Haul Road Construction 4

[ozarkgeologist]

We constructed a new utility waste landfill and within a week the haul road began to rut and quickly became unusable. The landfill and haul road is constructed on Mississippi River alluvium with most of the good high plasticity clay (CH) used for liner construction. The haul road subgrade material is mostly silty sand (SM) material. The original haul road engineering spec was 1 layer of tensar bx-1100 geogrid material overlaid with 8 inches of 1.5 inch minus rock. The haul road stabilization plan drafted by a 3rd party engineering firm calls for tensar bx-1200 geogrid overlaid with 13 inches of 2 inch minus overlaid with another blanket of tensar bx-1200 overlaid with a final cover of 13 inches of 2 inch minus rock.

I would appreciate any feedback.

 

[oldestguy]

It shows the design was based upon an assumed subgrade strength that was not really there. the season of the year probably has something to do with it.

If this were my job now, this is what I would do now. It is a practice I have found to save lots of bucks from excessive over-design. Let's face it, one tries to be efficient with his materials and it's tough to get it exactly right before the job starts.

You take a typical section and add a tapered thickness of your base course as a test road. I might even use a coarser material, say like what we call "breaker-run". This may have to be a length of maybe 100 feet. Then run your typical trucks or other traffic over it. Then you observe what happens. It may take several passes to develop the excessive pore pressure in the subgrade that may have happened before to cause a weak condition. I like to watch the traffic and the springing of the "road" under the loads. Some springiness may still be OK, but you don't want to leave excessive rutting.

Then finish off the rest of the job with a total thickness of base course a little heavier than what appears to be the suitable thickness at your test section.

I'd not get more involved with added fabric, considering what is already there as having some benefit toward allowing a reduced total base course thickness as compared to no fabric

 

[LCruiser]

Are you saying the section you are having a problem with is 8" and the one you're looking at is 26"? What is the gradation? Just saying 2" minus doesn't mean it's stable. Could be that's all that was spec'ed and the contractor put a lot of unsuitable material in with a little gravel. You might consider hauling in clean 3/4" or 1" crushed rock and continuing to fill the ruts - I'm not sure what the material looks like you're working with but that's generally worked for me. Just have them keep dumping and surfacing the softest spots (how much has failed?) until there aren't any more...

 

[motorbiketocrank]

First thought is that your gradation of aggregate used is critical. If you're using a relatively poorly graded, open aggregate, it would be relatively easy for the underlying silty sands to move up into that material and lead to failure. I'd use a well graded aggregate with a good range of appropriate particle sizes to help prevent that from happening. This denser gradation would also help limit water infiltration. You could also use a non-woven geotextile below the lower layer of geogrid.

I can't comment about the layer thicknesses without knowing more about your traffic loads, soil strengths, etc. But you will definitely get a big benefit from using the second geogrid layer in the middle of the aggregate. The aggregate below and above will really interlock well with the grid, helping to put it in tension and spread out the loads.

 

[ozarkgeologist]

I think part of the original problem was the 1.5 inch minus gravel was poorly sorted and didn't "lock" properly into the apertures in the geogrid material. Instead, they pushed through the apertures causing the pavement section to fail. I agree that a lift of 3/4 inch to 1 inch clean followed by a lift of 1.5 inch minus material would likely have prevented this issue.

The numbers used in the new pavement model were very conservative which has resulted in this over engineered pavement section design. I appreciate all of the feedback.

 

[LCruiser]

It's hard to really say without knowing the groundwater etc. situation. The clean 3/4" to 1" rock should definitely be crushed so it locks together though.

 

[DarthSoilsGuy]

i have used bx-1100, a lot, and over some real crap.
i've never been deeper than 2 feet of crushed stone, but it would be isolated layers.

can't you build on top of the 8" & grid that's out there... seems like such a waste to demo it. if it's pumping and rutting now, it will be pure goose s##t once you scrape off the placed materials. the best thing for you is to maximize the distance between the truck and the existing surface.

i don't like blanket stabilization designs, and if asked i would probably give a conservative one. i think having a pro in the field who represents the owner and 1.makes the calls as it goes 2.records materials used for unit fee pay items and 3.above all make sure it goes in right, would be best.

has soil-cementing been considered as an alternative? i've never worked with it personally but i've met plenty of graders who act like converted zealots for it.

---------------------------

Side topic that has been bouncing around in my head for a while (hope you don't mind Ozark):

Does anyone here know of any studies about intermediate layers of stabilization grid?

i see the benefits as described above by geobdg. But, i question if it also breaks up the angular interaction matrix of the aggregate in a negative way.

to oversimplify it with an example that may not be appropriate but demonstrates my question well:

A 16" deep concrete beam with two #5 bottom bars
is stronger than two 8" deep beams (each with two #5 bottom bars) placed directly on top of each other and cast on different days.

i ask this because i've had areas on some projects that turned to be "learning experiences" where i happened to use intermediate layers. the repairs involved removing all material to original subgrade (couldn't go deeper because of utilities) placement of 2" of same stone used before (but new), placement of grid, placement of same stone (but new)... and it worked where it had failed before.

i know there are other ways to explain this, but that's what got me thinking about it.

 

[msucog]

i doubt soil cement will fix what you're talking about unless the movement is only in the upper 12 inches or so (unless you cut out, fix what's underneath and then put it back on top).

my cutoff (while standing there in the field since i'm not a fan of blanket recommendations either) for using stone stabilization in roads is usually about 3' or so(2' can bridge over some pretty bad stuff--usually). i put seperation fabric below/around the bigger stone in the bottom and i'll usually go with at least 1 1/2 feet of 6-8" stone and/or #3 stone. then i cap it off with graded aggregate base type material.

i've had some contractors use reinforcing fabric under say 1' of GAB with good results, but that was on "marginal" subgrade (not goose poop type subgrade).

i've never personally used reinforcing fabric down deeper and it seems to me (based purely on my "hunch") that down deep, the reinforcing fabric doesn't do a whole lot. however, the seperation fabric does a better job of keeping the surrounding soils from migrating/oozing in to the stone layer and turning it in to an expensive mud layer full of aggregate.

as far as the layering, i have seen reports somewhere before but don't recall where. i envision that the intermediate layering would help to distribute the load in to larger areas and effectively help the cause of stabilizing. it should help limit particle migration to the underlying conditions too i suppose. i haven't run the numbers, but it almost seems more cost effective to just fix the problem instead of spending lots of money to bridge over the problem. i have seen instances where grid and stone by the contractor but simply didn't work for whatever reason so someone spent a lot of money just to dig it back up again. however, i know there are times where old, crappy utility backfill is the culprit and realistically can't be dug up and put back in without massive costs. luckily, they are usually more than 2-3' down in roadways ("usually" being the key word there).

i think my ramblings might be hitting on some of what ozarkgeologist was looking for. as others mention, there's a lot of factors involved with figuring out what is needed to "work"...heck, even the definition of "work" varies with the person you're talking to and the project.

 

[ozarkgeologist]

I appreciate all of the insight. The final design spec that I have approved will be to leave the current material in place including the bx-1100 and the 1.5 inch minus gravel. The new "subgrade" will be graded and the deep ruts filled with 2 inch minus. A new blanket of bx-1200 will be placed and overlaid with 12 inches of 2 inch minus followed by 16 inches of 9 inch crusher run followed by an additional 12 inches of 2 inch minus for a cap. The overall pavement thickness and intermediate layering should distribute the load and significantly reduce the impact on the "goose poop" subgrade.

Thanks again for the feedback!

 

[oldestguy]

Sounds like overkill if you were able to get trucks across the first installation Hope the owners don't get the same impression and for the next job go to another firm.

 

[chiraggdl]

i am new immigrant in CANADA. could i get job in Highway construction Project.
i am having more then 6 years of experience in Road construction in INDIA.
familiar with almost all facets of Highway Construction activities like Earthwork, Crust Construction, Quantity & Cross Sections, Construction Project Planning in M.S.Project & Primavera, etc.

 

[lovethecold]

I am not a Canadian, but a member of the Canadian Professional Engineers Society (name?) spoke at our annual banquet here in the U.S. His talk indicated there was a strong need for engineers of all stripes. Particularly Civil, mining, and PE's. He discussed about foreingers becoming licensed in Canada, a lot depended on where your education is from, the actual university as well as the country it obtained from. There seems to be a lot of work in the Alberta oil sands, and around Winnepeg. So, I would think you have a very good chance of finding a job. And, at least in my neck of the woods, Indian engineers have a good reputation for competence and ability.

Hope this helps, good luck.