roadbed stabilization
roadbed stabilization
(OP)
I am a mech engineer, building a home with 1500 ft lane in from the blacktop over mostly sandy but also clay and silty soil. I have an area on the lane that is soft and spongy and allows the dump truck to sink down and make big ruts. I had already planned to use some Propex separation fabric(200ST) but certain areas are so bad I can stand on them and they act list a tarp laying on water-- almost! Digging down I find clay on top covering a deposit of saturated and mushy sand. I can dig down with my bare hand and remove huge handfulls of the wet snotty sand with little effort, and deeply. There is about 100 yards of lane with this problem. Please offer ideas for remediation. thanks!





RE: roadbed stabilization
RE: roadbed stabilization
RE: roadbed stabilization
Oldestguy: It might be too late in this one area(overstressed?), smaller about 3 x 10ft . . . however, it is representative of much of the 100 yards where I cut this lane out of the side of a hill(very low grade). I believe I harmed (stressed?) the underlay by cutting out the topsoil-- not sure?? Anyway, based on what I hear I will use this as a test case as you suggest and dig out the muck, fill with broken concrete (which I have available in the gravel pit next door), fill further with class 5 and asphalt tailings.
Ron: thanks Ron. I will try a mix of your and oldest guy's suggestions on this test area and relate how it goes. 100 yards is a big area to be dumping bags of Portland, as you suggest, I will wait till last on that one!
I am surprised that NEITHER of you had any suggestions for stabilization or separation fabric as that seems to be "popular" with some builders in this area and norther Minnesota. Is that mostly because you have never used it and are not familiar with it? It's about $350 to $600/ 300 ft roll depending on what you get-- Propex is the company name.
Location: Sherburne County Minn, near Big Lake & Elk River, on acreage on the Elk River, edge of glacier tailings, esker nearby, mucky black / sandy soil in hay field very near.
I will try not to lose my track loader in this pot of muck!
RE: roadbed stabilization
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RE: roadbed stabilization
RE: roadbed stabilization
RE: roadbed stabilization
RE: roadbed stabilization
-- used my track loader to open up a sample area and removed soil as deep as the loader allowed-- about 18 to 24", but not uniformly.
-- re-filled partially with sand
-- placed broken concrete pieces like jigsaw puzzle and covered with sand
-- smoothed, added class 5 on top, final smoothed.
-- filled bucket with class 5 and ran track loader back and forth for some compaction.
RESULTS: most areas appeared to have increased support and stabilization; areas that I missed showed stress cracking. This method most closely resembles what oldest guy suggested as "undercut and replacement". See attached photos. Last one shows stress cracking on surface after job "complete", before second attempt at removal and refill. I tried to upload three and it looks like max is one photo?!
Two things of note: 1) for a home lane and 100 yards by 12 ft following this route seems like a pretty big deal; 2) new information: in recent weeks the gravel pit started pumping and dumping their water in ponds on north side of my property, higher in elevation than this lower hay field which abuts the Elk River. Recently they stopped pumping and are supposedly finished. However, the ponded areas remain and, I believe, are serving as high head(20 ft) hydraulic reservoirs for the lower water table in the swale of the hay field adjacent to my lane. If so, it seems reasonable that until the water table drops, it won't matter WHAT I do up above the sub-grade because it will ALL be just floating on this bed of fluidized material. What say you?!
I'm wondering if I waited a few months until the water table pressure is relieved maybe the problem will be relieved. The farmer who cuts my hay has never seen the water standing in the field like it is now.
I have put the fabric on back burner mainly due to the cost being excessive due to 12" min aggregate. . .
Finally, I'm considering Ron's advice in a new sample area(mix and compact) to see if that can be as effective as the concrete. However, I am hesitant due to the sub-grade being so deficient, so deep, that I would expect a continuous slab of concrete to float back and forth. Really, simply standing, I can rock my weight back and forth and watch a wave between my feet!
RE: roadbed stabilization
The test sections is very good advice or find a couple of local engineers who have a lot of experience with what does & does not work for your conditions.
RE: roadbed stabilization
The remove and replace is one option to spread the traffic loads down through the new fill to the sensitive lower stuff. Use of fabric is also OK, but designed, not just thrown in and hope it works. Stabilizing the sensitive stuff also works, but again needs some design, as with test areas. Mixing in lime, such as quick lime works, but not just a thin layer. Cement mixed in works, but not a thin layer. This stabilized layer has to function to spread the load, as the replacement fill does. However, being that there is some "beam strength" a thinner layer of stabilized soil is possible. I'd guess a foot of stabilization is not sufficient. The percentage to use should be selected from recommendations of lime or cement institute studies, if possible. You can mix with your loader, but a grader is better. Best is a rototiller.
If there is a ready mix plant nearby that may have a lot of old cement, a deal might work out.
Check out this paper.
http://www.graymont.com/sites/default/files/pdf/te...
RE: roadbed stabilization
RE: roadbed stabilization
Tomorrow I have a civil engineer / sales rep from Tensor stopping by! (thanks for the pointer emmgjld) His fix will likely include product sales of course not to mention class 5 over the stabilization fabric.
RE: roadbed stabilization
RE: roadbed stabilization
As to getting the info like we use, that may be difficult. But for a rough test, how deep can you shove a 1/2" rod with average body push? How easy was it? How far in can you shove your thumb? All this before any disturbance by vehicles on it at least for over night.
The Tensar grids are strong stuff and it may be over kill.
With regard to Msucog's recommendation "for non-commercial, best approach is fix at least the upper 3-5 feet...3' probably sufficient", I'd say major over -kill.
RE: roadbed stabilization
RE: roadbed stabilization
suggest you also investigate and mitigate the water problem as well. it sounds like there is poor drainage. it could be from the gravel pit or it could be from rain or both. Improving drainage may require some fill and a culvert to handle surface runoff or perhaps some sort of hydraulic barrier / cutoff wall or subdrain to handle groundwater
RE: roadbed stabilization
It is hard to answer your question that appears to be asking for something that can be related to CBR without taking a half inch rod and trying it. Maybe I will do that, but here is what the Tensar Engineer and I concluded:
-- without using an penetrometer and just walking on it, some of the worse areas appear to be on the order of 1.5 CBR
-- two remediation suggestions based on my readily available sand and his product fixes:
1) crown subgrade materials down roadbed, use triangle grid TX160 under 9” of class 5 aggregate, compact each 3 to 4” lift of the build if possible.
— 2) use a woven textile fabric first after crowning, place 3 to 4” lift of sand, wet, smooth, contour, and compact if possible, place TX160, use 5 to 6” of class 5 aggregate.
1) was his first recommendation and 2) was suggested as a way to “utilize” my own readily available sand resource and minimize amount of class 5 to buy. However, it requires two "fabrics". I have to analyze the costs to see if it is actually cheaper.
Whatever I do I will do a test area first. . . I am hoping I can convince the local Brock White dealer to let me buy short sections of grid / fabric for my experiment!
RE: roadbed stabilization
It is very cumbersome to place images on this forum I see, and my earlier attempt allowed only one to be placed at a time.
Going to Dropbox you can access the whole folder:
https://www.dropbox.com/sh/423o1rll20i9lyk/AADx0kP...
RE: roadbed stabilization
The 1/2 inch rod test is mentioned because around here in Wisconsin we use that a lot to check for low compaction of fill, or the need for improvement. A full shove by one hand to 2 feet is real bad. I'd have to guess you might get one foot. Not the worst, but would explain your situation better, not requiring the deep fix some recommend..
An estimate of CBR at 1.5 means ulta weak. The lowest I've ever designed for is 3 and that is mainly because of weak subgrade expected after thawing of silt soil that gained lots of water in frost lenses. The "design" by the sales person with reinforced by fabric seems light, but that is where a few test runs will tell what works. If it fails early on, I don't suppose there is any "guarantee".
Again taper the test run upper layer thicknesses. The test needs one of those loaded trucks, because that is the truck you want to support. A car or tractor not likely to mean much. The most useful layers are those on top of the fabric, spreading out the load on the fabric.
Those gradation numbers don't mean much to this OG, but any granular material may work with the proposed design. I don't quite see the need to crown the subgrade, other than removing ruts and humps. Surface crown later helps drain surface water. Too much crown and snow plowing will change that.
Your link shows a lot of the situation. Spot fixes with the broken concrete seems pretty deep, but a heck of a lot of work per foot of roadway. I assume you tried to vary the thickness of treatment. I'd estimate the concrete helps some, but not a significant difference from well graded sand and gravel. If broken up so no largest chunks were about 6 inches and well graded, maybe better yet.
The link works good, but try the "upload image" from the group up above for multiple shots.
RE: roadbed stabilization
RE: roadbed stabilization
Keep in mind the 1.5 CBR "rating" reflects only a seat-of-the-pants rating for the worst places on the road, mostly showing up where vehicles wheel travel and in the lowest area near the hayfields low spot. Much (70%?)of the concerning part of the roadbed(farm lane) is better than that by far, no sinking at all under human traffic, hard. The overall farm lane is about 1/4 mile long with only about 100 yards of concern due to likely high water table causing this localized low, apparent CBR.
In the meantime I plan to get a short piece (about 40 ft) of Propex 200ST and apply it thusly: over the "as is" subgrade of silty, wet sand at 20" depth, mixed topsoil and clay above that to the surface, I will spread 2 to 3" of sand from my pit, <<< all this exists already. . . then place the 200ST fabric, then two thicknesses of class 5 aggregate(2" over first 20 ft(A) and (B) 5" for the other 20 ft). Then, I will just start using the road and invite my neighbor to drive his single axle truck over it(no load) a few times. Depending on the response from A and B cross sections I may dump some more sand in his truck to increase load, or just STOP!
Experiment to follow.
RE: roadbed stabilization
So for a very weak subgrade, you might need 18 inches of gravel to drive over it. Instead, you have that fabric at or near the bottom and then carry the same traffic, but maybe with 10 inches.
I liken this to reinforcing concrete to carry a load as a beam. For a reinforced concrete beam the steel is needed near the bottom . Put that steel near the top instead, it then has minimal benefit. So a thin layer of gravel on the fabric is pretty much not going to do noticeable good.
For typical highway use of fabric in the bottom of the base course, and for say a CBR of 3, one may need 18 inches of base, instead of 24" without fabric, depending oon the strength of the fabric. I have seen many a failed use of fabric where the covering with base course is too thin.
For your test, I'd start with 6" at one end of the test and end up with 12 or more at the end, a tapered usage. Fabric on the bottom on the subgrade. Test area length probably 10 feet minimum. In a pinch I'd do the test on one wheel path maybe 4 feet wide.
RE: roadbed stabilization
RE: roadbed stabilization
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RE: roadbed stabilization
On that neighbor's truck load test be sure it has a full load and remember the ready mix trucks are much heavier yet.
RE: roadbed stabilization
So, my big question for oldest guy: How does the 1.5 CBR estimate square with these numbers? and! HOW bad is this?!
Ha!
RE: roadbed stabilization
RE: roadbed stabilization
RE: roadbed stabilization
-- virgin land for the most part. No gravel ever saw this road until I dropped some class 5 on top of the concrete pieces last week.
-- the "road" is really just a farm lane that until I bought the property was used only by the farmer who made hay off the grasses and we drove through 3' high grasses on this "lane" when viewing the property first time!
-- the farm lane is variable in width, but approx 10 ft wide. I will HAVE to make it 12.5 ft wide to accept the fabric. The North and South lanes are about 5 ft from the center data, not measured. I just plopped the rod down in the likely track location to within 14" or so.
-- I think the important thing here is to consider if the fabric will be affected enough to fail early when there is SO much variation across the width as these data indicate. I figure the fabric will be severely depressed on one side and be deformed there while the other might hold up OK.
-- the lane lays at the bottom of what I believe is likely a hill of sand, mostly and glacial till at the bottom. The hill probably exists because the original river eroded away the till eons ago and left silt in this narrow river valley up to the river edge 100 yards away. This is backed up by soil borings from my Septic designer and borings from he gravel pit north, and by my observations of the subgrade I unearthed last week, and by geology info found on my property on the net.
-- I get my sand from what really looks like an esker on my land. It is a long, narrow ridge of sand that runs through my land and north of it, north and south.
-- We have not heard much about the potential the (supposed) raised water table may have on this road stability. . . Wondering if I waited a year would it be gone?
-- The Tensar fellow gave me a cute little nomograph he used to calculate the CBR that is able to use seat of the pants criteria OR calculated numbers. We used seat of the pants criteria column to lead us to the 1.5 CBR because we had no CBR measurement tester OR the neat 1/2" rod data! Anyway, it is my belief without trying to analyze his little slide rule / nomograph thing that it takes into account the patch dimensions, pressure, number of passes a truck makes, and it has two sides to it. One side is to get a CBR related to a one inch rut and the other is for 3" ruts.
-- I agree with your conclusion about the location for a test area and will do "something" there. . . !
-- Remember the Tensar guy's recommendation were NOT for fabric originally. He wants me to use his nice, expensive $1660/ roll plastic triangular mesh-- TX160
-- I will run a test patch of Propex Geotex 200ST in the test area and if that fails look to his high buck product.
-- I have a local paving company looking to see if they have any left over Tx160 they could sell me. Brock White(dealer) will only sell full rolls.
RE: roadbed stabilization
RE: roadbed stabilization
I did not use the geogrid materials on this mushy area because it just cost too much(from Tensar). However, on a tough area where vehicles must make a hard turn ON a hill slope the grade was getting beaten up pretty badly and I was able to buy some material from a local paving company that was not even as strong as Tensar's TX140 and placed about 45x 13 ft of that on the turn (two pieces, $120) under some class 5 (clay, sand, gravel mix). I plan to top that with some ground blacktop to prevent erosion.
There is no way to tell the relative worth of the fabric (mushy area) in this test probably but I did leave some areas on that stretch untouched with a plan to use the knowledge gained after some "running" time to determine whether it is worthwhile. Two things appear to be major contributors better road so far: 1) got the road higher off the water table and 2) the total thickness enabled the forces to spread out the effect of weight and shear. Of course, fabric helped to accentuate that effect. I am hopeful the grid material used does help with the shear being generated as big trucks take the turn on the grade. For now, I am a lot smarter for having visiting you folks and have a neat 1/2" road bed tester to boot.
Thanks for everyone's help!