photos with a description of some techniques when I get to my friends High Speed connection.
zach
 

·
Terrain Sculptor
Joined
·
4,692 Posts
zachi, you had some photos of the first bridge that showed the construction process quite well. I remember seeing them a few months ago. I didn't find them all on the forestrailsalliance website. Are they on another website?
 

·
Zach Attack
Joined
·
174 Posts
Discussion Starter · #13 ·
Other Photos

I will get some more photos up on the foresttrailsalliance.org site soon. I am on dial up at home here. I have to do the real work at my friends house.

I had a 11ft earth cut for a underground structure collapse from heavy rain. I am hand digging out with buckets right now. Trail building is way more fun.

BTW, anyone in northern california who wants to check out these trails they are a few miles south of Downieville. The USFS has designated the ridge to the south of Downieville to be developed for riding. We have 100 miles of trail approved by the USFS to be developed. That is a lot of scratch and sniff layout for a couple dudes. Bit overwhelmed. Just got the green light on the MEXICAN TRAIL, 3000ft descent in 12 miles,1st Forest City to Downieville connector. The first phase has side slopes of 70% in places and huge bedrock ridges to build cool stone work passages through.

Last trail we built, High Grade, we broke from the strict interpretation of the 5% rule from the USFS and did a sustained 5% with 15% max unsustained pitch. Wider radius banked turns (even on steep side slope) and much more minor and major undulations.

I am looking to layout more of a slower paced tactical trials trail at the next opportunity with more severe pumptrack dips and twists. I have not worked on pump tracks before and if anyone is in the region of Sacramento > Tahoe doing this, I would love to come and help to get more experience prior to layout.

I should probably start a new thread for this request.

Zach
 

·
XC Ground Pounder
Joined
·
408 Posts
Wow. TRULY amazing work. I would PAY to ride those trails. After all, someone has to provide money for your budget, which, judging by your photos, is expansive,:thumbsup:
 

·
Machine Trail Builder
Joined
·
69 Posts
Yep, add me to the growing list of the truly impressed! The rock work is exquisite. I saw the vertical rebar uprights, but are you using any other expanded metal lath or chicken wire to help hold the cement mixture and rock together? Also, if you don't mind sharing, what is your mixture for your acrylic cement? If its a trade secret, I understand....
 

·
Zach Attack
Joined
·
174 Posts
Discussion Starter · #18 ·
Ferrocement concepts related to bridges

The basic concept of Ferrocement compared to Concrete.
Concrete is cement, sand and gravel. Its main strength is in compression. This does not allow for much ductility (flex) or design use.
Ferrocement is cement, sand and acrylic mixed with a variation of reinforcement techniques. The mortar impregnates a mesh of reinforcement which is ideally located toward the external stress plane. Example, if you flex a piece of plywood, the outer most layer will bare the most tension the other side compression. The mesh on the skin of the tension side is what makes it strong. FC is used a lot for water tanks, and ships hulls as well as some cool shaped structures.

With the arched bridges, the primary force is simple compression. The acrylic in the mortar helps waterproof it so that freeze thaw conditions in the high country do not pop rocks out. The larger or more open the arch is, the more potential for tension at the bottom. For arched bridges without stone, I would place layers of lath embedded with mortar onto the false works that would represent the bottom skin of the bridge and the most likely to experience tension. Then build the body to the desired thickness with another light skin at the top. For non stone facade bridges, they can be as thin as one inch think with a span of over 6 ft. Google Laminated Ferrocement for more about that.
I am using a lot of PV fiber now rather than steel reinforcement. Steel rusts and when that happens its expands causing cracks and spawls.

You can see examples of four stone arched bridges I have done at our website www.foresttrailsalliance.org on the gallery or at my business website, www.casaditerra.net

I would like to support a west coast trail builders retreat that provided fun venues for workshops on elements like trail features like bridges, switchbacks, mechanized use and other cool stuff that is hard to get hands on experience with. I am applying for membership with the PTBA but I was frustrated that there is no organization for trail builders who don't earn a living doing this stuff.

A different thread subject.

z
 

·
Terrain Sculptor
Joined
·
4,692 Posts
zachi said:
I am applying for membership with the PTBA but I was frustrated that there is no organization for trail builders who don't earn a living doing this stuff.

A different thread subject.

z
Start one. A thread, I mean. I'd join an Amateur Trail Builders Association. Maybe IMBA is interested in getting something like that off the ground.
 
1 - 20 of 27 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top