Poor Subgrade Road Section - Creative Ideas/ Experiences Needed! 2

[Ryan1111]

I would GREATLY appreciate any help with the following situation:

I have a poor section of road that I need to get a decent life span out of, but the muck and soils are terrible. It is a 1100 FT section of 5000 ADT road. The water table is very high and the marl and peat run from about 8'-33' deep. The road has been repaved and buried 3 times because it continues to sink.

I am looking for a good solution and cost is not too much of a factor. We have a ton of slag we would like to use if possible. Here are 3 ideas I have had so far.. please let me know if you have used any of these or know someplace that has or if you have any other comments or ideas...

1. remove the pavement. place slag in a sewed geotextile fabric to create a slag envelope. place sand/aggregate over the slag and concrete the top.

2. create a corduroy road joined with stainless steel wire. place concrete powder over the corduroy and then aggregate and asphalt.

3. drive steel plates along the sides. join the plates toward the bottom with a stainless steel line and pull the bottoms together to form a "V" with the road being at the top of the "V", kind of like a bottle cork.

4. try to find large pieces of syrafoam to build the road on.

Thanks!

 

[Maury]

We had a nearly identical subgrade situation and solved it by building a bridge. Precast concrete beams with curbs on concrete pile caps and steel h-piles. the adjacent storm sewer was constructed on timber piles. Backfill is to the top of curb so it looks like a standard roadway.

 

[SlideRuleEra]

We have a lot of soft soil in coastal SC. A properly selected geotextile is usually the most cost effective way to go. You don't need a bag, just a layer to provide separation between the "bad" material and the "good" material (possibly your slag, if it does not cause and environmental problems with groundwater). A geotechical report should provide information to round out the details, such as which fabric, how deep to install it, etc.

Here is a link to one vendor's website for general information (plenty other vendors have suitable products, too)

http://www.geotextile.com/tech/tech.htm#guide

Take a look at page 2 & 3 of Tech Note #1

http://www.geotextile.com/tech/pdf/t01a.pdf

http://www.SlideRuleEra.net

 

[BigH]

You have a settlement problem - I don't see how you will be reducing the potential settlement by adding more fill, or removing fill and replacing it with new encapsulated fill. The later is better for stability problems. The peat, especially, undergoes large secondary consolidation. You should be looking to use some concept of "preloading" whereby the fill that has already been placed and caused the sinking is removed and replaced by a lighter-weight fill material - in effect it will have acted as a preload. For such a long road - assuming that it is two lanes, it is doubtful that Elastizell (a good product)would be cost effective especially since it appears that you are wanting a more inexpensive solution. I used Elastizell (

http://www.elastizell.com

) for rehabing an entrance to a truck terminal built on raised ground over 8m peat and 8m soft clay - it worked great, but the volumes needed were not large.

You could consider using shredded tyres as a lightweight fill replacement (if you have abundant trees, like in British Columbia, hog fuel or tree bark would be an alternative). Say you can remove 3.5m of the road embankment (pavement and 3m) - then replace with shredded tyres at 40% of the weight of the fill removed - you will effectively unload your site by about 500 psf or so (rounded) - while you might get some settlement of the tyre shreds, the unloading should effectively stop the catch 22 situation of adding fill and settle; add more fill and settle, etc. Expanded shale would also be a possible material to consider - or a limited thickness of geofoam.

 

[easieE]

We usually undercut a min. of 2' and replace with rip-rap, then choke with a base material.

 

[mitchell54]

To add to sliderule's suggestion, double up your fabric. I have used this method in two different situations both are still in great shape.

I found that it is also helpful to remove about 2' of the "bad Material" and replacing it with a good clay, then your geofabric, and then sub-base and so forth. Essentially design a boat for your road....this is the cheap route and in both situiations I have had heavy truck traffic for several months before the roads were turned to service roads that now have little traffic.

 

[Rjeffery]

Why not cut 2 feet and replace the material with expanded polystryene blocks covered with an impermiable fabric and your typical section of stone and pavement. This fix has been used for repairs to mountain pass roads in Colorado for years.

 

[Loxobrown]

Our company has dealt with many different poor sub grade sections, and has employed Pavement Recycling Systems.

http://www.pavementrecycling.com/inplace/inplace.asp

has a variety of applications that may meet your needs.

 

[BigH]

loxobrown - while your system has been around in some form or another for years (I remember fugi-something back in the early 80s), it has its place and can be/is very effective under the right circumstances. But an embankment built on 8 to 30 ft of peat - I don't see how your system will improve the problems of the foundation settlement.
Thanks for the link!

 

[Geocontractor]

A fairly new technology in the US is dry soil mixing or lime cement mixing. I believe that it originated in Sweden. Maybe a good option to mix the bad soil in place and create "better" soil.

 

[Loxobrown]

True BigH, through most projects I have reviewed this system was the most effective for a given period of time for roadways. I figure the most simi-permanent fix would be the mentioned caisson or pile method. That may price the project way out of range, and could be at risk with weather and precipitation changes. As for foundation settlement the practical solution would be to set everything on piles embedded into the proper material.
Other methods (again costly) are to use stone or grout piles.

http://www.laynegeo.com/index.html

http://users.adelphia.net/~jdwooten/spider_goes_by.gif

 

[BigH]

The treatment way is okay for improving a poor subgrade - say of CBR = 1 or 2 clay and you want to use it as the capping layer requiring CBR = 6 or so. But, I still see that the problem is the long term settlement of the embankment - by now, with three attempts at keeping the level - there should be enough "crust" to keep the road stable - strength wise as far as pavement is concerned. One method other than tyre-shreds or tree-bark is the use of geofoam or geocomb. The former would have to be tied down so it wouldn't float away. The piled or stone column method, I would think, would be financially unacceptable. The main thing, though, is that there is very little use fo the slag in this case. At the beginning,he could have used the slag to displace the original peat/muck - and then built on a good causeway (see Rainy Lake Causeway in Ontario where they used blasting to remould sensitive silt and then used displacement). But now, I doubt it would work as the peat/muck has likely "strengthened" to a large degree.

 

[QAismylife]

I have had success with a Tensar BX1100 or BX1200 or equivalent type material. We have bridged some awful subgrade conditions with this material. Our rule of thumb if you can stand on it and not sink use BX1100 or equiv. if you sink to your knees or beyond use the BX1200. You need a good 4 feet of cover over this material for it to work.

Good Luck

 

[apmssoriano01]

It would help us if you converted the ADT to a design axle [i.e. - such as the industry standard 18,000 pound equivalent single axle load (ESAL)] since 5,000 cars and 5,000 tandem axle trucks will have a bearing on your pavement behavior and eventual solution.

Undercutting and replacing with select material (i.e. - cherty clay, granular fill, riprap, etc.) is a traditional fix, however, if the contractor gets caught in the middle of undercutting by rain or other weather calamity, a poor subgrade situation will typically become worse. Lime treatment is also a quick remedy, however, with the high water table that you indicated, the lime will eventually leach out of the treated soil. With these and other "surficial" treatments, long-term settlement (as indicated by BigH) is still a problem. SlideRuleEra has a good idea to use geotextiles' separator function to ensure the long-term integrity of your "good" material by keeping out the "bad" material. However, I think you should go a step further and design this roadway using the methodolgy for capping lagoons (see -

http://fixsoil.com/index.php?sub=app_display&main=4&subapp=62&cat=9).

Using this methodology should address long-term settlement (i.e. - through subgrade reinforcement, stabiliztion, and separation)and provide a construction platform for the contractor. After you have constructed this pavement subgrade, any pavement section designed using your local pavement design methodology should provide satisfactory long-term performance.

 

[mgray31]

By placing more weight on the roadway additional settlement will occur. From your statement the roadway has been buried 3 times already.

Remove the unsuitable soil to a acceptable depth and replace with either rubber tires or lightwieght styrofoam and float your road over the unsuitable soils. If you need to run utilities, I would suggest that you us a deep foundation system to prevent future breaks.