200 YARDS OF BOG ROAD

[PWS]

I'll probably end up paying to improve a gravel road which passes over parts of a bog in Northern Wisconsin. The road has been there for over 60 years and two spots sink into water table. Roadway is 15 feet wide. Low spots have been filled with stone several times. The stone sinks in about 5 years.
Is Geotextile fabric an option here? Is there a way to use it over the sink holes? Holes sink to 14 inches below water table.
Town refuses to pay for maintenance.
Phil

 

[layfieldman]

bogtrotter

Using a geogrid is fine but you still need a separator to keep from losing your granular into the peat/bog or just falling into the sink hole, which I think is his more immediate problem. If you plan on using a geogrid because of the idea that it is stronger, there are geotextiles available that are just as strong and would serve both as separator and reinforcement.

I don't think that the geotextile option should be entirely ruled out but you need to have someone who has experience in the design of bridging voids, originally created for landfill cover design for when metal objects rust and create an empty pocket I believe, design this possibility. You can contact any of the companies that deal in HS geotextiles such as Mirafi, Huesker or Synthetic Industries, I'm sure there are more but....

Good luck.

 

[PWS]

I'm currently caught between Texas and Wisconsin and have been putting the problem to anyone who's interested. I've had discussions about combining GEOFOAM (and) GEOTEXTILES (and) layering gravel. I won't have enough time before freeze-up to complete project. It'll have to wait until next spring I guess. Thanks for the ideas.

 

[KRSServices]

Rex was on the money. I have had to rebuild sections of road using this philosphy. If you have access to some cheap blast rock, say from a nearby mine or so, I would recommend excavation of the site below the natural gradeline (say four to three feet, depending on the type of soils and level of saturation, and place some medium to heavy geocloth in the trench and about three feet up each side of the excavation. Next I would place the quarry rock (plenty of fractured face) or a 4" minus pitrun. Static roll the fist lift of material, I'm assuming pit run, which should be about 8" or so. If the grade is too spongy, place more pitrun and static roll when the grade is firmer. If using blast rock, carefully place so as to avoid too many large a voids.

If using pit run, continue this fill to about 1 foot above the natural grade line. If using blast rock, fill only to the top of the excavation, then use some 2" minus pitrun to build your grade.

Construct the grade to approximately 2 feet above the natural grade line and finish by placing some road crush.

If you have filled to abour 6" above the natural grade line and the road has been sufficiently compacted, you may want to save some of the cost and construct using some good quality clay or other acceptable soils suitable for building H-20 or equivalent road grades. I've had to repair some of the old corduroy roads and while they may have worked for the time they were first installed, the cost to rebuild the grade was not worth it.

Since you mentioned the road has been around for 60 years, I am assuming it was constructed as a means of getting around an old lake, and likely is insuffieciently draining as well, or the clays keep "pumping" water to the surface.
Next, construct the

KRS Services

http://www.krs-services.com

 

[VAD]

PWS:

Many interesting answers/recommendations for your problem.
What are the risks. Try one. It can work or have the road settle after another five years. Sir Al has the correct approach, one that I personally like i.e try to find the reason for the problem and then decide on the solution. Now failure may still occur despite the best efforts. If it does then you are at least knowledgeable on the error and you are better able to move to another solution which you may have thought about, but chose the other one instead.

There are a lot of fixes which are often used by many of us and reasons for their good performance are not entirely known. Some call it experience. This is the beauty about the subject. However, when there is risk we often have to know the premise of why we apply a solution as we may have to defend ourselves at a later stage. Irrespective of the risk my personal approach is to wrestle with the problem and satisfy myself before applying a solution. If it fails then I am enriched by the reason and likewise if it succeeds I am able to discuss why, when providing a recommendation for its future use.

The missing links-site characteristics, understanding etc are in your domain and only you can decide at this time.

Good Luck

 

[PWS]

KRSSERVICES and REX,
My first thoughts were to excavate and to refill with large quarry stone with layers of smaller road grade fill in about three or four layers on top of that. However the bog material I think is at least 20 feet deep in these holes and sits on top of glacial sands and till. I think... it will be less costly to attempt to float the roadbed on the bog material with some of the above mentioned techniques. The coming winter will give me time to reflect and analyze my options.
As VAD so wisely put it, "wrestle with the problem and satisfy myself before applying a solution".

Happy Holidays!

 

[swBausch]

PWS,

Geofoam is currently a high-profile material as you can see from the various search-engine hits. Since many of the projects are public, there may be a public-affairs/liason officer who knows of the success or failure of the implementation.

There may be a project near you that would allow a site inspection?

 

[BigH]

Maybe I'm missing the point but the road only sinks at two locations for about 6m each - that's 12m by 4.5m or some 55 sq m. If if only sinks 1/2m, say in 5years, that is only a couple of truck-loads of gravel. I'd say it would be cheaper just to maintain the two sections. To dig out extensively to get down to "near" bottom would like incur a much greater cost than the couple of trucks every five years. You could dig out a few metres, replace it with encapsulated hog-fuel (tree barks - or saw dust) and then get at least 1m of good sand and gravel above it. This might reduce the pressures enough to make the maintenance once every 10 years.

I had a project somewhat like this in the Burnaby peat plain in British Columbia back in '84. 25 ft of peat over 25 ft of soft clay. The truck maintenance facility was on piles and 3 ft above the original ground level. Needless to say, they had to redo the sloping entrance every few years as the trucks couldn't take the sharp curve at the top. I dug out 6 ft or so and replaced it with Elastizel - foamed concrete - and it worked like a charm. But then, this is much more expensive - but you might want to consider it over geofoam since it has about 100psi compressive strength - better than most very stiff clays!!

 

[PWS]

No BigH, I think you restated the problem accurately and I think your solution parallels my own compilation of ideas and solutions from the other engineers who have weighed in on this forum. If I can't convince the local government unit to maintain this section of road then I'll seek to use the least expensive most practical solution and do the maintenance myself.
PWS

 

[bltseattle]

I worked on a county road project with very similar issues, albeit the entire roadway was settling, not just pockets of sinking material.

The County wanted to widen a road that was originally built on 40+/- feet of peat, through a lake. The solution to the roadway settlement for that project was two-pronged:

1. Preload areas prone to settlement to compact underlying peat soils. Time for preload varies depending on depth, underlying materials, etc.

2. Construct roadway using lightweight fill to minimize longterm settlements. Hogfuel (large conifer wood chips) was used.

3. Use geotextiles to hold lightweight fill lifts together. Geotextile was installed, then a lift of hogfuel, then another geotextile, etc. Used 12-18" lifts. Wraps were tied back about 6-10 feet (can't remember....) from the embankment face for the 80 ft wide road section. The geotextile wrapped around the embankment face at each lift. I believe this approach is called a Hilfiker wall, or something like that.

For your situation I would consider the following approach as a long-term solution:

0. Install silt fences or equal to prevent muddying up the lake.
1. Place all your surfacing materials over the first soft spot as preload. Configure in a way that is acceptable for temporary access, e.g. a "mound" shaped to be driven over. Allow the material to settle a while (ie months).
2. Move surfacing materials (preload) to next soft spot, retaining enough for step 4 below.
3. Excavate the roadway in the soft spot vicinity say 5 feet deep and install say two lifts, 12-18" thick, of hog fuel/wood chips with geotextile fabric separating layers from each other and native material. Place and compact hog fuel in 6 inch lifts for greater stability. Extend geotextile past the soft spot to tie into more stable material. Cover any exposed geotextile at embankment face with hand-placed riprap to protect from UV.
4. Install 12 inch +/- surfacing layer on top of upper lift to final grade. Could use 6 inch compacted native topped with 6 inch crushed.
5. repeat at other spot.

Good luck

 

[BigH]

bltseattle - nice case history!